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50-617: The W31 was produced from 1959, with the last versions phased out in 1989. All versions were roughly the same dimensions and weight: 28–30 in (710–760 mm) in diameter, 39–39.5 in (990–1,000 mm) long, and weighing 900–945 lb (408–429 kg). The W31 is a boosted fission nuclear bomb . The Nike Hercules was a surface-to-air or surface-to-surface missile system deployed around US cities and various locations in Europe and Japan. Most, but not all, of these missiles were deployed with nuclear warheads. In South Florida, half of

100-408: A chain reaction at the level of the nucleus. He did not envision fission as one of these neutron-producing reactions, since this reaction was not known at the time. Experiments he proposed using beryllium and indium failed. Later, after fission was discovered in 1938, Szilárd immediately realized the possibility of using neutron-induced fission as the particular nuclear reaction necessary to create

150-466: A chain-reaction, so long as fission also produced neutrons. In 1939, with Enrico Fermi, Szilárd proved this neutron-multiplying reaction in uranium. 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

200-504: A complete rate equation with a two-term denominator ( mixed-order kinetics ). The pyrolysis (thermal decomposition) of acetaldehyde , CH 3 CHO (g) → CH 4 (g) + CO (g), proceeds via the Rice-Herzfeld mechanism: The methyl and CHO groups are free radicals . This reaction step provides methane , which is one of the two main products. The product •CH 3 CO (g) of the previous step gives rise to carbon monoxide (CO), which

250-454: A hollow cavity at the center of the sphere of fission fuel, or into a gap between an outer layer and a "levitated" inner core, sometime before implosion. By the time about 1% of the fission fuel has fissioned, the temperature rises high enough to cause thermonuclear fusion , which produces relatively large numbers of high-energy neutrons. This influx of neutrons speeds up the late stages of the chain reaction, causing approximately twice as much of

300-515: A molecule excited by light, but could also start with two molecules colliding violently due to thermal energy as previously proposed for initiation of chemical reactions by van' t Hoff . Christiansen and Kramers also noted that if, in one link of the reaction chain, two or more unstable molecules are produced, the reaction chain would branch and grow. The result is in fact an exponential growth, thus giving rise to explosive increases in reaction rates, and indeed to chemical explosions themselves. This

350-519: A neutron with an energy of 14 MeV —a much higher energy than the 1 MeV of the neutron that began the reaction. This creation of high-energy neutrons, rather than energy yield, is the main purpose of fusion in this kind of weapon. This 14 MeV neutron then strikes an atom of uranium-238, causing fission: without this fusion stage, the original 1 MeV neutron hitting an atom of uranium-238 would probably have just been absorbed. This fission then releases energy and also neutrons, which then create more tritium from

400-414: A path of release over friction. Chemically, the equivalent to a snow avalanche is a spark causing a forest fire. In nuclear physics, a single stray neutron can result in a prompt critical event, which may finally be energetic enough for a nuclear reactor meltdown or (in a bomb) a nuclear explosion. Another metaphor for a chain reaction is the domino effect , named after the act of domino toppling , where

450-407: A self-amplifying chain of events . Chain reactions are one way that systems which are not in thermodynamic equilibrium can release energy or increase entropy in order to reach a state of higher entropy. For example, a system may not be able to reach a lower energy state by releasing energy into the environment, because it is hindered or prevented in some way from taking the path that will result in

500-456: A small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released due to fission, allowing for more neutron-induced fission reactions to take place. The rate of fission is thereby greatly increased such that much more of the fissile material is able to undergo fission before the core explosively disassembles. The fusion process itself adds only

550-449: A small amount of energy to the process, perhaps 1%. The alternative meaning is an obsolete type of single-stage nuclear bomb that uses thermonuclear fusion on a large scale to create fast neutrons that can cause fission in depleted uranium , but which is not a two-stage hydrogen bomb . This type of bomb was referred to by Edward Teller as "Alarm Clock", and by Andrei Sakharov as "Sloika" or "Layer Cake" (Teller and Sakharov developed

