BOMBS AT BIKINI 



lative effects are very difficult to predict. Studies have 

 been made, of course, of fission products produced in 

 the piles operating at Oak Ridge and elsewhere. But 

 those fission products are born of a different process ; 

 they result from fission produced by slow neutrons. 

 Only when an atomic bomb explodes can the fission 

 products of a fast neutron chain reaction be studied. 



From the tactical point of view^ this question was 

 important: How far out does the gamma radiation 

 reach ? It was well know^i that gamma radiation is ab- 

 sorbed, by air; but definite answers were lacking as 

 to just how many hundreds of yards of air were needed 

 to protect exposed personnel. For neutrons, too, in- 

 formation on shielding by air was incomplete. With 

 respect to both gamma and neutron radiations, more 

 information was needed as to the protection afforded 

 by steel walls. It was recognized that persons located 

 below decks would be relatively protected, but the exact 

 extent to which such protection really would save lives 

 was not known. 



Colonel Warren's group brought to Bikini more 

 than 20,000 devices for measuring nuclear radiations. 

 The commonest device used for measuring gamma ra- 

 diation consisted merely of a small piece of unexposed 

 photographic film wrapped so as to exclude all light. 

 This device, called a badge, does its job silently and 

 simply. When gamma rays strike the badge, they pene- 

 trate the wrapping and produce a slight change in the 

 photographic emulsion. When the badge's message is 



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