Quantitative methods for continuous particulate air monitoring

Quantitative methods for the estimation of concentrations and time integrals of concentrations of airborne radioactivity using continuous particulate air monitors are discussed. For fixed-filter and moving-filter monitors, methods based on count rate derivatives and integrals are summarized, with plots of simulation results. An approach for estimating a total-episode activity release, using moving-filter monitors, is described. Also presented is an unusual concentration measurement technique, that of an integrated-count step-advance filter (ICSAF) monitor. The instrument uses an integrated count for the concentration estimate and also advances the collection medium (“filter”), held fixed during the measurement interval, after each measurement is made. The measurement interval can be determined by either a preset count or a countrate-controlled integration time. This instrument´s performance is mathematically analyzed in some detail, with graphical simulation results. The ICSAF monitor has excellent transient-following abilities and good sensitivity. Its quantitative approach does not depend on assumptions of constant concentrations of long-lived activity, nor is there a need to wait for the monitor to attain some “equilibrium” countrate, as with moving-filter monitors. This instrument would be an excellent choice for many monitoring applications