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600-433: A strong electric field causes them to gain energy, and when they impact other atoms, the energy causes release of new free electrons and ions (ionization), which fuels the same process. If this process happens faster than it is naturally quenched by ions recombining, the new ions multiply in successive cycles until the gas breaks down into a plasma and current flows freely in a discharge. Electron avalanches are essential to

650-541: Is a very important advantage in using boosting. It appears that every weapon now in the U.S. arsenal is a boosted design. According to one weapons designer, boosting is mainly responsible for the remarkable 100-fold increase in the efficiency of fission weapons since 1945. Early thermonuclear weapon designs such as the Joe-4 , the Soviet "Layer Cake" ("Sloika", Russian : Слойка ), used large amounts of fusion to induce fission in

700-440: Is among the nuclides with the largest cross-section for neutron capture. Therefore, periodically the weapon must have its helium waste flushed out and its tritium supply recharged. This is because any helium-3 in the weapon's tritium supply would act as a poison during the weapon's detonation, absorbing neutrons meant to collide with the nuclei of its fission fuel. Tritium is relatively expensive to produce because each triton -

750-466: Is defined as the average number of times the propagation cycle is repeated, and equals the overall reaction rate divided by the initiation rate. Some chain reactions have complex rate equations with fractional order or mixed order kinetics. The reaction H 2 + Br 2 → 2 HBr proceeds by the following mechanism: As can be explained using the steady-state approximation , the thermal reaction has an initial rate of fractional order (3/2), and

800-418: Is limited in yield by practical concerns of mass and diameter to less than one megaton of TNT (4 PJ ) equivalent. Joe-4 yielded 400 kilotons of TNT (1.7 PJ). In comparison, a "true" hydrogen bomb can produce up to 97% of its yield from fusion , and its explosive yield is limited only by device size. Tritium is a radioactive isotope with a half-life of 12.355 years. Its main decay product is helium-3 , which

850-489: Is physical damage to the crystal). Certain devices, such as avalanche diodes , deliberately make use of the effect. Examples of chain reactions in living organisms include excitation of neurons in epilepsy and lipid peroxidation . In peroxidation, a lipid radical reacts with oxygen to form a peroxyl radical (L• + O 2 → LOO•). The peroxyl radical then oxidises another lipid, thus forming another lipid radical (LOO• + L–H → LOOH + L•). A chain reaction in glutamatergic synapses

900-421: Is reached at very low efficiencies, when less than 1% of the fissile material has fissioned (corresponding to a yield in the range of hundreds of tons of TNT). Since implosion weapons can be designed that will achieve yields in this range even if neutrons are present at the moment of criticality, fusion boosting allows the manufacture of efficient weapons that are immune to predetonation . Elimination of this hazard

950-521: Is reduced by a factor of about 8. A sense of the potential contribution of fusion boosting can be gained by observing that the complete fusion of one mole of tritium (3 grams) and one mole of deuterium (2 grams) would produce one mole of neutrons (1 gram), which, neglecting escape losses and scattering, could fission one mole (239 grams) of plutonium directly, producing 4.6 moles of secondary neutrons, which can in turn fission another 4.6 moles of plutonium (1,099 g). The fission of this 1,338 g of plutonium in

1000-422: Is responsible for the formation of as many as 10 molecules of the product HCl . Nernst suggested that the photon dissociates a Cl 2 molecule into two Cl atoms which each initiate a long chain of reaction steps forming HCl. In 1923, Danish and Dutch scientists J. A. Christiansen and Hendrik Anthony Kramers , in an analysis of the formation of polymers, pointed out that such a chain reaction need not start with

1050-428: Is the mechanism of a Geiger counter and also the visualization possible with a spark chamber and other wire chambers . An avalanche breakdown process can happen in semiconductors, which in some ways conduct electricity analogously to a mildly ionized gas. Semiconductors rely on free electrons knocked out of the crystal by thermal vibration for conduction. Thus, unlike metals, semiconductors become better conductors

