Retrospective assessment of radon exposure by measurements of 210Po implanted in surfaces using an alpha track detector technique

Abstract

The radon exposure of the past is important in epidemiological studies where an assessment of lung cancer risk from indoor radon exposure is evaluated. The long-lived decay product, 210Pb ( T 1 2 = 22 y ), is implanted into indoor surfaces by alpha recoils and can be monitored to give information about the previous radon history. This gives an alternative or complementary method to the traditional measurements of the current average radon concentration. Autoradiographic alpha-track methods to assess the 210Pb activity implanted in glass surfaces by measurement of 210Po alpha activity were investigated to find a simple and reliable method for field use. One limiting factor at low exposure levels is the alpha background activity in the sub-surface material. In the search for a practical field method, the use of two different alpha-track detector materials was found successful. By exposing one Kodak LR-115 cellulose-nitrate film and one CR-39 detector side by side on glass panes, the background of the glass is measured with the LR-115 and both the background and the signal by the CR-39 detector. Results from measurements in 31 dwellings show that an exposure of more than 1000 Bq·y·m −3 to a glass surface can be measured with the (CR-LR) difference technique. Experiences from the field measurements show the method to be accurate, simple, and reliable and therefore a promising tool for future radon epidemiological studies.