Comparison Between Historic Nuclear Explosion Yield Formulas

Lestone, J. P.; Rosen, M. D.; Adsley, P.

doi:10.1080/00295450.2021.1909372

Cited by 13 publications

(3 citation statements)

References 6 publications

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“…The prompt fission neutron spectrum (PFNS) was needed to inform calculations of the critical mass, and therefore to determine the amounts of highly enriched uranium (or plutonium) needed. It also determines the neutron velocities in dynamic calculations [4].…”

Section: Figurementioning

confidence: 99%

Manhattan Project 1940s research on the prompt fission neutron spectrum

Chadwick

Capote²

2023

Front. Phys.

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We describe how the prompt fission neutron spectrum (PFNS) was determined for the Manhattan Project at Los Alamos. Early work before World War II at American and British universities is described, together with theoretical work by Feather at Cambridge and Bethe at Los Alamos. As the Manhattan Project was being planned in 1942, two experiments on natural uranium were commissioned that proved to be influential: 1) An integral experiment at Chicago by Christy and Manley that accurately determined the average PFNS spectrum energy, 2.2 ± 0.2 MeV; 2) Bloch and Staub’s Stanford cyclotron measurement of the PFNS spectrum, which obtained an average energy of 1.70 ± 0.34 MeV. These two papers, previously unavailable outside of Los Alamos, are reproduced in the Supplementary Appendix. From these data, at the beginning of the project in 1943 Serber estimated an average 235U PFNS energy of 2 MeV, and indeed this agrees with today’s best estimate. The challenges facing the scientists involved both the availability of only very small samples of enriched uranium and plutonium targets, and fast neutron detection technologies. During the project, 235U and 239Pu PFNS were measured by Nicodemus and Staub. These also proved to be quite accurate and gave an average spectrum energy of 2 MeV for 235U. [This is not reproduced in the Appendix because it was published after the war in Physical Review 89, 1288 (1953)]. New methods were developed to enable more accurate measurements, and this paper describes how the PFNS was determined surprisingly well by 1945. We end by describing the post-war measurements in the 50s, including the PFNS data used by Ford and Wheeler in their simulations in 1951, the Bonner 1952 data, the seminal 1952 Watt paper with a new empirical parametrization of the PFNS, and the accurate PFNS measurement undertaken at Los Alamos by Cranberg et al. in 1956. We compare the measurements with our best understanding today as embodied in the Evaluated Nuclear Data File ENDF/B-VIII.0. Some images from historical documents in our Los Alamos National Security Research Center (NSRC) archives are shown.

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Section: Figurementioning

confidence: 99%

Manhattan Project 1940s research on the prompt fission neutron spectrum

Chadwick

Capote²

2023

Front. Phys.

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“…Bethe and Feynman, both future Nobel laureates, developed an important equation for predicting the expected nuclear fission efficiency, as described by Lestone. 11 Computing using both "human computers" and IBM punched-card machines enabled these Theoretical Division efforts, too, as described by Lewis 12 and Archer. 13 It is well known that Little Boy entered combat without a full-scale test, but there is more to the story.…”

Section: All Possible Prioritymentioning

confidence: 99%

Thirty Minutes Before the Dawn

Carr

2021

Nuclear Technology

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The Trinity test of July 16, 1945, marked the scientific apex of the Manhattan Project. Often recognized as the symbolic birth of the nuclear age, Trinity's multifaceted legacy remains just as captivating and complex today as it did 75 years ago. This paper examines why the test was necessary from a technical standpoint, shows how Los Alamos scientists planned the event, and explores the physical and emotional aftermaths of Trinity. The author also uses rarely accessed original records to reconstruct the story of Trinity's health hazards, as seen through the eyes of radiation technicians and medical doctors as events unfolded.Trinity was conducted as the Potsdam Conference began, weeks after the collapse of Nazi Germany. It was considered necessary to let President Harry S. Truman know whether the United States possessed a nuclear capability ahead of his negotiations with Joseph Stalin, the Soviet premier. The author examines the competing priorities that drove the timetable for the test: international politics, security, and safety. Three weeks after Trinity, a gun-assembled enriched-uranium bomb called Little Boy was used against the Japanese city of Hiroshima. Three days later, Fat Man, a weaponized version of the imploding Trinity device, was dropped on Nagasaki. The author briefly examines these strikes and what impact they may have had on the Japanese surrender. The paper concludes by examining the legacy of the Trinity test 75 years into the age it helped usher in.

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“…This work has had an enduring influence over the past 75 years; our classified research journal on Trinity has no fewer than five papers on different aspects of the formula--three from Los Alamos, one from Livermore, and one from AWE. A short paper by Lestone and Rosen (Livermore) 24 describes, for the first time, the formula and its relationship to earlier wartime British work by Frisch and Peierls and by Pryce and Dirac. (Wigner, who was Dirac's brother-in-law, said that "Feynman is a second Dirac, only this time human" 25 !…”

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Foreword: Manhattan Project Nuclear Science & Technology Developments at Los Alamos

Chadwick

2021

Preprint

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The year 2020 marked the 75th anniversary of the Trinity experiment, the world's first nuclear explosion, on July 16, 1945, near Alamogordo, New Mexico. Trinity was a vital proof step toward the culmination of the Manhattan Project and the end of World War II. The technical accomplishments made by scientists and engineers from the US, UK, and Canada (some originating in Germany, Hungary, Italy, France, and other countries) were recognized by many events in 2020, including a visit to New Mexico's Los Alamos National Laboratory by Department of Energy (DOE) National Nuclear Security Administration (NNSA) dignitaries, historical documentaries, 1, 2 and the publication of an excellent book, Trinity, by physicist Frank Close. 3 The importance of Trinity as a foundational accomplishment for the broad nuclear science and engineering community is clear; indeed, New Mexico's chapter of the American Nuclear Society (ANS) is referred to as the "Trinity Section." The events surrounding Trinity have even entered into high culture with re-

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Comparison Between Historic Nuclear Explosion Yield Formulas

Cited by 13 publications

References 6 publications

Manhattan Project 1940s research on the prompt fission neutron spectrum

Manhattan Project 1940s research on the prompt fission neutron spectrum

Thirty Minutes Before the Dawn

Foreword: Manhattan Project Nuclear Science & Technology Developments at Los Alamos

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