Lebedyte M, Butkus D, Morkŭnas G
Institute of Physics, A. Gostauto 12, 2600 Vilnius, Lithuania.
J Environ Radioact. 2003;64(1):45-57. doi: 10.1016/s0265-931x(02)00057-7.
The ambient dose equivalent rate is caused by ionizing radiation of radionuclides in the atmosphere and on the ground surface as well as by cosmic radiation. Seasonal and diurnal variations of the ambient dose equivalent rate (ADER) in the ground level air are influenced by the concentration of 222Rn daughters. The 222Rn concentration in the ground level atmosphere, in turn, depends on the rate of the 222Rn exhalation from soil and turbulent air mixing. Its diurnal and seasonal variations depend on meteorological conditions. The aim of this study is to estimate the influence of variations of the rate of the 222Rn exhalation from soil and its concentrations in the ground level air on variations of ADER in the ground level air, as well as the dependence of these parameters on meteorological conditions. The 222Rn diffusion coefficient and its exhalation rate in undisturbed loamy soil have been determined. The 222Rn concentration in the soil air and its concentration in the ground level air correlate inversely (correlation coefficient is r = -0.62). The main factors determining the 222Rn exhalation from soil are: the soil temperature (r = 0.64), the difference in temperature of soil and air (r = 0.57), and the precipitation amount (r = 0.50). The intensity of gamma radiation in the ground level air is mostly related to the 222Rn concentration in the air (r = 0.62), while the effect of the exhalation rate from soil is relatively low (r = 0.36). It has been shown that ADER due to 222Rn progeny causes only 7-16% of the total ADER and influences its variation. The comparison of variations of ADER due to 222Rn progeny and the total ADER during several years shows that these parameters correlate positively.
环境剂量当量率是由大气和地面上放射性核素的电离辐射以及宇宙辐射引起的。地面空气中环境剂量当量率（ADER）的季节性和昼夜变化受222Rn子体浓度的影响。而地面大气中222Rn的浓度又取决于土壤中222Rn的析出率和湍流空气混合情况。其昼夜和季节变化取决于气象条件。本研究的目的是评估土壤中222Rn析出率及其在地面空气中浓度的变化对地面空气中ADER变化的影响，以及这些参数对气象条件的依赖性。已测定了原状壤土中222Rn的扩散系数及其析出率。土壤空气中222Rn的浓度与其在地面空气中的浓度呈负相关（相关系数r = -0.62）。决定土壤中222Rn析出的主要因素有：土壤温度（r = 0.64）、土壤与空气的温差（r = 0.57）以及降水量（r = 0.50）。地面空气中伽马辐射强度主要与空气中222Rn的浓度有关（r = 0.62），而土壤析出率的影响相对较小（r = 0.36）。研究表明，由222Rn子体引起的ADER仅占总ADER的7 - 16%并影响其变化。对多年来222Rn子体引起的ADER变化与总ADER变化的比较表明，这些参数呈正相关。
