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^o-sr%-<?/^7 Backgrounds Estimates for the PMT Region

By P. Skensved and B. C. Robertson


The support frame and PMT properties have recently been characterized with enough detail to make it worthwhile to update the previous estimates of backgrounds in the PMT region [1]. In addition, the modelling of the geometry of the PMT has been improved, a model of the reflector has been introduced and the effect of additional PMT components has been considered. Geometry The "active " components of the support frame were taken to be 8.05 tonnes of stainless steel 3 " dia., 1/8 " thick tubing. The stainless steel was assumed to have 10 ppbU/Th, and to be 22.95 cm center to center away from 3000 phototube bulbs out of the total of 10000 PMTs. The hexagons used to hold the PMTs are assumed to be "clean " plastic so they contribute nothing to the background. The PMTs themselves were assumed to have 0.75 kg of glass with 40ppbU/Th and to have in- de the bulb 0.25 kg of dynode metal (no radioactivity) and 0.029 kg of al mina ceramic with 1.29 ppmTh and 1.23 ppmU

Year: 1991
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