Any such claim should be "objectively" true, relating to weapons, war, fissionable nuclear materials or an "emergency in international relations," according to the ruling.
|
|
"Just imagine what will happen if the material stockpiled by the Iranians becomes fissionable, at military enrichment grade, and then an actual bomb," he told the Herzliya security conference befiore Zarif's announcement.
|
|
"Just imagine what will happen if the material stockpiled by the Iranians becomes fissionable, at military enrichment grade, and then an actual bomb," Joseph Cohen, head of Israel's Mossad intelligence agency, told a security conference.
|
|
A thermonuclear bomb (also known as a hydrogen bomb) is a more advanced and powerful design, where a fission bomb ignites a second stage of fissionable material to induce a fusion reaction, resulting in a much larger explosion.
|
|
The panel also confirmed the WTO's right to review national security claims, denting U.S. claims that national security was not subject to review, and said any such claim should be "objectively" true, relating to weapons, war, fissionable materials or an "emergency in international relations".
|
|
First, fission products must be removed. Second, plutonium must be separated from other actinides. Third, fissionable isotopes of plutonium must be separated from non-fissionable isotopes, which is more difficult than separating fissionable from non-fissionable isotopes of uranium, not least because the mass difference is one atomic unit instead of three. All processes require operation on strongly radioactive materials.
|
|
The others are typically produced in smaller quantities through further neutron absorption. "Fissile" is distinct from "fissionable". A nuclide capable of undergoing fission (even with a low probability) after capturing a neutron of high or low energy is referred to as "fissionable". A fissionable nuclide that can be induced to fission with low- energy thermal neutrons with a high probability is referred to as "fissile".
|
|
Consequently, uranium-238 is a fissionable material but not a fissile material. An alternative definition defines fissile nuclides as those nuclides that can be made to undergo nuclear fission (i.e., are fissionable) and also produce neutrons from such fission that can sustain a nuclear chain reaction in the correct setting. Under this definition, the only nuclides that are fissionable but not fissile are those nuclides that can be made to undergo nuclear fission but produce insufficient neutrons, in either energy or number, to sustain a nuclear chain reaction.
|
|
As such, while all fissile isotopes are fissionable, not all fissionable isotopes are fissile. In the arms control context, particularly in proposals for a Fissile Material Cutoff Treaty, the term "fissile" is often used to describe materials that can be used in the fission primary of a nuclear weapon.Fissile Materials and Nuclear Weapons, International Panel on Fissile Materials These are materials that sustain an explosive fast neutron nuclear fission chain reaction. Under all definitions above, uranium-238 () is fissionable, but because it cannot sustain a neutron chain reaction, it is not fissile.
|
|
During World War II, he researched isotope separation, which is necessary to produce fissionable material for use in making nuclear weapons.
|
|
Led by the very young Philip Abelson, the lab developed the liquid thermal diffusion process for separating fissionable from nonfissionable uranium.
|
|
This usually means changing the fuel arrangement within the core, or using different fuel types. is more likely to absorb a high-speed neutron than . A benefit of fast reactors is that they can be designed to be breeder reactors. As these reactors produce energy, they also let off enough neutrons to transmute non- fissionable elements into fissionable ones.
|
|
In combination with fissionable materials, neutrons produced by ICF can potentially be used in Hybrid Nuclear Fusion designs to produce electric power.
|
|
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel.Andrews, A. (2008, March 27). Nuclear Fuel Reprocessing: U.S. Policy. CRS Report For Congress.
|
|
More efficient use of fissionable material as a result of Operation Sandstone would increase the U.S. nuclear stockpile from 56 bombs in June 1948 to 169 in June 1949.
|
|
Fast fission is fission that occurs when a heavy atom absorbs a high-energy neutron, called a fast neutron, and splits. Most fissionable materials need thermal neutrons, which move more slowly.
|
|
The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fission cross-section), density, shape, enrichment, purity, temperature, and surroundings. The concept is important in nuclear weapon design.
|
|
The actual mass of a critical mass of nuclear fuel depends strongly on the geometry and surrounding materials. Not all fissionable isotopes can sustain a chain reaction. For example, 238U, the most abundant form of uranium, is fissionable but not fissile: it undergoes induced fission when impacted by an energetic neutron with over 1 MeV of kinetic energy. However, too few of the neutrons produced by 238U fission are energetic enough to induce further fissions in 238U, so no chain reaction is possible with this isotope.
|
|
Perhaps the most notable nuclear reactions are the nuclear chain reactions in fissionable materials that produce induced nuclear fission, and the various nuclear fusion reactions of light elements that power the energy production of the Sun and stars.
|
|
Fissionable materials include also those (such as uranium-238) that can be fissioned only with high-energy neutrons. As a result, fissile materials (such as uranium-235) are a subset of fissionable materials. Uranium-235 fissions with low-energy thermal neutrons because the binding energy resulting from the absorption of a neutron is greater than the critical energy required for fission; therefore uranium-235 is a fissile material. By contrast, the binding energy released by uranium-238 absorbing a thermal neutron is less than the critical energy, so the neutron must possess additional energy for fission to be possible.
|
|
In this reaction, a neutron plus a fissionable atom causes a fission resulting in a larger number of neutrons than the single one that was consumed in the initial reaction. Thus was born the practical nuclear chain reaction by the mechanism of neutron-induced nuclear fission. Specifically, if one or more of the produced neutrons themselves interact with other fissionable nuclei, and these also undergo fission, then there is a possibility that the macroscopic overall fission reaction will not stop, but continue throughout the reaction material. This is then a self-propagating and thus self-sustaining chain reaction.
|
|
Dodewaard nuclear power plant awaiting demolition. In Dodewaard, the Dodewaard nuclear power plant with a boiling water reactor has been decommissioned. It was operational in the period 1968-1997. It had a capacity of 58 MW. In 2003 the last fissionable material was removed.
|
|
The United States provided "10,000 fissile material storage containers by the end of 1995 and a total of nearly 33,000 containers by early 1997". These containers aided in Russia's ability to store nuclear material from dismantled warheads. Another contribution from the United States to Russia was "75 million dollars to help Russia build a new fissile material storage facility at Chelyabinsk for plutonium "pits" from dismantled warheads". The Nuclear Threat Reduction program was not just used to remove everything fissionable from Russia; it also included ideas for safe storage and transportation of fissionable material in Russia built up during the Cold War and nuclear escalation.
|
|
229mTh has the lowest known excitation energy of any isomer, measured to be . This is so low that when it undergoes isomeric transition, the emitted gamma radiation is in the ultraviolet range. Different isotopes of thorium are chemically identical, but have slightly differing physical properties: for example, the densities of pure 228Th, 229Th, 230Th, and 232Th are respectively expected to be 11.5, 11.6, 11.6, and 11.7 g/cm3. The isotope 229Th is expected to be fissionable with a bare critical mass of 2839 kg, although with steel reflectors this value could drop to 994 kg. 232Th is not fissionable, but it is fertile as it can be converted to fissile 233U by neutron capture and subsequent beta decay.
|
|
The design utilized a new hollow core concept.Newsletter published and written by the (United States of America) National Association of Atomic Veterans, Inc. (ed. R.J.Ritter) Retrieved 2015-11-28 (c.f. Atomic veteran) The concept was termed as "radical implosion system" aiming towards reducing the amount of fissionable materials present in the weapon's core while generating moderately high yield.
|
|
Thorium is about 3.5 times more common than uranium in the Earth's crust, and has different geographic characteristics. This would extend the total practical fissionable resource base by 450%. India's three-stage nuclear power programme features the use of a thorium fuel cycle in the third stage, as it has abundant thorium reserves but little uranium.
|
|
Over 90% of the cost was for building factories and producing the fissionable materials, with less than 10% for development and production of the weapons. Two types of atomic bombs were developed during the war. A relatively simple gun-type fission weapon was made using uranium-235, an isotope that makes up only 0.7 percent of natural uranium.
|
|
These fast reactors are better suited for the transmutation of other actinides than thermal reactors. Because thermal reactors use slow or moderated neutrons, the actinides that are not fissionable with thermal neutrons tend to absorb the neutrons instead of fissioning. This leads to buildup of heavier actinides and lowers the number of thermal neutrons available to continue the chain reaction.
|
|
This reduces it to a diffusion problem. However, as the typical linear dimensions are not significantly larger than the mean free path, such an approximation is only marginally applicable. Finally, note that for some idealized geometries, the critical mass might formally be infinite, and other parameters are used to describe criticality. For example, consider an infinite sheet of fissionable material.
|
|
As is revealed in the story, society has attained a state where, like a critical mass of fissionable material, one random event will lead to a complete transformation. The metaphor is extended by the story explicitly likening one character to a neutron, another to a nucleus, and the President to a neutron moderator. The accidental collision of the characters initiates the chain reaction.
|
|
This allows the reactor to be constructed with an excess of fissionable material, which is nevertheless made relatively safe early in the reactor's fuel burn cycle by the presence of the neutron-absorbing material which is later replaced by normally produced long-lived neutron poisons (far longer-lived than xenon-135) which gradually accumulate over the fuel load's operating life.
|
|
These designs (for instance the molten salt reactor) have yet to be commercialized. Thorium is a fissionable material used in thorium-based nuclear power. The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation and reduced plutonium production. Therefore, it is sometimes referred as sustainable.
|
|
Converting between percent and energy/mass requires knowledge of κ, the thermal energy released per fission event. A typical value is 193.7 MeV () of thermal energy per fission (see Nuclear fission). With this value, the maximum burnup of 100%FIMA, which includes fissioning not just fissile content but also the other fissionable nuclides, is equivalent to about 909 GWd/t.
|
|
The plant produced fission cores for nuclear weapons, used to "ignite" fusion and fissionable fuel. Fission cores resemble miniaturized versions of the Fat Man nuclear bomb detonated above Nagasaki. They are often called "triggers" in official and news documents to obfuscate their function. For much of its operational lifetime, Rocky Flats was the sole mass-producer of plutonium components for America's nuclear stockpile.
|
|
There are three main components to the hybrid fusion fuel cycle: deuterium, tritium, and fissionable elements. Deuterium can be derived by separation of hydrogen isotopes in sea water (see heavy water production). Tritium may be generated in the hybrid process itself by absorption of neutrons in lithium bearing compounds. This would entail an additional lithium bearing blanket and a means of collection.
|
|
Hydronuclear tests do involve nuclear reactions, but very small ones. A technique that actually may have more explosive yield, of high explosive, is hydrodynamic testing, in which extremely fast X-ray, neutron, or other specialized camera measure, in microseconds, the explosive compression of a fissionable material simulant. Depleted uranium, for example, has the same physical properties as enriched uranium, and is similar to plutonium.
