DETERMINATION OF RADON EMANATION AND BACK-DIFFUSION CHARACTERISTICS OF BUILDING-MATERIALS IN SMALL CHAMBER TESTS

A methodology has been established to estimate the radon emanation rat es and back diffusion rates of different building materials in small c hamber tests. The two parameters, emanation rate and back diffusion ra te, can be obtained from the growth curve of the chamber radon activit y. Small impervious containers with a volume of 14900 c.c. were used i n the measurement and solid-state radon detectors were used to monitor the chamber radon levels continuously. In the study, the building mat erials were left inside the chamber for more than 400 hours in order t o reach equilibrium radon concentrations. The emanation rates and the back diffusion rates of the samples were found to be fairly constant u nder the experimental conditions. The emanation rate was determined by the initial slope of the growth curve and the back diffusion rate was determined by the equilibrium value of the activity curve. Leakage of the chamber was estimated by checking the radon free decay rate insid e the chamber before each experiment and a correction was included in the calculation. Two kinds of granite and one bare concrete were selec ted as test samples. The first granite sample had a mean emanation rat e of 13.44 Bq.m(-2).hr(-1) and a back diffusion rate of 6.89 x 10(-4) hr(-1). The second granite sample had an emanation rate of 0.58 Bq.m(- 2).hr(-1) and a back diffusion rate of 6.18 x 10(-3) hr-1. The methodo logy has been found to provide an accurate method of estimating radon emanation and back diffusion characteristics of commonly used building materials. (C) 1997 Elsevier Science Ltd.