Hulse S E, Ibrahim S A, Whicker F W, Chapman P L
Department of Radiological Health Sciences, Colorado State University, Fort Collins 80523, USA.
Health Phys. 1999 Mar;76(3):275-87. doi: 10.1097/00004032-199903000-00009.
Gamma spectroscopy measurements were used to estimate concentrations of 241Am and 137Cs in soil profiles to depths of 21 cm at on-site and off-site locations around the Rocky Flats Environmental Technology Site and at regional background locations east of the Front Range between Colorado's borders with New Mexico and Wyoming. Concentrations of these radionuclides were compared with concentrations of (239,240)Pu in the same samples. Concentrations of 241Am in soil from depths of 0 to 3 cm decreased in an easterly direction from more than 5.3 kBq kg(-1) near the 903 pad to background levels of 1.3 Bq kg(-1) 5 to 7 km away at a rate that was nearly proportional to the inverse square of distance. Deposits of 137Cs were ubiquitous, averaging 0.12 kBq kg(-1) in soil from depths of 0 to 3 cm, but were unevenly distributed around Rocky Flats and the regional background locations. Deviations from the uniform exponential rate at which soil concentrations of 137Cs typically decreased with depth, -0.25 cm(-1) at undisturbed sites, enabled us to determine that about 10% of our sampling sites had been disturbed by erosion, tillage, or other factors. The mean rate at which (239,240)Pu decreased with depth was about the same, -0.23 cm(-1), throughout the study area. Soil concentrations of 241Am decreased with depth at a similar mean rate of -0.22 cm(-1) at locations close to the 903 pad where measurements were robust. Ratios between 241Am or (239,240)Pu and 137Cs proved more useful for delineating the extent and pattern of contamination from Rocky Flats than did activity concentrations in soil.
利用伽马能谱测量法估算了落基山平地环境技术场地及其周边非场地位置以及科罗拉多州与新墨西哥州和怀俄明州边界之间前山以东区域背景位置处土壤剖面中深度达21厘米的241Am和137Cs浓度。将这些放射性核素的浓度与同一样品中(239,240)Pu的浓度进行了比较。0至3厘米深度土壤中241Am的浓度从903号平台附近的超过5.3 kBq kg(-1)向东方向降低至5至7公里外的背景水平1.3 Bq kg(-1)，其降低速率几乎与距离的平方成反比。137Cs的沉积无处不在，0至3厘米深度土壤中的平均含量为0.12 kBq kg(-1)，但在落基山平地及其周边区域背景位置分布不均。137Cs土壤浓度通常随深度呈均匀指数下降速率（未受干扰场地为-0.25 cm(-1)）出现偏差，这使我们能够确定约10%的采样点受到了侵蚀、耕作或其他因素的干扰。在整个研究区域，(239,240)Pu随深度下降的平均速率大致相同，为-0.23 cm(-1)。在测量数据可靠的靠近903号平台的位置，241Am的土壤浓度随深度以类似的平均速率-0.22 cm(-1)下降。事实证明，241Am或(239,240)Pu与137Cs的比率比土壤中的活度浓度更有助于描绘落基山平地的污染范围和模式。
