A Comparative Study of Field Gamma-ray Spectrometry by NaI(Tl) and HPGe Detectors in the South Caspian Region

Natural radionuclides present in soil as well as certain anthropogenic radionuclides released to the environment are the major contributors to terrestrial outdoor exposures. In the assessment of human exposures from environmental radioactivity, besides the conventional method of soil and vegetation sampling combined with laboratory based analyses of environmental media, the other choice would be field spectrometry which is a rapid, efficient and economical means of identification of radionuclides in the environment. Newly developed high resolution solid state gamma-ray detectors provide a state of art means for such a purpose. However, they are relatively expensive, may not provide the highest intrinsic efficiency possible and their use is complicated by the need for cryogenic cooling of the detector. Scintillation detector spectrometry systems are considered to be capable of yielding satisfactory results particularly for natural background measurements at a fraction of cost. This paper describes a comparative study on application of NaI(Tl) scintillation and HPGe solid state systems for in-situ measurements of 40K, 226Ra, 232Th and 137Cs soil inventories at selected regions on the south coast of Caspian Sea, along with the results from laboratory analyses of collected soil samples in the area. Based on in-situ measurement results and field experience, it is concluded that NaI(Tl) spectrometry system provide satisfactory results which might be even improved by incorporating special spectrum analysis techniques, is relatively less expensive and is operationally easier to carry out than either HPGe system or direct laboratory based analyses of soil samples.