Measurement and analysis of radio-nuclides contents in soil of the northeast China

Objective: Radio-nuclides contents in soil of the Northeast China were measured. Based on the results, the relationship 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 estimated value of annual effective dose was obtained. Methods: Using Nal(TI) detectors, the radio-nuclides contents of standard soil sample, provided by the National Institute of Metrology of R.P. China, was measured to determine the efficiency (defined at full-energy-peak) of gamma-rays with the biggest branching ratio which were emitted from the radio-nuclides of ²³²Th, ²²⁶Ra, ²³⁸U and ⁴⁰K. By analyzing the energy spectrum obtained by Nal(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 ²³⁸U, 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-material soils and minimum in deposit-parent-material soils, the contents of ²³⁶Ra and ²³⁸U 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 samples from the plain land was smaller than sample from the mountain land, while the contents of ²²⁶Ra and ²³⁸U were the contrary. 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. (authors)