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152-582: The Smyth Report (officially Atomic Energy for Military Purposes ) is the common name of an administrative history written by American physicist Henry DeWolf Smyth about the Manhattan Project , the Allied effort to develop atomic bombs during World War II . The subtitle of the report is A General Account of the Development of Methods of Using Atomic Energy for Military Purposes . It

304-700: A master's degree like MSc, MPhil, MPhys or MSci. For research-oriented careers, students work toward a doctoral degree specializing in a particular field. Fields of specialization include experimental and theoretical astrophysics , atomic physics , biological physics , chemical physics , condensed matter physics , cosmology , geophysics , gravitational physics , material science , medical physics , microelectronics , molecular physics , nuclear physics , optics , particle physics , plasma physics , quantum information science , and radiophysics . The three major employers of career physicists are academic institutions, laboratories, and private industries, with

456-594: 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 a neutron, harnessed and exploited by humans, a natural form of spontaneous radioactive decay (not requiring a neutron) 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,

608-445: 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

760-623: A consultant at Chicago, where he was in charge of designing a nuclear reactor that used heavy water as a neutron moderator , and commuted from Princeton, working in Chicago on alternate weeks. In early 1944, Smyth raised the possibility of producing an unclassified report for the general public on the achievements of the Manhattan Project. The director of the Metallurgical Laboratory, Arthur Compton , supported

912-401: 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

1064-413: A documented official history nor a technical treatise for experts. Secrecy requirements have affected both the detailed content and general emphasis so that many interesting developments have been omitted. This contrasted somewhat with what Groves wrote in the foreword: All pertinent scientific information which can be released to the public at this time without violating the needs of national security

1216-448: 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

1368-480: 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,

1520-432: 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

1672-413: 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

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1824-408: 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

1976-413: A meeting with Groves and Conant, and he accepted their point of view. "I am now convinced," he wrote, "that the very special circumstances arising from the nature of the project, and of its organization, demand special treatment, and a report of this kind may well be necessary to maintain security of the really essential facts of the project." A thousand copies of the report were printed by lithography at

2128-452: A minimum, the owner must possess a three-year bachelors or equivalent degree in physics or a related field and an additional minimum of six years' experience in a physics-related activity; or an Honor or equivalent degree in physics or a related field and an additional minimum of five years' experience in a physics-related activity; or master or equivalent degree in physics or a related field and an additional minimum of three years' experience in

2280-469: 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

2432-667: 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

2584-416: 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

2736-404: 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

2888-622: 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

3040-741: A number of cases, the Soviets consulted the Smyth Report to see how they might deal with certain obstacles that had arisen in their project. The deletion between the original text and the Princeton version concerning the poisoning effect was soon noticed by the Russian translators, and only served to highlight its importance to the Soviet project. As pioneering French nuclear weapons scientist Bertrand Goldschmidt later said, The details revealed in

3192-565: A physics-related activity; a Doctorate or equivalent degree in Physics or a related field; or training or experience which, in the opinion of the Council, is equivalent to any of the above. Physicists may be a member of a physical society of a country or region. Physical societies commonly publish scientific journals, organize physics conferences and award prizes for contributions to the field of physics. Some examples of physical societies are

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3344-416: A professional practice examination must also be passed. An exemption can be granted to a candidate that has practiced physics for at least seven years and provide a detailed description of their professional accomplishments which clearly demonstrate that the exam is not necessary. Work experience will be considered physics-related if it uses physics directly or significantly uses the modes of thought (such as

3496-559: A publisher's biggest worries was finding adequate supplies of paper. Smith approached Manny and Leonard Relles from Central Paper, told them about the Smyth Report and its significance, and asked them if they could deliver 30 short tons (27 t) of paper to Maple Press in twelve days. They found a carload of paper on a siding in New England and sent it to York, providing enough paper for 30,000 copies, only half what Princeton University Press wanted. The first edition of 30,000 copies