|
|
The representative of France stated that the sole purpose of the reactor was scientific research. Agreements between France and Iraq excluded military use. The United Kingdom said it did not believe Iraq had the capacity to manufacture fissionable materials for nuclear weapons. The IAEA Director-General confirmed that inspections of the nuclear research reactors near Baghdad revealed no non-compliance with the safeguards agreement.
|
|
The Stable Salt Reactor is a relatively recent concept which holds the molten salt fuel statically in traditional LWR fuel pins. Pumping of the fuel salt, and all the corrosion/deposition/maintenance/containment issues arising from circulating a highly radioactive, hot and chemically complex fluid, are no longer required. The fuel pins are immersed in a separate, non-fissionable fluoride salt which acts as primary coolant.
|
|
Changes in the composition of a MSR fast neutron (kg/GW) Reprocessing refers to the chemical separation of fissionable uranium and plutonium from spent fuel. Such recovery could increase the risk of nuclear proliferation. In the United States the regulatory regime has varied dramatically across administrations. In the 1971 Molten Salt Breeder Reactor proposal, uranium reprocessing was scheduled every ten days as part of reactor operation.
|
|
In the late 1940s, Stanislaw Ulam invented the modern version of the Markov Chain Monte Carlo method while he was working on nuclear weapons projects at the Los Alamos National Laboratory. Immediately after Ulam's breakthrough, John von Neumann understood its importance. Von Neumann programmed the ENIAC computer to perform Monte Carlo calculations. In 1946, nuclear weapons physicists at Los Alamos were investigating neutron diffusion in fissionable material.
|
|
The IAEA recommends that 99Mo concentrations exceeding more than 0.15µCi/mCi 99mTc or 0.015% should not be administered for usage in humans. Typically quantification of 99Mo breakthrough is performed for every elution when using a 99Mo/99mTc generator during QA-QC testing of the final product. There are alternative routes for generating 99Mo that do not require a fissionable target, such as high or low enriched uranium (i.e., HEU or LEU).
|
|
The critical size is the minimum size of a nuclear reactor core or nuclear weapon that can be made for a specific geometrical arrangement and material composition. The critical size must at least include enough fissionable material to reach critical mass. If the size of the reactor core is less than a certain minimum, too many fission neutrons escape through its surface and the chain reaction is not sustained.
|
|
In 1943, Alvin M. Weinberg et al. believed that there were serious limitations on nuclear energy if only U-235 were used as a nuclear power plant fuel. They concluded that breeding was required to usher in the age of nearly endless energy. In 1956, M. King Hubbert declared world fissionable reserves adequate for at least the next few centuries, assuming breeding and reprocessing would be developed into economical processes.
|
|
The meson bomb was a proposed nuclear weapon that would derive its destructive force from meson interactions with fissionable material like uranium. The idea behind the bomb was rejected by most scientists, but during the Cold War, American intelligence managed to trick the Soviet Union into conducting research on this topic, which resulted in several years of wasted labor by one of the Soviet nuclear weapon research bureaus.
|
|
Jeremy Bernstein, "John von Neumann and Klaus Fuchs: an Unlikely Collaboration", Physics in Perspective 12, no. 1 (March 2010), 36-50. In 1951, Stanislaw Ulam had the idea to use hydrodynamic shock of a fission weapon to compress more fissionable material to incredible densities in order to make megaton-range, two-stage fission bombs. He then realized that this approach might be useful for starting a thermonuclear reaction.
|
|
He suggested 100 neutrons each to be run for 100 collisions and estimated the computational time to be five hours on ENIAC. Richtmyer proposed suggestions to allow for multiple fissionable materials, no fission spectrum energy dependence, single neutron multiplicity, and running the computation for computer time and not for the number of collisions. The code was finalized in December 1947. The first calculations were run in April/May 1948 on ENIAC.
|
|
Thermal reactors generally depend on refined and enriched uranium. Some nuclear reactors can operate with a mixture of plutonium and uranium (see MOX). The process by which uranium ore is mined, processed, enriched, used, possibly reprocessed and disposed of is known as the nuclear fuel cycle. Under 1% of the uranium found in nature is the easily fissionable U-235 isotope and as a result most reactor designs require enriched fuel.
|
|
By merely placing cheap unenriched uranium into such a core, the non-fissionable U-238 will be turned into Pu-239, "breeding" fuel. In thorium fuel cycle thorium-232 absorbs a neutron in either a fast or thermal reactor. The thorium-233 beta decays to protactinium-233 and then to uranium-233, which in turn is used as fuel. Hence, like uranium-238, thorium-232 is a fertile material.
|
|
LWR. Speed of transmutation varies greatly by nuclide, and percentages are relative to total transmutation and decay. After removal of fuel from reactor, decay will predominate for shorter-lived isotopes such as 238Pu, 241Pu, 242–244Cm; but 245–248Cm are all long-lived. Fertile material is a material that, although not itself fissionable by thermal neutrons, can be converted into a fissile material by neutron absorption and subsequent nuclei conversions.
|
|
John von Neumann immediately saw the significance of this insight. In March 1947 he proposed a statistical approach to the problem of neutron diffusion in fissionable material. Because Ulam had often mentioned his uncle, Michał Ulam, "who just had to go to Monte Carlo" to gamble, Metropolis dubbed the statistical approach "The Monte Carlo method". Metropolis and Ulam published the first unclassified paper on the Monte Carlo method in 1949.
|
|
The Soviets subsequently rejected the Baruch Plan, and the United States then rejected a Soviet counter-proposal for a ban on all nuclear weapons.The History Channel: The United States presents the Baruch Plan In 1953, the U.S. proposed its Atoms for Peace plan. In a speech to the UN General Assembly in New York City on December 8, 1953, U.S. President Dwight D. Eisenhower called on the United States with the Soviet Union "to make joint contributions from their stockpiles of normal uranium and fissionable materials to an international Atomic Energy Agency" that would then "devise methods whereby this fissionable material would be allocated to serve the peaceful pursuits of mankind."Eisenhower Archive: Press Release, "Atoms for Peace" Speech, December 8, 1953 [DDE's Papers as President, Speech Series, Box 5, United Nations Speech 12/8/53] The plan also proposed a new International Atomic Energy Agency and “uranium bank” as simple steps to establish international trust and start a cooperative arms control dialogue.
|
|
This can be seen as a shortcut to viable fusion power until more efficient pure fusion technologies can be developed, or as an end in itself to generate power, and also consume existing stockpiles of nuclear fissionables and waste products. In the LIFE project at the Lawrence Livermore National Laboratory LLNL, using technology developed at the National Ignition Facility, the goal is to use fuel pellets of deuterium and tritium surrounded by a fissionable blanket to produce energy sufficiently greater than the input (laser) energy for electrical power generation. The principle involved is to induce inertial confinement fusion (ICF) in the fuel pellet which acts as a highly concentrated point source of neutrons which in turn converts and fissions the outer fissionable blanket. In parallel with the ICF approach, the University of Texas at Austin is developing a system based on the tokamak fusion reactor, optimising for nuclear waste disposal versus power generation.
|
|
The surrounding blanket can be a fissile material (enriched uranium or plutonium) or a fertile material (capable of conversion to a fissionable material by neutron bombardment) such as thorium, depleted uranium or spent nuclear fuel. Such subcritical reactors (which also include particle accelerator-driven neutron spallation systems) offer the only currently-known means of active disposal (versus storage) of spent nuclear fuel without reprocessing. Fission by- products produced by the operation of commercial light water nuclear reactors (LWRs) are long-lived and highly radioactive, but they can be consumed using the excess neutrons in the fusion reaction along with the fissionable components in the blanket, essentially destroying them by nuclear transmutation and producing a waste product which is far safer and less of a risk for nuclear proliferation. The waste would contain significantly reduced concentrations of long-lived, weapons-usable actinides per gigawatt-year of electric energy produced compared to the waste from a LWR.
|
|
He was contacted by Harry Gold (codename: "Raymond"), an NKGB agent in early 1944. Los Alamos ID badge From August 1944, Fuchs worked in the Theoretical Physics Division at the Los Alamos Laboratory, under Hans Bethe. His chief area of expertise was the problem of imploding the fissionable core of the plutonium bomb. At one point, Fuchs did calculation work that Edward Teller had refused to do because of lack of interest.
|
|
Explosive lenses are used to compress a fissile core inside an implosion-type nuclear weapon. Work on an alternative method of bomb design, known as implosion, had begun by Neddermeyer's E-5 (Implosion) group. Serber and Tolman had conceived implosion during the April 1943 conferences as a means of assembling pieces of fissionable material together to form a critical mass. Neddermeyer took a different tack, attempting to crush a hollow cylinder into a solid bar.
|
|
The treaty also provides for a central supply agency, thereby creating a monopoly of all fissionable material produced in or imported to the Community. EURATOM is owner of all such materials. Its control functions are linked to this ownership. The Treaty provided further for the establishment of so-called "Common Enterprises", which have certain obligations to the Community but also enjoy certain privileges, among them tax privileges which they could not enjoy under national law.
|
|
Neptunium is fissionable, and could theoretically be used as fuel in a fast neutron reactor or a nuclear weapon, with a critical mass of around 60 kilograms. In 1992, the U.S. Department of Energy declassified the statement that neptunium-237 "can be used for a nuclear explosive device"."Restricted Data Declassification Decisions from 1946 until Present", accessed Sept 23, 2006. It is not believed that an actual weapon has ever been constructed using neptunium.
|
|
Free neutrons, while not directly ionizing atoms, cause ionizing radiation. As such they can be a biological hazard, depending upon dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by cosmic ray showers, and by the natural radioactivity of spontaneously fissionable elements in the Earth's crust. Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation and in neutron scattering experiments.
|
|
The Iowa plant started handling fissionable material in 1956, when it assembled the AIR-2 Genie, in addition to other missiles and artillery shells. The company started operating Pantex in October 1956, and opened a development lab in 1960. From 1958 until 1966, the company operated AEC Modification Centers at Medina Base, near San Antonio, and Clarksville Base, near Clarksville, Tennessee. Pantex assumed stockpile surveillance in 1985, and the Iowa facility was merged into Pantex by 1975.
|
|
Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. All the Little Boy units were withdrawn from service by the end of January 1951. The Smithsonian Institution displayed a Little Boy (complete, except for enriched uranium), until 1986. The Department of Energy took the weapon from the museum to remove its inner components, so the bombs could not be stolen and detonated with fissile material.
|
|
Cheryl Rofer: "Whoo-Hoo! Atoms of Fissionable Material Everywhere! – Updated 2/22/09" According to the American Institute of Physics, the most difficult step in building a nuclear weapon is the production of fissile material.American Institute of Physics: The gas centrifuge and nuclear weapons proliferation Iran has enriched uranium to "less than 5%", consistent with fuel for a nuclear power plant and well below the purity of WEU (around 90%) typically used in a weapons program.
