Tiểu ban C Ghi đo bức xạ, An toàn bức xạ và Quan trắc môi trường Section C Radiation measurement, Radiation safety and Environmental 225 ĐÁNH GIÁ MỘT SỐ KỸ THUẬT HIỆU CHUẨN HIỆU SUẤT CỦA ĐẦU DÒ HPGE T[.]
Tiểu ban C: Ghi đo xạ, An toàn xạ Quan trắc môi trường Section C: Radiation measurement, Radiation safety and Environmental ĐÁNH GIÁ MỘT SỐ KỸ THUẬT HIỆU CHUẨN HIỆU SUẤT CỦA ĐẦU DÒ HPGE TRONG PHÉP ĐO HOẠT ĐỘ PHĨNG XẠ MẪU MƠI TRƯỜNG EVALUATION OF EFFICIENCY CALIBRATION TECHNIQUES OF HPGE DETECTOR FOR RADIOACTIVITY MEASUREMENTS IN ENVIRONMENTAL SAMPLES HO VAN DOANH1*, DOAN THI THANH NHAN1, VO VAN TIEN1, NGUYEN VAN HOAI NAM1, DAO VAN HOANG1, HO MANH DUNG1, PHAN BAO QUOC HIEU2, TRAN QUOC DUONG2 Center for Nuclear Technologies, 217 Nguyen Trai Street, TP.HCM, Vietnam Dalat Nuclear Research Institute, 01 Nguyen Tu Luc, Dalat, Vietnam * E-mail: hovandoanh@gmail.com Tóm tắt: Để trì hạng mục công nhận phép thử dùng hệ phổ kế gamma phịng thí nghiệm chúng tơi Đường cong hiệu suất đầu dò HPGe mẫu mơi trường dạng hình học Marinelli xác định nguyên lý chuyển đổi hiệu suất thông qua phần mềm thương mại ANGLE3 mô Monte Carlo MCNP5 GEANT4 Hiệu suất thu từ phép đo thực nghiệm nguồn chuẩn sử dụng hiệu suất tham khảo phần khai báo phần mềm ANGLE3 dùng cho việc hiệu chỉnh code mô MCNP5 GEANT4 Kết hiệu suất mẫu đất hộp Marinelli đạt từ MCNP5 GEANT4 so sánh với hiệu suất đạt từ phần mềm ANGLE3 Hơn nữa, độ hiệu suất đầu dò đạt nghiên cứu đánh giá thông qua phép đo hoạt độ phóng xạ hạt nhân 40K, 137Cs, 232Th 226Ra mẫu chuẩn (IAEA-375) Từ khóa: Đồng vị phóng xạ tự nhiên, đầu dị HPGe, hiệu suất, hộp dựng mẫu Marinelli Abstract: To keep the accredited category for the gamma spectrometry test in our laboratory, the efficiency curves of a HPGe detector for soil sample in Marinelli geometry were determined by “efficiency transfer” principle via the ANGLE3 commercial software and Monte Carlo simulations via MCNP5 and GEANT4 The efficiency obtained from experimental measurement of point standard sources was used as a reference efficiency curve for the input of ANGLE3 software as well as for correction of simulation codes of MCNP5 and GEANT4 The results of the efficiency for soil sample in Marinelli beaker obtained from the MCNP5 and GEANT4 were compared with the efficiency obtained from the ANGLE3 software Moreover, the trueness of the detector efficiency obtained in this work was evaluated by the radioactivity measurement of 40 K, 137Cs, 232Th and 226Ra in a reference material (IAEA-375) Keywords: Natural radionuclides, HPGe detector, efficiency, Marinelli beaker INTRODUCTION For measurement of voluminous samples as environmental radioactivity, their dimensions and elemental components in the sample have to be considered for detector efficiency calibrations, as well as the self-attenuation of gamma-rays Typically, the calibration of detector efficiency needs standard samples or standard sources which contain known radionuclides with a known quantity of radioactivity The standards are required same size, density, elemental composition and multiple gamma-emitting radionuclides as the sample From a practical point of view, there are some difficulties for preparation of standard according to the requirements or for cases where the conduct of experimental measurement is impossible or very difficult such as samples of non-standard geometry and for large sized samples or standards was not easily available These difficulties can be solved by using Monte Carlo simulation such as MCNP and GEANT4 [1] It is a powerful tool to simulate the detector response and applicable to a variety of matrices and sample geometries Thus the simulation codes have been used