Determination of radioactivity based on unfolded gamma spectra using the GRAVEL method and response matrix from MCNP simulation
Main Article Content
Abstract
Accurate determination of radionuclide activity is crucial in ensuring radiation safety and effective environmental monitoring. In this study, we propose a method based on gamma spectrum deconvolution to improve the accuracy of activity quantification from spectra measured using HPGe detector. The GRAVEL algorithm, implemented in the UMG software package, is employed to unfold experimental spectra, particularly in the low-energy region around 59.5 keV, where background noise and detector limitations significantly affect measurement results. A detailed detector response matrix is constructed using Monte Carlo simulations with the MCNP6 code, in which each incident photon has an energy exactly matching the channel energies of the experimentally measured gamma spectrum. This response matrix is developed up to 1 MeV and integrated into the deconvolution process to enhance peak separation and activity determination. The proposed method is validated using experimental gamma spectra from a point source containing multiple radionuclides with the certified reference activity. Results show that the combination of MCNP-based response modelling and GRAVEL deconvolution significantly improves the reliability of activity measurements. This improvement in reliability, particularly for low-energy and weak gamma emitters, is a significant step forward in the field, with the maximum relative deviation remaining below 4.3%.
Keywords
Gamma Spectrometry, MCNP, Unfolding, FEP efficiency, Radioactivity
Article Details
References
Boukhalfa, S., Ould Mohamed Sidi Mohamed, M., & Khelifi, R. (2021). Monte Carlo simulation of NaI(Tl) detector and GRAVEL deconvolution for biological, geological samples and their dosimetry evaluation. Journal of Instrumentation, 16(09), P09024. https://doi.org/10.1088/1748-0221/16/09/P09024
Byon, J., Park, S., Kim, Y., & Ahn, S. (2022). External exposure specific analysis for radiation worker in reuse of containment building for Kori Unit 1. Nuclear Engineering and Technology, 54(5), 1781-1788. https://doi.org/https://doi.org/10.1016/j.net.2021.11.015
Chen, Y., Chen, X., Lei, J., An, L., Zhang, X., Shao, J.,…Wang, X. (2014). Unfolding the fast neutron spectra of a BC501A liquid scintillation detector using GRAVEL method. Science China Physics, Mechanics & Astronomy, 57(10), 1885-1890. https://doi.org/10.1007/s11433-014-5553-7
Dombrowski, H. (2024). Comparison of the conversion method with gravel unfolding to obtain dose values from photon spectra. Radiation Protection Dosimetry, 200(1), 32-59. https://doi.org/10.1093/rpd/ncad251
Dryak, P., Kovar, P., & Gudelis, A. (2010). Total efficiency of GE detectors—dead layer signal effect. Applied Radiation and Isotopes, 68(7), 1451-1453. https://doi.org/https://doi.org/10.1016/j.apradiso.2009.11.026
Eckert & Ziegler. Mixed nuclide solutions. https://www.ezag.com/products/isotope-products/isotrak-calibration-sources/standardized-solutions/calibrated-solutions/mixed-nuclide-solutions/
GUM. (2008). Evaluation of Measurement Data – Guide to the Expression of Uncertainty in Measurement. JCGM 100:2008, http://www.bipm.org. http://www.bipm.org
He, J.-F., Yang, Y.-Z., Qu, J.-H., Wu, Q.-F., Xiao, H.-L., & Yu, C.-C. (2016). An inversion decomposition method for better energy resolution of NaI(Tl) scintillation detectors based on a Gaussian response matrix. Nuclear Science and Techniques, 27(3), 58. https://doi.org/10.1007/s41365-016-0062-1
Kurniasari, D., Warsono, W., Indryani, N., Usman, M., & Hadi, S. (2021). Simulation of generalized Gamma distribution with maximum likelihood estimation and expectation-maximization algorithm on right censored data type 1. Decision Science Letters, 10, 415-424. https://doi.org/10.5267/j.dsl.2021.1.003
Li, F., Gu, Z., Ge, L., Li, H., Tang, X., Lang, X., & Hu, B. (2019). Review of recent gamma spectrum unfolding algorithms and their application. Results in Physics, 13, Article 102211. https://doi.org/https://doi.org/10.1016/j.rinp.2019.102211
Li, F., Lang, X., Chen, Y., Ge, L., Feng, L., & Li, S. (2019). Evaluation on least square method applied to gamma spectrum de-noising. Journal of Physics: Conference Series, 1423(1), 012002. https://doi.org/10.1088/1742-6596/1423/1/012002
Li, X., Wang, Z., Lv, H., Wei, S., Liu, J., Wang, Y.,…Yang, C. (2020). Measurement of the energy of fast neutrons in the presence of gamma rays using a NaI(Tl) and a plastic scintillator. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 976, 164257. https://doi.org/https://doi.org/10.1016/j.nima.2020.164257
Liu, B., Yang, H., Lv, H., Jing, F., Gao, X., & Yan, M. (2020). A deconvolution method for scintillator gamma-ray spectrum analysis based on convex optimization. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 957, 163399. https://doi.org/https://doi.org/10.1016/j.nima.2020.163399
Loan, T. T. H. (2016). Study on analyzing overlaped peaks using the Gold algorithm of unfolding. Science & Technology Development, 19.
Maestro-32. (2003). Software user's manual vesion 6.
Ménesguen, Y., & Lépy, M. C. (2021). COLEGRAM, a flexible user-friendly software for processing of ionizing radiation spectra. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1003, Article 165341. https://doi.org/https://doi.org/10.1016/j.nima.2021.165341
Pelowitz, P. (2013). MCNP6TM User's manual, Version 1.0. Los Alamos National Laboratory report LA-CP-13-00634.
PTB. (2004). UMG 3.3, Analysis of data measured with spectrometers using unfolding techniques. https://www.oecd-nea.org/tools/abstract/detail/nea-1665/
Thanh, T. T., Vuong, L. Q., Ho, P. L., Chuong, H. D., Nguyen, V. H., & Tao, C. V. (2018). Validation of an advanced analytical procedure applied to the measurement of environmental radioactivity. J Environ Radioact, 184-185, 109-113. https://doi.org/https://doi.org/10.1016/j.jenvrad.2017.12.020
Trang, L. T. N., Chuong, H. D., & Thanh, T. T. (2019). Efficiency calibration for HPGe detector by Monte Carlo efficiency transfer method. Science & Technology Development Journal - Natural Sciences, 3, 9-17.