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Ultimately, polonium-based neutron initiators were used in both the gun-type Little Boy and the implosion-type Fat Man used in the atomic bombings of Hiroshima and Nagasaki respectively. The fact that polonium was used as an initiator was classified until the 1960s, but George Koval , a technician with the Manhattan Project's Special Engineer ...
The initiator used in the early devices, located at the center of the bomb's plutonium pit, consisted of a beryllium pellet and a beryllium shell with polonium between the two. The pellet, 0.8 cm in diameter, was coated with nickel and then a layer of gold .
Polonium and beryllium were the key ingredients of the 'Urchin' initiator at the center of the bomb's spherical pit. [44] 'Urchin' initiated the nuclear chain reaction at the moment of prompt-criticality to ensure that the weapon did not fizzle. 'Urchin' was used in early U.S. weapons; subsequent U.S. weapons utilized a pulse neutron generator ...
Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon and has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nuclear weapons are the most common examples.
[16] 210 Po was also used in initiators for atomic bombs through the (α,n) reaction with beryllium. [17] Small neutron sources reliant on the (α,n) reaction also usually use polonium as a convenient source of alpha particles due to its comparatively low gamma emissions (allowing easy shielding) and high specific activity.
Early weapons used a modulated neutron generator code named "Urchin" inside the pit containing polonium-210 and beryllium separated by a thin barrier. Implosion of the pit crushes the neutron generator, mixing the two metals, thereby allowing alpha particles from the polonium to interact with beryllium to produce free neutrons.
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These reactors were also required for the production (by irradiation of bismuth-209) of polonium-210, which was used in the initiators, a critical component of the nuclear weapons. Some 62 kilograms (137 lb) of bismuth-209 had to be irradiated for 100 days to produce 600 curies of polonium-210, a little over 132 milligrams (2.04 gr).