Terrestrial background radiation study in Bathalegoda, North-Western province of Sri Lanka

Terrestrial radiation originates from natural radio-nuclides present in soils, rocks, air, and water. For all the living beings, the major source of radiation exposure is natural radioactivity in their living environment. Higher levels of radioactivity levels are harmful to human health. Bathalegoda area lies between longitudes 80.10190 East and latitudes 7.59950 North. The area located in the North western province, Kurunegala, Sri Lanka. Superficial soil samples from twenty-one locations from Bathalegoda area were analysed by gamma spectrometry. Top 2cm of soil was scraped off from a 1m² area and 1kg of soil samples were taken and the samples were immediately brought to the laboratory for analysis. Samples were homogenized by hand mixing and allowed them to air dry and then oven dried for 24hours. 2 mm mesh was used to separate the gravel from soil. A sub sample from the weighed fine fraction were filled into a specific container and kept for 21 days to achieve secular equilibrium .The activity concentrations of radionuclides were measured using a Hyper Pure Germanium (HPGe) detector installed at the Gamma spectroscopy laboratory (17025:2017 accredited laboratory from 2006), Life Sciences Division of the Sri Lanka Atomic Energy Board, with the relative efficiency of 30% and the resolution of 2.20 KeV at the gamma energy of 1332.5 KeV of 60Co. Each sample was counted for 72,000 seconds. The ISOCS/LabSOCS software calibration method was used for efficiency calibration. Soil 6 was used as a reference material for detector calibration. The spectra were analysed by using the Genie 2000 software. The median activity concentrations (range) of ²³² Th, ⁴⁰K, ²²⁶Ra & ²¹⁰Pb were 46.9Bq/kg (30.6-67.5), 1028.6Bq/kg (882.9-1213.0), 16.5Bq/kg (11.8-20.8), and 27.9 Bq/kg (19.8-44.3) respectively. Activity concentration of ²³²Th was higher than the world average of 30 Bq/kg and the activity concentration of ⁴⁰K was higher than the world average of 400Bq/kg. All the soil samples from Bathalegoda area showed the radium equivalent activity below 370Bq/kg(NEA) and it was ranged from 130.8-192.5Bq/kg. Criteria formula was less than 1 in all the soil samples. Median Activity Utilization Index (AUI) in the area was below the recommended limit indicating that the dose levels in the soil samples were safe for the environment. The median external hazardous index (Hex) in Bathalegoda area was below the recommended limit of 1 and the annual effective dose was within the safe limit of 1mSv/y. Soil from this area is safe for human health. (author)