Tiểu ban C Ghi đo bức xạ, An toàn bức xạ và Quan trắc môi trường Section C Radiation measurement, Radiation safety and Environmental 251 SO SÁNH QUỐC TẾ LIÊN VÙNG CÙNG IAEA/ARPANSA VỀ ĐỊNH LIỀU CÁ NHÂ[.]
Tiểu ban C: Ghi đo xạ, An toàn xạ Quan trắc môi trường Section C: Radiation measurement, Radiation safety and Environmental SO SÁNH QUỐC TẾ LIÊN VÙNG CÙNG IAEA/ARPANSA VỀ ĐỊNH LIỀU CÁ NHÂN CHIẾU NGOÀI NĂM 2018 JOINT IAEA/ARPANSA REGIONAL INTERCOMPARISON ON PERSONAL DOSIMETRY FOR EXTERNAL EXPOSURE 2018 PHAN VAN TOAN, PHAM VAN DUNG, LE VIET PHONG, BUI NGOC HUY, HUYNH THI TINH, NGUYEN VAN HUNG Dalat Nuclear Research Institute (01 Nguyen Tu Luc St., ward 8, Dalat city) *E-mail: toan9999@gmail.com Tóm tắt: Mục đích chương trình so sánh quốc tế năm 2018 thực Phịng thí nghiệm Chuẩn liều cấp I (PSDL) Cơ quan An toàn xạ hạt nhân Úc (ARPANSA) hợp tác với IAEA nhằm đánh giá khả dịch vụ định liều cá nhân nước thành viên châu Á Thái Bình Dương đại lượng tương đương liều cá nhân Hp(10) trường xạ photon (gamma tia-X), từ hỗ trợ dịch vụ định liều đạt kết xác cung cấp hướng dẫn cải tiến việc thực dịch vụ định liều có Có 29 thành viên (phịng thí nghiệm) 20 nước tham gia chương trình đo so sánh này, thành viên gửi liều PSDL để chiếu xạ (chiếu xạ photon dải lượng 70 662 keV, liều tương đương từ mSv đến 20 mSv góc tới 0° and 20°), sau gửi chúng trở lại cho thành viên đọc liều Các kết nghiên cứu chúng tơi (Phịng thí nghiệm No 3) định liều nhiệt phát quang với việc sử dụng TLD loại CaSO4:Dy dạng bột toàn giá trị liều đo gần với giá trị liều thực chiếu ARPANSA Điều khẳng định TLD tự chế tạo chúng tơi dùng dịch vụ định liều có độ tin cậy tốt Việt Nam Từ khóa: Chương trình so sánh quốc tế, tương đương liều cá nhân - Hp(10), liều kế nhiệt phát quang (TLD), dịch vụ đo liều cá nhân (IMS) Abstract: The aim of the 2018 Intercomparison exercise implemented by the Primary Standard Dosimetry Laboratory (PSDL) of Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) collaborated with IAEA is to assess the capabilities of the dosimetry services in participating member states in Asia and the Pacific region for the personal dose equivalent, Hp(10), in photon (gamma and X-ray) fields, thus supporting them to achieve a more accurate dosimetry service and to provide them with guidelines to improve the performance of the existing dosimetry services There were 29 participants (laboratories) from 20 countries participated in the intercomparison The participants send dosimeters to the PSDL for irradiation (irradiated photons with range of energy 70 and 662 keV, dose equivalent from mSv to 20 mSv and angle of incidence at 0° and 20°, and then returned them to the participants for reading doses Our research results (Participant No 3) on thermoluminescense dosimetry with using home-made TLDs in the type of CaSO 4:Dy powder) shown that the all values of measured doses were near with those of the delivered doses respectively given by ARPANSA This has affirmed that our TLDs using in the dosimetry service have had good confidence in Vietnam Keywords: Intercomparison exercise, personal dose equivalent - Hp(10), thermoluminescence dosemeter (TLD), Individual monitoring service (IMS) INTRODUCTION Regional Intercomparison exercise of the Joint IAEA/ARPANSA (Australian Radiation Protection and Nuclear Safety Agency) on individual monitoring for external exposure was conducted under the Regional Technical Cooperation Project of RAS/9/080 The purpose of the project is to strengthen national capacities for occupational radiation protection in compliance with the International Basic Safety Standards (BSS) This is formulated through the promotion of self-assessment tools, including harmonization and implementation of the relevant IBSS for improved provisions for dosimetry, workplace monitoring and harmonized capacity in the region Improvement of the quality management system (QMS) in the individual monitoring services (IMS) laboratory in the region is still a challenge Systematic training for the staff in the laboratory and Intercomparison exercises on individual monitoring is indispensable Therefore, RAS/9/080 supported an IC exercise for participating