for detector efficiency calibration However, these simulation codes need to be verified in terms of the accuracy Therefore, the ANGLE3 software have been applied in this study for verifying the efficiency results from simulation codes of MCNP5 and GEANT4 [2-4] ANGLE3 software is commercial computer program which performs the detector efficiency calculations by solid angle method [5] The accuracy of the software for efficiency calculation was verified in appreciation The software can be applied to practically all situations encountered in gamma-laboratory practice: point, disc, cylindrical or Marinelli samples, small and large, of any matrix composition No standards are required, but a start-up “reference efficiency curve” should be obtained by measuring a calibrated source at some reference counting geometry EXPERIMENTAL The detector used in this experiment is a coaxial HPGe detector It has relative efficiency of 40% and resolution of 2.0 keV at 1.33 MeV The ratio of Peak to Compton is 59:1 It is a horizontal detector with 225 Tuyển tập báo cáo Hội nghị Khoa học Cơng nghệ hạt nhân tồn quốc lần thứ 14 Proceedings of Vietnam conference on nuclear science and technology VINANST-14 volume of crystal is 200 cm3 All detector dimensions are taken from the manufacturer provided documents and these are summarized in table The measurements of reference efficiency curve were carried out using a set of point standard sources emitting gamma rays over the energy range of 50–1500 keV, including 241Am, 131Ba, 152Eu, 137Cs and 60Co They originated from Isotope Products laboratory of the US by Eckert & Ziegler manufacture The sources have the same cylinder size with a diameter of mm, a height of 3.18 mm covered by an Acrylic layer The outer cover has the diameter of 25.4 mm and the height of 6.35 mm Figure shows the geometry and dimensions of these standard sources Figure Dimension of point standard source In order to calculate the efficiency of a HPGe detector for soil sample in Marinelli geometry by ANGLE3, MCNP5 and GEANT4, the following should be known: (1) reference efficiency curve, usually obtained by counting calibrated sources at reference geometry and covering gamma-energies in the region of interest; (2) Geometrical and compositional data about the source, detector, and all intercepting layers (for the latter e.g source container and holder, detector end-cap and housing, dead layers, etc.) and (3) Gamma-attenuation coefficients for all materials involved These parameters were shown in table 1, figure and figure Figure Dimension of detector Figure Dimension of Marinelli Beaker (mm) Table 1: Detector dimension of detector, Marinelli Beaker and Components of Matrix Sample (presentative of soil) A B C D HPGe Detector (mm) Crystal Diameter 61.5 Crystal Length 68 Hole Diameter 9.2 Hole Depth 60.1 Marinelli Beaker (mm) Container inside radius Marinelli cavity radius Marinelli cavity depth Marinelli upper bottom thickness 226 52.0 39.5 59.5 2.0 Tiểu ban C: Ghi đo xạ, An toàn xạ Quan trắc môi trường Section C: Radiation measurement, Radiation safety and Environmental E F Nominal Radius Cup Length 105 G H I J K L M N P Space Al Be Nominal Radius Al Al Ge/B Dead Layer Ge/Li Dead Layer Al Cover Diameter 0.03 0.5 0.8 0.0003 0.7 76 Marinelli inner side thickness Marinelli lower bottom thickness Element H C O Na Mg Al Si 2.0 2.0 Matrix Source (Soil) % Weight Element 0.380 K 1.283 Ca 49.912 Fe 0.668 1.568 7.727 27.906 Density % Weight 2.656 3.431 4.469 0.95 g/cm3 RESULTS AND DISCUSSION In oder to evaluate the reliability of simulation codes, the results of detector efficiency for point standard sources obtained by MCNP5 and GEANT4 were