INTEGRATED MEASUREMENT OF EQUILIBRIUM EQUIVALENT RADON AND THORON CONCENTRATIONS USING CELLULOSE NITRATE FILM

A highly sensitive integral equilibrium equivalent radon and thoron co ncentration (EEC(Rn), EEC(Tn)) monitor was developed to determine conc entrations in the natural environment. Cellulose nitrate film (LR-115, Type 2, Kodak Pathe) was used as a detector. The unit is based on the ''Integrated System for Dosimetry'' (ISD) used in France. Characteris tics of this monitor are as follows: (i) a virtual collimating system was used instead of a structural collimating System, This minimizes th e plate-out of unattached radon/thoron progeny. Each virtual collimati ng system has a separate collecting area; (ii) the monitor can detect alpha particles from Po-216, U-234 and Th-230 in addition to the short lived radon/thoron progeny which are the main measurement subject; (i ii) three independent measuring systems that do not interfere with eac h other are used in the monitor; (iv) the EEC(Rn) and EEC(Tn) can be a ccurately determined with a collecting period of 8 h. When the collect ing period is 8 h with a flow rate of 0.4 l min(-1) and the measuremen t period is 3 h, the minimum detectable concentration is estimated to be 4.8 Bq m(-3) h for EEC(Rn). For a measurement period of 2 days, it is 0.54 Bq m(-3) h for EEC(Tn). Copyright (C) 1996 Elsevier Science Lt d