3648-583: 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

3800-420: A stipulation of its own: that Groves's approval be secured. Smyth obtained this in a letter dated August 25, 1945. Princeton University Press received a copy of the typescript lithograph edition with hand corrections from Smyth on August 17, 1945. The typographers had already started work from another copy. Maple Press of York, Pennsylvania , was lined up to do the printing. Because of wartime shortages, one of

3952-601: 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

4104-631: 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

4256-411: 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

4408-457: A well-equipped college lab in a year's time or less. Writing to Oppenheimer in April 1945, Smyth noted that All discussion of ordnance work is also to be removed. There is no objection to including the general statement of the ordnance problem and all the other parts of the problem, but the approaches to solution that have been made will be omitted. On the other hand, the feeling is that there

4560-496: 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

4712-426: Is already generally known by competent scientists or (B) that it can be deduced or guessed by competent scientists from what is already known, combined with the knowledge that the project was in the overall successful or III. (A) That it has no real bearing on the production of atomic bombs or (B) That it could be discovered by a small group (15 of whom not over 5 would be senior men) of competent scientists working in

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4864-506: 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

5016-427: 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

5168-438: 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

5320-413: 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

5472-450: Is constructed or how it works but there is in this country a substantial group of engineers and scientists who can understand such things and who can explain the potentialities of atomic bombs to their fellow citizens. The present report is written for this professional group and is a matter-of-fact, general account of work in the USA since 1939 aimed at the production of such bombs. It is neither

5624-493: Is contained in this volume. No requests for additional information should be made to private people or organizations associated directly or indirectly with the project. People disclosing or securing additional information by any means whatsoever without authorization are subject to severe penalties under the Espionage Act. Smyth possessed security clearances necessary to visit project sites, access documents and to discuss

5776-407: 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

5928-423: Is no objection to including the nuclear physics. The General believes that the metallurgical work and a considerable amount of the chemistry work should be excluded on the ground that it would be extremely difficult for the average scientist to carry out any of this work without supplies and material which would not be available to him. I am not entirely clear how this criterion should be applied, but it probably means

6080-417: 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

6232-402: 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

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6384-615: Is the Nobel Prize in Physics , awarded since 1901 by the Royal Swedish Academy of Sciences . National physical societies have many prizes and awards for professional recognition. In the case of the American Physical Society , as of 2023, there are 25 separate prizes and 33 separate awards in the field. Chartered Physicist (CPhys) is a chartered status and a professional qualification awarded by

6536-423: 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

6688-418: 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

6840-667: 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

6992-572: The American Physical Society , the Institute of Physics , with the oldest physical society being the German Physical Society . Nuclear fission Nuclear fission is a reaction in which 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

7144-697: The Institute of Physics . It is denoted by the postnominals "CPhys". Achieving chartered status in any profession denotes to the wider community a high level of specialised subject knowledge and professional competence. According to the Institute of Physics, holders of the award of the Chartered Physicist (CPhys) demonstrate the "highest standards of professionalism, up-to-date expertise, quality and safety" along with "the capacity to undertake independent practice and exercise leadership" as well as "commitment to keep pace with advancing knowledge and with

7296-548: The Islamic medieval period , which saw the development of scientific methodology emphasising experimentation , such as the work of Ibn al-Haytham (Alhazen) in the 11th century. The modern scientific worldview and the bulk of physics education can be said to flow from the scientific revolution in Europe, starting with the work of astronomer Nicolaus Copernicus leading to the physics of Galileo Galilei and Johannes Kepler in

7448-707: 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

7600-421: 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

7752-621: 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

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7904-493: 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

8056-579: The 19th century. Many physicists contributed to the development of quantum mechanics in the early-to-mid 20th century. New knowledge in the early 21st century includes a large increase in understanding physical cosmology . The broad and general study of nature, natural philosophy , was divided into several fields in the 19th century, when the concept of "science" received its modern shape. Specific categories emerged, such as "biology" and "biologist", "physics" and "physicist", "chemistry" and "chemist", among other technical fields and titles. The term physicist

