Nuclear weapons at 70: reflections on the context and legacy of the Manhattan Project

Abstract

August 2015 marks the 70th anniversary of the atomic bombings of Hiroshima and Nagasaki. These bombs, the products of the United States Army's Manhattan Project, helped to end World War II and had enormous long-term effects on global political strategies by setting the stage for the Cold War and nuclear proliferation. This article explores the context and legacy of the Manhattan Project. The state of the war in the summer of 1945 is described, as are how the target cities came to be chosen, deliberations surrounding whether the bombs should be used directly or demonstrated first, and the long-term effects of the Project on individual scientists, the relationship between scientists and society, the subsequent development of nuclear arsenals around the world, and the current status of these arsenals and how they might evolve in the future.

A physicists guide to The Los Alamos Primer

“…This paper is the third in a series of Invited Comments in this journal on the topic of the Manhattan Project. The first paper dealt with the organization and physics of the Project, and the second with its legacy [1,2]. In a sense, the present paper is really a prequel to these earlier papers, but as explained in what follows there are good reasons to publish it as a sequel.…”

“…One issue that was discussed would eventually almost doom the plutonium bomb: the possibility that light-element impurities in reactor-produced plutonium might cause a sufficiently high a Inferred from his quoted 4 barn transport cross-section and 1.5 barn fission cross-section. 2 The organizational history of the Manhattan Project is related in chapter 4…”

“…To estimate brightness we can use the Stefan-Boltzmann law, which says that the total radiant power output of an object of radius R and absolute temperature T is proportional to R 2 T 4 . 'Brightness' is the power received per unit area by an observer, which for somebody located at distance d is the power divided by the area of the sphere over which the energy has spread, 4πd 2 . The brightnesses of the fireball (F) and Sun (S) will then compare as…”

“…The memoranda were largely qualitative (although based on underlying calculations), but the Primer was a physics paper intended to bring its readers, many of whom already knew parts of its contents quite intimately, up to speed on a much larger project of which their work had been but one of many components. The Primer assumed much prior knowledge, and it is for this reason that this paper is published as a sequel to [1,2].…”