Misplaced Pages

#803196

116-504: RDS-6 utilized a scheme in which fission and fusion fuel ( lithium-6 deuteride ) were " layered ", a design known as the Sloika (Russian: Слойка , named after a type of layered puff pastry ) or the so-called layer cake design, model in the Soviet Union. A ten-fold increase in explosive power was achieved by a combination of fusion and fission, yet it was still 26 times less powerful than

232-628: A candidate member of the Central Committee . A loyal Stalinist , he was promoted rapidly as other leaders fell victim to Joseph Stalin 's Great Purge in 1937 and 1938. In July 1937, Bulganin was appointed Chairman of the Council of People's Commissars (the equivalent of Prime Minister) of the Russian Soviet Federative Socialist Republic (RSFSR) after the arrest of the previous incumbent, Daniil Sulimov . Bulganin became

348-445: A capacity of 398 GWE , with about 85% being light-water cooled reactors such as pressurized water reactors or boiling water reactors . Energy from fission is transmitted through conduction or convection to the nuclear reactor coolant , then to a heat exchanger , and the resultant generated steam is used to drive a turbine or generator. The objective of an atomic bomb is to produce a device, according to Serber, "...in which energy

464-760: A chain reaction. All of the things which H. G. Wells predicted appeared suddenly real to me." After the Hahn-Strassman paper was published, Szilard noted in a letter to Lewis Strauss , that during the fission of uranium, "the energy released in this new reaction must be very much higher than all previously known cases...," which might lead to "large-scale production of energy and radioactive elements, unfortunately also perhaps to atomic bombs." Nikolai Bulganin Nikolai Alexandrovich Bulganin ( Russian : Никола́й Алекса́ндрович Булга́нин ; 11 June [ O.S. 30 May] 1895 – 24 February 1975)

580-427: A competing idea of alternating layers of deuterium and uranium-238 around a fissile core (Sakharov's 'first idea'). This second design was code named Sloika (RDS-6s) or 'Layer Cake' after the layering. In March 1949 Vitaly Ginzburg proposed to replace the deuterium by lithium-6 deuteride ('second idea'). The proposal was based on the better efficiency due to the generation of tritium by the neutron capture of lithium and

696-411: A criminal and irresponsible manner; [...] which will place a question [mark] upon the very existence of Israel as a State." Khrushchev, in his memoirs, admitted the threat was designed simply to divide Western opinion, especially since at the time he did not have enough ICBMs to launch the rockets, and in any case he had no intention of going to war in 1956. By 1957, however, Bulganin had come to share

812-401: A deformed nucleus relative to a spherical form for the surface and Coulomb terms. Additional terms can be included such as symmetry, pairing, the finite range of the nuclear force, and charge distribution within the nuclei to improve the estimate. Normally binding energy is referred to and plotted as average binding energy per nucleon. According to Lilley, "The binding energy of a nucleus B

928-448: A fast neutron. This energy release profile holds for thorium and the various minor actinides as well. When a uranium nucleus fissions into two daughter nuclei fragments, about 0.1 percent of the mass of the uranium nucleus appears as the fission energy of ~200 MeV. For uranium-235 (total mean fission energy 202.79 MeV ), typically ~169 MeV appears as the kinetic energy of the daughter nuclei, which fly apart at about 3% of

1044-480: A fission bomb where growth is at an explosive rate. If k is exactly unity, the reactions proceed at a steady rate and the reactor is said to be critical. It is possible to achieve criticality in a reactor using natural uranium as fuel, provided that the neutrons have been efficiently moderated to thermal energies." Moderators include light water, heavy water , and graphite . According to John C. Lee, "For all nuclear reactors in operation and those under development,

1160-432: A fission reaction is produced by its fission products , though a large majority of it, about 85 percent, is found in fragment kinetic energy , while about 6 percent each comes from initial neutrons and gamma rays and those emitted after beta decay , plus about 3 percent from neutrinos as the product of such decay. Nuclear fission can occur without neutron bombardment as a type of radioactive decay. This type of fission

1276-694: A full member of the Central Committee later that year. In September 1938, he became Deputy Prime Minister of the Soviet Union and head of the State Bank of the USSR (Gosbank). During World War II , Bulganin played a leading role in the government and Red Army , although he was never a front-line commander. His first posting was as chief political commissar on the Western Front, which was commanded by Marshal Timoshenko . He held similar posts until July 1944, when he

SECTION 10

#1733085812804

1392-413: A limitation associated with the energy of his alpha particle source. Eventually, in 1932, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues Ernest Walton and John Cockcroft , who used artificially accelerated protons against lithium-7, to split this nucleus into two alpha particles. The feat was popularly known as "splitting the atom", and would win them

1508-408: A major gamma ray emitter. All actinides are fertile or fissile and fast breeder reactors can fission them all albeit only in certain configurations. Nuclear reprocessing aims to recover usable material from spent nuclear fuel to both enable uranium (and thorium) supplies to last longer and to reduce the amount of "waste". The industry term for a process that fissions all or nearly all actinides

1624-463: A mass ratio of products of about 3 to 2, for common fissile isotopes . Most fissions are binary fissions (producing two charged fragments), but occasionally (2 to 4 times per 1000 events), three positively charged fragments are produced, in a ternary fission . The smallest of these fragments in ternary processes ranges in size from a proton to an argon nucleus. Apart from fission induced by an exogenous neutron, harnessed and exploited by humans,

