Monitoring of 232Th in soil of the state of Pernambuco, Brazil

where the control of radionuclides in the environment is of extreme importance for attaining information on potential sources of radioactive contamination. The gamma spectrometry with high resolution detector is a rapid and efficient method in the determination of natural radionuclides in environment samples. Using the gamma spectrometry with HPGe, it was possible to measure the radiological concentrations of 232Th in seventy eight soil samples, collected in an area of approximately 40,000 m2, around a natural radioactive occurrence, located in the rural region of the state Pernambuco, Brazil. The samples of 200 g, were reduced to a granulometry less than 63 μm, homogenized, conditioned in hermetically sealed polyethylene containers for thirty days, and measured in the laboratory for 43,200 seconds, each. The measurements of the activities of 232Th were based on the gamma emissions of the photo peaks at 338 keV and 911 keV of 228Ac in secular radioactive balance, and allowed the evaluation of the distribution of these radionuclides in the environment. For the calculation of the specific activities of 232Th, the average of the rates of counting in the energies of 338 keV and 911 keV was used (discrepancy of approximately 5 %). The values of the measured activities have variations of 77 to 423 Bq.kg-1 (arithmetic mean 227 Bq.kg-1; median 217 Bq.kg-1). The average factor concentration was approximately 6. (author)