APPLICATION OF A PHOSWICH DETECTOR FOR SIMULTANEOUS COUNTING OF ALPHA- AND BETA(GAMMA)-RAYS IN A ROTATING DRUM-CELL TYPE MONITOR1

This paper deals with an application of a ZnS(Ag)/NE102A phoswich detector to a rotating drum-cell type monitor installed at the NUCEF of JAERI. The monitor was modified for the performance tests and the phoswich detector, developed for simultaneous counting of a- and b(including g)-rays, has been applied to the monitor, instead of a Si detector which is suitable only for a-counting. The capabilities of the monitor with the phoswich detector were examined and compared with those of the Si detector by using 10 % enriched uranium solutions. Excellent correlations between both a- and b(g)-activities and the uranium concentrations were obtained over three orders of magnitude with the phoswich detector by using a pulse-shape discrimination technique. The detector is considered suitable for the monitoring of low concentrations of a-emitting solutions because of its high sensitivity. Since b(g)-activities could be independently measured, it is also available for estimating quantities of b(g)- emitters, such as fission products. Some inherent difficulties for quantitative and reliable monitoring with this type monitor were, however, revealed, viz., instability of wetting width on the drum surface and an increase in background.