member states in Asia and the Pacific region to support the improvement of QMS of the laboratories in the region The 2018 IC exercises focused on external monitoring, specifically on passive dosimeters (such as TLDs, OSLDs, etc.) used for the assessment of personal dose equivalent, Hp(10), in photon (gamma and X-ray) fields and each participant was limited to one dosemeter type for the Intercomparison Irradiation of personnel dosimeters was carried out at the Primary Standard Dosimetry Laboratory (PSDL) of ARPANSA and the Intercomparison exercise was participated by 29 IMS from 20 countries in Asia and the Pacific region Our Personal Dosimetry Laboratory (Participant No 3) from Dalat Nuclear Research Institute (DNRI) used home-made TLDs in the type of CaSO4:Dy powder for this Intercomparison Because TLDs has been a good technique to measure ionization radiations, it has become common among IMS laboratories in Asia and the Pacific region 251 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 EXPERIMENT AND RESULT 2.1 Arrangement The Intercomparison exercise was announced to the member states in January 2018 An IMS wishing to participation was asked to submit a completed nomination form and questionnaire before st June 2018 The participant of each service in the Intercomparison was confirmed on 1st June 2018 The participants were required to perform a linearity test of their reader prior to the Intercomparison The participants were required to send their dosimeters to the irradiation facility of the PSDL, by courier to enable tracking of the packages, such that they arrived by 30th July 2018 A total of 25 dosimeters are required from each participant for the Intercomparison as follows: dosimeters for background, transit and 20 ones for irradiation (exposures for each participant will be at different doses) The irradiating facility exposed the dosimeters through August 2018 The dosimeters from each participant were sorted into groups as follows: Five dosimeters for measurement of irradiation during storage and transport (Control dosimeters); five ones to be exposed to the 137Cs beam at an incident angle of 0°; five ones to be exposed to the 137Cs beam at an incident angle of 20°; five ones to be exposed to the X-ray beam at an incident angle of 0° and five ones to be exposed to the X-ray beam at an incident angle of 20° The dosimeters for each exposure group were stored together in a bag labelled with the exposure All of the dosimeters were stored together at ARPANSA except during the actual exposures The irradiating facility of the PSDL then returned the dosimeters to the participants throughout September 2018 The participants were required to evaluate the dose on each of dosimeters and report the net personal dose equivalent, Hp(10), on each of the exposed dosimeters by 30 th October 2018 The participants were provided preliminary results in November 2018 The IAEA General Safety Guide on occupational radiation protection (GSG-7) [1] recommends that the allowable accuracy interval for the measurement of personal dose equivalent can be smoothed as a function of dose level as follows: 𝐻1 1.5 2𝐻0 (1 − 𝐻 +𝐻1 𝐻0 ) ≤ 𝐻𝑀 ≤ 1.5𝐻1 (1 + 2𝐻 +𝐻1 ) for H1 ≥ H0 (1) Here H0 is the lowest dose that needs to be measured; H1 is conventional true dose and HM is the dose measured by the participant For the purposes of this exercise, H0 is taken to be 0.08 mSv, based on the formula given in GSG-7 (equation 24, pp 150) for an annual dose of mSv and monthly measurements 2.2 Irradiation to the 137Cs beam The schematic arrangement for the irradiations to the 137Cs beam is shown in Figure The 137Cs beam was supplied by a teletherapy source with no added attenuators, providing a nominal dose rate of 35 µSv/s at a distance of m The beam diameter is 40 cm at a distance of m, but the dosimeters were placed within a 10 cm diameter circle to avoid loss of beam uniformity Figure Arrangement for exposures to the 137Cs beam The dosimeters were placed on a Polymethylmethacrylate (PMMA) slab phantom with dimensions of 30x30x15 cm3, as recommended by ICRU [3] The dosimeters were then covered by a build-up plate 252 Tiểu ban C: Ghi đo