van Dijk W, de Jong P
TNO Environmental and Energy Research, Delft, The Netherlands.
Health Phys. 1991 Oct;61(4):501-9. doi: 10.1097/00004032-199110000-00005.
A new method for determining the free 222Rn exhalation rate from building materials is described. The sample is enclosed in a container from which the exhaled Rn is continuously purged by nitrogen gas. After 2-3 h, when the Rn level in the container has reached a steady-state concentration, the outflowing Rn is trapped on silica gel at about -190 degrees C. About 16 h after sampling, the silica gel is analyzed by liquid scintillation counting to determine the area exhalation rate. The method described has a good repeatability and reproducibility with coefficients of variation of 7.8% and 8.3%, respectively, at 5 Bq m-2 h-1. The low limit of detection of 11 mBq 222Rn offers the opportunity to quantify the exhalation rate of almost all kinds of building materials. It was found that the air humidity strongly influences the exhalation rates of building material and, therefore, should be controlled. Two typical building materials were investigated. For gypsum, an increase in the exhalation rate with increasing water vapor pressure was found, whereas for concrete, a linear decrease with increasing water vapor pressure was observed. The 222Rn area exhalation rates of 20 Dutch building materials, including some experimental ones, were determined at 50% RH, 20 degrees C, showing a range of less than 0.02-15.8 Bq m-2 h-1. The lowest values were found for natural gypsum board, the highest for phosphogypsum blocks. Building materials containing fly ash gave area exhalation rates comparable to those of similar materials without fly ash.
本文描述了一种测定建筑材料中游离²²²Rn析出率的新方法。将样品置于一个容器中，用氮气持续吹扫容器中呼出的Rn。2 - 3小时后，当容器中的Rn水平达到稳态浓度时，流出的Rn在约 - 190℃下捕集在硅胶上。采样约16小时后，通过液体闪烁计数法分析硅胶以确定面积析出率。所述方法具有良好的重复性和再现性，在5 Bq m⁻² h⁻¹时变异系数分别为7.8%和8.3%。11 mBq ²²²Rn的低检测限为几乎所有类型建筑材料的析出率定量提供了机会。发现空气湿度强烈影响建筑材料的析出率，因此应加以控制。研究了两种典型的建筑材料。对于石膏，发现析出率随水蒸气压力增加而增加，而对于混凝土，观察到析出率随水蒸气压力增加呈线性下降。在50%相对湿度、20℃条件下测定了20种荷兰建筑材料（包括一些实验材料）的²²²Rn面积析出率，范围为小于0.02 - 15.8 Bq m⁻² h⁻¹。天然石膏板的析出率最低，磷石膏砌块的析出率最高。含粉煤灰的建筑材料的面积析出率与不含粉煤灰的类似材料相当。
