东北地区土壤中放射性核素含量的抽样测量与分析

Measurement and Analysis of Radio- Nuclides Contents in Soil of the Northeast China

目的测量东北地区土壤中放射性核素含量,从当地气候、成土母岩分布、植被分布、受放射性污染的程度等角度研究不同区域土壤中放射性核素含量存在差异的原因,并评估其对地表γ辐射量的贡献。方法应用北京核仪器厂生产的BH 1936型低本底多道γ谱仪对由中国计量科学研究院提供的混合体标准源进行测量,得到探测器对232Th、226Ra、238U和40K四种核素所发出的最大γ分支比的全能峰探测效率。测量土壤样品的γ能谱,分析计算得到土壤样品中的放射性核素的含量。结果通过对东北地区不同区域26份常见土壤样品中天然放射性核素的放射性活度进行抽样测量与数据处理,得出土壤中232Th、226Ra、238U和40K的含量均值分别为:52.9 Bq/kg,44.8 Bq/kg,50.3 Bq/kg,820.3 Bq/kg,较以往年所得数值略有增加。结论结果表明,232Th含量在残积母质类土壤中最高,在沉积母质类土壤中最低;226Ra和238U含量在冲积母质类土壤中最高,在残积母质类土壤中最低;40K含量在沉积母质类土壤中最高,在冲积母质类土壤中最低。232Th和40K含量在山地中最高,在平原中最低,而226Ra和238U含量则是在平原中最高,在山地中最低。根据土壤中放射性核素含量估算东北地区的年有效环境剂量(0.54 mSv),其值符合正常标准。

Objective Radio - nuclides contents in soil of the Northeast China were measured. Based on the results, the re- lationship between the radio -nuclides contents of different soil samples and some impact factors, such as the local climate, the source rocks, vegetation distribution, the degree of radioactive contamination and so on, was investigated. And the esti- mated value of annual effective dose was obtained. Methods Using NaI （TI） detectors, the radio - nuclides contents of stand- ard soil sample, provided by the National Institute of Metrology of R. P. China, was measured to determine the efficiency （ de- fined at full - energy - peak） of gamma - rays with the biggest branching ratio which were emitted from the radio - nuclides of 232Th 226 Ra,238U and 40 K. By analyzing the energy spectrum obtained by NaI （TI）detectors, the contents of radio -nuclides in soil samples were calculated out. Results By measuring the radioactivity of radio - nuclides in 26 soil samples from different zones of Northeast China, the radio - nuclides contents were calculated. The results indicated that the contents, namely 52.9 Bq/kg for 232Th, 44.8 Bq/kg for 226Ra, 50.3 Bq/kg for 23SU, 820.3 Bq/kg for 40K, increased slightly compared with the data obtained in past years. Conclusion The results showed that the contents of 232Th had a maximum in residual - parent - mate- rial soils and minimum in deposit - parent - material soils, the contents of 236Ra and 238 U had a maximum in alluvial - parent - material soils and minimum in residual - parent - material soils and the contents of 40K had a maximum in deposit - parent - material soils and minimum in alluvial - parent - material soils. As for the terrain, the contents of 232Th and 40K in soil sam- ples from the plain land was smaller than sample from the mountain land, while the contents of 226 Ra and 238 U were the contra- ry. Theoretical calculation using the contents of Radio - nuclides in soils from different zones of Northeast China was carried and the estimated value of annual effective dose was obtained. With a value of 0.54 mSv/a, the calculated annual effective dose was in the normal range.