ASSESMENT OF NATURALLY OCCURING RADIOACTIVE MATERIALS (NORM) IN MISSION, TEXAS SURFACE SOILS

摘要

Residents living near decommissioned chemical plants in the city of Mission, Texas have been noted to complain of physiological abnormalities and health related problems associated with low dose radiation exposure. The purpose of this study was to quantify the natural radioactivity levels in the entire Mission area by measuring gamma emissions from radionuclides in representative naturally occurring radioactive materials (NORM). Surface soil samples were collected from 30 undisturbed fields with a depth of 0-10 cm for each station. Samples were dried in an oven at 110 ℃ for 24 h, pulverized, and sieved through a 2 mm mesh to remove stones and other impurities. The homogenized samples were transferred to Marinelli beakers, sealed, and stored for 30 days to allow for the secular equilibrium of ~(226)Ra and its daughter isotopes before gamma-ray analysis of the radionuclides. Concentration levels of the radionuclides ~(226)Ra and ~(137)Cs were determined in surface soil samples using a high purity germanium detector (HPGe) and gamma spectroscopy software. Studies have not yet been conducted for these radionuclides in this region. The activity concentrations of ~(226)Ra and ~(137)Cs were measured as 453-1600 pCi/Kg with an average value of 907 pCi/Kg and 53-144 pCi/Kg with an average value of 97 pCi/Kg respectively. The absorbed gamma does rates in the air and outdoor annual effective dose equivalents were evaluated and compared to records from similar geographical sites. The present data can be utilized as a basis for a radioactivity mapping of the South Texas Mission area.