RESUMO
In this study, a novel method to determine the surface and lateral dead layers of p-type HPGe detector is proposed to compute the full energy peak efficiency (FEPE). The method employed standard radioactive point sources 241Am, 133Ba and FEPE measurement at low energies to estimate the thickness of frontal and lateral dead layers. The method is simple to apply, requires only two standard radioactive sources to estimate the optimum thickness of frontal and lateral dead layers. The proposed method is validated by measuring the efficiency of various point sources and a volume source in the energy range from 59 to 1408 keV. The measured efficiencies agree to simulation with relative deviation less than 4.0% at each energy. The proposed detector model enables to calibrate the detector for environmental radioactivity measurement without standard volume sources.
RESUMO
Measurements of radionuclides' activities in air, water, and soil give clues about the anthropogenic activities in the region, and imperative to assess the overall radiological risk for individuals. Such an investigation was carried out to characterize the soil activities in the region hosting a research center, and to calculate the associated elements of radiological risk in terms of radiation doses and hazard indices. The soil samples were collected within the radius of 10 km in local area, Nilore, and analysed for activity using a high-purity germanium (HPGe) gamma spectrometric system. In all samples, only the basic nuclides, contributing to terrestrial activity, i.e., 40 K, 232Th, 226Ra, and 137Cs, were observed within the detectable limits of activity. The distribution of the data set and the correlation between the measured activities were studied with the use of the principal component analysis (PCA). The measured average specific activities of 226Ra, 232Th, 40 K, and 137Cs were 40.65 ± 9.84 Bq/kg, 59.31 ± 16.53 Bq/kg, 528.24 ± 131.18 Bq/kg, and 5.16 ± 4.56 Bq/kg respectively. The corresponding dose rate in air was found to be 76.63 ± 18.39 nGy/h, which is slightly higher than the world median value of 51 nGy/h calculated from concentration of terrestrial radionuclides in soil but falls within the world average value range of outdoor external exposure of 18-93 nGy/h obtained through direct measurement, and therefore not harmful for the living species. The standard hazard indices for all soil samples such as radium equivalent activity ([Formula: see text]), external hazard index (Hex), and internal hazard index (Hin) were also found within safe limits for the soil to be used as construction of building material. This investigation led to conclusion that the soil activities are consistent with the usual background level of terrestrial activities, and their associated dose rates are well within the safe limits for public.
