CALIBRATING AND TESTING TISSUE-EQUIVALENT PROPORTIONAL-COUNTERS WITH AR-37

A method for testing and calibrating tissue equivalent proportional co unters with Ar-37 is described. Ar-37 is produced by exposure of argon in its normal isotope composition to thermal neutrons. It is shown th at - up to volume ratios of 0.01 of argon to the tissue equivalent gas - there is no appreciable effect of the argon admixture on the functi on of the proportional counter. Conventional calibration methods with characteristic x-rays or with alpha-particles require modifications of the detectors, and they test only small sub-volumes in the counters. In contrast, argon permits calibrations and tests of the resolution th at are representative for the entire counter volume and that do not re quire changes in detector construction. The method is equally applicab le to multi-element proportional counters; it is here exemplified by i ts application to a long cylindrical counter of simplified design that is part of such a multi-element configuration.