compared with the detector efficiency obtained by experimental measurements Figure shows the results obtained using the MCNP, GEANT4 and experimental measurement for point standard sources at distances of 50 mm, 100 mm and 150 mm The efficiency results at distance 100 mm were compared in Table The efficiency ratios of MCNP5 to experimental measurement vary between 0.90 and 1.04 according to gamma energy peaks The average of ratios was 0.97 with relative standard deviation of 5% The efficiency ratios of GEANT4 to experimental measurement (Exp.) vary between 0.91 and 1.04 according to gamma energy peaks The average of ratios was 0.99 with relative standard deviation of 4% The results indicated that efficiency for point source obtained from MCNP and GEANT4 are in line with the efficiency obtained from experimental measurements There is a clear possibility that MCNP5 and GEANT4 simulation codes were created correctly, thereby it can be used for calculations of detector efficiency of soil sample in marinelli beaker Table 2: The result of detector efficiency for point standard sources at distance of 100 mm obtained by experimental measurements and simulation of MCNP and GEANT4 E (keV) 59.5 81.0 121.8 244.7 356.0 444.0 661.7 964.0 1332.5 Experiment MCNP5 (Exp.) 0.0136 0.0123 0.0135 0.0125 0.0128 0.0118 0.0083 0.0086 0.0064 0.0065 0.0054 0.0054 0.0038 0.0039 0.0032 0.0030 0.0024 0.0023 Average of (MCNP/Exp.) Standard Deviation Relative Standard Deviation GEANT4 0.0136 0.0135 0.0125 0.0086 0.0063 0.0053 0.0039 0.0029 0.0023 227 MCNP5 /Exp 0.90 0.93 0.92 1.04 1.02 1.00 1.03 0.94 0.96 0.97 0.05 5.2% GEANT4 /Exp 1.00 1.00 0.98 1.04 0.98 0.98 1.03 0.91 0.96 0.99 0.04 3.9% Tuyển tập báo cáo Hội nghị Khoa học Cơng nghệ hạt nhân tồn quốc lần thứ 14 Proceedings of Vietnam conference on nuclear science and technology VINANST-14 Figure The result of efficiency curves for point standard sources at distance 50 mm, 100 mm and 150 mm The result of detector efficiency for soil sample in marinelli beaker (Marinelli efficiency) obtained by ANGLE3 software and simulation of MCNP5 and GEANT4 were presented in table and figure The efficiency ratios of MCNP5 to ANGLE3 vary between 0.90 and 1.01 according to gamma energy peaks It would be appear that most values obtained from MCNP5 are less than the values obtained from ANGLE3 software The average of ratios was 0.95 with relative standard deviation of 4.6% The efficiency ratios of GEANT4 to ANGLE3 vary between 0.95 and 1.36 according to gamma energy peaks The average of ratios was 1.04 with relative standard deviation of 11% There seems is a tendency to differ between GEANT4 and ANGLE3 at low energy region (59.5 keV and 81 keV) In general, the results indicated that Marinelli efficiency values obtained from MCNP and GEANT4 are in good agreement with the values obtained ANGLE3 Table 3: The result of detector efficiency for soil sample in marinelli beaker obtained by ANGLE3 software and simulation of MCNP5 and GEANT4 ENERGY ANGLE3 MCNP5 GEANT4 (keV) 59.5 0.07708 0.07059 0.10733 81.0 0.10290 0.09983 0.11917 121.8 0.10817 0.11195 0.11895 344.3 0.06101 0.06146 0.06340 356.0 0.05955 0.05978 0.06159 411.1 0.05357 0.05288 0.05438 609.3 0.04013 0.03818 0.03968 661.7 0.03781 0.03566 0.03728 795.8 0.03313 0.03103 0.03258 911.2 0.03014 0.02804 0.02958 1120.3 0.02616 0.02400 0.02524 1173.2 0.02536 0.02320 0.02438 1332.5 0.02331 0.02107 0.02223 1408.1 0.02248 0.02013 0.02131 Average of (MCNP/ANGLE3) and (GEANT4/ANGLE3) Standard Deviation Relative Standard Deviation 228 MCNP5/ ANGLE3 0.92 0.97 1.04 1.01 1.00 0.99 0.95 0.94 0.94 0.93 0.92 0.91 0.90 0.90 0.95 0.04 4.6% GEANT4/ ANGLE3 1.39 1.16 1.10 1.04 1.03 1.02 