8208-544: The Auspices of the United States Government, 1940–1945 . The word "nuclear" was changed to "atomic" because while the former was favored by physicists, it was not in common use by the general public at that time. This was the title used on the copyright certificate. The book was copyrighted to Smyth but issued with the statement that "reproduction in whole or in part is authorized and permitted". Groves had

8360-588: The British Embassy represented Britain. The meeting went on for two hours, as Groves and Conant sought to reassure Stimson that the report would not give vital secrets away to the Soviet Union . For his part, Chadwick, who had not yet read the manuscript, could not fathom why the Americans wanted to publish such a document. When he did read it, he became quite alarmed. His concerns were addressed in

8512-779: The Canadian government was added as Appendix 8. The Smyth Report was translated into over 40 different languages. In addition to Princeton University Press, it was also published by the Government Printing Office, the Infantry Journal , and His Majesty's Stationery Office , and was reprinted in the October 1945 issue of Reviews of Modern Physics . The first copies were delivered to bookstores on September 10. Many were wary of it, due to its technical nature, and feared that sales would be low. An exception

8664-421: The Manhattan Project was all about physics. The Smyth Report sold almost 127,000 copies in its first eight printings, and was on The New York Times best-seller list from mid-October 1945 until late January 1946. It has been translated into over 40 languages. Henry D. Smyth was a professor of physics and chairman of the physics department of Princeton University from 1935 to 1949. During World War II , he

8816-568: The Manhattan Project's governing body, the Military Policy Committee, in May 1944. The Report was to serve two functions. First, it was to be the public and official U.S. government account of the development of the atomic bombs, outlining the development of the then-secret laboratories and production sites at Los Alamos, New Mexico , Oak Ridge, Tennessee , and Hanford, Washington , and the basic physical processes responsible for

8968-812: The Pentagon , and deposited in Groves's office in the New War Department Building in Washington, D.C., where they were kept securely locked away. Final approval was sought from the President , Harry S. Truman , in a meeting at the White House on August 9, 1945, three days after the bombing of Hiroshima . Stimson, Harrison, Groves, Conant, Vannevar Bush , and Fleet Admiral William D. Leahy presented their views, and Truman authorized

9120-438: The Smyth Report had given away too much information, including the exact locations of the atomic materials production plants. Physicist Physicists can apply their knowledge towards solving practical problems or to developing new technologies (also known as applied physics or engineering physics ). The study and practice of physics is based on an intellectual ladder of discoveries and insights from ancient times to

9272-487: The Smyth Report went out of print in 1973, it went through eight printings, and Princeton University Press sold 62,612 paperback and 64,129 hardback copies. Groves did not intend the Smyth Report to be the last word on the project. It formed an addendum to the Manhattan District History , the official history of the project. This eventually consisted of 35 volumes with 39 appendices or supplements. It

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9424-478: The Smyth Report's security-driven focus on physics at the expense of chemistry, metallurgy, and ordnance promoted a public perception of the Manhattan Project as primarily the achievement of physics and physicists. According to Schwartz, postwar histories and popular writing tended to follow the Smyth Report in this regard, creating a lasting historiographical legacy. "Ever since", wrote Jon Agar, "the atomic bomb has been seen as an achievement of physics." In particular,

9576-533: The Smyth Report. A meeting was held on August 2, 1945, in the office of the Secretary of War , Henry Stimson . Accompanying Stimson were his two assistants, Harvey Bundy and George L. Harrison , and his military aide, Colonel William H. Kyle. Groves, Conant, and Tolman represented the Manhattan Project. James Chadwick , the head of the British scientific mission to the Manhattan Project , and Roger Makins from

9728-459: The Smyth report were invaluable for any country launching into atomic work; for nothing is more important, when undertaking technical research over a wide field than knowing in advance which lines of approach can or cannot lead to success, even if this knowledge relates only to basic principles. Nonetheless, Goldschmidt believed, just as Chadwick had ultimately believed, that publication of the report

