Lively R S, Ney E P
Health Phys. 1987 Apr;52(4):411-5. doi: 10.1097/00004032-198704000-00001.
Studies of indoor radiation environments typically involve measurements of 222Rn, airborne 222Rn decay products, and the degree of radioactive equilibrium. This paper describes the relationship between the 222Rn in air, and the level of surface radioactivity that results from the build-up and decay of the daughter isotope, 210Pb. Samples of 222Rn were collected from Mystery Cave, which is located in southeastern Minnesota and from the basement of a house in Minneapolis, MN. Lead-210 was measured on surfaces within the cave, on a rock removed from the cave, and on a basement window. Surface alpha activities were measured on the rock sample and on the window. Radon-222 concentrations in the cave air ranged from 3 to 13 kBq m-3. In the basement, 222Rn levels were between 0.2 and 0.4 kBq m-3. Virtually all the surface radioactivity resulted from the deposition and decay of airborne 222Rn daughter products and was not produced by the decay of U in the rock. Radon-222 concentrations in the cave air were almost 30 times higher than in the basement air; however, the surface 210Pb activity in the cave was 100 times higher than that in the basement. This suggests that in the cave air, 222Rn daughter products are more likely to reach the walls and decay to 210Pb. The measurements of surface alpha activity did not show a similar trend primarily because 210Pb had diffused further into the coating of dirt on the rock than into the glass of the window. The resulting surface activity of the rock was lower than expected based on the 210Pb concentration, because many of the alpha-emitting nuclei were at depths beyond the range of emitted alpha particles. On surfaces where the penetration range of alpha particles is greater than the diffusion depth of 210Pb atoms, either the 210Pb concentration or surface alpha-activity measurements should provide estimates of average long-term 222Rn concentrations.
室内辐射环境研究通常涉及对²²²Rn、空气中²²²Rn衰变产物以及放射性平衡程度的测量。本文描述了空气中²²²Rn与子同位素²¹⁰Pb积累和衰变所导致的表面放射性水平之间的关系。²²²Rn样本采集自位于明尼苏达州东南部的神秘洞穴以及明尼阿波利斯市一所房屋的地下室。对洞穴内表面、从洞穴取出的一块岩石以及地下室窗户上的²¹⁰Pb进行了测量。对岩石样本和窗户进行了表面α活度测量。洞穴空气中²²²Rn浓度范围为3至13 kBq m⁻³。在地下室，²²²Rn水平在0.2至0.4 kBq m⁻³之间。几乎所有表面放射性均由空气中²²²Rn子产物的沉积和衰变产生，而非岩石中U的衰变产生。洞穴空气中²²²Rn浓度几乎比地下室空气中高30倍；然而，洞穴中表面²¹⁰Pb活度比地下室中的高100倍。这表明在洞穴空气中，²²²Rn子产物更有可能到达墙壁并衰变为²¹⁰Pb。表面α活度测量未显示类似趋势，主要是因为²¹⁰Pb在岩石上的污垢涂层中扩散得比在窗户玻璃中更远。基于²¹⁰Pb浓度，岩石产生的表面活度低于预期，因为许多发射α粒子的核位于发射的α粒子射程之外的深度。在α粒子穿透范围大于²¹⁰Pb原子扩散深度的表面，²¹⁰Pb浓度或表面α活度测量均应能提供平均长期²²²Rn浓度的估计值。
