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5.
The uranium in the example above is both a neutron reflector and an inertial material. This is the so-called tamper surrounding the fissile core as they are popularly described:
6. There are two general techniques tor assembling a supercritical mass described in the literature: the gun method where subcritical masses are "shot" together, and the implosion method where a subcritical mass is made supercritical by compression.
For a gun assembly, suppose that
the fissile hemispheres become critical and the time they meet.
For an implosion assembly, suppose that
It appears that the implosion method can be made to give faster assembly times than the gun method.
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