|
|
An isotope (or nuclide) can be classified according to its neutron cross section and how it reacts to an incident neutron. Nuclides that tend to absorb a neutron and either decay or keep the neutron in its nucleus are neutron absorbers and will have a capture cross section for that reaction. Isotopes that fission are fissionable fuels and have a corresponding fission cross section. The remaining isotopes will simply scatter the neutron, and have a scatter cross section.
|
|
The first nuclear explosion, named "Trinity", was detonated on July 16, 1945.The Allied team produced two nuclear weapons for use in the war, one powered by uranium-235 and the other by plutonium as fissionable material, named "Little Boy" and "Fat Man". These were dropped on the Japanese cities of Hiroshima and Nagasaki on August 6 and 9, 1945 each. This, in combination with the Soviet invasion of Japanese- controlled territory, convinced the Japanese government to surrender unconditionally.
|
|
Instead, the atom will become a new isotope of the original element, such as beryllium-13 becoming beryllium-12 after emitting one of its neutrons. In nuclear engineering, a prompt neutron is a neutron immediately emitted by a nuclear fission event. Prompt neutrons emerge from the fission of an unstable fissionable or fissile heavy nucleus almost instantaneously. Delayed neutron decay can occur within the same context, emitted after beta decay of one of the fission products.
|
|
Unequal fissions are energetically more favorable because this allows one product to be closer to the energetic minimum near mass 60 u (only a quarter of the average fissionable mass), while the other nucleus with mass 135 u is still not far out of the range of the most tightly bound nuclei (another statement of this, is that the atomic binding energy curve is slightly steeper to the left of mass 120 u than to the right of it).
|
|
U-235 is fissionable by thermal (i.e. slow-moving) neutrons. A thermal neutron is one which is moving about the same speed as the atoms around it. Since all atoms vibrate proportionally to their absolute temperature, a thermal neutron has the best opportunity to fission U-235 when it is moving at this same vibrational speed. On the other hand, U-238 is more likely to capture a neutron when the neutron is moving very fast.
|
|
He wanted the case of the vibration problems thoroughly investigated, and the cause definitely known before corrective action was taken. Three SNPO staff (known at LASL as the "three blind mice") were assigned to LASL to ensure that his instructions were carried out. Finger assembled a team of vibration specialists from other NASA centers, and along with staff from LASL, Aerojet and Westinghouse, conducted a series of "cold flow" reactor tests using fuel elements without fissionable material. RIFT was cancelled in December 1963.
|
|
In May 1972 at the Tricastin uranium enrichment, Pierrelatte, France, routine mass spectrometry comparing UF6 samples from the Oklo Mine, located in Gabon, showed a discrepancy in the amount of the isotope. Normally the concentration is 0.72% while these samples had only 0.60%, a significant difference. This discrepancy required explanation, as all civilian uranium handling facilities must meticulously account for all fissionable isotopes to ensure that none are diverted for weapons purposes. Thus the French Commissariat à l'énergie atomique (CEA) began an investigation.
|
|
Ratios of capture reactions to fission reactions are also worse (more captures without fission) in most nuclear fuels such as plutonium-239, making epithermal-spectrum reactors using these fuels less desirable, as captures not only waste the one neutron captured but also usually result in a nuclide that is not fissile with thermal or epithermal neutrons, though still fissionable with fast neutrons. The exception is uranium-233 of the thorium cycle, which has good capture-fission ratios at all neutron energies.
|
|
According to the International Atomic Energy Agency there are at least 100 research reactors in the world fueled by highly enriched (weapons- grade/90% enrichment) uranium. Theft risk of this fuel (potentially used in the production of a nuclear weapon) has led to campaigns advocating conversion of this type of reactor to low-enrichment uranium (which poses less threat of proliferation). Fissile U-235 and non-fissile but fissionable and fertile U-238 are both used in the fission process.
|
|
The civilization is advanced, but appears to have taken on some aspects of a frontier society. It is unclear if each planet has its own government, but some central government still has control over all planets. When the Fafnir lands on Earth, decommissioned and then put up for sale as scrap, the decommissioning process involves the Bureau of Space Commerce (BSC) removing the "bricks of fissionable material from her atomic pile." So some government oversight still exists to monitor and regulate certain dangerous substances.
|
|
Soon after the Japanese bombing of Pearl Harbor brought the United States into World War II, Wheeler accepted a request from Arthur Compton to join the Manhattan Project's Metallurgical Laboratory at the University of Chicago. He moved there in January 1942, joining Eugene Wigner's group, which was studying nuclear reactor design. He co-wrote a paper with Robert F. Christy on "Chain Reaction of Pure Fissionable Materials in Solution", which was important in the plutonium purification process. It would not be declassified until December 1955.
|
|
Plutonium-242 (242Pu) is one of the isotopes of plutonium, the second longest- lived, with a half-life of 373,300 years. The half-life of 242Pu is about 15 times longer than that of 239Pu; therefore, it is one-fifteenth as radioactive, and not one of the larger contributors to nuclear waste radioactivity. 242Pu's gamma ray emissions are also weaker than those of the other isotopes. It is not fissile (though it is fissionable by fast neutrons) and its neutron capture cross section is also low.
|
|
While waiting for ENIAC to be physically relocated, Enrico Fermi invented a mechanical device called FERMIAC to trace neutron movements through fissionable materials by the Monte Carlo method. Monte Carlo methods for particle transport have been driving computational developments since the beginning of modern computers; this continues today. In the 1950s and 1960s, these new methods were organized into a series of special-purpose Monte Carlo codes, including MCS, MCN, MCP, and MCG. These codes were able to transport neutrons and photons for specialized LANL applications.
|
|
Caesium-137 (), or radiocaesium, is a radioactive isotope of caesium which is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from natural fission of uranium-238. It is among the most problematic of the short-to-medium-lifetime fission products because it easily moves and spreads in nature due to the high water solubility of caesium's most common chemical compounds, which are salts.
|
|
In August 1957, the US assented to a two-year testing moratorium proposed by the Soviet Union, but required that it be linked to restrictions on the production of fissionable material with military uses, a condition that the Soviet Union rejected. While Eisenhower insisted on linking a test ban to a broader disarmament effort (e.g., the production cut- off), Moscow insisted on independent consideration of a test ban. On 19 September 1957, the US conducted the first contained underground test at the Nevada Test Site, codenamed Rainier.
|
|
The Fast Neutron Physics Group used the R-process to determine the neutrons' behaviour in the fissionable device. End of 1974, Pakistan's Parliament passed a bill with a majority, declaring Ahmadis to be non-Muslims after which Abdus Salam, a senior scientist and Ahmadi, left Pakistan for Great Britain in protest. After the departure of Salam Munir Ahmad Khan continued the organizations. The Nuclear Engineering Division, under Bashiruddin Mahmood set up a 238U production facility and the construction began under Munir Ahmad Khan's direction.
|
|
While many fissionable isotopes exist in nature, the only usefully fissile isotope found in any quantity is 235U. About 0.7% of the uranium in most ores is the 235 isotope, and about 99.3% is the non-fissile 238 isotope. For most uses as a nuclear fuel, uranium must be enriched - purified so that it contains a higher percentage of 235U. Because 238U absorbs fast neutrons, the critical mass needed to sustain a chain reaction increases as the 238U content increases, reaching infinity at 94% 238U (6% 235U).
|
|
GE Hitachi's PRISM reactor is a modernized and commercial implementation of the technology developed for the Integral Fast Reactor(IFR), developed by Argonne National Laboratory between 1984 and 1994. With the primary purpose of PRISM differing in the focus on burning up spent nuclear fuel from other reactors, rather than breeding new fuel. Presented as an alternative to burying the spent fuel/waste, the design reduces the half lives of the fissionable elements present in spent nuclear fuel while generating electricity largely as a by-product.
|
|
339–348, (1977) Then, Qadir opted the Pati–Salam model for solving the fission problem and suggested that the Salam's model can be used to develop an effective boosted fissionable reflector in a device.Equivalence of the theories of reciprocity and general relativity, Asghar Qadir, Journal of Theoretical Physics, Vol: 15(1976) pp. 25–30 Qadir then continued to develop mathematical models and to evaluate critical mass problems. Riazuddin introduced Qadir to Salam where Salam encourage Qadir to research in mathematical physics in more depth.
|
|
The U.S. Government air transport regulations permit the transport of plutonium by air, subject to restrictions on other dangerous materials carried on the same flight, packaging requirements, and stowage in the rearmost part of the aircraft. In 2012 media revealed that plutonium has been flown out of Norway on commercial passenger airlines—around every other year—including one time in 2011. Regulations permit an airplane to transport 15 grams of fissionable material. Such plutonium transportation is without problems, according to a senior advisor (seniorrådgiver) at Statens strålevern.
|
|
Enriched uranium was first manufactured in the early 1940s when the United States and Britain began their nuclear weapons programs. Later in the decade, France and the Soviet Union began their nuclear weapons and nuclear power programs. Depleted uranium was originally stored as an unusable waste product (uranium hexafluoride) in the hope that improved enrichment processes could extract additional quantities of the fissionable U-235 isotope. This re-enrichment recovery of the residual uranium-235 is now in practice in some parts of the world; e.g.
|
|
This is a hybrid approach in which antiprotons are used to catalyze a fission/fusion reaction or to "spike" the propulsion of a fusion rocket or any similar applications. The antiproton-driven Inertial confinement fusion (ICF) Rocket concept uses pellets for the D-T reaction. The pellet consists of a hemisphere of fissionable material such as U235 with a hole through which a pulse of antiprotons and positrons is injected. It is surrounded by a hemisphere of fusion fuel, for example deuterium-tritium, or lithium deuteride.
|
|
Its first division, the New Labs was dedicated to the production of the weapon grade plutonium of 239Pu. In 1983, Nuclear Physics Division working under Ishfaq Ahmad successfully produced the 239Pu, a weapon grade plutonium. Throughout the formulative year, the scientists and engineers at PINSTECH carried out technologically advanced research at the PINSTECH. On May 30, 1998, the PAEC scientists and engineers had performed the second nuclear test—codename Chagai-II— of a fissionable device, and the device's weapon grade plutonium was produced at the New Labs.
|
|
Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon or has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nuclear weapons are the most common examples. (These nuclear materials have other categorizations based on their purity.) Only fissile isotopes of certain elements have the potential for use in nuclear weapons. For such use, the concentration of fissile isotopes uranium-235 and plutonium-239 in the element used must be sufficiently high.
|
|
Hubbert models have been used to predict the production trends of various resources, such as natural gas (Hubbert's attempt in the late 1970s resulted in an inaccurate prediction that natural gas production would fall dramatically in the 1980s), Coal, fissionable materials, Helium, transition metals (such as copper), and water. At least one researcher has attempted to create a Hubbert curve for the whaling industry and caviar,Ugo Bardi and Leigh Yaxley. How General is the Hubbert Curve? Proceedings of the 4th ASPO Workshop, Lisbon 2005 while another applied it to cod.
