교차분석 시료를 이용한 HPGe 검출기의 동시합성효과 평가

Abstract

Many radionuclides emit multiple gamma rays or X-rays when they decay into their ground states. If two or more gamma rays (or a gamma ray and an X-ray) which are emitted in a cascade from an excited nucleus, the detector can not distinguish them and considers them as a single event because they are detected within the resolution time of the detector. As a result of them, the energy that transferred to the detector becomes the sum of the multiple events. This is known as “Cascade” or “True Coincidence” summing effect. It causes the inaccurate count rate and the erroneous results in data analysis. To date, many sophisticated efforts have been done for correcting the cascade summing-effect in HPGe detectors. The well-known methods are the Monte Carlo Simulation for the source geometry and the Peak-to-Total correction using singlet sources.

In this study, We calibrated for the HPGe detectors with different efficiencies by using the reference materials that are certified by Korea Research Institute of Standards Science(KRISS). Also, we corrected the efficiency by using the KCl solution in order to correct the problem of efficiency undervaluation occurring in the energy range above 661.66 keV because of the cascade summing effect of 60Co and 88Y. In order to confirm the deviation due to the efficiency and cascade summing effect, we measured the samples for 80,000 seconds and we have identified how much the nuclide, 60Co, 134Cs and 152Eu are evaluated according to the energy range. As a result, CANBERRA’s 30% has affected by cascade summing effect a 60Co of less than 1 %, 134Cs of 12.5 %, 152Eu of 3.83 % and 40% has a 60Co of 3.33 %, 134Cs of 14.3 %, 152Eu of 7.88 %. Also, ORTEC’s 30% has a 60Co of 3.39 %, 134Cs of 14.0 %, 152Eu of 7.95 % and 40% has a 60Co of 6.48 %, 134Cs of 15.7 %, 152Eu of 9.46 %.

In conclusion, we corrected peak efficiency by using 40K as a natural radionuclide and evaluated the cascade summing effect of 450mL Marinelli beaker for the HPGe detectors with different efficiency through a cross analysis sample of Korea Institute of Nuclear Safety(KINS). This method is a easier and simpler than other methods, and saves cost and time.