Physics

Problem

A marginally subcritical plutonium-239 core of fixed mass is being modified. Consider the following proposed changes: I. Surround the core with a thick layer of neutron-reflecting beryllium. II. Compress the core to twice its original density using chemical explosives. III. Cool the core from

600\,\text{K}

300\,\text{K}

while keeping its volume constant. IV. Replace

1\%

of the plutonium with boron impurity evenly mixed throughout the core. Which combination of modifications would most effectively drive the core to a prompt supercritical state? a) II and III only b) I and IV only c) I and II only d) I, II, and III

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