Application of ISOCS system in the laboratory efficiency calibration

Publication date: August 2018
Source:Journal of Environmental Radioactivity, Volume 188
Author(s): Dominik Grządziel, Krzysztof Kozak, Jadwiga Mazur, Mariusz Mroczek
ISOCS (In Situ Counting Object System) from Canberra is applied in laboratory for creating efficiency calibrations of good quality without using radioactive standards. Besides of typical sample containers used in laboratory, ISOSC system also allows modelling containers and objects of almost any shape and elemental composition.The study was based on gamma spectrometry with HPGe semiconductor detector with electronics and software spectrum analysis GENIE 2000 + ISOCS. Measuring set is equipped with portable shield system with set of collimators ISOCS Shield Systems Model ISOXSHLD from Canberra. This shielding system provides attenuation of gamma background radiation with average value 33 (for gamma energies from 186 keV to 2615.5 keV).The portable shield system can be used for low-background laboratory measurements. For this purpose a measuring vessel of new geometry was constructed: the polystyrene cylinder with a height of 40 mm and a diameter of 70 mm. The efficiency calibration for this container was performed using both ISOCS system and classical calibration standard in the same geometry. In order to verify the correctness of performed calibration procedures, the measurements of radioactive standard CBSS 2 were made. The results of both calibrations were compared with the data from the standard certificate. Satisfactory agreement was achieved. Mean percentage difference between results from ISOCS calibration compared to reference values is 6% for all isotopes activities in CBSS 2 standard.The set of collimators was used to develop efficiency calibration for in situ measurements of the soil surface. Test measurements were carried out at the area of the Institute of Nuclear Physics Polish Academy of Sciences in Kraków, Poland (IFJ PAN). Two measurement methods were compared: in situ and laboratory gamma spectroscopy. The obtained average results (from all 10 measuring points) are consistent within the range of measurement uncertainty.



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