The use of long-lived 222Rn decay products (LRnD) as natural tracers in the indoor environment

In the radioactive decay chain following 222Rn (radon) the first long-lived product 210Pb (t1/2 = 22.3 y) acts like a stopper and its decay products can be utilized as integrators of passed radon gas levels and a tracer reflecting long-term aerosol particle deposition processes. Long-term integration is feasible only if the LRnD activity is hidden away from the destructive practices of everyday life, such as cleaning and refurbishing. Three type of LRnD hide away places (traps) can be identified: i) Inside the human body, ii) Inside porous volumes, and iii) In surface implants. The volume trap (ii) is advantageous as it is a pure radon gas detector and as such not influenced by the indoor aerosol conditions. The drawbacks are that suitable samples is difficult to find and that tedious radio chemistry is mandatory. Alpha-recoil implanted LRnD activity (iii) into hard surfaces is the only type of trap that is suitable for large-scale retrospective measurements and the main emphasis of this contribution will be on implanted activity. Fortunately, cheap in-situ track-etch methods are now available for specific detection of implanted 210Po into flat glass surfaces. In the ongoing Swedish non-smoker radon study only samples older than 20 years are accepted and a tentative calibration factor of 0.84 Bq.m-2 of implanted 210Po per kBq.y.m-3 radon gas exposure is used. The aim of this contribution is to draw attention to a fairly recent field of application in the radon indoor environment, where long-lived radon daughter are used to indicate past radon concentration levels