I have, now, gold leaf
over my tin foil. Others
have raised your same thoughts,
and tin foil hardcores
have -- of course -- whipped up answers
rich in, at least, words:
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While 238Pu is fissionable, it has been advertised as not fissile, or in others words this would mean it can produce a fission reaction that is difficult to sustain, but a 1962 test proved Pu-238 to be very fissile:
"The Department of Energy is providing additional information related to a 1962 underground nuclear test at the Nevada Test Site that used reactor-grade [Pu-238 and Pu-240] plutonium in the nuclear explosive.
Specifically: -A successful test was conducted in 1962, which used reactor-grade plutonium in the nuclear explosive in place of weapon-grade [Pu-239] plutonium. –The yield was less than 20 kilotons.
Background: This test was conducted to obtain nuclear design information concerning the feasibility of using reactor-grade plutonium as the nuclear explosive material. –The test confirmed that reactor-grade plutonium could be used to make a nuclear explosive. This fact was declassified in July 1977 . … In short it would be quite possible for a potential proliferator to make a nuclear explosive from reactor-grade plutonium using a simple design that would be assured of having a yield in the range of one to a few kilotons, and more using an advanced design." 8
The Nuclear Control Institute (NCI) stated that reactor-grade plutonium could be more desirable for a simple bomb because it eliminates the need to use a neutron initiator. 9 In addition to these facts, note the following in a report entitled "Plutonium-238, Use, Origin and Properties":
"If Pu-238 sits in the reactor long enough, it will absorb a neutron and become Pu-239 fuel." ...