|
|
The uranium isotope 235U is used as the fuel for nuclear reactors and nuclear weapons. It is the only isotope existing in nature to any appreciable extent that is fissile, that is, fissionable by thermal neutrons. The isotope 238U is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope 239Pu (plutonium), which also is fissile. Uranium in its natural state comprises just 0.71% 235U and 99.3% 238U, and the main focus of uranium metallurgy is the enrichment of uranium through isotope separation.
|
|
Stone & Webster wartime were involved in the Manhattan Project, which designed and built the atomic bomb. Stone & Webster was involved in creating the facilities and laboratories for the Manhattan Project. Prior to its acquisition it was also part of the Maine Yankee decommissioning project. The company was selected in June 1942 by the first MED District Engineer, Colonel James C. Marshall, as the main subcontractor for the project. Eventually the company established a completely separate engineering organization employing 800 engineers and draftsmen to study ways to separate large quantities of fissionable uranium-235.
|
|
Other natural energies exploited by human technology originate directly or indirectly with the Sun, including fossil fuel, conventional hydroelectric, wind, biofuel, wave and solar energy. Nuclear energy makes use of Earth's mineral deposits of fissionable elements, while geothermal power utilizes the Earth's internal heat, which comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). A tidal generator converts the energy of tidal flows into electricity. Greater tidal variation and higher tidal current velocities can dramatically increase the potential of a site for tidal electricity generation.
|
|
Several heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous fission, a form of radioactive decay and induced fission, a form of nuclear reaction. Elemental isotopes that undergo induced fission when struck by a free neutron are called fissionable; isotopes that undergo fission when struck by a slow-moving thermal neutron are also called fissile. A few particularly fissile and readily obtainable isotopes (notably 233U, 235U and 239Pu) are called nuclear fuels because they can sustain a chain reaction and can be obtained in large enough quantities to be useful.
|
|
Plutonium is fissionable with both fast and thermal neutrons, which make it ideal for either nuclear reactors or nuclear bombs. Most reactor designs in existence are thermal reactors and typically use water as a neutron moderator (moderator means that it slows down the neutron to a thermal speed) and as a coolant. But in a fast breeder reactor, some other kind of coolant is used which will not moderate or slow the neutrons down much. This enables fast neutrons to dominate, which can effectively be used to constantly replenish the fuel supply.
|
|
The successful testing of the new cores in the Sandstone tests had a profound effect. Practically every component of the old weapons was rendered obsolete. Even before the third test had been carried out, Bradbury had halted production of the old cores, and ordered that all effort was to be concentrated on the Mark 4 nuclear bomb, which would become the first mass-produced nuclear weapon. The more efficient use of fissionable material would increase the nuclear stockpile from 56 bombs in June 1948 to 169 in June 1949.
|
|
In the interior of a critical mass sphere, neutrons are spontaneously produced by the fissionable material. A very small portion of these neutrons are colliding with other nuclei, while a larger portion of the neutrons are escaping through the surface of the sphere. Peierls calculated the equilibrium of the system, where the number of neutrons being produced equalled the number escaping. Niels Bohr had theorised that the rare uranium-235 isotope, which makes up only about 0.7% of natural uranium, was primarily responsible for fission with fast neutrons, although this was not yet universally accepted.
|
|
Liquid core nuclear engines are fueled by compounds of fissionable elements in liquid phase. A liquid-core engine is proposed to operate at temperatures above the melting point of solid nuclear fuel and cladding, with the maximum operating temperature of the engine instead being determined by the reactor pressure vessel and neutron reflector material. The higher operating temperatures would be expected to deliver specific impulse performance on the order of 1300 to 1500 seconds (12.8-14.8 kN·s/kg). A liquid-core reactor would be extremely difficult to build with current technology.
|
|
CIC units were also involved in providing security for the Manhattan Project, including duty as couriers of fissionable bomb materials from Los Alamos, New Mexico to Tinian. They also operated in 1945 at the United Nations Organizing Conference in San Francisco, over which Alger Hiss presided as secretary-general.For the account of one agent working under cover at the San Francisco conference and photos of fellow agents there, see Special Agent Leonard L. (Igor) Gorin "United Nations Formation 1945—CIC Security Role". Golden Sphinx, Serial Issue #2004-3, Winter 2004-5, pp. 16–20.
|
|
In 1944 he returned to the University of Chicago where he served first as an associate mathematical physicist and then as a physicist in its Metallurgical Laboratory, as part of the Manhattan Project. Working under the direction of Arthur Holly Compton and Enrico Fermi, Wilkins researched the extraction of fissionable nuclear materials, but was not told of the research group's ultimate goal until after the atomic bomb was dropped on Hiroshima. Wilkins was the codiscoverer or discoverer of a number of phenomena in physics such as the Wilkins effect and the Wigner–Wilkins and Wilkins spectra.Gates, Henry Louis & Higginbotham, Evelyn Brooks.
|
|
Uranium mononitride is being considered as a potential fuel for generation IV reactors such as the Hyperion Power Module reactor created by Hyperion Power Generation. It has also been proposed as nuclear fuel in some fast neutron nuclear test reactors. UN is considered superior because of its higher fissionable density, thermal conductivity and melting temperature than the most common nuclear fuel, uranium oxide (UO2), while also demonstrating lower release of fission product gases and swelling, and decreased chemical reactivity with cladding materials. It also has a superior mechanical, thermal and radiation stability compared to standard metallic uranium fuel.
|
|
By relying on a large nuclear arsenal for deterrence, President Eisenhower believed that conventional forces could be reduced while still maintaining military prestige and power and the capability to defend the western bloc. A shift to relying on nuclear weapons for deterrence would allow the United States to keep abreast of the Soviet Union's military strength. In 1953, one tonne of TNT cost $1700 to produce while fissionable material of similar explosive power cost a mere $23 to manufacture. Upon a conventional attack on Berlin, for instance, the United States would undertake a massive retaliation on the Soviet Union with nuclear weapons.
|
|
In the 2013 Red 2, red mercury was the fissionable ingredient used to create a nuclear bomb with no fallout. The "red matter" seen in the 2009 reboot of Star Trek may have been inspired by red mercury. In the Bengali movie Sagardwipey Jawker Dhan, red mercury is described as a possible substitute for exhausting fossil fuels. In season four of Chilling Adventures of Sabrina, Lucifer offers red mercury to Nick Scratch as a powerful drug. In the season four episode “Mayhem” of Criminal Minds, Reid claims that a bomb that had exploded was likely made from oxidizing agents including red mercury.
|
|
In general, most actinide isotopes with an odd neutron number are fissile. Most nuclear fuels have an odd atomic mass number (A = Z + N = the total number of nucleons), and an even atomic number Z. This implies an odd number of neutrons. Isotopes with an odd number of neutrons gain an extra 1 to 2 MeV of energy from absorbing an extra neutron, from the pairing effect which favors even numbers of both neutrons and protons. This energy is enough to supply the needed extra energy for fission by slower neutrons, which is important for making fissionable isotopes also fissile.
|
|
This means that the lighter elements, such as hydrogen and helium, are in general more fusible; while the heavier elements, such as uranium, thorium and plutonium, are more fissionable. The extreme astrophysical event of a supernova can produce enough energy to fuse nuclei into elements heavier than iron. In 1920, Arthur Eddington suggested hydrogen-helium fusion could be the primary source of stellar energy. Quantum tunneling was discovered by Friedrich Hund in 1929, and shortly afterwards Robert Atkinson and Fritz Houtermans used the measured masses of light elements to show that large amounts of energy could be released by fusing small nuclei.
|
|
This often means that simple concrete blocks or even paraffin-loaded plastic blocks afford better protection from neutrons than do far more dense materials. After slowing, neutrons may then be absorbed with an isotope that has high affinity for slow neutrons without causing secondary capture radiation, such as lithium-6. Hydrogen-rich ordinary water affects neutron absorption in nuclear fission reactors: Usually, neutrons are so strongly absorbed by normal water that fuel enrichment with fissionable isotope is required. The deuterium in heavy water has a very much lower absorption affinity for neutrons than does protium (normal light hydrogen).
|
|
All fissionable and fissile isotopes undergo a small amount of spontaneous fission which releases a few free neutrons into any sample of nuclear fuel. Such neutrons would escape rapidly from the fuel and become a free neutron, with a mean lifetime of about 15 minutes before decaying to protons and beta particles. However, neutrons almost invariably impact and are absorbed by other nuclei in the vicinity long before this happens (newly created fission neutrons move at about 7% of the speed of light, and even moderated neutrons move at about 8 times the speed of sound).
|
|
It also recommended concentrating on the gaseous diffusion process for enriching uranium and building only a small electromagnetic plant. Conant supported building a large electromagnetic plant, which Nichols says was essential to dropping the bomb in August rather than months later. The committee also suggested suitable industrial organisations and ... furnished us with a blueprint for the complete industrial organization of the project which Groves mostly followed ... and gave us more confidence concerning the feasibility of producing sufficient quantities of fissionable material.Kenneth D. Nichols; The Road to Trinity: A Personal Account of How America’s Nuclear Policies Were Made pp.
|
|
Traditional criticality analyses assume that the fissile material is in its most reactive condition, which is usually at maximum enrichment, with no irradiation. For spent nuclear fuel storage and transport, burnup credit may be used to allow fuel to be more closely packed, reducing space and allowing more fuel to be handled safely. In order to implement burnup credit, fuel is modeled as irradiated using pessimistic conditions which produce an isotopic composition representative of all irradiated fuel. Fuel irradiation produces actinides consisting of both neutron absorbers and fissionable isotopes as well as fission products which absorb neutrons.
|
|
Breeder reactors are specifically designed to create more fissionable material than they consume. MOX fuel has been in use since the 1980s, and is widely used in Europe. In September 2000, the United States and the Russian Federation signed a Plutonium Management and Disposition Agreement by which each agreed to dispose of 34 tonnes of weapons- grade plutonium. The U.S. Department of Energy plans to dispose of 34 tonnes of weapons-grade plutonium in the United States before the end of 2019 by converting the plutonium to a MOX fuel to be used in commercial nuclear power reactors.
|
|
The third component is externally derived fissionable materials from demilitarized supplies of fissionables, or commercial nuclear fuel and waste streams. Fusion driven fission also offers the possibility of using thorium as a fuel, which would greatly increase the potential amount of fissionables available. The extremely energetic nature of the fast neutrons emitted during the fusion events (up to 0.17 the speed of light) can allow normally non-fissioning U-238 to undergo fission directly (without conversion first to Pu-239), enabling refined natural Uranium to be used with very low enrichment, while still maintaining a deeply subcritical regime.
