Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, UPS, CNES, Observatoire Midi-Pyrénées, Toulouse, France; CEA, DAM, DIF, F-91297, Arpajon - Cedex, France.
Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, UPS, CNES, Observatoire Midi-Pyrénées, Toulouse, France.
J Environ Radioact. 2021 Oct;237:106695. doi: 10.1016/j.jenvrad.2021.106695. Epub 2021 Jul 28.
This study describes and discusses the results of a 14 month-long campaign (April 2019 to June 2020) aimed at characterizing and quantifying the influence of environmental factors (cosmic rays, rainfall events, soil moisture and atmospheric radon) on airborne radiometric surveys, which are used for mapping the concentrations of potassium (K), uranium (U) and thorium (Th), or for monitoring the natural radioactivity in the environment. A large NaI(Tl) airborne spectrometer (4 down + 1 up detectors of 4 L) was installed at a height of 50 m on a meteorological tower to simulate an airborne hover at the Pyrenean Platform for Observation of the Atmosphere (P2OA) in Lannemezan. The continuous, high frequency acquisition of gamma-rays was accompanied by measurements of rainfall intensity, soil moisture content, atmospheric radon activity and meteorological parameters. A semi-diurnal cycle of apparent Th and K was observed and explained by atmospheric thermal tides. Both diurnal and seasonal cycles are also evident in the gamma-ray signal, mostly due to variations of soil moisture at these timescales with a maximum during summer when surface soil moisture (0-5 cm depth) is the lowest. An increase of 25% vol. of the soil moisture content, representing the range of variation between the end of summer (18% vol.) and the beginning of spring (43% vol.) leads to a decrease of gamma-rays in the K and Th window by the same amount. Conversely, these results illustrate the potential of using airborne gamma-ray spectrometry to monitor soil moisture at hectometer scales. The washout of radon-222 progeny during rainfall events influences the count of gamma-rays in the U window by adding an atmospheric component to the soil component. The amplitude of the signal increase in the U window varies with the precipitation rate and reaches 30% for an average event. By clear weather, atmospheric radon-222 volumic activity influences the count rate in the U window by about ±3.8% per Bq m, which translates into an influence of 148%/Bq m/kg Bq (U). This comprehensive, multi-compartment approach is necessary to optimize and improve the processing and analysis of airborne gamma-ray spectrometry data for high sensitivity environmental studies. These results show the importance of environmental factors on the variability of gamma-ray spectrometry and the importance of taking them into account to accurately map radionuclides activities.
本研究描述并讨论了一项为期 14 个月的活动（2019 年 4 月至 2020 年 6 月）的结果，该活动旨在描述和量化环境因素（宇宙射线、降雨事件、土壤湿度和大气氡）对航空放射性测量的影响，这些测量用于绘制钾（K）、铀（U）和钍（Th）的浓度图，或监测环境中的天然放射性。一个大型的碘化钠（Tl）航空光谱仪（4 个向下+1 个向上的 4L 探测器）安装在气象塔上 50 米的高度，以模拟在朗格米赞的比利牛斯大气观测平台（P2OA）上的航空悬停。伽马射线的连续高频采集伴随着降雨强度、土壤湿度、大气氡活度和气象参数的测量。观测到并解释了一个明显的 Th 和 K 半日潮周期。伽马射线信号中也明显存在日循环和季节循环，主要是由于这些时间尺度上土壤湿度的变化，在夏季达到最大值，此时地表土壤湿度（0-5cm 深度）最低。土壤湿度含量增加 25%（体积），代表夏季末（18%）和春季初（43%）之间的变化范围，导致 K 和 Th 窗口中的伽马射线减少相同数量。相反，这些结果说明了利用航空伽马射线光谱法在 hectometer 尺度上监测土壤湿度的潜力。降雨事件期间氡-222 子体的淋洗作用，通过向土壤成分中添加大气成分，影响 U 窗口中的伽马射线计数。U 窗口中信号增加的幅度随降水率而变化，对于平均事件达到 30%。在晴朗天气下，大气氡-222 体积活度通过每 Bq m 左右影响 U 窗口的计数率 ±3.8%，这相当于 148%/Bq m/kg Bq（U）的影响。这种综合的、多隔室方法对于优化和改进航空伽马射线光谱数据的处理和分析是必要的，以便进行高灵敏度的环境研究。这些结果表明了环境因素对伽马射线光谱变化的重要性，以及考虑这些因素对准确绘制放射性核素活动图的重要性。