9880-399: The approach to problem-solving) developed in your education or experience as a physicist, in all cases regardless of whether the experience is in academia, industry, government, or elsewhere. Management of physics-related work qualifies, and so does appropriate graduate student work. The South African Institute of Physics also delivers a certification of Professional Physicist (Pr.Phys). At

10032-698: 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

10184-456: 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

10336-446: 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

10488-420: The circumstances, he felt that he could not risk this. After the Smyth Report was officially released, Smith immediately offered to publish it. Smyth patiently explained that anyone was free to publish it, but Princeton University Press was only willing to do so on the understanding that this would be "Smyth's edition". Meanwhile, Smyth approached McGraw-Hill about publishing it. The editors at McGraw-Hill found

10640-419: 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

10792-405: 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

10944-414: 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

11096-549: The danger of security breaches. After Smyth made a series of changes in response to this, Groves sent the manuscript to his scientific adviser, Richard Tolman . Tolman was assisted by two physicists who were working in his office at the National Defense Research Committee as technical aides, Paul C. Fine from the University of Texas , and William Shurcliff from Harvard University . They had

11248-520: The designation of Professional Engineer (P. Eng.). This designation was unveiled at the CAP congress in 1999 and already more than 200 people carry this distinction. To get the certification, at minimum proof of honours bachelor or higher degree in physics or a closely related discipline must be provided. Also, the physicist must have completed, or be about to complete, three years of recent physics-related work experience after graduation. And, unless exempted,

11400-416: The dual task of editing and censoring the manuscript. Smyth and Tolman accepted a set of criteria, agreeing that information could be released under the conditions: I. (A) That it is important to a reasonable understanding of what had been done on the project as a whole or (B) That it is of true scientific interest and likely to be truly helpful to scientific workers in this country and II. (A) That it

11552-459: The early 1600s. The work on mechanics , along with a mathematical treatment of physical systems, was further developed by Christiaan Huygens and culminated in Newton's laws of motion and Newton's law of universal gravitation by the end of the 17th century. The experimental discoveries of Faraday and the theory of Maxwell's equations of electromagnetism were developmental high points during

11704-416: 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

11856-401: The elimination of the metallurgical work on plutonium and at least of some of the chemistry. Tolman and his assistants finished making their changes in July 1945, and Groves had copies sent out by courier to selected personnel. Each submitted a written report, which was returned with the courier and the manuscript. These were busy people who sometimes only had a few days or even hours to look at

12008-406: 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

12160-699: 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

12312-450: 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

12464-449: 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,

12616-424: 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 the fragments ( heating the bulk material where fission takes place). Like nuclear fusion , for fission to produce energy,

12768-432: 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

12920-424: 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

13072-426: 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

13224-492: The first twelve chapters, leaving only the final chapter to be completed. Groves and Conant reviewed the drafts, and made several criticisms. They felt that it was too technical for general readers, did not mention the names of enough participants, and dwelt too much on the activities at the Los Alamos Laboratory . Groves was particularly anxious that deserving people be mentioned, as he felt that this would lessen

13376-409: 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

13528-450: 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

13680-443: 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

13832-431: 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

13984-410: 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

14136-448: The functioning of nuclear weapons, in particular nuclear fission and the nuclear chain reaction . Second, it served as a reference for other scientists as to what information was declassified—anything said in the Smyth Report could be said freely in open literature. For this reason, the Smyth Report focused heavily on information already available in declassified literature, such as much of the basic nuclear physics used in weapons, which

14288-434: The government during a two-week summer shutdown so that Smyth could produce 5,000 copies of a top secret report. Smith's response was that he found it hard to imagine anyone needing to print 5,000 copies of a top secret report. He found it much easier to imagine delays due to unexpected printing problems, and his workers returning from summer vacation to find themselves locked out of a plant filled with top secret material. Under

