The bomb casing can be a significant sources of neutron-activated radioisotopes . The neutron flux in the bombs , especially thermonuclear devices , is sufficient for high-threshold nuclear reactions . The induced isotopes include cobalt-60 , 57 and 58 , iron-59 and 55 , manganese-54 , zinc-65 , yttrium-88 , and possibly nickel-58 and 62 , niobium-63 , holmium-165 , iridium-191 , and short-lived manganese-56 , sodium-24 , silicon-31 , and aluminium-28 . Europium-152 and 154 can be present , as well as two nuclear isomers of rhodium-102 . During the Operation Hardtack , tungsten-185 , 181 and 187 and rhenium-188 were produced from elements added as tracers to the bomb casings , to allow identification of fallout produced by specific explosions . Antimony-124 , cadmium-109 , and cadmium-113m are also mentioned as tracers
Operation Hardtack
Operation Hardtack I
Mushroom cloud