Farmer C Neal, Kathren Ronald L, Christensen Craig
Washington State University at Tri-Cities, Richland, WA 99354, USA.
J Environ Radioact. 2008 Aug;99(8):1355-9. doi: 10.1016/j.jenvrad.2008.02.004. Epub 2008 Apr 28.
Since 1996, higher than background levels of naturally occurring radioactivity have been documented in both fossil and mineral deposits at Hagerman Fossil Beds National Monument in south-central Idaho. Radioactive fossil sites occur primarily within an elevation zone of 900-1000 m above sea level and are most commonly found associated with ancient river channels filled with sand. Fossils found in clay rich deposits do not exhibit discernable levels of radioactivity. Out of 300 randomly selected fossils, approximately three-fourths exhibit detectable levels of natural radioactivity ranging from 1 to 2 orders of magnitude above ambient background levels when surveyed with a portable hand held Geiger-Muller survey instrument. Mineral deposits in geologic strata also show above ambient background levels of radioactivity. Radiochemical lab analysis has documented the presence of numerous natural radioactive isotopes. It is postulated that ancient groundwater transported radioactive elements through sand bodies containing fossils which precipitated out of solution during the fossilization process. The elevated levels of natural radioactivity in fossils may require special precautions to ensure that exposures to personnel from stored or displayed items are kept as low as reasonably achievable (ALARA).
自1996年以来，爱达荷州中南部哈格曼化石床国家纪念区的化石和矿床中记录到高于本底水平的天然放射性。放射性化石地点主要出现在海拔900 - 1000米的高程带内，最常见于与充满沙子的古代河道相关的地方。在富含粘土的沉积物中发现的化石未显示出可辨别的放射性水平。在随机挑选的300块化石中，约四分之三在用便携式手持式盖革 - 米勒测量仪器进行检测时，显示出可检测到的天然放射性水平，比环境本底水平高出1至2个数量级。地质层中的矿床也显示出高于环境本底水平的放射性。放射化学实验室分析已记录到多种天然放射性同位素的存在。据推测，古代地下水通过含有化石的砂体输送放射性元素，这些元素在化石形成过程中从溶液中沉淀出来。化石中天然放射性水平的升高可能需要采取特殊预防措施，以确保储存或展示物品对人员的照射保持在合理可行尽量低的水平（ALARA）。
