PHOTOPEAK EFFICIENCY OF A WELL-TYPE SCINTILLATION DETECTOR

The detection and photopeak efficiences of a NaI cylindrical crystal, 7.62 cm diam and 7.62 cm high, containing a 0.63 cm diam well, 4.13 cm deep, were experimentally determined for 0.51 MeV gamma radiation from 11C positron annihilation. The pulse-height distribution measured with the source on top of the crystal was used with probability theory to obtain an approximate synthetic summed spectrum for the source in the well. This in turn was used to analyze the observed pulse-height distribution for the source in the well. The detection and photopeak efficiencies are 0.70±0.02 and 0.49±0.01, respectively, from which the photofraction is 0.70±0.03. Agreement with calculated values is good. © 1968 The American Institute of Physics.