416 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



chair across the room, then takes the observed movement of the chair 

 as proof of the existence of the poltergeist. 



The story of these exciting times and the ingenious and painstaking 

 efforts made to test the neutrino hypothesis is told at length in the 

 technical and popular literature, an introduction to which is given 

 as a part of the bibliography More detailed and complete accoimts 

 of the properties of the neutrino as anticipated before its observation 

 and as they have developed since that time are also to be found there. 

 Suffice it to say that physics had a genuine poltergeist in its house by 

 the time the 1950's were drawing to an end, for by then a considerable 

 list of reactions of the elementary particles called upon this ghostly 

 particle to help conserve the conservation laws. 



PROJECT POLTERGEIST — I 



We have said that the extreme reluctance of the hypothesized neu- 

 trino to interact and so reveal itself might be overcome if an astro- 

 nomical number of such reluctant particles were allowed to fall on a 

 reasonable amount of absorber. Such astronomical quantities were 

 presumably becoming available during the years following World 

 War II, if indeed neutrinos did exist, as nuclear explosions were set 

 off from time-to-time. These explosions of fissioning uranium and 

 plutonium resulted in great concentrations of radioactive nuclei, 

 known as "fission fragments." In general, the fission of one atom of 

 uranium will produce a chain of some six or more radioactive decays, 

 each one a beta decay. Thus, each fission should produce on the 

 average some six or more neutrinos. 



Here we must particularize somewhat. We have said that Fermi's 

 applications of Dirac's equations to his theory would predict that both 

 neutrinos and antineutrinos are made in nature. Just what the dif- 

 ference between the two sorts of neutrino might be was not understood 

 at that time, except that beta decay which produces negative electrons 

 as beta particles must also produce antineutrinos, while beta decay 

 producing positrons would produce neutrinos. And as all the radio- 

 active fission fragments being made in the nuclear explosions resulted 

 in negatron decays, then the six small partners from these decays must 

 be a/ntineutrmos. 



We also have said that the only field the neutrino (let us continue 

 to use this word to indicate both sorts, except where it is necessary to 

 specify one kind only) carries with it is the weak field which causes 

 beta decay. This means that the only reaction one can reasonably 

 expect the neutrino to produce is another beta decay. Such a forced 

 decay, if made by neutrinos in a detector, would constitute the first 

 synthetic beta decay and would signal the possible capture of a neu- 

 trino. To tag the neutrino as the culprit which stole the energy from 



