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A few days (weeks?) ago someone was asking about
dose rate from an air filter collecting radon progeny. Perhaps someone
else gave the answer directly the interested person.
A back-of-an-envelope calculation gives the
following for a Rn concentration of 37 Bq/m3 (1 pCi/L) at equilibrium 0.7, 0.5,
0.3 for Po 218, Pb 214, Bi 214 respectively, a sampling rate of 60 L/min (1 L/s)
and a gamma constant of 2.25 e-6 Sv/h.Bq (ORNL/RSIC-45/R1 Report
(1982) :
Bi 214 is the only significant
gamma-emitting radon decay product. The equilibrium activity for Bi 214
(sampling time more than 5 hours) on the filter is about 6 e4 Bq, giving a
steady state dose rate at one meter of
6 e4 Bq x 2.25 e-6 Sv/h.Bq = about 1.4 e-7
Sv/h or 0.14 microSv/h for 37 Bq/L of radon at stated equilibrium
factors.
IT IS WORTH DOUBLE CHECKING MY CALCULATIONS
!!!
Philippe Duport
International Centre for Low Dose Radiation Research University of Ottawa 555 King Edward Ave. Ottawa, ON, Canada, K1N 6N5 Tel: (613) 562 5800, ext. 1270 pduport@uottawa.ca |