Editing Emilio Segrè (section)

==Manhattan Project==
[[File:Segre-emilio.jpg|thumb|right|Segrè's ID badge photo from [[Los Alamos National Laboratory|Los Alamos]]]]

The Japanese [[attack on Pearl Harbor]] in December 1941 and the subsequent [[United States declaration of war upon Italy]] rendered Segrè an [[enemy alien]] and cut him off from communication with his parents. Physicists began leaving the Radiation Laboratory to do war work, and [[Raymond T. Birge]] asked him to teach classes to the remaining students. This provided a useful supplement to Segrè's income, and he established important friendships and professional associations with some of these students, who included [[Owen Chamberlain]] and [[Clyde Wiegand]].{{sfn|Segrè|1993|pp=170–172}}

In late 1942, Oppenheimer asked Segrè to join the [[Manhattan Project]] at its [[Los Alamos Laboratory]].{{sfn|Segrè|1993|pp=177–180}} Segrè became the head of the laboratory's P-5 (Radioactivity) Group, which formed part of [[Robert Bacher]]'s P (Experimental Physics) Division.{{sfn|Hawkins|1961|p=101}} For security reasons, he was given the cover name of Earl Seaman.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=96}} He moved to Los Alamos with his family in June 1943.{{sfn|Segrè|1993|p=186}}

Segrè's group set up its equipment in a disused [[United States Forest Service|Forest Service]] cabin in the Pajarito Canyon near Los Alamos in August 1943.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=234–236}} His group's task was to measure and catalog the radioactivity of various [[fission product]]s. An important line of research was determining the degree of [[isotope enrichment]] achieved with various samples of [[enriched uranium]]. Initially, the tests using [[mass spectrometry]], used by [[Columbia University]], and neutron assay, used by Berkeley, gave different results. Segrè studied Berkeley's results and could find no error, while [[Kenneth Bainbridge]] likewise found no fault with New York's. However, analysis of another sample showed close agreement.{{sfn|Hawkins|1961|pp=120–121}} Higher rates of spontaneous fission were observed at Los Alamos, which Segrè's group concluded were due to [[cosmic rays]], which were more prevalent at Los Alamos due to its high altitude.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=234–236}}

The group measured the activity of [[thorium]], [[uranium-234]], [[uranium-235]] and [[uranium-238]], but only had access to [[microgram]] quantities of [[plutonium-239]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=234–236}}  The first sample plutonium produced in the [[nuclear reactor]] at [[Oak Ridge National Laboratory|Oak Ridge]] was received in April 1944. Within days the group observed five times the rate of [[spontaneous fission]] as with the cyclotron-produced plutonium.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=236–239}}  This was not news that the leaders of the project wanted to hear. It meant that [[Thin Man nuclear bomb|Thin Man]], the proposed plutonium [[gun-type nuclear weapon]], would not work and implied that the project's investment in plutonium production facilities at the [[Hanford Site]] was wasted. Segrè's group carefully checked their results and concluded that the increased activity was due to the [[plutonium-240]] isotope.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=239–244}}

In June 1944, Segrè was summoned into Oppenheimer's office and informed that while his father was safe, his mother had been rounded up by the Nazis in October 1943. Segrè never saw either of his parents again. His father died in Rome in October 1944.{{sfn|Segrè|1993|pp=195, 214–215}} In late 1944, Segrè and Elfriede became [[naturalized citizen]]s of the United States.{{sfn|Segrè|1993|pp=204–205}} His group, now designated R-4, was given responsibility for measuring the [[gamma radiation]] from the [[Trinity nuclear test]] in July 1945.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=357}} The blast damaged or destroyed most of the experiments, but enough data was recovered to measure the gamma rays.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=375}}