Plutonium Monitoring

Monitoring for airborne plutonium presents special problems because the physical and biological properties of plutonium are such that the permissible concentration in air is less than the normal background concentration arising from naturally occurring ¿-emitters. Because of this difficulty it is desirable to examine the basic health-physics requirements, so as to evaluate the usefulness of the limited information which might be available from relatively simple equipment. The now generally accepted concept of averaging dose over a period of 13 weeks or a year or even longer allows considerable flexibility in operational control, so that the immediate indication of small increases in concentration over the normal level, although it may be very desirable, is not essential, and its value must be weighed against such factors as cost, difficulties in use and interpretation, and the potential loss of reliability of a complex instrument. The various instrumental systems which have been suggested may be divided into three broad classes: (a) direct, in which the plutonium and background radioactive particles are collected and measured together, (b) selective, in which an attempt is made to collect only the plutonium dust, and (c) compensative, in which the background and plutonium dusts are collected together but the counting system is designed to remove the counts due to background before readout. There are inherent difficulties in each of these systems, but several prototype instruments have been made which show promise of a considerable measure of success.