Counting efficiency of Co56, Co58 and Co60 with 2 counters and 3 counting technics.

Abstract

A NaI well scintillation counter and a beaker adapted to fit on and around the Nal well as well as a plastic well scintillation counter, were used to compare efficiency of Co/sup 56/, Co/sup 58/, and Co/sup 60/ as a function of volume. The plastic well counter is as efficient for Co/sup 56/ as the NaI well and more efficient for Co/sup 58/ and Co/sup 60/ than the NaI well for small volumes (1 to 4 ml). For intermediate volumes (4 to 250 ml) the plastic well is the more efficient and the efficiency is almost independent of sample volume from 10 to 100 ml. Mice or small rats up to about 75 g and tissue samples can be counted in the plastic well without correction for geometry. The efficiency of 150 ml in the plastic scintillation counter is 22.6, 11.6, and 18.3% for Co/sup 56/, Co/sup 58/, and Co/sup 60/, respectively and 7.8, 3.5, and 3.8%, respectively for 1000 ml using the beaker on the NaI well. The choice of instrument for counting large volumes is discussed. (auth)