14440-405: 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

14592-435: 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

14744-492: 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

14896-446: The idea. He arranged a meeting with James B. Conant , the President of Harvard University and one of the senior administrators of the Manhattan Project, who had similar thoughts. Conant took up the matter with the Manhattan Project's director, Major General Leslie R. Groves, Jr. In April, Smyth received a formal letter from Groves asking him to write such a report. Both the report and the choice of Smyth as its author were approved by

15048-468: The immediate release of the report. The War Department released the thousand copies of the report that had been kept in Groves's office to the media for use by the radio broadcasters with an embargo time of 9:00 pm on August 11, 1945, and for the newspapers of August 12. The original title of the report, before it was published in book form, was Nuclear Bombs: A General Account of the Development of Methods of Using Nuclear Energy for Military Purposes Under

15200-756: The increasing expectations and requirements for which any profession must take responsibility". Chartered Physicist is considered to be equal in status to Chartered Engineer, which the IoP also awards as a member of the Engineering Council UK, and other chartered statuses in the UK. It is also considered a "regulated profession" under the European professional qualification directives. The Canadian Association of Physicists can appoint an official designation called Professional Physicist ( P. Phys. ), similar to

15352-1180: The largest employer being the last. Physicists in academia or government labs tend to have titles such as Assistants, Professors , Sr./Jr. Scientist, or postdocs . As per the American Institute of Physics , some 20% of new physics Ph.D.s holds jobs in engineering development programs, while 14% turn to computer software and about 11% are in business/education. A majority of physicists employed apply their skills and training to interdisciplinary sectors (e.g. finance ). Job titles for graduate physicists include Agricultural Scientist , Air Traffic Controller , Biophysicist , Computer Programmer , Electrical Engineer , Environmental Analyst , Geophysicist , Medical Physicist , Meteorologist , Oceanographer , Physics Teacher / Professor / Researcher , Research Scientist , Reactor Physicist , Engineering Physicist , Satellite Missions Analyst, Science Writer , Stratigrapher , Software Engineer , Systems Engineer , Microelectronics Engineer , Radar Developer, Technical Consultant, etc. The majority of Physics terminal bachelor's degree holders are employed in

15504-412: 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

15656-427: 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

15808-570: The manuscript dull and somewhat technical for a general audience and suggested a rewrite. Smyth balked at this, as it would have meant going through the censorship process again. James S. Thompson, the president of McGraw-Hill, pointed out the U.S. Government Printing Office would be putting out an edition, probably more cheaply than he could, and there would likely be little profit in a McGraw-Hill edition. Smyth then turned back to Princeton University Press. He had only one condition: that he receive no royalties. Princeton University Press agreed, but added

15960-536: The manuscript. Many, but not all, merely signed a statement saying that they were happy with it. Nichols, the commander of the Manhattan District, sent back a detailed review. He had concerns about the amount of credit being given to different people and organizations, and recommended that "full credit be given to H. D. Smyth for preparing it and that the statement be made that the Army has no responsibility for

16112-478: 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

16264-465: 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,

16416-523: 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

16568-399: 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

16720-433: 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

16872-441: 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

17024-457: 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

17176-470: 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

17328-517: The path that the Manhattan Project had found success with, commissioned a Russian translation of Atomic Energy for Military Purposes . It was in typeset form by mid-November 1945, and then was published by the State Railway Transportation Publishing House on January 30, 1946. Some 30,000 copies were printed and it was widely distributed to the many scientists and engineers working in the Soviet effort. In

17480-430: 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

17632-410: 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

17784-620: The present. Many mathematical and physical ideas used today found their earliest expression in the work of ancient civilizations, such as the Babylonian astronomers and Egyptian engineers , the Greek philosophers of science and mathematicians such as Thales of Miletus , Euclid in Ptolemaic Egypt , Archimedes of Syracuse and Aristarchus of Samos . Roots also emerged in ancient Asian cultures such as India and China, and particularly

