Abstract
Knothole is a cylindrical crystal of NaI(TI) 8.9 cm in dia. and 7.6 cm long. Piercing the curved side along a central diameter is a well 2.1 cm in dia. and 7.3 cm deep. Optically coupled to each of its two plane surfaces is a RCA 8054 photomultiplier tube. Resolution for the 662 keV gamma-ray of 137Cs was measured to be 8.3%. The intrinsic peak efficiencies (counts in “photo-peak” per emitted gamma-ray) are about 61% at 88 keV, 47% at 513 keV, 37% at 662 keV, 19% at 1120 keV and 15% at 1460 keV. Limits of detection in pCi (3 standard deviations of background) using 60-min counting periods are: 137Cs, 4; 131I, 5; 226Ra via 214Bi, 11 (at 1760 keV); and 40K, 58 (0.068 g K).
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