Time-dependent 222Rn samples loss from small samples

An analytical study was performed to determine the length of time required to reach steady-state flux of 222Rn from uranium ore samples stored in sealed cans for long periods and then opened to allow the free radon to escape. Results indicate that non-steady-state conditions must be considered in monitoring samples that have been previously sealed. Small samples with large diffusion coefficients reach steady-state flux in 0.25-1.25 hr. With very small diffusion coefficients the nonsteady-state 222Rn loss becomes important. Either time to reach equilibrium must be allowed (>70 hr) or the pore fluid with its trapped 222Rn must be removed to shorten waiting time. Calculations using large diffusion coefficients show that essentially all of the 222Rn released to the pore spaces escapes from the sample, but 222Rn appears trapped in the model with a 1 x 10-6 cm2sec-1 diffusion coefficient. (U.K.)