|
|
The feasibility of a plutonium bomb had been questioned in 1942. James Conant heard on 14 November from Wallace Akers, the director of the British Tube Alloys project, that James Chadwick had "concluded that plutonium might not be a practical fissionable material for weapons because of impurities." Conant consulted Ernest Lawrence and Arthur Compton, who acknowledged that their scientists at Berkeley and Chicago respectively knew about the problem, but could offer no ready solution. Conant informed the director of the Manhattan Project, Brigadier General Leslie R. Groves, Jr., who in turn assembled a special committee consisting of Lawrence, Compton, Oppenheimer, and McMillan to examine the issue.
|
|
Fission-fragment propulsion concept a fissionable filaments arranged in disks, b revolving shaft, c reactor core, d fragments exhaust A design by the Idaho National Engineering Laboratory and Lawrence Livermore National LaboratoryChapline, G.; Dickson, P.; Schnitzler, B. Fission Fragment Rockets -- A Potential Breakthrough uses fuel placed on the surface of a number of very thin carbon fibres, arranged radially in wheels. The wheels are normally sub-critical. Several such wheels were stacked on a common shaft to produce a single large cylinder. The entire cylinder was rotated so that some fibres were always in a reactor core where surrounding moderator made fibres go critical.
|
|
Wallace Akers, the director of the British "Tube Alloys" project, told James Bryant Conant on 14 November that James Chadwick had "concluded that plutonium might not be a practical fissionable material for weapons because of impurities." Conant consulted Ernest Lawrence and Arthur Compton, who acknowledged that their scientists at Berkeley and Chicago respectively knew about the problem, but they could offer no ready solution. Conant informed Manhattan Project director Brigadier General Leslie R. Groves Jr., who in turn assembled a special committee consisting of Lawrence, Compton, Oppenheimer, and McMillan to examine the issue. The committee concluded that any problems could be overcome simply by requiring higher purity.
|
|
In response to the public alarm over fallout, an effort was made to design a clean multi-megaton weapon, relying almost entirely on fusion. The energy produced by the fissioning of unenriched natural uranium, when used as the tamper material in the secondary and subsequent stages in the Teller-Ulam design, can far exceed the energy released by fusion, as was the case in the Castle Bravo test. Replacing the fissionable material in the tamper with another material is essential to producing a "clean" bomb. In such a device, the tamper no longer contributes energy, so for any given weight, a clean bomb will have less yield.
|
|
This nuclide rapidly emits an electron, decaying into an element with a mass of 239 and an atomic number of 93. This nuclide then emits another electron to become a new element still of mass 239, but with an atomic number 94 and a much greater half-life. Bretscher and Feather showed theoretically feasible grounds that element 94 would be readily 'fissionable' by both slow and fast neutrons, and had the added advantage of being chemically different from uranium and therefore could easily be separated from it. This was confirmed independently in 1940 by Edwin M. McMillan and Philip Abelson at the Berkeley Radiation Laboratory.
|
|
Canada provided food aid, project financing and technical assistance to India. In the past five decades India has been one of the largest recipients of Canadian bilateral aid, amounting to over $3.8 billion Canadian dollars. In the 1960s, Canada supported the Kundah hydro-electric power house project through Colombo Plan. Indo-Canadian relations deteriorated in the wake of India's Smiling Buddha nuclear test of May 1974 when the Canadian government severed bilateral nuclear cooperation with both India and Pakistan in 1976 after claims that the fissionable material used to construct India's first nuclear device had been obtained from the Canadian-supplied CIRUS nuclear research reactor.
|
|
Historical marker and access sign On March 11, 1958 a U.S. Air Force B-47 Stratojet with a nuclear payload left for nuclear training exercises for war preparations in the United Kingdom and South Africa. The navigator mistakenly pulled the emergency release pin which resulted in the bomb falling out of the plane. Although the bomb was not armed with the trigger (a removable capsule of fissionable material which was securely stored in a containment area on board the plane), it nevertheless contained a high-explosive detonator. The resulting explosion created a crater estimated to be wide and 25-35 feet (7.6-10.7 m) deep.
|
|
The Cooperative Threat Reduction Act helped Russia move the nuclear arsenals in these countries back to Russia or dismembering these weapons in these countries. The United States sent "nearly 700 emergency response items to help guarantee safe and secure transportation of nuclear weapons" to Belarus for the aid of the elimination of nuclear power in this country. The Cooperative Threat Reduction Act played a major role in a huge decrease in the quantity of nuclear weapons that had been stockpiled during the nuclear escalation period. Another important contribution was when the United States sent storage containers to Russia to store fissionable material under their control.
|
|
ICAN-II was a proposed manned interplanetary spacecraft that used the Antimatter Catalyzed Micro-Fission (ACMF) engine as its main form of propulsion. The spacecraft was designed at Penn State University in the 1990s as a way to accomplish a manned mission to Mars. The proposed ACMF engine would require only 140 nanograms of antiprotons in conjunction with traditional fissionable fuel sources to allow a one-way transit time to Mars of 30 days. This is a considerable improvement over many other forms of propulsion that can be used for interplanetary missions, due to the high thrust-to-weight ratio and specific impulse of nuclear fuels.
|
|
In an attempt to make their refusal more difficult, he proposed that both sides agree to dedicate fissionable material away from weapons toward peaceful uses, such as power generation. This approach was labeled "Atoms for Peace". The U.N. speech was well received but the Soviets never acted upon it, due to an overarching concern for the greater stockpiles of nuclear weapons in the U.S. arsenal. Indeed, Eisenhower embarked upon a greater reliance on the use of nuclear weapons, while reducing conventional forces, and with them the overall defense budget, a policy formulated as a result of Project Solarium and expressed in NSC 162/2.
|
|
Salted versions of both fission and fusion weapons can be made by surrounding the core of the explosive device with a material containing an element that can be converted to a highly radioactive isotope by neutron bombardment. When the bomb explodes, the element absorbs neutrons released by the nuclear reaction, converting it to its radioactive form. The explosion scatters the resulting radioactive material over a wide area, leaving it uninhabitable far longer than an area affected by typical nuclear weapons. In a salted hydrogen bomb, the radiation case around the fusion fuel, which normally is made of some fissionable element, is replaced with a metallic salting element.
|
|
Salted fission bombs can be made by replacing the neutron reflector between the fissionable core and the explosive layer with a metallic element. The energy yield from a salted weapon is usually lower than from an ordinary weapon of similar size as a consequence of these changes. The radioactive isotope used for the fallout material would be a high intensity gamma ray emitter, with a half-life long enough that it remains lethal for an extended period. It would also have to have a chemistry that causes it to return to earth as fallout, rather than stay in the atmosphere after being vaporized in the explosion.
|
|
The key to maintaining a nuclear chain reaction within a nuclear reactor is to use, on average, exactly one of the neutrons released from each nuclear fission event to stimulate another nuclear fission event (in another fissionable nucleus). With careful design of the reactor's geometry, and careful control of the substances present so as to influence the reactivity, a self-sustaining chain reaction or "criticality" can be achieved and maintained. Natural uranium consists of a mixture of various isotopes, primarily 238U and a much smaller amount (about 0.72% by weight) of 235U. 238U can only be fissioned by neutrons that are relatively energetic, about 1 MeV or above.
|
|
His "reactor" was a bored-out block of lead, and he used lithium from $1,000 worth of purchased batteries to purify the thorium ash using a Bunsen burner. Hahn posed as an adult scientist or high school teacher to gain the trust of many professionals in letters—and succeeded, despite misspellings and obvious errors. Hahn ultimately hoped to create a breeder reactor, using low-level isotopes to transform samples of thorium and uranium into fissionable isotopes. His homemade neutron source was often incorrectly referred to as a reactor, but it did end up emitting dangerous levels of radiation, likely well over 1,000 times normal background radiation.
|
|
The objectives of the Sandstone series of tests were to: # test nuclear cores and initiators; # improve the theory and knowledge of implosion type weapons; # test levitated cores; # test composite cores; and # determine the most economic designs in terms of efficient use of fissionable material. Levitation meant that instead of being immediately inside the tamper, there would be an air gap between the tamper and the core, which would be suspended inside on wires. This would allow the tamper to gain more momentum before striking the core. The principle was similar to swinging a hammer at a nail versus putting the hammerhead directly on the nail and pushing as hard as possible.
|
|
For Sandstone, however, it was decided that at least two of the three tests would use levitated cores. The motivation behind the composite core was to make better use of the available fissionable material. The use of uranium-235 in an implosion weapon instead of the inefficient gun type Little Boy was an obvious development. However, while plutonium was more expensive and harder to produce than uranium-235, it fissions faster, because it makes better use of the neutrons its fission produces. On the other hand, the slower reaction of uranium-235 permits the assembly of super-critical masses, making it theoretically possible to produce weapons with high yields.
|
|
Cascades of alt=A photo of a large hall filled with arrays of long white standing cylinders. In nature, uranium is found as uranium-238 (99.2742%) and uranium-235 (0.7204%). Isotope separation concentrates (enriches) the fissionable uranium-235 for nuclear weapons and most nuclear power plants, except for gas cooled reactors and pressurised heavy water reactors. Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the nuclear chain reaction. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass'. To be considered 'enriched', the uranium-235 fraction should be between 3% and 5%.
|
|
Finger assembled a team of vibration specialists from other NASA centers, and along with staff from LASL, Aerojet and Westinghouse, conducted a series of "cold flow" reactor tests using fuel elements without fissionable material. Nitrogen, helium and hydrogen gas was pumped through the engine to induce vibrations. It was determined that they were caused by instability in the way the liquid flowed through the clearance gaps between adjacent fuel elements. A series of minor design changes were made to address the vibration problem. In the Kiwi B4D test on 13 May 1964, the reactor was automatically started and briefly run at full power (990 MW) with no vibration problems.
|
|
Cyril Stanley Smith (4 October 1903 – 25 August 1992) was a British metallurgist and historian of science. He is most famous for his work on the Manhattan Project where he was responsible for the production of fissionable metals. A graduate of the University of Birmingham and Massachusetts Institute of Technology (MIT), Smith worked for many years as a research metallurgist at the American Brass Company. During World War II he worked in the Chemical- Metallurgical Division of the Los Alamos Laboratory, where he purified, cast and shaped uranium-235 and plutonium, a metal hitherto available only in microgram amounts, and whose properties were largely unknown.
|
|
The idea of simply halting key aspects of the nuclear arms race arose in the early stages of the Cold War. Probably the first suggestion of this kind, discussed in letters between US President Dwight Eisenhower and Soviet Premier Nikolai Bulganin in the mid-1950s, called for a freeze on fissionable material. Concrete policy proposals began in the 1960s, with a formal proposal from the United States to the Soviet Union for a partial freeze on the number of offensive and defensive nuclear vehicles. However, the idea was rejected by the Soviet government, which feared that such a freeze would leave the Soviet Union in a position of strategic inferiority.
