Christy pit

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Pit (nuclear weapon)

Named after Canadian-American physicist Robert F. Christy, who worked on the Manhattan Project to produce the first nuclear weapons.

Christy pit (plural Christy pits)

An early design of pit (core of an implosion-type nuclear weapon), used in the detonation over Nagasaki, Japan, in August 1945.
The principal insight behind the Christy pit was that a solid, subcritical core of plutonium could be compressed to criticality.
- 2017, Demon core, entry in Benjamin C. Garrett, Historical Dictionary of Nuclear, Biological, and Chemical Warfare, Bowman & Littlefield, 2nd Edition, page 90,
  Nickname given to the Christy pit because of its association with two fatalities during hands-on Dragon Experiments; it replaced “Rufus,” an earlier nickname. The Christy pit, a solid sphere of plutonium-239, was initially fabricated as two hemispheres of an alloy of plutonium and gallium.

The Christy pit was tested in experiments to confirm the plutonium core was close to its critical mass as well as to observe its behaviour. Two fatalities during these tests led to procedures being changed and the design being given the nickname demon core.