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Outdoor thoron and progeny in a thorium rich area with old decommissioned mines and waste rock

机译:储量丰富的地区的室外和后代,其中有废弃的地雷和废石

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Radon (Rn-222), thoron (Rn-220) and their decay products may reach high levels in areas of high natural background radiation, with increased risk associated with mining areas. Historically, the focus has mostly been placed upon radon and progeny (RnP), but recently there have been reports of significant contributions to dose from thoron progeny (TnP). However, few direct measurements of TnP exist under outdoor conditions. Therefore, we assessed the outdoor activity concentrations of radon, thoron and TnP in an area of igneous bedrock with extreme levels of radionuclides in the thorium decay series. The area is characterized by decommissioned mines and waste rock deposits, which provide a large surface area for radon and thoron emanation and high porosity enhancing exhalation. Extreme levels of thorium and thoron have previously been reported from this area and to improve dose rate estimates we also measured TnP using filter sampling and time-integrating alpha track detectors. We found high to extreme levels of thoron and TnP and the associated dose rates relevant for inhalation were up to 8 eta Svh(-1) at 100 cm height. Taking gamma irradiation and RnP into account, significant combined doses may result from occupancies in this area. This applies to recreational use of the area and especially previous and planned road-works, which in the worst case could involve doses as large as 23.4 mSv y(-1). However, radon and thoron levels were much more intense on a hot September day than during time-integrated measurements made the subsequent colder and wetter month, especially along the ground. This may be explained by cold air observed flowing out from inside the mines through a drainage pipe adjacent to the measurement stations. During warm periods, activity concentrations may therefore be due to both local exhalation from the ground and air ventilating from the mines. However, a substantially lower level of TnP was measured on the September day using filter sampling, as compared to what was measured with time-integrative alpha track detectors. A possible explanation could be reduced filter efficiency related to the attached progeny of some aerosol sizes, but a more likely cause is an upwards bias on TnP detectors associated with assumed deposition velocity, which may be different in outdoor conditions with wind or a larger fraction of unattached progeny. There is thus a need for. better instrumentation when dealing with outdoor TnP. (C) 2016 Elsevier Ltd. All rights reserved.
机译:natural(Rn-222),(Rn-220)及其衰变产物在自然本底辐射较高的地区可能会达到很高的水平,而与采矿区相关的风险也会增加。从历史上看,重点主要放在pro和后代(RnP)上,但是最近有报道称对后代(TnP)的剂量有重大贡献。但是,在室外条件下几乎没有直接测量TnP的方法。因此,我们用with衰变系列中放射性核素的极端水平评估了火成岩基岩地区area 、,和TnP的户外活动浓度。该地区的特点是退役的矿山和废石沉积物,为for和的散发提供了较大的表面积,并提高了孔隙率,增强了呼出气。先前已从该地区报告了previously和的极端水平,为提高剂量率估计值,我们还使用过滤器采样和时间积分α轨迹检测器测量了TnP。我们发现高和极高的tho和TnP含量以及与吸入有关的相关剂量率在100 cm高时高达8 eta Svh(-1)。考虑到伽马射线和RnP,该区域的占用可能导致大量的联合剂量。这适用于该地区的娱乐用途,尤其是先前和计划中的道路工程,在最坏的情况下,其涉及的剂量可能高达23.4 mSv y(-1)。但是,在9月的高温天,ra和的水平要强于时间积分测量的强度,这使得随后的月份更冷和潮湿,尤其是沿地面。这可以通过观察到的冷空气从矿山内部通过邻近测量站的排水管流出来解释。因此,在温暖时期,活动集中可能是由于地面的局部呼气和矿井的通风造成的。但是,与使用时间积分式α径迹检测器测得的TnP相比,在9月的一天使用过滤器采样测得的TnP值要低得多。一种可能的解释可能是降低了与某些气溶胶尺寸的后代相关的过滤器效率,但更可能的原因是与假定的沉积速度相关的TnP检测器的向上偏差,这在室外条件下可能会有所不同,例如风速较大或独立的后代。因此需要。处理室外TnP时使用更好的仪器。 (C)2016 Elsevier Ltd.保留所有权利。

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