|
|
As a member of the Board of Consultants to a committee appointed by Truman, Oppenheimer strongly influenced the Acheson–Lilienthal Report. In this report, the committee advocated creation of an international Atomic Development Authority, which would own all fissionable material and the means of its production, such as mines and laboratories, and atomic power plants where it could be used for peaceful energy production. Bernard Baruch was appointed to translate this report into a proposal to the United Nations, resulting in the Baruch Plan of 1946. The Baruch Plan introduced many additional provisions regarding enforcement, in particular requiring inspection of the Soviet Union's uranium resources.
|
|
In September 1943, John von Neumann, who had experience with shaped charges used in armor-piercing shells, argued that not only would implosion reduce the danger of predetonation and fizzle, but would make more efficient use of the fissionable material.. He proposed using a spherical configuration instead of the cylindrical one that Neddermeyer was working on. alt=Diagram showing fast explosive, slow explosive, uranium tamper, plutonium core and neutron initiator By July 1944, Oppenheimer had concluded plutonium could not be used in a gun design, and opted for implosion. The accelerated effort on an implosion design, codenamed Fat Man, began in August 1944 when Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion.
|
|
A P2V takes off from in 1951 At the end of World War II, the US Navy felt the need to acquire a nuclear strike capability to maintain its political influence. In the short term, carrier- based aircraft were the best solution. The large Fat Man nuclear munitions at that time were bulky and required a very large aircraft to carry them. The US Navy Bureau of Ordnance built 25 outdated but more compact Little Boy nuclear bomb designs to be used in the smaller bomb bay of the P2V Neptune, there was enough fissionable material available by 1948 to build ten complete uranium projectiles and targets, although there were only enough initiators to complete six.
|
|
Between 1971 and 1974, a group of 15 nuclear supplier states held a series of informal meetings in Vienna chaired by Professor Claude Zangger of Switzerland. The group's objective was to reach a common understanding on: (a) the definition of "equipment or material especially designed or prepared for the processing, use or production of special fissionable material;" and (b) the conditions and procedures that would govern exports of such equipment or material in order to meet the obligations of Article III.2 on the basis of fair commercial competition. The group, which became known as the Zangger Committee, decided that it would be informal and that its decisions would not be legally binding upon its members.
|
|
Especially energetic alpha particles deriving from a nuclear process are produced in the relatively rare (one in a few hundred) nuclear fission process of ternary fission. In this process, three charged particles are produced from the event instead of the normal two, with the smallest of the charged particles most probably (90% probability) being an alpha particle. Such alpha particles are termed "long range alphas" since at their typical energy of 16 MeV, they are at far higher energy than is ever produced by alpha decay. Ternary fission happens in both neutron-induced fission (the nuclear reaction that happens in a nuclear reactor), and also when fissionable and fissile actinides nuclides (i.e.
|
|
The expense of the fissionable materials required was thought to be high, until the physicist Ted Taylor showed that with the right designs for explosives, the amount of fissionables used on launch was close to constant for every size of Orion from 2,000 tons to 8,000,000 tons. The larger bombs used more explosives to super- compress the fissionables, increasing efficiency. The extra debris from the explosives also serves as additional propulsion mass. The bulk of costs for historical nuclear defense programs have been for delivery and support systems, rather than for production cost of the bombs directly (with warheads being 7% of the U.S. 1946–1996 expense total according to one study).
|
|
"After spending a lot of time trying to estimate success by combinatorial calculations, I wondered whether a more practical method...might be to lay it out say one hundred times and simply observe and count the number of successful plays." In 1947, John von Neumann sent a letter to Robert Richtmyer proposing the use of a statistical method to solve neutron diffusion and multiplication problems in fission devices. His letter contained an 81-step pseudo code and was the first formulation of a Monte Carlo computation for an electronic computing machine. Von Neumann's assumptions were: time-dependent, continuous-energy, spherical but radially- varying, one fissionable material, isotropic scattering and fission production, and fission multiplicities of 2, 3, or 4.
|
|
In practice, buildup of reactor poisons in nuclear fuel is what determines the lifetime of nuclear fuel in a reactor: long before all possible fissions have taken place, buildup of long-lived neutron-absorbing fission products damps out the chain reaction. This is the reason that nuclear reprocessing is a useful activity: solid spent nuclear fuel contains about 97% of the original fissionable material present in newly manufactured nuclear fuel. Chemical separation of the fission products restores the fuel so that it can be used again. Other potential approaches to fission product removal include solid but porous fuel which allows escape of fission products and liquid or gaseous fuel (molten salt reactor, aqueous homogeneous reactor).
|
|
These are devices incorporated in nuclear weapons which produce a pulse of neutrons when the bomb is detonated to initiate the fission reaction in the fissionable core (pit) of the bomb, after it is compressed to a critical mass by explosives. Actuated by an ultrafast switch like a krytron, a small particle accelerator drives ions of tritium and deuterium to energies above the 15 keV or so needed for deuterium-tritium fusion and directs them into a metal target where the tritium and deuterium are adsorbed as hydrides. High-energy fusion neutrons from the resulting fusion radiate in all directions. Some of these strike plutonium or uranium nuclei in the primary's pit, initiating nuclear chain reaction.
|
|
The fusion process alone currently does not achieve sufficient gain (power output over power input) to be viable as a power source. By using the excess neutrons from the fusion reaction to in turn cause a high-yield fission reaction (close to 100%) in the surrounding subcritical fissionable blanket, the net yield from the hybrid fusion–fission process can provide a targeted gain of 100 to 300 times the input energy (an increase by a factor of three or four over fusion alone). Even allowing for high inefficiencies on the input side (i.e. low laser efficiency in ICF and Bremsstrahlung losses in Tokamak designs), this can still yield sufficient heat output for economical electric power generation.
|
|
In 1942, at the outset of the Manhattan Project, three methods of uranium enrichment were under consideration: gaseous diffusion, thermal diffusion, and electromagnetic separation. The gaseous diffusion method involves passing uranium hexafluoride (UF6) gas through a series of semipermeable membranes to achieve the separation of the fissionable uranium-235 (235U) isotope from the more abundant but non-fissile isotope uranium-238 (238U). It was first necessary however to develop non-reactive chemical compounds that could be used as coatings, lubricants and gaskets for the surfaces which would come into contact with the UF6 gas, which is a highly reactive and corrosive substance. Because of Miller's expertise in organofluorine chemistry, he was recruited by scientists of the Manhattan Project to synthesize and develop such materials.
|
|
In a nuclear weapon, an array of explosive lenses is used to change the several approximately-spherical diverging detonation waves into a single spherical converging one. The converging wave is then used to collapse the various shells (tamper, reflector, pusher, etc.) and finally compresses the core (pit) of fissionable material to a prompt critical state. They are usually machined from a plastic bonded explosive and an inert insert, called a wave-shaper, which is often a dense foam or plastic, though many other materials can be used. Other, mainly older explosive lenses do not include a wave shaper, but employ two explosive types that have significantly different velocities of detonation (VoD), which are in the range from 5 to 9 km/s.
|
|
Critical Nuclear Weapon Design Information (CNWDI, often pronounced SIN-widdy or SIN-wuh-dee) is a U.S. Department of Defense (DoD) category of Top Secret Restricted Data or Secret Restricted Data that reveals the theory of operation or design of the components of a thermonuclear or fission bomb, warhead, demolition munition, or test device. Specifically excluded is information concerning arming, fuzing, and firing systems; limited life components; and total contained quantities of fissionable, fusionable, and high explosive materials by type. Among these excluded items are the components that DoD personnel set, maintain, operate, test or replace. The sensitivity of DoD CNWDI is such that access is granted to the absolute minimum number of employees who require it for the accomplishment of assigned responsibilities on a classified contract.
|
|
Nuclear material refers to the metals uranium, plutonium, and thorium, in any form, according to the IAEA. This is differentiated further into "source material", consisting of natural and depleted uranium, and "special fissionable material", consisting of enriched uranium (U-235), uranium-233, and plutonium-239. Uranium ore concentrates are considered to be a "source material", although these are not subject to safeguards under the Nuclear Non- Proliferation Treaty.IAEA Safeguards Glossary, sections 4.1, 4.4, 4.5 According to the Nuclear Regulatory Commission(NRC), there are four different types of regulated nuclear materials: special nuclear material, source material, byproduct material and radium. Special nuclear materials have plutonium, uranium-233 or uranium with U233 or U235 that has a content found more than in nature.
|
|
The critical mass for 85% highly enriched uranium is about , which at normal density would be a sphere about in diameter. Later US nuclear weapons usually use plutonium-239 in the primary stage, but the jacket or tamper secondary stage, which is compressed by the primary nuclear explosion often uses HEU with enrichment between 40% and 80% along with the fusion fuel lithium deuteride. For the secondary of a large nuclear weapon, the higher critical mass of less-enriched uranium can be an advantage as it allows the core at explosion time to contain a larger amount of fuel. The 238U is not said to be fissile but still is fissionable by fast neutrons (>2 MeV) such as the ones produced during D-T fusion.
|
|
The earliest known incidence of a three-stage device being tested, with the third stage, called the tertiary, being ignited by the secondary, was May 27, 1956 in the Bassoon device. This device was tested in the Zuni shot of Operation Redwing. This shot used non-fissionable tampers; an inert substitute material such as tungsten or lead was used. Its yield was 3.5 megatons, 85% fusion and only 15% fission. The public records for devices that produced the highest proportion of their yield via fusion reactions are the peaceful nuclear explosions of the 1970s, with the 3 detonations that excavated part of Pechora–Kama Canal being cited as 98% fusion each in the Taiga test's 15 kiloton explosive yield devices; that is, a total fission fraction of 0.3 kilotons in a 15 kt device.
|
|
Von Neumann made his principal contribution to the atomic bomb in the concept and design of the explosive lenses that were needed to compress the plutonium core of the Fat Man weapon that was later dropped on Nagasaki. While von Neumann did not originate the "implosion" concept, he was one of its most persistent proponents, encouraging its continued development against the instincts of many of his colleagues, who felt such a design to be unworkable. He also eventually came up with the idea of using more powerful shaped charges and less fissionable material to greatly increase the speed of "assembly". When it turned out that there would not be enough uranium-235 to make more than one bomb, the implosive lens project was greatly expanded and von Neumann's idea was implemented.
|
|
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non- fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239. 238U cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. Doppler broadening of 238U's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control. Around 99.284% of natural uranium's mass is uranium-238, which has a half-life of 1.41 seconds (4.468 years, or 4.468 billion years).
