a * external initiator would be particularly important if hollow eores of fissionable material were to be needed for a’ very hifgh yield implosion-type weapon of the order of 500 kilotons TNT equivalent, now under development. 4O, Long-life Initiator. Several experimental initiators have been produced Prom actinium 227, which has a half-life many times longer than polonium 210, the radioactive isotope presently being used in initiators. Additional development work 15 required, however, before an actinium initiator can be recommended for stockpile use. 43. High Explosives and Detonators. The extensive re- search and development cffort on high explosives and detonators has produced a number of improvements, development mentioned above. including the cored H.E. | This development makes possible a thinner lens more space for the inner portion of the H.E. system, providing | sphere in implosion- type weapons, which in turn makes possible greater compression of the core and thus greater yield from the same amount of fissionable mitertal. uu. The proportion of RDX explosive in the RDX-INT mixture can be increased, which will also give somewhat greater compression and a corresponding increase in yield for the new models. | This technique is particularly important in the development of implosion-type warheads for rockets and