Detection of airborne long-lived alpha emitters based on the simultaneous measurement of alpha and beta activity in the laboratory conditions

Abstract Online measurement of a transuranic alpha emitting radioisotopes in the air is a perennial challenge due to the presence of short-lived progenies of the ubiquitous gas, radon, and thoron, present in the atmosphere. A persistent obstacle in continuous air monitoring (CAM) of suspect radionuclides is the interference caused by the co-deposition of radon and thoron daughter products (RDPs) on the filtration media, hindering prompt detection and analysis. These progenies emit alpha and beta and interfere with the radionuclide of concern. Various methods such as “alpha energy discrimination,” “particle size discrimination,” and “delay and decay” technique exist to discriminate this natural radioactivity present in air. In the present work, the “alpha-to-beta-disintegration-ratio” technique has been utilized as a discriminator in online air monitoring in a once-through-ventilated radiological lab. This technique utilizes the observed bias in the ratio of alpha and beta activity against the natural value when the RDPs and transuranic alpha emitting isotope of interest are simultaneously present on the air sampling filter paper media. In continuous sampling, total alpha as well as beta activity on the filter paper due to radon progenies is saturated after the certain period of initial sampling. The presence of long-lived alpha activity in the atmosphere alters this ratio, enabling its detection. Based on this technique, a CAM is designed and developed for the measurement of long-lived airborne alpha activity concentration. The system is capable to detect alpha activity exposure of 0.25 Bq m −3 h over the radon concentration of around ~5 Bq m −3 .