0.99 0.99 0.98 0.98 0.96 0.96 0.95 0.95 1.04 0.11 11.0% Tiểu ban C: Ghi đo xạ, An tồn xạ Quan trắc mơi trường Section C: Radiation measurement, Radiation safety and Environmental 0.14 Absolute Efficiency 0.12 A NG L E MC NP G E A NT4 0.1 0.08 0.06 0.04 0.02 Energy (keV) 0 300 600 900 1200 1500 Figure Efficiency curves of detector for soil sample in marinelli beaker obtained by ANGLE3 software and simulation of MCNP and GEANT4 The result of detector efficiency for soil sample in marinelli beaker obtained by GEANT4 were used for determination of radioactivity of radionuclides in IAEA-375 (Radionuclides in Soil) including 40K, 137 Cs and 232Th The radioactivity results of the measurement were compared with recommended values in table The measued values of radioactivity are consistent with recommended values for 40K, 137Cs, 226Ra and 232Th Table 4: The measurement results of some radionuclides in IAEA-375 Certified Value (CV)* Radionuclide Measured Value (MV) MV/ CV Radioactivity (Bq/Kg) Uncertainty (Bq/Kg) Radioactivity (Bq/Kg) Uncertainty (Bq/Kg) K 424 425 14 1.00 Cs 2677 30 2664 1.00 232 Th 20.5 1.35 19.9 1.00 0.97 226 Ra 19.7 2.00 18.2 1.4 0.92 40 137 * Radioactivity in reference standard material was corrected decay factors at measurement time June 23, 2021 CONCLUSION The efficiency curve of point standard sources obtained from MCNP and GEANT4 are in line with the efficiency obtained from experimental measurements In addition, the efficiency results for the soil sample in Marinelli geometry obtained by MCNP5 and GEANT4 are in good agreement with the efficiency results obtained ANGLE3 Moreover, the trueness of efficiency values obtained in this work was validated through the gamma measurement of IAEA reference material (IAEA-375) Therefore, there is a clear possibility that MCNP5 and GEANT4 simulation codes produced in this study are useful for further calculations of detector efficiency in various sample geometries The results of simulation codes and detector efficiency obtained in this work have contributed to keep the accredited category for the gamma spectrometry test in our laboratory ACKNOWLEDGEMENTS The Ministry of Science and Technology (MOST) of Vietnam through a ministerial project coded ĐTCB.12/20TTHN is gratefully acknowledged 229 Tuyển tập báo cáo Hội nghị Khoa học Công nghệ hạt nhân toàn quốc lần thứ 14 Proceedings of Vietnam conference on nuclear science and technology VINANST-14 REFERENCES [1] [2] [3] [4] [5] Geant4 Collaboration, Geant4 Users guide for application deverlopers, Version geant4.10.00, 2013 Radu D., Transfer of detector efficiency calibration from a point source to other geometries using ETNA software, Romanian Reports in Physics, 2010 Loan T.T.H., Mô Monte Carlo số toán vật lý hạt nhân, Luận án tiến sĩ, Trường Đại học Khoa học Tự nhiên Tp.HCM, 2009 P.B.Q Hiếu, P.N Sơn, H.V Doanh, Chuẩn hóa hiệu suất ghi tồn phần hấp thụ quang điện cho đầu dị HPGe mơ Monte Carlo, Hội nghị Khoa học Công nghệ Hạt nhân lần thứ 11, 2015 ANGLE3 Semiconductor Detector Efficiency Calculations, User guide, Ortec 230 ... beaker obtained by ANGLE3 software and simulation of MCNP and GEANT4 The result of detector efficiency for soil sample in marinelli beaker obtained by GEANT4 were used for determination of radioactivity. .. efficiency for soil sample in marinelli beaker (Marinelli efficiency) obtained by ANGLE3 software and simulation of MCNP5 and GEANT4 were presented in table and figure The efficiency ratios of. .. GEANT4 are in line with the efficiency obtained from experimental measurements In addition, the efficiency results for the soil sample in Marinelli geometry obtained by MCNP5 and GEANT4 are in good