1740-459: A natural form of spontaneous radioactive decay (not requiring an exogenous neutron, because the nucleus already has an overabundance of neutrons) is also referred to as fission, and occurs especially in very high-mass-number isotopes. Spontaneous fission was discovered in 1940 by Flyorov , Petrzhak , and Kurchatov in Moscow, in an experiment intended to confirm that, without bombardment by neutrons,

1856-469: A neutron-driven chain reaction using beryllium. Szilard stated, "...if we could find an element which is split by neutrons and which would emit two neutrons when it absorbs one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction." On 25 January 1939, after learning of Hahn's discovery from Eugene Wigner , Szilard noted, "...if enough neutrons are emitted...then it should be, of course, possible to sustain

1972-659: A new, heavier element 93, that "it is conceivable that the nucleus breaks up into several large fragments." However, the quoted objection comes some distance down, and was but one of several gaps she noted in Fermi's claim. Although Noddack was a renowned analytical chemist, she lacked the background in physics to appreciate the enormity of what she was proposing. After the Fermi publication, Otto Hahn , Lise Meitner , and Fritz Strassmann began performing similar experiments in Berlin . Meitner, an Austrian Jew, lost her Austrian citizenship with

2088-416: A nuclear reaction. Cross sections are a function of incident neutron energy, and those for U and Pu are a million times higher than U at lower neutron energy levels. Absorption of any neutron makes available to the nucleus binding energy of about 5.3 MeV. U needs a fast neutron to supply the additional 1 MeV needed to cross the critical energy barrier for fission. In

2204-404: A nuclear reactor or nuclear weapon, the overwhelming majority of fission events are induced by bombardment with another particle, a neutron, which is itself produced by prior fission events. Fissionable isotopes such as uranium-238 require additional energy provided by fast neutrons (such as those produced by nuclear fusion in thermonuclear weapons ). While some of the neutrons released from

2320-622: A nuclear reactor, ternary fission can produce three positively charged fragments (plus neutrons) and the smallest of these may range from so small a charge and mass as a proton ( Z  = 1), to as large a fragment as argon ( Z  = 18). The most common small fragments, however, are composed of 90% helium-4 nuclei with more energy than alpha particles from alpha decay (so-called "long range alphas" at ~16 megaelectronvolts (MeV)), plus helium-6 nuclei, and tritons (the nuclei of tritium ). Though less common than binary fission, it still produces significant helium-4 and tritium gas buildup in

2436-583: A small fraction of fission products. Neutron absorption which does not lead to fission produces plutonium (from U ) and minor actinides (from both U and U ) whose radiotoxicity is far higher than that of the long lived fission products. Concerns over nuclear waste accumulation and the destructive potential of nuclear weapons are a counterbalance to the peaceful desire to use fission as an energy source . The thorium fuel cycle produces virtually no plutonium and much less minor actinides, but U - or rather its decay products - are

SECTION 20

#1733085812804

2552-601: A supercritical chain-reaction (one in which each fission cycle yields more neutrons than it absorbs). Without their existence, the nuclear chain-reaction would be prompt critical and increase in size faster than it could be controlled by human intervention. In this case, the first experimental atomic reactors would have run away to a dangerous and messy "prompt critical reaction" before their operators could have manually shut them down (for this reason, designer Enrico Fermi included radiation-counter-triggered control rods, suspended by electromagnets, which could automatically drop into

2668-631: A superior breeding potential for fast reactors." Critical fission reactors are the most common type of nuclear reactor. In a critical fission reactor, neutrons produced by fission of fuel atoms are used to induce yet more fissions, to sustain a controllable amount of energy release. Devices that produce engineered but non-self-sustaining fission reactions are subcritical fission reactors . Such devices use radioactive decay or particle accelerators to trigger fissions. Critical fission reactors are built for three primary purposes, which typically involve different engineering trade-offs to take advantage of either

2784-411: A third particle is emitted. This third particle is commonly an α particle . Since in nuclear fission, the nucleus emits more neutrons than the one it absorbs, a chain reaction is possible. Binary fission may produce any of the fission products, at 95±15 and 135±15 daltons . However, the binary process happens merely because it is the most probable. In anywhere from two to four fissions per 1000 in

2900-748: A while, but in March 1958, at a session of the Supreme Soviet , Khrushchev forced his resignation. Bulganin was appointed Chairman of the Soviet State Bank, a job he had held two decades before, but in August was dispatched to Stavropol as Chairman of the Regional Economic Council , a token position, and on 12 November he was expelled from the Presidium (Politburo) of the Central Committee. In September he

3016-496: Is a " closed fuel cycle ". Younes and Loveland define fission as, "...a collective motion of the protons and neutrons that make up the nucleus, and as such it is distinguishable from other phenomena that break up the nucleus. Nuclear fission is an extreme example of large- amplitude collective motion that results in the division of a parent nucleus into two or more fragment nuclei. The fission process can occur spontaneously, or it can be induced by an incident particle." The energy from

3132-503: Is by definition a reactor that produces more fissile material than it consumes and needs a minimum of two neutrons produced for each neutron absorbed in a fissile nucleus. Thus, in general, the conversion ratio (CR) is defined as the ratio of fissile material produced to that destroyed ...when the CR is greater than 1.0, it is called the breeding ratio (BR)... U offers a superior breeding potential for both thermal and fast reactors, while Pu offers

