One safety device for hollow centre nuclear devices apparently is/was to fi=
ll it with=20
steel ball bearings through a hole in the top. Even if every other saftey f=
ailed and=20
the initiating explosive charges went off the material could not be compres=
sed to=20
form a critical mass. Final(?) arming step... turn it over and the ball bea=
rings roll out!

On a related note I recently had a trip to Japan and visited Hiroshima. Gar=
dens,=20
castles, temples, city, Mazda factory, Shinkansen (bullet train). Amazing=20
experience, sobering history, eerie to stand more or less on the spot of th=
e 1945=20
explosion... at the hypocentre (not epicentre, as blast was at altitude of =
approx 600=20
metres) there is a small plaque, with peace memorials, museum & parks etc c=
lose=20
by.



--=20
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