SECTION 20

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1100-496: Is the second main product. The sum of the two propagation steps corresponds to the overall reaction CH 3 CHO (g) → CH 4 (g) + CO (g), catalyzed by a methyl radical •CH 3 . This reaction is the only source of ethane (minor product) and it is concluded to be the main chain ending step. Although this mechanism explains the principal products, there are others that are formed in a minor degree, such as acetone (CH 3 COCH 3 ) and propanal (CH 3 CH 2 CHO). Applying

1150-626: The Steady State Approximation for the intermediate species CH 3 (g) and CH 3 CO(g), the rate law for the formation of methane and the order of reaction are found: The rate of formation of the product methane is ( 1 ) . . . d [ CH 4 ] d t = k 2 [ CH 3 ] [ CH 3 CHO ] {\displaystyle (1)...{\frac {d{\ce {[CH4]}}}{dt}}=k_{2}{\ce {[CH3]}}{\ce {[CH3CHO]}}} For

1200-446: The dielectric breakdown process within gases. The process can culminate in corona discharges , streamers , leaders , or in a spark or continuous electric arc that completely bridges the gap. The process may extend huge sparks — streamers in lightning discharges propagate by formation of electron avalanches created in the high potential gradient ahead of the streamers' advancing tips. Once begun, avalanches are often intensified by

1250-401: The fissile fuel is "assembled" quickly by a uniform spherical implosion created with conventional explosives , producing a supercritical mass . In this state, many of the neutrons released by the fissioning of a nucleus will induce fission of other nuclei in the fuel mass, also releasing additional neutrons, leading to a chain reaction . This reaction consumes at most 20% of the fuel before

1300-549: The uranium-238 atoms that make up depleted uranium . These weapons had a fissile core surrounded by a layer of lithium-6 deuteride , in turn surrounded by a layer of depleted uranium. Some designs (including the layer cake) had several alternate layers of these materials. The Soviet Layer Cake was similar to the American Alarm Clock design, which was never built, and the British Green Bamboo design, which

1350-680: The Nike Hercules missiles of the Homestead-Miami Defense were armed with the T-45 high-explosive warheads. Three yield variants, of 2, 20, and 40 kilotons , were deployed on these missiles starting in 1958 and finally retired in 1989. 2,550 of these models were produced. The 20 kt version of the W-31 was solely used in the Nike Hercules system. A similar variant, the XW-37, was a high yield version of

1400-517: The W31 Mod 1 was stockpiled as an atomic demolition munition . Allegedly, four of the five stockpiled W31 yields were used in the ADM version of the weapon, i.e. four of 1, 2, 12, 20 or 40 kilotonnes of TNT (4.2, 8.4, 50.2, 83.7 or 167.4 TJ). 300 weapons were produced. Boosted fission weapon A boosted fission weapon usually refers to a type of nuclear bomb that uses

1450-634: The XW-31. Development started in January 1956. Three months later, the XW-31 was redesignated XW-31Y1 (for yield 1) and the XW-37 designation was changed to XW-31Y2 (for yield 2). The Honest John was a short-range surface-to-surface tactical ballistic rocket used by the US Army. Three yield variants, also apparently 2, 20 and 40 kilotons, were deployed on Honest John missiles from 1959 to 1987. A total of 1,650 Honest John W31 warheads were produced. Between 1960 and 1965,

1500-498: The bomb blows itself apart, or possibly much less if conditions are not ideal: the Little Boy (gun type mechanism) and Fat Man (implosion type mechanism) bombs had efficiencies of 1.38% and 13%, respectively. Fusion boosting is achieved by introducing tritium and deuterium gas. Solid lithium deuteride -tritide has also been used in some cases, but gas allows more flexibility (and can be stored externally) and can be injected into

1550-544: The chain reaction can continue beyond the second generation after fusion boosting. Fusion-boosted fission bombs can also be made immune to neutron radiation from nearby nuclear explosions, which can cause other designs to predetonate, blowing themselves apart without achieving a high yield. The combination of reduced weight in relation to yield and immunity to radiation has ensured that most modern nuclear weapons are fusion-boosted. The fusion reaction rate typically becomes significant at 20 to 30 megakelvins . This temperature

