Abstract
HPGe detectors are currently being used in a wide range of applications ranging from basic and applied research to homeland security. The combination of large detection efficiency and the excellent energy resolution make the detector a good choice for measuring gamma rays to detect, identify, and quantify the amount of nuclear materials in the environment and specific samples. Therefore, it is necessary to have available, reliable and precise analytical methods to determine their bulk concentrations as well as their isotopic compositions. There are many methods used for calibration, one is the so-called relative method where Ra-226 point-source is used at a representative point (25 cm from the detector). Another method is the absolute full-energy peak (photopeak) efficiency where standard multisource including different radionuclides (U-238, Ra-226, Th-232, K-40, Cs-134, Cs-137, Am-241 and Pb-210) covering the energy range from 681 to 1860 KeV is used.
In this paper, the methods used in efficiency calibration for HPGe in Central Laboratory for Environmental Radioactivity Measurements Inter-comparison and Training (CLERMIT) are evaluated. It is important for laboratory accreditation according to the requirements of the standard ISO/17025: 2005 which is implied in the radioactive content measurement of samples collected from the environment, food chain or industrial products.
All the necessary calibration corrective actions were taken in consideration to improve the quality of the radioactivity measurements performed in the laboratory. Also, the effect of some regular matrices such as water, soil and sediment on the detector efficiency is investigated.
As a result, the detection efficiency curves are obtained and a remarkable agreement between the two methods is achieved with discrepancies less than 5%.