DISCOVERY OF THE NEUTRINO — COWAN 421 



liquid scintillator made of toluene. We learned how to connect these 

 tubes into two interleaved banks for operation m coincidence to reduce 

 the spurious "dark-current" signals generated by the tubes themselves. 

 As for the cadmium salt, we found that the propionate of cadmium 

 would dissolve in the scintillator quite well without reducing its light 

 output seriously. 



The winter was spent in testing the system in an isolated and 

 unheated building while keeping the detector warm with several 

 electrical bowl fires. Some of our group swept the snow away from 

 outside the building and set about casting many large blocks of 

 paraflm wax and borax for use as neutron shielding when we would 

 go to a reactor. Others began mixing gallons of liquid scintillator 

 in batches with varying composition. We found that we could also 

 make a scintillating liquid from just one of the several brands of 

 mineral oil carried by the local druggists. This would give us a 

 different hydrogen density in our detector from that of toluene, 

 allowing us to test the fact that it is a proton which reacts to yield 

 a neutrino signal. We ordered several barrels of the oil, and this was 

 duly mixed with the chemicals to make it scintillate. 



It was during this testing period that we also investigated the radio- 

 active content of the materials which were used to construct the 

 detectors. We built a cylindrical well into one of the detectors and 

 proceeded to put quantities of steel, liquids, wax, and other materials 

 into it for testing. We found that brass and aluminum were quite 

 radioactive compared to iron and steel, and that the potassium in the 

 glass envelopes of our photomultiplier tubes would contribute to the 

 detector backgrounds. By putting the detector "into itself" in this 

 manner, piece-by-piece, we were able to avoid the more seriously 

 contaminated materials in its construction. 



During this time, one of our group, Robert Shuch, proposed making 

 the well in the detector a bit larger so that we might be able to put 

 a human being into the detector. This was done, and a number of 

 people, including our secretary, were trussed up and lowered into 

 the 18-inch hole. We found quite a detectable counting rate from 

 everyone. It was due to the radioactive potassium-40 naturally 

 present in the body. Using small radium sources strapped near the 

 navel of a subject, we found that extremely minute quantities of radio- 

 active contaminants were measurable in the human body. This brief 

 interlude thus saw the birth of the total-immersion, or "whole-body" 

 coimter. The two neutrino detectors were later to be placed into 

 service as the first of many such large clinical and medical research 

 counters. 



In the very early spring of 1953 we set out for Hanford, Wash., 

 where the largest and newest of the country's fission reactors was just 

 being put into operation. The work at Hanford, while tedious in 



766-74&— 65^—32 



