Determination of radon emanation and back diffusion characteristics of building materials in small chamber tests

Abstract

A methodology has been established to estimate the radon emanation rates and back diffusion rates of different building materials in small chamber tests. The two parameters, emanation rate and back diffusion rate, can be obtained from the growth curve of the chamber radon activity. Small impervious containers with a volume of 14900c.c. were used in the measurement and solid-state radon detectors were used to monitor the chamber radon levels continuously. In the study, the building materials were left inside the chamber for more than 400 hours in order to reach equilibrium radon concentrations. The emanation rates and the back diffusion rates of the samples were found to be fairly constant under 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 inside the chamber before each experiment and a correction was included in the calculation. Two kinds of granite and one bare concrete were selected as test samples. The first granite sample had a mean emanation rate of 13.44 Bq · m −2 · hr −1 and a back diffusion rate of 6.89 × 10 −4 hr −1. The second granite sample had an emanation rate of 0.58 Bq · m −2 · hr −1 with a back diffusion rate of 5.40 × 10 −3 · hr −1. The bare concrete had an emanation rate of 8.69 Bq · m −2 · hr −1 and a back diffusion rate of 6.18 × 10 −3 hr −1. The methodology has been found to provide an accurate method of estimating radon emanation and back diffusion characteristics of commonly used building materials.