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1600-444: The creation of photoelectrons as a result of ultraviolet radiation emitted by the excited medium's atoms in the aft-tip region. The extremely high temperature of the resulting plasma cracks the surrounding gas molecules and the free ions recombine to create new chemical compounds. The process can also be used to detect radiation that initiates the process, as the passage of a single particles can be amplified to large discharges. This

1650-452: The energy release. If a reaction results in a small energy release making way for more energy releases in an expanding chain, then the system will typically collapse explosively until much or all of the stored energy has been released. A macroscopic metaphor for chain reactions is thus a snowball causing a larger snowball until finally an avalanche results (" snowball effect "). This is a result of stored gravitational potential energy seeking

1700-435: The first two generations would release 23 kilotons of TNT equivalent (97 TJ ) of energy, and would by itself result in a 29.7% efficiency for a bomb containing 4.5 kg of plutonium (a typical small fission trigger). The energy released by the fusion of the 5 g of fusion fuel itself is only 1.73% of the energy released by the fission of 1,338 g of plutonium. Larger total yields and higher efficiency are possible, since

1750-412: The fissile material to fission before the critical mass is disassembled by the explosion. Deuterium-tritium fusion neutrons are extremely energetic, seven times more energetic than an average fission neutron, which makes them much more likely to be captured in the fissile material and lead to fission. This is due to several reasons: Consequently, the time for the neutron population in the core to double

1800-421: The higher the temperature. This sets up conditions for the same type of positive feedback—heat from current flow causes temperature to rise, which increases charge carriers, lowering resistance, and causing more current to flow. This can continue to the point of complete breakdown of normal resistance at a semiconductor junction, and failure of the device (this may be temporary or permanent depending on whether there

1850-439: The idea independently, as far as is known). The idea of boosting was originally developed between late 1947 and late 1949 at Los Alamos . The primary benefit of boosting is further miniaturization of nuclear weapons as it reduces the minimum inertial confinement time required for a supercritical nuclear explosion by providing a sudden influx of fast neutrons before the critical mass would blow itself apart. This would eliminate

1900-1766: The intermediates ( 2 ) . . . d [ CH 3 ] d t = k 1 [ CH 3 CHO ] − k 2 [ CH 3 ] [ CH 3 CHO ] + k 3 [ CH 3 CO ] − 2 k 4 [ CH 3 ] 2 = 0 {\displaystyle (2)...{\frac {d{\ce {[CH_3]}}}{dt}}=k_{1}{\ce {[CH3CHO]}}-k_{2}{\ce {[CH3]}}{\ce {[CH3CHO]}}+k_{3}{\ce {[CH3CO]}}-2k_{4}{\ce {[CH3]}}^{2}=0} and ( 3 ) . . . d [ CH 3 CO ] d t = k 2 [ CH 3 ] [ CH 3 CHO ] − k 3 [ CH 3 CO ] = 0 {\displaystyle (3)...{\frac {d{\ce {[CH3CO]}}}{dt}}=k_{2}{\ce {[CH3]}}{\ce {[CH3CHO]}}-k_{3}{\ce {[CH3CO]}}=0} Adding (2) and (3), we obtain k 1 [ CH 3 CHO ] − 2 k 4 [ CH 3 ] 2 = 0 {\displaystyle k_{1}{\ce {[CH3CHO]}}-2k_{4}{\ce {[CH3]}}^{2}=0} so that ( 4 ) . . . [ CH 3 ] = k 1 2 k 4 [ CH 3 CHO ] 1 / 2 {\displaystyle (4)...{\ce {[CH3]}}={\frac {k_{1}}{2k_{4}}}{\ce {[CH3CHO]}}^{1/2}} Using (4) in (1) gives