17936-419: The press or the public. The lumbering subtitle therefore became the title. A side effect of this was that it became generally known as the "Smyth Report". Over the years, the term "nuclear" gradually gained traction, and by 1960 it had become more common than "atomic". In mid-1945, Smyth approached Datus C. Smith, the director of Princeton University Press , about the possibility of renting his printing plant to

18088-493: The previous use of abbreviations. In response to public concerns about radioactivity, Groves had text added to paragraph 12.18 explaining how the height of the explosions over Hiroshima and Nagasaki reduced fallout and allowed fission products to be drawn up into the upper atmosphere. He also had a one-sentence allusion to a poisoning effect of fission products in the production reactors redacted. Later editions also incorporated changes. Four typographical errors were found, and

18240-433: The private sector. Other fields are academia, government and military service, nonprofit entities, labs and teaching. Typical duties of physicists with master's and doctoral degrees working in their domain involve research, observation and analysis, data preparation, instrumentation, design and development of industrial or medical equipment, computing and software development, etc. The highest honor awarded to physicists

18392-419: The project including access to necessary documents ... [and] information and advice from you and your principal assistants. Since Smyth still had his commitments at Princeton and Chicago, he could only work on the report part-time. He wrote the report in his office in Princeton's Palmer Laboratory. Bars were installed on the windows of Smyth's office and the one adjacent to it. The hallway door to his office

18544-567: The prominence given to Einstein's mass–energy equivalence equation indelibly associated it with the Manhattan Project. The Smyth Report, wrote Robert P. Crease , "more than any other single document made E = mc an emblem of atomic energy and weaponry." Groves felt that: on the whole, and considering the rather difficult conditions under which it was prepared, the Smyth Report was extraordinarily successful in its efforts to distribute credit fairly and accurately. It would have been impossible to have prepared any document for publication covering

18696-522: 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

18848-404: The report copyrighted by Smyth in order to prevent someone else from copyrighting it. Groves was concerned about the security implications of the title, so instead of having "Atomic Bombs" on the cover, it was left blank, and a rubber stamp was made. The intention was for this to be used on each copy before it was distributed. This was done for the copyright deposit copies, but not those given to

19000-537: The report except for asking him to do it." Smyth was given credit, but no such statement was issued. To prepare the final draft for the printer, Groves brought typists with the required security clearances to Washington, D.C., from the Manhattan District's headquarters in Oak Ridge. Because the Manhattan Project was an Allied endeavor, Groves had to obtain permission from the British and American governments to publish

19152-406: 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

19304-475: 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

19456-403: 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

19608-543: 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

19760-615: 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 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

19912-414: 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

20064-588: 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

20216-481: The word " photon " in paragraph 1.44 aroused so much correspondence from readers who mistakenly believed that it should be " proton " that it was decided to re-word the paragraph. The British government became concerned that the Smyth Report did not cover the British part in the project, and issued its own 40-page report, which was incorporated into the fifth printing in November 1945 as Appendix 7. A two-page report by

20368-428: 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

20520-535: The work of the Manhattan District that every reader would have found to his liking. But the fact is that all those who had the greatest knowledge of the subject were nearly unanimous in approving its publication as it was finally written. And there can be no question that it excellently served its purpose as an essential source of accurate information, particularly for a news-hungry America in the early days after Nagasaki. The Soviet Union, eager to make progress on its own atomic weapon development and determined to follow

20672-604: The work with the research personnel. Groves approved Smyth's request to hire another Princeton physicist, Lincoln G. Smith, as a research assistant. A letter to the Manhattan Project's senior managers, Kenneth Nichols , Robert Oppenheimer , Ernest Lawrence , Harold Urey , and Franklin Matthias , explained: The purpose is to give clearly and promptly recognition to those who have worked so long and necessarily so anonymously ... To accomplish his purpose, Dr. Smyth must have rather complete information concerning your phase of