|
|
The neutrons in nuclear reactors are generally categorized as slow (thermal) neutrons or fast neutrons depending on their energy. Thermal neutrons are similar in energy distribution (the Maxwell–Boltzmann distribution) to a gas in thermodynamic equilibrium; but are easily captured by atomic nuclei and are the primary means by which elements undergo nuclear transmutation. To achieve an effective fission chain reaction, neutrons produced during fission must be captured by fissionable nuclei, which then split, releasing more neutrons. In most fission reactor designs, the nuclear fuel is not sufficiently refined to absorb enough fast neutrons to carry on the chain reaction, due to the lower cross section for higher-energy neutrons, so a neutron moderator must be introduced to slow the fast neutrons down to thermal velocities to permit sufficient absorption.
|
|
Thus it is important that the frequency at which free neutrons occur is kept low, compared with the assembly time from this point. This also means that the speed of the projectile must be sufficiently high; its speed can be increased but this requires a longer and heavier barrel. In the case of Little Boy, the 20% U-238 in the uranium had 70 spontaneous fissions per second. With the fissionable material in a supercritical state, each gave a large probability of detonation: each fission creates on average 2.52 neutrons, which each have a probability of more than 1:2.52 of creating another fission. During the 1.35 ms of supercriticality prior to full assembly, there was a 10% probability of a fission, with somewhat less probability of pre-detonation.
|
|
Instead, bombarding 238U with slow neutrons causes it to absorb them (becoming 239U) and decay by beta emission to 239Np which then decays again by the same process to 239Pu; that process is used to manufacture 239Pu in breeder reactors. In-situ plutonium production also contributes to the neutron chain reaction in other types of reactors after sufficient plutonium-239 has been produced, since plutonium-239 is also a fissile element which serves as fuel. It is estimated that up to half of the power produced by a standard "non-breeder" reactor is produced by the fission of plutonium-239 produced in place, over the total life-cycle of a fuel load. Fissionable, non-fissile isotopes can be used as fission energy source even without a chain reaction.
|
|
Uranium-238, for example, has a near-zero fission cross section for neutrons of less than one MeV energy. If no additional energy is supplied by any other mechanism, the nucleus will not fission, but will merely absorb the neutron, as happens when U-238 absorbs slow and even some fraction of fast neutrons, to become U-239. The remaining energy to initiate fission can be supplied by two other mechanisms: one of these is more kinetic energy of the incoming neutron, which is increasingly able to fission a fissionable heavy nucleus as it exceeds a kinetic energy of one MeV or more (so-called fast neutrons). Such high energy neutrons are able to fission U-238 directly (see thermonuclear weapon for application, where the fast neutrons are supplied by nuclear fusion).
|
|
The resolution called on the UN Secretary-General to investigate the circumstances under which non- nuclear weapon states would give up the nuclear option. In March 1962, Sweden joined seven other neutral countries, members of the Eighteen Nation Committee on Disarmament, a predecessor to the Conference on Disarmament (CD). In 1968, Sweden signed the Nuclear non-proliferation Treaty (NPT) and thereby publicly committed itself against the acquisition of nuclear weapons. Shortly after joining the NPT, Sweden became a founding member of the Zangger Committee, which was designed to work out the exact definitions of the material and equipment to be restricted by the NPT. The Committee drafted a “Trigger List” of "source or special fissionable materials" and "equipment or materials specially designed or prepared for the processing, use, or production of fissile materials".
|
|
In practice, buildup of reactor poisons in nuclear fuel is what determines the lifetime of nuclear fuel in a reactor: long before all possible fissions have taken place, buildup of long-lived neutron absorbing fission products damps out the chain reaction. This is the reason that nuclear reprocessing is a useful activity: spent nuclear fuel contains about 96% of the original fissionable material present in newly manufactured nuclear fuel. Chemical separation of the fission products restores the nuclear fuel so that it can be used again. Nuclear reprocessing is useful economically because chemical separation is much simpler to accomplish than the difficult isotope separation required to prepare nuclear fuel from natural uranium ore, so that in principle chemical separation yields more generated energy for less effort than mining, purifying, and isotopically separating new uranium ore.
|
|
Because the thermal neutron spectrum is not very good for fissioning Pu-239 the fuel shifts from 100% Uranium at start of cycle to 96% Uranium, 1% Plutonium and 3% mixture of Transuranic Actinide and Fission Products. The longer the fuel remain in the reactor undergoing fission the more the Uranium percentage decreases while the other materials increase. In effect all power reactors have been long known to be capable of operating with a mixed fissionable core containing 1% reactor grade Plutonium without issues arising like those caused by the more highly concentrated MOX fuel used in western reactors. Russia spent nearly a decade developing techniques similar to Nuclear Pyroprocessing that allows them to reprocess spent nuclear fuel without separating the recycled Uranium and Plutonium from the other metals as is done in the PUREX chemical reprocessing system used to manufacture MOX fuel.
|
|
This energy, resulting from the neutron capture, is a result of the attractive nuclear force acting between the neutron and nucleus. It is enough to deform the nucleus into a double-lobed "drop", to the point that nuclear fragments exceed the distances at which the nuclear force can hold two groups of charged nucleons together and, when this happens, the two fragments complete their separation and then are driven further apart by their mutually repulsive charges, in a process which becomes irreversible with greater and greater distance. A similar process occurs in fissionable isotopes (such as uranium-238), but in order to fission, these isotopes require additional energy provided by fast neutrons (such as those produced by nuclear fusion in thermonuclear weapons). The liquid drop model of the atomic nucleus predicts equal-sized fission products as an outcome of nuclear deformation.
|
|
Typical fission events release about two hundred million eV (200 MeV) of energy, the equivalent of roughly >2 trillion Kelvin, for each fission event. The exact isotope which is fissioned, and whether or not it is fissionable or fissile, has only a small impact on the amount of energy released. This can be easily seen by examining the curve of binding energy (image below), and noting that the average binding energy of the actinide nuclides beginning with uranium is around 7.6 MeV per nucleon. Looking further left on the curve of binding energy, where the fission products cluster, it is easily observed that the binding energy of the fission products tends to center around 8.5 MeV per nucleon. Thus, in any fission event of an isotope in the actinide's range of mass, roughly 0.9 MeV is released per nucleon of the starting element.
|
|
Materials included the cavity magnetron which was essential to RADAR, British information related to the German Enigma machines, Jet Engine designs as well as "Tube Alloys". Canada's role in the Manhattan Project besides providing raw material, including uranium ore from a northern mine which may have been used in the construction of the atom bomb that was dropped on Hiroshima in 1945, was to provide at least one scientist working at Los Alamos (Louis Slotin), and hosting the Montreal Laboratory which took over from Tube Alloys. Canada would continue to supply fissionable material to the US and other allies throughout the Cold War although Canada never developed indigenous nuclear weapons as did NATO allies France and the United Kingdom. After briefly allowing nuclear weapons to be temporarily stationed in Goose Bay, Labrador, Canada agreed to a long term lease of the Goose Bay base to the US Strategic Air Command.
|
|
No amount of 238U can be made "critical" since it will tend to parasitically absorb more neutrons than it releases by the fission process. 235U, on the other hand, can support a self-sustained chain reaction, but due to the low natural abundance of 235U, natural uranium cannot achieve criticality by itself. The trick to achieving criticality using only natural or low enriched uranium, for which there is no "bare" critical mass, is to slow down the emitted neutrons (without absorbing them) to the point where enough of them may cause further nuclear fission in the small amount of 235U which is available. (238U which is the bulk of natural uranium is also fissionable with fast neutrons.) This requires the use of a neutron moderator, which absorbs virtually all of the neutrons' kinetic energy, slowing them down to the point that they reach thermal equilibrium with surrounding material.
|
|
At the recommendation of Dulles (who had recently come to support a test ban), the review prompted Eisenhower to propose technical negotiations with the Soviet Union, effectively detaching test-ban negotiations from negotiations over a halt to nuclear weapons production (the one-time US demand). In explaining the policy shift, Eisenhower privately said that continued resistance to a test ban would leave the US in a state of "moral isolation." On 8 April 1958, still resisting Khrushchev's call for a moratorium, Eisenhower invited the Soviet Union to join these technical negotiations in the form of a conference on the technical aspects of a test-ban, specifically the technical details of ensuring compliance with a ban. The proposal was, to a degree, a concession to the Soviet Union, as a test ban would be explored independent of the previously demanded cutoff in fissionable-material production.
|
|
Munir Ahmad Khan, "How Pakistan Made Nuclear Fuel", pp. 5–9 The breakthrough with plutonium experiment was at the PINSTECH Laboratory by Iqbal Hussain Qureshi of NCD and Ishfaq Ahmad of Nuclear Physics Group (NPG). The scientists realized that a slow neutron reactor fuelled with uranium would theoretically produce substantial amounts of 239Pu as a by-product. The experiments also showed theoretically feasible grounds that element 94 would be readily fissionable by both slow and fast neutrons, and had the added advantage of being chemically different from uranium, and could easily be separated from it.Munir Ahmad Khan, "How Pakistan Made Nuclear Fuel", pp. 9–10 After the discovery, the PAEC used Shaukat Hameed Khan's MLIS method to separate plutonium isotopes at Neutron Facility at PINSTECH. From 1974, Shaukat Hameed Khan had continuously worked on this complex and difficult method and successfully used the method to separate the isotopes of plutonium.
|
|
Supergirl is introduced to the world on the cover of Action Comics #285 (February 1962) Art by Curt Swan Kara Zor-El (originally, just Kara; Kryptonians during the Golden Era used a single name for most women, and a two-syllable name for men; thus the addition of the patronymic to the female name is a contemporary convention) is the last survivor of Argo City, which had survived the explosion of the planet Krypton and drifted through space. The city had been covered by a plastic dome for weather moderation, devised by Zor-El, the younger brother of Jor-El, a climatologist and engineer, the father of Superman (Kal-El). The dome held together a large chunk of land mass under the city as it drifted through space in the general direction of our solar system. However, the bottom-most layers of bedrock were affected by the explosion of the great planet's fissionable core and underwent a slow but steady chain reaction, turning into green Kryptonite.
|
|
Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as "Nuclear Weapon States" by the Treaty on the Non-Proliferation of Nuclear Weapons, commonly known as the Non-Proliferation Treaty or NPT. Proliferation has been opposed by many nations with and without nuclear weapons, as governments fear that more countries with nuclear weapons will increase the possibility of nuclear warfare (up to and including the so-called countervalue targeting of civilians with nuclear weapons), de-stabilize international or regional relations, or infringe upon the national sovereignty of nation states. Four countries besides the five recognized Nuclear Weapons States have acquired, or are presumed to have acquired, nuclear weapons: India, Pakistan, North Korea, and Israel. None of these four is a party to the NPT, although North Korea acceded to the NPT in 1985, then withdrew in 2003 and conducted announced nuclear tests in 2006, 2009, 2013, 2016, and 2017.