3248-427: Is called spontaneous fission , and was first observed in 1940. During induced fission, a compound system is formed after an incident particle fuses with a target. The resultant excitation energy may be sufficient to emit neutrons, or gamma-rays, and nuclear scission. Fission into two fragments is called binary fission, and is the most common nuclear reaction . Occurring least frequently is ternary fission , in which

3364-438: Is called the odd–even effect on the fragments' charge distribution. This can be seen in the empirical fragment yield data for each fission product, as products with even Z have higher yield values. However, no odd–even effect is observed on fragment distribution based on their A . This result is attributed to nucleon pair breaking . In nuclear fission events the nuclei may break into any combination of lighter nuclei, but

3480-413: Is characterized by the neutron multiplication factor k , which is defined as the ratio of the number of neutrons in one generation to the number in the preceding generation. If, in a reactor, k is less than unity, the reactor is subcritical, the number of neutrons decreases and the chain reaction dies out. If k > 1, the reactor is supercritical and the chain reaction diverges. This is the situation in

3596-407: Is much less than the prompt energy, but it is a significant amount and is why reactors must continue to be cooled after they have been shut down and why the waste products must be handled with great care and stored safely." John Lilley states, "...neutron-induced fission generates extra neutrons which can induce further fissions in the next generation and so on in a chain reaction. The chain reaction

RDS-6s - Misplaced Pages Continue

3712-417: Is recoverable, Prompt fission fragments amount to 168 MeV, which are easily stopped with a fraction of a millimeter. Prompt neutrons total 5 MeV, and this energy is recovered as heat via scattering in the reactor. However, many fission fragments are neutron-rich and decay via β emissions. According to Lilley, "The radioactive decay energy from the fission chains is the second release of energy due to fission. It

3828-402: Is released by a fast neutron chain reaction in one or more of the materials known to show nuclear fission." According to Rhodes, "Untamped, a bomb core even as large as twice the critical mass would completely fission less than 1 percent of its nuclear material before it expanded enough to stop the chain reaction from proceeding. Tamper always increased efficiency: it reflected neutrons back into

3944-423: Is the atomic mass of a hydrogen atom, m n is the mass of a neutron, and c is the speed of light . Thus, the mass of an atom is less than the mass of its constituent protons and neutrons, assuming the average binding energy of its electrons is negligible. The binding energy B is expressed in energy units, using Einstein's mass-energy equivalence relationship. The binding energy also provides an estimate of

4060-418: Is the energy required to separate it into its constituent neutrons and protons." m ( A , Z ) = Z m H + N m n − B / c 2 {\displaystyle m(\mathbf {A} ,\mathbf {Z} )=\mathbf {Z} m_{H}+\mathbf {N} m_{n}-\mathbf {B} /c^{2}} where A is mass number , Z is atomic number , m H

4176-598: The Anschluss , the union of Austria with Germany in March 1938, but she fled in July 1938 to Sweden and started a correspondence by mail with Hahn in Berlin. By coincidence, her nephew Otto Robert Frisch , also a refugee, was also in Sweden when Meitner received a letter from Hahn dated 19 December describing his chemical proof that some of the product of the bombardment of uranium with neutrons

4292-637: The Bolshoi Theatre . He was a man without any political principles, only the obedient servant of any leader. In March 1949, Bulganin was replaced as Minister for Defence by a career soldier, Aleksandr Vasilevsky , and then was responsible for the arms industry. Conversely, a 1955 report from the US Central Intelligence Agency suggests that Bulganin's tenure at the State Bank demonstrated high intelligence and his ability to learn quickly: Bulganin impressed those who had worked with him in

4408-554: The Ivy Mike device tested by the US in 1952. A similar design was earlier theorized by Edward Teller , but never tested by the US, as the " Alarm Clock ". The Soviet Union started studies of advanced nuclear bombs and a hydrogen bomb, code named RDS-6, in June 1948. The studies would be done by KB-11 (usually referred to as Arzamas-16 , the name of the town) and FIAN . The first hydrogen bomb design

4524-684: The Kaiser Wilhelm Society for Chemistry, today part of the Free University of Berlin , following over four decades of work on the science of radioactivity and the elaboration of new nuclear physics that described the components of atoms. In 1911, Ernest Rutherford proposed a model of the atom in which a very small, dense and positively charged nucleus of protons was surrounded by orbiting, negatively charged electrons (the Rutherford model ). Niels Bohr improved upon this in 1913 by reconciling

4640-508: The Suez Crisis of October–November 1956, Bulganin sent letters to the governments of the United Kingdom , France , and Israel threatening rocket attacks on London , Paris , and Tel Aviv if they did not withdraw their forces from Egypt. In a letter to Israeli prime minister David Ben-Gurion , Bulganin wrote, "Israel is playing with the fate of peace, with the fate of its own people, in

4756-421: The nuclear fuel cycle is based on one of three fissile materials, U, U, and Pu, and the associated isotopic chains. For the current generation of LWRs , the enriched U contains 2.5~4.5 wt% of U, which is fabricated into UO 2 fuel rods and loaded into fuel assemblies." Lee states, "One important comparison for the three major fissile nuclides, U, U, and Pu, is their breeding potential. A breeder

RDS-6s - Misplaced Pages Continue

4872-621: The nuclear shell model for the nucleus. The nuclides that can sustain a fission chain reaction are suitable for use as nuclear fuels . The most common nuclear fuels are U (the isotope of uranium with mass number 235 and of use in nuclear reactors) and Pu (the isotope of plutonium with mass number 239). These fuels break apart into a bimodal range of chemical elements with atomic masses centering near 95 and 135 daltons ( fission products ). Most nuclear fuels undergo spontaneous fission only very slowly, decaying instead mainly via an alpha - beta decay chain over periods of millennia to eons . In

