418 Al^NUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



that it would scintillate. Tests using radioactive sources of electrons 

 and gamma rays showed us that the scheme could be made to work, 

 and that we could "see" into almost any size container we wished to use. 



The second problem was a stickler. The extreme violence of a large 

 nuclear explosion, accompanied by a searing heat wave and vast num- 

 bers of gamma rays and neutrons, was hardly reduced at all at a dis- 

 tance of several hmidred feet. A detector placed on the ground at 

 that distance would be melted, torn apart, and scattered in small pieces 

 over the countryside. We could put it into a heavy concrete block- 

 house, but the shock alone would still damage it beyond use, and only 

 a few neutrons leaking through the walls would completely obscure 

 our hoped-for-signal. We would have to shield it by at least a hmidred 

 feet of earth from the ordinary neutrons and gamma rays to reduce 

 their intensity sufficiently. 



The plan evolved was jBnally this: We would dig a shaft near 

 "gromid zero" about 10 feet in diameter and about 150 feet deep. We 

 would put a tank, 10 feet in diameter and about 75 feet long on end 

 at the bottom of the shaft. We would then suspend our detector from 

 the top of the tank, along with its recording apparatus, and back-fill 

 the shaft above the tank. 



As the time for the explosion approached, we would start vacuum 

 pumps and evacuate the tank as highly as possible. Then, when the 

 countdown reached "zero," we would break the suspension with a small 

 explosive, allowing the detector to fall freely in the vacuum. For 

 about 2 seconds, the falling detector would be seeing antineutrinos 

 and recording the pulses from them while the earth shock passed 

 harmlessly by, rattling the tank mightily but not disturbing our falling 

 detector. When all was relatively quiet, the detector would reach the 

 bottom of the tank, landing on a thick pile of foam rubber and feathers 

 (fig. 4). 



We would return to the site of the shaft in a few days (when the 

 surface radioactivity had died away sufficiently) and dig down to the 

 tank, recover the detector, and know the truth about neutrinos ! We 

 did a lot of thinking about this matter before we broached the idea 

 to anyone. Our first conversation on the matter was with Enrico 

 Fermi. He questioned us closely and examined our plan in detail. 

 His was the first encouragement we received for our plan, and we felt 

 that the race was at least half won at that point. We approached the 

 laboratory director, Norris Bradbury, and received more encourage- 

 ment — plus permission to proceed ! Assembling a group of physicists, 

 engineers, and teclinicians from around the laboratory who were suf- 

 ficiently intrigued by the project to take on work additional to their 

 own, we set out to catch a neutrino. 



As it made little difference precisely where we placed our shaft, 

 we chose to put it 137 feet from the base of the tower for luck. (If 



