Community Research and Development Information Service - CORDIS

Application of CR-39 track etch detectors to low background counting and particle sizing of air samples

The technique of alpha particle registration on CR-39 plastic was developed with a view to its use for the routine assay of long lived alpha activity collected on personal air samplers (PAS), which are used for routine individual monitoring of workers at risk of exceeding 30% of the annual limit on intake (ALI) of long lived alpha emitters. The activity on the filters is usually measured using alpha drawer counters, but, in monitoring chromic exposures to plutonium, the sensitivity is too low, the minimum detectable activity being equivalent to about0.1 ALI. The results of the study were as follows:
autoradiography of PAS filters could provide a sensitivity at least a factor of 5 greater than present counting techniques;
activity attached to aerosols of greater than 400 nm could be assessed separately;
the dynamic range of the technique was limited by tracks overlapping in the centre of the autoradiograph on high activity samples; these could be remeasured by exposing them to CR-39 for a shorter period;
even with automatic image analysis, the technique was more labour intensive than present techniques;
clusters of tracks were difficult to identify among evenly spread tracks unless there was a large difference in track density;
quality control of etched-track counting was difficult;
the technique entailed a delay of several weeks before obtaining a result;
although antoradiography of PAS filters provided useful extra information, it was deemed unsuitable for routine use.

Reported by

National Radiation Protection Board
OX11 0RQ Didcot
United Kingdom
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