1950-452: The need for an aluminum pusher and uranium tamper and the explosives needed to push them and the fissile material into a supercritical state. While the bulky Fat Man had a diameter of 5 feet (1.5 m) and required 3 tons of high explosives for implosion, a boosted fission primary can be fitted on a small nuclear warhead (such as the W88 ) to ignite the thermonuclear secondary. In a fission bomb,

2000-412: The parent molecules with a far larger probability than the initial reactants. (In the new reaction, further unstable molecules are formed besides the stable products, and so on.) In 1918, Walther Nernst proposed that the photochemical reaction between hydrogen and chlorine is a chain reaction in order to explain what is known as the quantum yield phenomena. This means that one photon of light

2050-438: 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. This is the principle for nuclear reactors and atomic bombs . Demonstration of a self-sustaining nuclear chain reaction

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2100-399: The rate law ( 5 ) d [ CH 4 ] d t = k 1 2 k 4 k 2 [ CH 3 CHO ] 3 / 2 {\displaystyle (5){\frac {d{\ce {[CH4]}}}{dt}}={\frac {k_{1}}{2k_{4}}}k_{2}{\ce {[CH3CHO]}}^{3/2}} , which is order 3/2 in

2150-649: The reactant CH 3 CHO. A nuclear chain reaction was proposed by Leo Szilard in 1933, shortly after the neutron was discovered, yet more than five years before nuclear fission was first discovered. Szilárd knew of chemical chain reactions, and he had been reading about an energy-producing nuclear reaction involving high-energy protons bombarding lithium, demonstrated by John Cockcroft and Ernest Walton , in 1932. Now, Szilárd proposed to use neutrons theoretically produced from certain nuclear reactions in lighter isotopes, to induce further reactions in light isotopes that produced more neutrons. This would in theory produce

2200-423: The remaining lithium-6, and so on, in a continuous cycle. Energy from fission of uranium-238 is useful in weapons: both because depleted uranium is much cheaper than highly enriched uranium and because it cannot go critical and is therefore less likely to be involved in a catastrophic accident. This kind of thermonuclear weapon can produce up to 20% of its yield from fusion, with the rest coming from fission, and

2250-521: The simple action of toppling one domino leads to all dominoes eventually toppling, even if they are significantly larger. Numerous chain reactions can be represented by a mathematical model based on Markov chains . In 1913, the German chemist Max Bodenstein first put forth the idea of chemical chain reactions. If two molecules react, not only molecules of the final reaction products are formed, but also some unstable molecules which can further react with

2300-408: The tritium nucleus - requires production of at least one free neutron, which is used to bombard a feedstock material (lithium-6, deuterium, or helium-3). Furthermore, because of losses and inefficiencies, the number of free neutrons needed is closer to two for each triton, as tritium begins decaying immediately, so there are losses during collection, storage, and transport from the production facility to

2350-414: The weapons in the field. The production of free neutrons demands the operation of either a breeder reactor or a particle accelerator (with a spallation target) dedicated to the tritium production facility. Chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to

2400-465: Was accomplished by Enrico Fermi and others, in the successful operation of Chicago Pile-1 , the first artificial nuclear reactor, in late 1942. An electron avalanche happens between two unconnected electrodes in a gas when an electric field exceeds a certain threshold. Random thermal collisions of gas atoms may result in a few free electrons and positively charged gas ions, in a process called impact ionization . Acceleration of these free electrons in

2450-409: Was built but never tested. When this type of bomb explodes, the fission of the highly enriched uranium or plutonium core creates neutrons , some of which escape and strike atoms of lithium-6 , creating tritium . At the temperature created by fission in the core, tritium and deuterium can undergo thermonuclear fusion without a high level of compression. The fusion of tritium and deuterium produces

2500-475: Was the first proposal for the mechanism of chemical explosions. A quantitative chain chemical reaction theory was created later on by Soviet physicist Nikolay Semyonov in 1934. Semyonov shared the Nobel Prize in 1956 with Sir Cyril Norman Hinshelwood , who independently developed many of the same quantitative concepts. The main types of steps in chain reaction are of the following types. The chain length

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