|
|
In 1972 the United States government declassified a document stating "[I]n thermonuclear (TN) weapons, a fission 'primary' is used to trigger a TN reaction in thermonuclear fuel referred to as a 'secondary'", and in 1979 added, "[I]n thermonuclear weapons, radiation from a fission explosive can be contained and used to transfer energy to compress and ignite a physically separate component containing thermonuclear fuel." To this latter sentence the US government specified that "Any elaboration of this statement will be classified."emphasis in original The only information that may pertain to the spark plug was declassified in 1991: "Fact that fissile or fissionable materials are present in some secondaries, material unidentified, location unspecified, use unspecified, and weapons undesignated." In 1998 the DOE declassified the statement that "The fact that materials may be present in channels and the term 'channel filler,' with no elaboration", which may refer to the polystyrene foam (or an analogous substance).
|
|
This proposal, which closely reflected a prior Anglo-French proposal, was initially part of a comprehensive disarmament proposal meant to reduce conventional arms levels and eliminate nuclear weapons. Despite the closeness of the Soviet proposal to earlier Western proposals, the US reversed its position on the provisions and rejected the Soviet offer "in the absence of more general control agreements," including limits on the production of fissionable material and protections against a surprise nuclear strike. The May 1955 proposal is now seen as evidence of Khrushchev's "new approach" to foreign policy, as Khrushchev sought to mend relations with the West. The proposal would serve as the basis of the Soviet negotiating position through 1957. Eisenhower had supported nuclear testing after World War II. In 1947, he rejected arguments by Stafford L. Warren, the Manhattan Project's chief physician, concerning the detrimental health effects of atmospheric testing, agreeing instead with James Bryant Conant, a chemist and participant in the Manhattan Project, who was skeptical of Warren's then-theoretical claims.
|
|
The panel argued that a successful U.S. test would only encourage the Soviets to intensify their efforts towards an H-bomb, both out of an urgent need to match the American achievement and because a successful test would prove that a thermonuclear device was technically possible.Holloway, Stalin and the Bomb, p. 311. In propaganda terms, conducting a test would be to the disadvantage of the United States, since it would appear to be the country marching towards nuclear war. Militarily, the advent of hydrogen bombs on both sides could prove to be an overall negative for the United States, since the United States and its Western European allies had more targets within their territory that were suitable for attack by the hydrogen bomb than the Soviet Union and its Eastern European allies did, and the Soviets could more effectively use their smaller amount of fissionable materials in H-bombs than they could in A-bombs.
|
|
As he was the only one of the five commissioners who was a scientist—an important factor in his decision to accept the post—he played a leading role in the selection of the Atomic Energy Commission's influential General Advisory Committee to which nine scientists were appointed: James Conant, Lee DuBridge, Enrico Fermi, Robert Oppenheimer, Isidor Isaac Rabi, Hartley Rowe, Glenn Seaborg, Cyril Stanley Smith and Hood Worthington. Bacher and fellow commissioner Sumner Pike began with an inspection of Los Alamos and the Hanford Site, and conducted an inventory of the fissionable material at Los Alamos with Norris Bradbury, who had succeeded Oppenheimer as its director. He found that only nine atomic bombs had been built in 1946; only four would be in 1947, primarily due to production problems with the reactors at Hanford. These problems were on their way to resolution when Bacher observed the Operation Sandstone nuclear tests at Enewetak Atoll in 1948 as the Atomic Energy Commission's representative.
|
|
This fraction includes the actinides most easily reusable as nuclear fuel in a thermal reactor, and the two long-lived fission products best suited to disposal by transmutation, Tc-99 and I-129, as well as Se-79. Noble gases (xenon, krypton) are volatile even without fluoridation, and will not condense except at much lower temperatures. Left behind are alkali metals (caesium, rubidium), alkaline earth metals (strontium, barium), lanthanides, the remaining actinides (americium, curium), remaining transition metals (yttrium, zirconium, palladium, silver) and post-transition metals (tin, indium, cadmium). This fraction contains the fission products that are radiation hazards on a scale of decades (Cs-137, Sr-90, Sm-151), the four remaining long-lived fission products Cs-135, Zr-93, Pd-107, Sn-126 of which only the last emits strong radiation, most of the neutron poisons, and the higher actinides (americium, curium, californium) that are radiation hazards on a scale of hundreds or thousands of years and are difficult to work with because of gamma radiation but are fissionable in a fast reactor.
|
|
Fission occurs when a heavy nuclide such as uranium-235 absorbs a neutron and breaks into lighter components such as barium or krypton, usually with the release of additional neutrons. Like all nuclides with a high atomic number, these uranium nuclei require many neutrons to bolster their stability, so they have a large neutron-proton ratio (N/Z). The nuclei resulting from a fission (fission products) inherit a similar N/Z, but have atomic numbers that are approximately half that of uranium. Isotopes with the atomic number of the fission products and an N/Z near that of uranium or other fissionable nuclei have too many neutrons to be stable; this neutron excess is why multiple free neutrons but no free protons are usually emitted in the fission process, and it is also why many fission product nuclei undergo a long chain of β− decays, each of which converts a nucleus N/Z to (N − 1)/(Z + 1), where N and Z are, respectively, the numbers of neutrons and protons contained in the nucleus.
|
|
The fission of a heavy nucleus requires a total input energy of about 7 to 8 million electron volts (MeV) to initially overcome the nuclear force which holds the nucleus into a spherical or nearly spherical shape, and from there, deform it into a two-lobed ("peanut") shape in which the lobes are able to continue to separate from each other, pushed by their mutual positive charge, in the most common process of binary fission (two positively charged fission products + neutrons). Once the nuclear lobes have been pushed to a critical distance, beyond which the short range strong force can no longer hold them together, the process of their separation proceeds from the energy of the (longer range) electromagnetic repulsion between the fragments. The result is two fission fragments moving away from each other, at high energy. About 6 MeV of the fission-input energy is supplied by the simple binding of an extra neutron to the heavy nucleus via the strong force; however, in many fissionable isotopes, this amount of energy is not enough for fission.
|
|
UN vote on adoption of the Treaty on the Prohibition of Nuclear Weapons on 7 July 2017 Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as "Nuclear Weapon States" by the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), commonly known as the Non-Proliferation Treaty or NPT. Proliferation has been opposed by many nations with and without nuclear weapons, as governments fear that more countries with nuclear weapons will increase the possibility of nuclear warfare (up to and including the so-called "countervalue" targeting of civilians with nuclear weapons), de-stabilize international or regional relations, or infringe upon the national sovereignty of states. Four countries besides the five recognized Nuclear Weapons States have acquired, or are presumed to have acquired, nuclear weapons: India, Pakistan, North Korea, and Israel. None of these four is a party to the NPT, although North Korea acceded to the NPT in 1985, then withdrew in 2003 and conducted announced nuclear tests in 2006, 2009, 2013, 2016, and 2017.
|
|
Finally, any energy loss not through radiation that is redirected precisely to aft but is instead conducted away by engine supports, radiated in some other direction, or lost via neutrinos or so will further degrade the efficiency. If we were to set 80% of the mass of the photon rocket = fissionable fuel, and recognizing that nuclear fission converts about 0.10% of the mass into energy: then if the photon rocket masses 300,000 kg then 240,000 kg of that is atomic fuel. Therefore, the fissioning of all of the fuel will result in the loss of just 240 kg of mass. Then 300,000/299,760 kg = an mi/mf of 1.0008. Using the rocket equation, we find vf = ln 1.0008 × c where c = 299,792,458 m/s. vf then may be 239,930 m/s which is about 240 km/s. The nuclear fission powered photon rocket may accelerate at a maximum of perhaps 1/10,000 m/s² (0.1 mm/s²) which is 10−5g. The velocity change would be at the rate of 3,000 m/s per year of thrusting by the photon rocket.
|
|
Article II of the IAEA Statute defines the Agency's twin objectives as promoting peaceful uses of atomic energy and "ensur[ing], so far as it is able, that assistance provided by it or at its request or under its supervision or control is not used in such a way as to further any military purpose." To do this, the IAEA is authorised in Article III.A.5 of the Statute "to establish and administer safeguards designed to ensure that special fissionable and other materials, services, equipment, facilities, and information made available by the Agency or at its request or under its supervision or control are not used in such a way as to further any military purpose; and to apply safeguards, at the request of the parties, to any bilateral or multilateral arrangement, or at the request of a State, to any of that State's activities in the field of atomic energy." The Department of Safeguards is responsible for carrying out this mission, through technical measures designed to verify the correctness and completeness of states' nuclear declarations.
|
|
Because uranium-235 was known to be fissionable, it was the first material pursued in the approach to bomb development. As the first design developed (as well as the first deployed for combat), it is sometimes known as the Mark I. The vast majority of the work came in the form of the isotope enrichment of the uranium necessary for the weapon, since uranium-235 makes up only 1 part in 140 of natural uranium. Enrichment was performed at Oak Ridge, Tennessee, where the electromagnetic separation plant, known as Y-12, became fully operational in March 1944. The first shipments of highly enriched uranium were sent to the Los Alamos Laboratory in June 1944. Most of the uranium necessary for the production of the bomb came from the Shinkolobwe mine and was made available thanks to the foresight of the CEO of the High Katanga Mining Union, Edgar Sengier, who had of uranium ore transported to a New York warehouse in 1940. At least part of the in addition to the uranium ore and uranium oxide captured by the Alsos Mission in 1944 and 1945 went to Oak Ridge for enrichment, as did of uranium oxide captured on the Japan-bound after Germany's surrender in May 1945.
|
|
The group repeated the oft-cited fact, which was supported by Freeman Dyson, that the Soviet Union could conduct secret nuclear tests. In 1958, at the request of Igor Kurchatov, Soviet nuclear physicist and weapons designer Andrei Sakharov published a pair of widely circulated academic papers challenging the claim of Teller and others that a clean, fallout-free nuclear bomb could be developed, due to the formation of carbon-14 when nuclear devices are detonated in the air. A one-megaton clean bomb, Sakharov estimated, would cause 6,600 deaths over 8,000 years, figures derived largely from estimates on the quantity of carbon-14 generated from atmospheric nitrogen and the contemporary risk models at the time, along with the assumption that the world population is "thirty billion persons" in a few thousand years. In 1961, Sakharov was part of the design team for a 50 megaton "clean bomb", which has become known as the Tsar Bomba, detonated over the island of Novaya Zemlya. Macmillan (second from left) with Eisenhower in March 1957 In the spring of 1957, the US National Security Council had explored including a one-year test moratorium and a "cut-off" of fissionable-material production in a "partial" disarmament plan.
|
|