xạ, An tồn xạ Quan trắc mơi trường Section C: Radiation measurement, Radiation safety and Environmental comprising mm PMMA The arrangement was rotated about the midpoint between the dosimeters to create the 20° angle of incidence 2.3 Irradiation to the X-ray beam The schematic arrangement for the irradiations to the X-ray beam is shown in Figure The X-ray beam was supplied by a constant potential, tungsten target X-ray tube The beam quality was 70 kVp, 15 mA with an additional mm of aluminium filtration, producing an effective energy of 34 keV (HVL = 3.19 mm Al) This is similar to the code TH70 PTB therapy beam The apparatus provides a nominal dose rate of 90 µSv/s at a distance of m The beam diameter is 45 cm at a distance of m, but the dosimeters were placed within an 11 cm diameter circle to avoid loss of beam uniformity Figure Arrangement for exposures to the X-ray beam The dosimeters were placed on a 30x30x15 cm3 water slab phantom (32x32x16.3 cm3 including PMMA walls) The arrangement was rotated about the midpoint between the dosimeters to create the 20° angle of incidence 2.4 Intercomparison report The participants reported with the sheet form as in the application form After confirmation for the data, APRANSA reported the result of the Intercomparison with certificate (Figure 3) The information of report would be composed of the net personal dose equivalent, Hp(10), which used method to compare with delivered dose from APANSAR and overall uncertainties for all irradiations 2.5 Results The Participant No from DNRI used home-made TLDs in the type of CaSO4:Dy powder (each TLD contained about 25 mg CaSO4:Dy powder) for the Intercomparison Results of net dose evaluation measured by Rexon-320 TLD reader and comparison by IAEA/ARPANSA presented in Table (Column (4): Measured dose, one (5): Measurement uncertainty at 95% confidential level, one (6): Conventional true dose, one (7) and one (8) are the upper and lower limits for acceptable results by using the formulae (equations 25 and 26) as given in the IAEA GSG-7 [1], respectively 253 Figure The certificate of participation in the join the IAEA/Arpansa regional the IC on the individual monitoring for external exposure-2018(RAS/9/080) 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 Table Results of dose evaluation of the Participant No and comparison by IAEA/ARPANSA No Dosemeter (1) 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Beam quality Monitor ID (2) (3) V1831-55728 V1831-55729 V1831-55730 V1831-55731 V1831-55732 V1831-55733 V1831-55734 V1831-55735 V1831-55736 V1831-55737 V1831-55738 V1831-55739 V1831-55740 V1831-55741 V1831-55742 V1831-55743 V1831-55744 V1831-55745 V1831-55746 V1831-55747 V1831-55748 V1831-55749 V1831-55750 V1831-55751 V1831-55752 Background 137 Cs beam at 0o 137 Cs beam at 20o X-ray beam at 0o X-ray beam at 20o HM (mSv) (4) Control Control Control Control Control 3.3 3.3 3.4 3.3 3.0 3.1 2.9 2.8 2.7 3.1 4.8 4.9 5.1 5.4 5.4 5.2 5.1 4.7 5.0 4.4 Unc (mSv) (5) H1 (mSv) (6) Upper limit (7) Lower limit (8) 1.0 1.0 1.0 1.0 0.9 0.9 0.9 0.8 0.8 0.9 1.4 1.5 1.5 1.6 1.6 1.6 1.5 1.4 1.5 1.3 3.18 3.18 3.18 3.18 3.18 3.21 3.21 3.21 3.21 3.21 5.44 5.44 5.44 5.44 5.44 5.34 5.34 5.34 5.34 5.34 4.89 4.89 4.89 4.89 4.89 4.93 4.93 4.93 4.93 4.93 8.28 8.28 8.28 8.28 8.28 8.13 8.13 8.13 8.13 8.13 2.01 2.01 2.01 2.01 2.01 2.03 2.03 2.03 2.03 2.03 3.52 3.52 3.52 3.52 3.52 3.45 3.45 3.45 3.45 3.45 The measured air kerma was converted to ambient dose equivalent using the factors given by ISO 4037 Part [2] For the irradiation to the beam of 137Cs, applying the factor of 1.21 Sv/Gy (at 0°) and 1.22 Sv/Gy (at 20°) given by ISO 4037 Part 3, Table 33 [2], the personal dose equivalent delivered to the dosimeters at an incident angle of 0° was 3.18 mSv and at an incident angle of 20° was 3.21 mSv, with a 95% confidence interval of ±6% For the irradiation to the X-ray beam, applying the factors of 1.47 Sv/Gy (at 0°) and 1.44 Sv/Gy (at 20°), given by ISO 4037 Part 3, Table 27 [2], The personal dose equivalent delivered to the dosimeters at an incident angle of 0° was 5.44 mSv and at an incident angle of 20° was 5.34 mSv, with a 95% confidence