4988-588: The nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons , and releases a very large amount of energy even by the energetic standards of radioactive decay . Nuclear fission was discovered by chemists Otto Hahn and Fritz Strassmann and physicists Lise Meitner and Otto Robert Frisch . Hahn and Strassmann proved that a fission reaction had taken place on 19 December 1938, and Meitner and her nephew Frisch explained it theoretically in January 1939. Frisch named

5104-652: The 'first' and 'second' idea were used in the RDS-6s. The result was similar to the US 'Alarm Clock', but there is no indication that the Soviets were aware of the concept of the 'Alarm Clock'. After the United States tested Ivy Mike in November 1952, Lavrentiy Beria sent a memo to spare no effort on the development of the RDS-6s. In the final development report from June 1953 the yield was estimated at 300 +/- 100 kilotons. The RDS-6s

5220-543: The 1951 Nobel Prize in Physics for "Transmutation of atomic nuclei by artificially accelerated atomic particles" , although it was not the nuclear fission reaction later discovered in heavy elements. English physicist James Chadwick discovered the neutron in 1932. Chadwick used an ionization chamber to observe protons knocked out of several elements by beryllium radiation, following up on earlier observations made by Joliot-Curies . In Chadwick's words, "...In order to explain

5336-671: The Communist Party. Later in March 1947, he succeeded Stalin as Minister for the Armed Forces, and was again Deputy Prime Minister of the Soviet Union, under Stalin, from 1947 to 1950. In November 1947, he was promoted to the rank of Marshal of the Soviet Union . By February 1948, he became a full member of the 18th Politburo . Bulganin reached the highest rank in the Red Army, despite only having served as political officer. His role

5452-455: The Council of Ministers was furious with his style of work, especially when Stalin left him in charge while he vacationed in the Caucasus.... Bulganin's appearance was deceiving. Unlike Khrushchev or Beria , Bulganin was always smartly dressed and looked like an old nobleman, with well-groomed grey hair and goatee. Later I learnt he was a heavy drinker and an admirer of ballerinas and singers from

5568-630: The Moscow City Soviet with the support of Lazar Kaganovich . A loyal Stalinist , Bulganin rose through the Soviet hierarchy in the middle of Stalin's purges , and in 1937 he was named premier of the Russian SFSR and a full member of the Central Committee of the Communist Party . A year later he was appointed Deputy Prime Minister of the Soviet Union and head of the Soviet State Bank . Although he

5684-530: The RDS-27 but reduced the yield from 400 kilotons to 250 kilotons. The RDS-27 was intended as a warhead for the R-7 ICBM. The RDS-27 was tested November 6, 1955 (Joe 18). Despite the inability of the RDS-6s to be scaled into the megaton range, the detonation was still used by Soviet diplomats as leverage. The Soviets claimed that they too had a hydrogen bomb, but unlike the United States' first thermonuclear device, theirs

5800-466: The RDS-6t was also stopped after it was proven that thermonuclear ignition was not possible in the RDS-6t. Both the RDS-6s and the RDS-6t were dead ends and research focused again on a two-stage thermonuclear weapon. A variant of the RDS-6s was developed later, code named RDS-27. The difference between the RDS-6s and the RDS-27 was that the RDS-27 did not use tritium. This improved the operational usefulness of

5916-671: The Soviet Union . He was generally seen as a supporter of Khrushchev's reforms and destalinisation . In July 1955, he attended the Geneva Summit , with U.S. President Dwight D. Eisenhower , French Prime Minister Edgar Faure , and British Prime Minister Anthony Eden . He and Khrushchev travelled together to India , Yugoslavia and in April 1956 to Britain , where they were known in the press as "the B and K show" or "Bulge and Crush". In his memoirs, however, Khrushchev recounted that he believed that he "couldn't rely on [Bulganin] fully." During

SECTION 50

#1733085812804

6032-545: The Soviet Union. Initially a close ally of Khrushchev, Bulganin came to doubt his policies and became associated with an opposition group led by Vyacheslav Molotov . The group's defeat led to the fall of Bulganin, and in 1958 he was dismissed as premier and expelled from the Politburo. Forced into retirement, Bulganin died in 1975 at the age of 79. Bulganin was born in 1895 in Nizhny Novgorod . The son of an office worker, he

6148-624: The State Bank, including a famous expert on banking, with his high intelligence, mild manners, and capacity to learn in a very short time the most special and difficult of problems. After Stalin's death in March 1953, Bulganin moved into sixth place in the Soviet leadership, when he was reappointed to the post of Defense Minister, but with Marshal Zhukov as his deputy. He was an ally of Nikita Khrushchev during his power struggle with Georgy Malenkov , and in February 1955 he succeeded Malenkov as Premier of

6264-698: The binding energy as the sum of five terms, which are the volume energy, a surface correction, Coulomb energy, a symmetry term, and a pairing term: B = a v A − a s A 2 / 3 − a c Z 2 A 1 / 3 − a a ( N − Z ) 2 A ± Δ {\displaystyle B=a_{v}\mathbf {A} -a_{s}\mathbf {A} ^{2/3}-a_{c}{\frac {\mathbf {Z} ^{2}}{\mathbf {A} ^{1/3}}}-a_{a}{\frac {(\mathbf {N} -\mathbf {Z} )^{2}}{\mathbf {A} }}\pm \Delta } where

6380-456: The case of U however, that extra energy is provided when U adjusts from an odd to an even mass. In the words of Younes and Lovelace, "...the neutron absorption on a U target forms a U nucleus with excitation energy greater than the critical fission energy, whereas in the case of n + U , the resulting U nucleus has an excitation energy below the critical fission energy." About 6 MeV of

6496-446: The center of Chicago Pile-1 ). If these delayed neutrons are captured without producing fissions, they produce heat as well. The binding energy of the nucleus is the difference between the rest-mass energy of the nucleus and the rest-mass energy of the neutron and proton nucleons. The binding energy formula includes volume, surface and Coulomb energy terms that include empirically derived coefficients for all three, plus energy ratios of

6612-419: The core and its inertia...slowed the core's expansion and helped keep the core surface from blowing away." Rearrangement of the core material's subcritical components would need to proceed as fast as possible to ensure effective detonation. Additionally, a third basic component was necessary, "...an initiator—a Ra + Be source or, better, a Po + Be source, with the radium or polonium attached perhaps to one piece of

6728-405: The core and the beryllium to the other, to smash together and spray neutrons when the parts mated to start the chain reaction." However, any bomb would "necessitate locating, mining and processing hundreds of tons of uranium ore...", while U-235 separation or the production of Pu-239 would require additional industrial capacity. The discovery of nuclear fission occurred in 1938 in the buildings of

6844-414: 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 mass range, roughly 0.9 MeV are released per nucleon of the starting element. The fission of U by a slow neutron yields nearly identical energy to the fission of U by

6960-420: The directive of Nikolai Bulganin (influenced by Nikita Khrushchev ), code-named RDS-37 . All were at Semipalatinsk Test Site , Kazakh SSR . Like RDS-6, it was a "dry" weapon, using lithium-6 deuteride instead of liquid deuterium. 50°26′16″N 77°48′51″E  /  50.43778°N 77.81417°E  / 50.43778; 77.81417 Nuclear fission Nuclear fission is a reaction in which

7076-404: The doubts held about Khrushchev's policies by the opposition group (which Khrushchev and his supporters labelled the " Anti-Party Group ") led by Vyacheslav Molotov . In June, when the dissenters tried to remove Khrushchev from power at a meeting of the Politburo, Bulganin vacillated between the two camps. When the dissenters were defeated and removed from power, Bulganin held on to his position for

SECTION 60

#1733085812804

7192-458: The electricity administration until 1927. He was the director of the Moscow electricity supply from 1927 to 1931. From 1931 to 1937, he served as chairman of the executive committee of the Moscow City Soviet (the equivalent of mayor). He came into office soon after Kaganovich had been put in charge of the Moscow party organisation. In 1934, the 17th Congress of the Communist Party elected Bulganin as

7308-416: The element thorium was slowly and spontaneously transmuting itself into argon gas!" In 1919, following up on an earlier anomaly Ernest Marsden noted in 1915, Rutherford attempted to "break up the atom." Rutherford was able to accomplish the first artificial transmutation of nitrogen into oxygen, using alpha particles directed at nitrogen N + α → O + p.  Rutherford stated, "...we must conclude that

7424-406: The energy spectrum for fast fission is similar. ) Among the heavy actinide elements, however, those isotopes that have an odd number of neutrons (such as U with 143 neutrons) bind an extra neutron with an additional 1 to 2 MeV of energy over an isotope of the same element with an even number of neutrons (such as U with 146 neutrons). This extra binding energy is made available as a result of

7540-661: The energy thus released. The results confirmed that fission was occurring and hinted strongly that it was the isotope uranium 235 in particular that was fissioning. The next day, the Fifth Washington Conference on Theoretical Physics began in Washington, D.C. under the joint auspices of the George Washington University and the Carnegie Institution of Washington . There, the news on nuclear fission

7656-450: 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

7772-449: The excitation energy is sufficient, the nucleus breaks into fragments. This is called scission, and occurs at about 10 seconds. The fragments can emit prompt neutrons at between 10 and 10 seconds. At about 10 seconds, the fragments can emit gamma rays. At 10 seconds β decay, β- delayed neutrons , and gamma rays are emitted from the decay products . Typical fission events release about two hundred million eV (200 MeV) of energy,

7888-432: The explosion of nuclear weapons . Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they break apart. This makes a self-sustaining nuclear chain reaction possible, releasing energy at a controlled rate in a nuclear reactor or at a very rapid, uncontrolled rate in a nuclear weapon. The amount of free energy released in

8004-424: The fact that effective forces in the nucleus are stronger for unlike neutron-proton pairs, rather than like neutron–neutron or proton–proton pairs. The pairing term arises from the fact that like nucleons form spin-zero pairs in the same spatial state. The pairing is positive if N and Z are both even, adding to the binding energy. In fission there is a preference for fission fragments with even Z , which

8120-426: The fast neutrons are supplied by nuclear fusion). However, this process cannot happen to a great extent in a nuclear reactor, as too small a fraction of the fission neutrons produced by any type of fission have enough energy to efficiently fission U . (For example, neutrons from thermal fission of U have a mean energy of 2 MeV, a median energy of 1.6 MeV, and a mode of 0.75 MeV, and

8236-409: The fission of U are fast enough to induce another fission in U , most are not, meaning it can never achieve criticality. While there is a very small (albeit nonzero) chance of a thermal neutron inducing fission in U , neutron absorption is orders of magnitude more likely. Fission cross sections are a measurable property related to the probability that fission will occur in

8352-450: The fission of an equivalent amount of U is a million times more than that released in the combustion of methane or from hydrogen fuel cells . The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem. However, the seven long-lived fission products make up only

8468-443: The fission rate of uranium was negligible, as predicted by Niels Bohr ; it was not negligible. The unpredictable composition of the products (which vary in a broad probabilistic and somewhat chaotic manner) distinguishes fission from purely quantum tunneling processes such as proton emission , alpha decay , and cluster decay , which give the same products each time. Nuclear fission produces energy for nuclear power and drives

8584-431: 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. Uranium-238, for example, has a near-zero fission cross section for neutrons of less than 1 MeV energy. If no additional energy is supplied by any other mechanism, the nucleus will not fission, but will merely absorb

8700-491: The fragments ( heating the bulk material where fission takes place). Like nuclear fusion , for fission to produce energy, the total binding energy of the resulting elements must be greater than that of the starting element. Fission is a form of nuclear transmutation because the resulting fragments (or daughter atoms) are not the same element as the original parent atom. The two (or more) nuclei produced are most often of comparable but slightly different sizes, typically with

8816-410: The fuel rods of modern nuclear reactors. Bohr and Wheeler used their liquid drop model , the packing fraction curve of Arthur Jeffrey Dempster , and Eugene Feenberg's estimates of nucleus radius and surface tension, to estimate the mass differences of parent and daughters in fission. They then equated this mass difference to energy using Einstein's mass-energy equivalence formula. The stimulation of

8932-405: The great penetrating power of the radiation we must further assume that the particle has no net charge..." The existence of the neutron was first postulated by Rutherford in 1920, and in the words of Chadwick, "...how on earth were you going to build up a big nucleus with a large positive charge? And the answer was a neutral particle." Subsequently, he communicated his findings in more detail. In

9048-435: The group dubbed ausenium and hesperium . However, not all were convinced by Fermi's analysis of his results, though he would win the 1938 Nobel Prize in Physics for his "demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons". The German chemist Ida Noddack notably suggested in 1934 that instead of creating

9164-487: The heat or the neutrons produced by the fission chain reaction: While, in principle, all fission reactors can act in all three capacities, in practice the tasks lead to conflicting engineering goals and most reactors have been built with only one of the above tasks in mind. (There are several early counter-examples, such as the Hanford N reactor , now decommissioned). As of 2019, the 448 nuclear power plants worldwide provided

9280-412: The latter are used in fast-neutron reactors , and in weapons). According to Younes and Loveland, "Actinides like U that fission easily following the absorption of a thermal (0.25 meV) neutron are called fissile , whereas those like U that do not easily fission when they absorb a thermal neutron are called fissionable ." After an incident particle has fused with a parent nucleus, if

9396-427: The line has the slope N = Z , while the heavier nuclei require additional neutrons to remain stable. Nuclei that are neutron- or proton-rich have excessive binding energy for stability, and the excess energy may convert a neutron to a proton or a proton to a neutron via the weak nuclear force, a process known as beta decay . Neutron-induced fission of U-235 emits a total energy of 207 MeV, of which about 200 MeV

9512-474: The mechanism of neutron pairing effects , which itself is caused by the Pauli exclusion principle , allowing an extra neutron to occupy the same nuclear orbital as the last neutron in the nucleus. In such isotopes, therefore, no neutron kinetic energy is needed, for all the necessary energy is supplied by absorption of any neutron, either of the slow or fast variety (the former are used in moderated nuclear reactors, and

9628-465: The most common event is not fission to equal mass nuclei of about mass 120; the most common event (depending on isotope and process) is a slightly unequal fission in which one daughter nucleus has a mass of about 90 to 100 daltons and the other the remaining 130 to 140 daltons. Stable nuclei, and unstable nuclei with very long half-lives , follow a trend of stability evident when Z is plotted against N . For lighter nuclei less than N = 20,

9744-523: The neutron, as happens when U absorbs slow and even some fraction of fast neutrons, to become U . 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 1 MeV or more (so-called fast neutrons). Such high energy neutrons are able to fission U directly (see thermonuclear weapon for application, where

9860-399: The news and carried it back to Columbia. Rabi said he told Enrico Fermi; Fermi gave credit to Lamb. Bohr soon thereafter went from Princeton to Columbia to see Fermi. Not finding Fermi in his office, Bohr went down to the cyclotron area and found Herbert L. Anderson . Bohr grabbed him by the shoulder and said: "Young man, let me explain to you about something new and exciting in physics." It

9976-433: The nitrogen atom is disintegrated," while the newspapers stated he had split the atom . This was the first observation of a nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. It also offered a new way to study the nucleus. Rutherford and James Chadwick then used alpha particles to "disintegrate" boron, fluorine, sodium, aluminum, and phosphorus before reaching

10092-441: The nuclear binding energy is proportional to the nuclear volume, while nucleons near the surface interact with fewer nucleons, reducing the effect of the volume term. According to Lilley, "For all naturally occurring nuclei, the surface-energy term dominates and the nucleus exists in a state of equilibrium." The negative contribution of Coulomb energy arises from the repulsive electric force of the protons. The symmetry term arises from

10208-452: The nuclear force approaches a constant value for large A , while the Coulomb acts over a larger distance so that electrical potential energy per proton grows as Z increases. Fission energy is released when a A is larger than 120 nucleus fragments. Fusion energy is released when lighter nuclei combine. Carl Friedrich von Weizsäcker's semi-empirical mass formula may be used to express

10324-465: The nucleus after neutron bombardment was analogous to the vibrations of a liquid drop, with surface tension and the Coulomb force in opposition. Plotting the sum of these two energies as a function of elongated shape, they determined the resultant energy surface had a saddle shape. The saddle provided an energy barrier called the critical energy barrier. Energy of about 6 MeV provided by the incident neutron

10440-430: The plutonium-239 is later fissioned. On the other hand, so-called delayed neutrons emitted as radioactive decay products with half-lives up to several minutes, from fission-daughters, are very important to reactor control , because they give a characteristic "reaction" time for the total nuclear reaction to double in size, if the reaction is run in a " delayed-critical " zone which deliberately relies on these neutrons for

10556-410: The possibility of a nuclear chain reaction. The 11 February 1939 paper by Meitner and Frisch compared the process to the division of a liquid drop and estimated the energy released at 200 MeV. The 1 September 1939 paper by Bohr and Wheeler used this liquid drop model to quantify fission details, including the energy released, estimated the cross section for neutron-induced fission, and deduced U

10672-470: The process "fission" by analogy with biological fission of living cells. In their second publication on nuclear fission in February 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction . For heavy nuclides , it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of

10788-514: The quantum behavior of electrons (the Bohr model ). In 1928, George Gamow proposed the Liquid drop model , which became essential to understanding the physics of fission. In 1896, Henri Becquerel had found, and Marie Curie named, radioactivity. In 1900, Rutherford and Frederick Soddy , investigating the radioactive gas emanating from thorium , "conveyed the tremendous and inevitable conclusion that

10904-406: The rest as kinetic energy of fission fragments (this appears almost immediately when the fragments impact surrounding matter, as simple heat). Some processes involving neutrons are notable for absorbing or finally yielding energy — for example neutron kinetic energy does not yield heat immediately if the neutron is captured by a uranium-238 atom to breed plutonium-239, but this energy is emitted if

11020-475: The speed of light, due to Coulomb repulsion . Also, an average of 2.5 neutrons are emitted, with a mean kinetic energy per neutron of ~2 MeV (total of 4.8 MeV). The fission reaction also releases ~7 MeV in prompt gamma ray photons . The latter figure means that a nuclear fission explosion or criticality accident emits about 3.5% of its energy as gamma rays, less than 2.5% of its energy as fast neutrons (total of both types of radiation ~6%), and

11136-403: The techniques were well-known. Meitner and Frisch then correctly interpreted Hahn's results to mean that the nucleus of uranium had split roughly in half. Frisch suggested the process be named "nuclear fission", by analogy to the process of living cell division into two cells, which was then called binary fission . Just as the term nuclear "chain reaction" would later be borrowed from chemistry, so

11252-536: The term "fission" was borrowed from biology. News spread quickly of the new discovery, which was correctly seen as an entirely novel physical effect with great scientific—and potentially practical—possibilities. Meitner's and Frisch's interpretation of the discovery of Hahn and Strassmann crossed the Atlantic Ocean with Niels Bohr, who was to lecture at Princeton University . I.I. Rabi and Willis Lamb , two Columbia University physicists working at Princeton, heard

11368-414: The total energy released from fission. The curve of binding energy is characterized by a broad maximum near mass number 60 at 8.6 MeV, then gradually decreases to 7.6 MeV at the highest mass numbers. Mass numbers higher than 238 are rare. At the lighter end of the scale, peaks are noted for helium-4, and the multiples such as beryllium-8, carbon-12, oxygen-16, neon-20 and magnesium-24. Binding energy due to

11484-415: The uranium-238 fission by the 14 MeV neutrons from D + T fusion. At that time Ginzburg did not know that the cross section for D + T reaction was much larger than that for D + D reaction. In April 1949 the group received D + T cross section data obtained from intelligence gathering without mentioning the source. The large advantage of lithium deuteride became evident and the deuterium design was abandoned. Both

11600-584: The vicinity of the nucleus, and that gave it more time to be captured." Fermi's team, studying radiative capture which is the emission of gamma radiation after the nucleus captures a neutron, studied sixty elements, inducing radioactivity in forty. In the process, they discovered the ability of hydrogen to slow down the neutrons. Enrico Fermi and his colleagues in Rome studied the results of bombarding uranium with neutrons in 1934. Fermi concluded that his experiments had created new elements with 93 and 94 protons, which

11716-428: The words of Richard Rhodes , referring to the neutron, "It would therefore serve as a new nuclear probe of surpassing power of penetration." Philip Morrison stated, "A beam of thermal neutrons moving at about the speed of sound...produces nuclear reactions in many materials much more easily than a beam of protons...traveling thousands of times faster." According to Rhodes, "Slowing down a neutron gave it more time in

11832-438: Was barium . Hahn suggested a bursting of the nucleus, but he was unsure of what the physical basis for the results were. Barium had an atomic mass 40% less than uranium, and no previously known methods of radioactive decay could account for such a large difference in the mass of the nucleus. Frisch was skeptical, but Meitner trusted Hahn's ability as a chemist. Marie Curie had been separating barium from radium for many years, and

11948-576: Was appointed the Soviet representative on the Polish Committee of National Liberation . On 18 November 1944, he was given the rank of General, and three days later he replaced Marshal Voroshilov on the State Defence Committee. He was also appointed USSR Deputy Minister for Defence, the Minister being Joseph Stalin . In March 1946, Bulganin became a candidate member of the 18th Politburo of

12064-496: Was clear to a number of scientists at Columbia that they should try to detect the energy released in the nuclear fission of uranium from neutron bombardment. On 25 January 1939, a Columbia University team conducted the first nuclear fission experiment in the United States, which was done in the basement of Pupin Hall . The experiment involved placing uranium oxide inside of an ionization chamber and irradiating it with neutrons, and measuring

12180-450: Was deployable by air. The Soviet claim did not fool the American scientists: their fallout analysis demonstrated to them that the Soviet device was similar to Teller's Alarm Clock concept. The United States didn't develop a deployable version of the hydrogen bomb until five months after the RDS-6s test, in 1954. The first Soviet test of a "true" hydrogen bomb was on November 22, 1955, under

12296-494: Was necessary to overcome this barrier and cause the nucleus to fission. According to John Lilley, "The energy required to overcome the barrier to fission is called the activation energy or fission barrier and is about 6 MeV for A  ≈ 240. It is found that the activation energy decreases as A increases. Eventually, a point is reached where activation energy disappears altogether...it would undergo very rapid spontaneous fission." Maria Goeppert Mayer later proposed

12412-607: Was never a front-line commander, Bulganin held a number of important political posts in the Red Army during World War II, and served in Stalin's State Defense Committee . In 1947, he succeeded Stalin as Minister for the Armed Forces and was named a Marshal of the Soviet Union . In early 1948, he became a full member of the Politburo . After Stalin's death in 1953, Bulganin supported Nikita Khrushchev during his power struggle with Georgy Malenkov . In 1955, he replaced Malenkov as Premier of

12528-852: Was of Russian ethnicity. He joined the Bolshevik Party in March 1917 and was recruited in 1918 into the Cheka , the Bolshevik regime's political police, where he served until 1922. During the summer of 1918, he worked with Lazar Kaganovich , the local communist leader, in imposing the Red Terror in Nizhny Novgorod. He worked with Kaganovich again in Turkestan in 1920. After the Russian Civil War (1917–1923), Bulganin became an industrial manager and worked in

12644-406: Was removed from the Central Committee and deprived of the title of Marshal, and in February 1960 he was retired on a pension. His wife was Elena Mikhailovna Korovina, an English teacher from a Moscow school . The couple had two children : son Leo and daughter Vera. Vera married the son of Admiral Nikolai Kuznetsov . Bulganin died on February 24, 1975, after a long illness at the age 79 and

12760-509: Was similar to this classical super. The difference was that the light shell of beryllium oxide was replaced by a heavy shell. The assumption was that the deuterium tritium mixture could be easily heated and compressed, and the shock would start the thermonuclear reaction prematurely. A heavy shell opaque to radiation would prevent this unwanted preheating more than the light shell. In September-October 1948 Andrei Sakharov , working in FIAN, came up with

12876-415: Was spread even further, which fostered many more experimental demonstrations. The 6 January 1939 Hahn and Strassman paper announced the discover of fission. In their second publication on nuclear fission in February 1939, Hahn and Strassmann used the term Uranspaltung (uranium fission) for the first time, and predicted the existence and liberation of additional neutrons during the fission process, opening up

12992-402: Was tested on August 12, 1953 (Joe 4). The measured yield was 400 kilotons, 10% from fission of the uranium-235 core, 15-20% from fusion and 70 - 75% from fission of the uranium-238 layers. After the successful test Sakharov proposed a more powerful version of the RDS-6s, code named RDS-6sD. Attempts to increase the yield of the RDS-6s however proved unfeasible. In December 1953, all research on

13108-518: Was the Premier of the Soviet Union from 1955 to 1958. He also served as Minister of Defense , following service in the Red Army during World War II . Born in Nizhny Novgorod , Bulganin joined the Bolshevik Party in 1917 and became a member of the Soviet political police Cheka a year later. After the Russian Civil War , he held a number of administrative positions until 1931, when he became chairman of

13224-457: Was the Truba ( Russian : Труба , pipe/cylinder) (RDS-6t)). In March 1948 Klaus Fuchs had provided the USSR with documents of the US 'Classical Super' . In these documents the classical super was described as consisting of a gun-type uranium-235 primary with beryllium oxide tamper and a secondary consisting of a long cylinder with deuterium, doped with tritium near the primary. The design of the RDS-6t

13340-511: Was the major contributor to that cross section and slow-neutron fission. During this period the Hungarian physicist Leó Szilárd realized that the neutron-driven fission of heavy atoms could be used to create a nuclear chain reaction. Such a reaction using neutrons was an idea he had first formulated in 1933, upon reading Rutherford's disparaging remarks about generating power from neutron collisions. However, Szilárd had not been able to achieve

13456-509: Was to ensure that none of the genuine wartime commanders, particularly Marshal Zhukov , became powerful enough to threaten Stalin . Pavel Sudoplatov , who participated in conferences in the Kremlin with him, wrote contemptuously about how Bulganin failed to understand elementary military concepts. Sudoplatov added: Bulganin was notorious for avoiding decisions. Letters requesting urgent action remained unsigned for months. The entire secretariat of

#803196