20824-456: Was Scribner's Bookstores , which placed large early orders. At Oak Ridge, the Manhattan Project's major production site, 8,000 copies were sold through the employee welfare organization. Similar arrangements were made for Los Alamos and Richland, Washington , which were located in areas where bookstores were scarce. The Smyth Report was on The New York Times bestseller list from October 14, 1945, until January 20, 1946. Between 1946 and when

20976-438: 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

21128-406: Was declassified ; anything in the Smyth Report could be discussed openly. For this reason, the Smyth Report focused heavily on information, such as basic nuclear physics , which was either already widely known in the scientific community or easily deducible by a competent scientist, and omitted details about chemistry , metallurgy , and ordnance . This would ultimately give a false impression that

21280-563: 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

21432-746: Was coined by William Whewell (also the originator of the term "scientist") in his 1840 book The Philosophy of the Inductive Sciences . A standard undergraduate physics curriculum consists of classical mechanics , electricity and magnetism , non-relativistic quantum mechanics , optics , statistical mechanics and thermodynamics , and laboratory experience. Physics students also need training in mathematics ( calculus , differential equations , linear algebra , complex analysis , etc.), and in computer science . Any physics-oriented career position requires at least an undergraduate degree in physics or applied physics, while career options widen with

21584-579: 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 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

21736-478: Was either already widely known in the scientific community or could have been easily deduced by a competent scientist. Smyth stated the purpose of the Smyth Report in the Preface: The ultimate responsibility for our nation's policy rests on its citizens and they can discharge such responsibilities wisely only if they are informed. The average citizen cannot be expected to understand clearly how an atomic bomb

21888-764: Was involved in the Manhattan Project from early 1941, initially as a member of the National Defense Research Committee 's Committee on Uranium , and later as an associate director of the Metallurgical Laboratory in Chicago. In late 1943, the President of Princeton University , Harold W. Dodds , began insisting that Smyth work part-time at Princeton, where there was a shortage of physicists because so many of them were engaged in war work. Princeton had commitments to teach army and navy personnel, and he needed physicists like Smyth to meet those commitments. Smyth therefore became

22040-475: Was locked and blocked by a large safe so that the only access was through the adjacent office, where there was an armed guard. The guards worked in eight-hour shifts, and one was present around the clock. When Smyth sent papers to Groves in Washington, D.C., they went by military courier. Smyth sent an outline and rough draft of the report to Groves for approval in August 1944, followed in February 1945 by drafts of

22192-494: 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

22344-425: Was on balance wise, in that not revealing anything about the new weapon would lead to a public hunger for information and resultant leaks and unwarranted disclosures of information. Not everyone would agree: in 1947, United States Atomic Energy Commission member Lewis Strauss would call publication of the Smyth Report "a serious breach of security"; and in late 1952, President-elect Dwight D. Eisenhower would say

22496-473: Was printing when word was received that paper had been found for another 30,000 copies. The presses were held for three hours while the train made its way to a siding in York, where the paper was unloaded and brought to the printing plant by trucks. There were minor differences between the original text and the version published by Princeton. In the Princeton publication, first and middle names were added instead of

22648-445: Was released to the public on August 12, 1945, just days after the atomic bombings of Hiroshima and Nagasaki on August 6 and 9. Smyth was commissioned to write the report by Major General Leslie R. Groves, Jr. , the director of the Manhattan Project. The Smyth Report was the first official account of the development of the atomic bombs and the basic physical processes behind them. It also served as an indication as to what information

22800-415: 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

22952-516: 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

23104-504: Was written in the immediate postwar years by the chemists, metallurgists, physicists, and administrators who had worked on the project. Since there were no security restrictions, it covered every aspect of the Manhattan Project, but was itself classified. Most of it was declassified in the 1960s and 1970s and became available to scholars, except for some technical details on the construction of the bombs. In her 2008 PhD dissertation, Rebecca Schwartz argued that Smyth's academic background and

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