interval of ±6% 2.6 Discussion The figure show the results for each dosemeter (blue dots) analyzed by our personal dosimetry laboratory (Participant No 3) that were shown in the Table in comparison with the lower and upper limits for acceptable results (red dotted lines) and the reference level for each exposure scenario (solid yellow line) The error bars indicate the 95% confidence interval reported for the measurements In the following figure, dosimeters No – were exposed to the 137Cs beam at 0°; ones No – 10 were exposed to the 137 Cs beam at 20°; ones No 11 – 15 were exposed to the X-ray beam at 0°; and ones No 16 -20 were exposed to the X-ray beam at 20° 254 Tiểu ban C: Ghi đo xạ, An tồn xạ Quan trắc mơi trường Section C: Radiation measurement, Radiation safety and Environmental Figure Graph of presenting the data in Table The average measurement of dose for our dosimeters exposed to the 137Cs and X-ray beam shows that all of the values reported acceptable measurements for this exposure scenario Although there is significant scatter in the results, our result reported 95% confidence intervals that included the reference level for this exposure scenario The following graphs (Figure 5, Figure 6, Figure and Figure 8) present the average measurement of dose reported by each participant for this exposure scenario These figures show that all of the participants reported acceptable measurements for this exposure scenario Figure Measurement of Exposure to the 137Cs Beam at Normal Incidence Figure Measurement of Exposure to the 137Cs Beam at a 20° angle of incidence Figure Measurement of Exposure to the X-ray Beam at Normal Incidence Figure Measurement of Exposure to the X-ray Beam at a 20° angle of incidence In the Figure and Figure 6, the reference level was within the 95% confidence interval reported by only twelve of the participants In many cases, this could be due to under-estimation of the confidence interval However, it could also mean that some of the participants are systematically under- or overreporting personal dose equivalent 255 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 While Figure and Figure 8, it also indicates that there is significant scatter in the results Furthermore, only six participants reported 95% confidence intervals that included the reference level for this exposure scenario These results indicate that the measurement of personal dose equivalent, Hp(10), for low energy radiation poses a significant challenge for most participants CONCLUSION Our research results shown that the all values of measured doses were near with those of the true doses respectively given by ARPANSA, and the all uncertainties of measured doses were within the upper limits and the lower limits (within the trumpet curves) according to the criteria of GSG-7 These results showed a good agreement among the participants participating the Intercomparison exercise (according to the evaluation of IAEA/ARPANSA) This has affirmed that our home-made TLDs using in the dosimetry service have had good confidence in Vietnam REFERENCES [1] IAEA (2018), Occupational Radiation Protection, International Atomic Energy Agency, Vienna, (GSG-7), ISSN 1020-525X [2] ISO 4037-3:1999 (1990), X and gamma reference radiation Part 3: Calibration of area and personal dosimeters and the measurement of their response as a function of energy and angle of incidence, International Organization for Standardization (ISO) [3] ICRU (1992), Measurement of dose equivalents from external photon and electron Radiations, International Commission on Radiation Units and Measurements (ICRU), Bethesda, ISSN 1473-6691 [4] IEC 62387 (2012), Radiation protection instrumentation - Passive integrating dosimetry systems for personal and environmental monitoring of photon and beta radiation, International Electrotechnical Commission (IEC), Geneva 256 ... then returned the dosimeters to the participants throughout September 2018 The participants were required to evaluate the dose on each of dosimeters and report the net personal dose equivalent,... measurement of personal dose equivalent can be smoothed as a function of dose level as follows: