# 감마선 스펙트럼 비율을 이용한 매립 선원의 깊이 평가 방법론 개발 연구

• Accepted : 2020.02.27
• Published : 2020.03.30

#### Abstract

This study was conducted to develop a method for depth assessment of embedded sources using gamma-spectrum ratio and for the evaluation of field applicability. To this end, Peak to Compton and Peak to valley ratio changes were evaluated according to 137Cs, 60Co, 152Eu point source depth using HPGe detector and MCNP simulation. The effects of measurement distance of PTV and PTC methods were evaluated. Using the results, the source depth assessment equation using the PTC and PTV methods was derived based on the detection distance of 50 cm. In addition, the sensitivity of detection distance changes was assessed when using PTV and PTC methods, and error increased by 3 to 4 cm when detection distance decreased by 20 cm based on 50 cm. However, it was confirmed that if the detection distance was increased to 100 cm, the effects of detection distance were small. And PTV and PTC methods were compared with the two distance measurement method which evaluates the depth of source by the change of net peak counting rate according to the detection distance. As a result of source depth assessment, the PTV and PTC showed a maximum error of 1.87 cm and the two distance measurement method showed maximum error of 2.69 cm. The results of the experiment confirmed that the accuracy of the PTV and PTC methods was higher than two distance measurement. In addition, Sensitivity evaluation by horizontal position error of source has maximum error of less than 25.59 cm for the two distance measurement method. On the other hand, PTV and PTC method showed high accuracy with maximum error of less than 8.04 cm. In addition, the PTC method has lowest standard deviation for the same time measurement, which is expected to enable rapid measurement.

#### Acknowledgement

Grant : 해체 전주기 방사선학적 특성평가 기술 개발

Supported by : 한국연구재단

#### References

1. International Atomic Energy Agency, "Characterization of radioactively contaminated sites for remediation purposes", IAEA-TECDOC-1017, 1998.
2. C. Andrieu, T. Boisserie, Y. Desnoyers, C.O. Dehaye, and F. Tardy et al, Radiological Characterisation for Decommissioning of Nuclear Installations, Final Report of the Task Group on Radiological Characterization and Decommissioning (RCD) of the Working Party on Decommissioning and Dismantling (WPDD), NEA/OECD, NEA/RWM/WPDD(2013)2, 2013.
3. E.W. Abelquist, W.S. Brown, G.E. Powers, and A.M. Huffert, "Minimum Detectable Concentrations With Typical Radiation Survey Instruments for Various Contaminants and Field Conditions", Nuclear Regulatory Commission (NRC), NUREG-1507 (1998).
4. A. Al-Ghamdi and X.G. Xu, "Estimating the depth of embedded contaminants from in-situ spectroscopic measurement", Health Phys., 84(5), 632-636 (2003). https://doi.org/10.1097/00004032-200305000-00009
5. R.B. Oberer, C.A. Gunn, and L.G. Chiang, "Small-angle Compton scattering used to determine the depth of a radioactive source in material and to estimate gamma-ray attenuation", Nucl. Instrum. Methods in Phys. Res., 722, 65-70 (2013). https://doi.org/10.1016/j.nima.2013.04.059
6. A.N. Tyler, D.C.W. Sandersor, and E.M. Scott, "Estimating and Accounting for $^{137}Cs$ Source Burial through In-Situ Gamma Spectrometry in Salt Marsh Environments", J. Env. Radioactivity, 33(3), 195-212 (1996). https://doi.org/10.1016/0265-931X(95)00098-U
7. C.J. Werner, J. Armstrong, F.B. Brown, J.S. Bull, and L. Casswell et al, "MCNP user's manual code version 6.2", Los Alamos National Laboratory, LA-UR-17-29981 (2017).
8. W.H. Ha, J.R. Yoo, S.W. Yoon, M.J. Park, and J.K. Kim, "Simulation of Counting Efficiencies of Portable NaI Detector for Rapid Screening of Internal Exposure in Radiation Emergencies", J. Radiat. Prot. Res., 40(4), 211-215 (2015). https://doi.org/10.14407/jrp.2015.40.4.211
9. J.H. Hubbell and S.M. Seltzer, "Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients 1 keV to 20 MeV for Elements Z = 1 to 92 and 48 Additional Substances of Dosimetric Interest", National Institute of Standards and Technology, NISTIR 5632 (1995).