Establishment of ISO 4037‐1 X‐ray narrow‐spectrum series
2019; Institution of Engineering and Technology; Volume: 2019; Issue: 23 Linguagem: Inglês
10.1049/joe.2018.9126
ISSN2051-3305
AutoresDeliang Zhang, Wanchang Lai, Jinjie Wu, Haiyan Du, Rui Zhao, Song Fan,
Tópico(s)Radiation Shielding Materials Analysis
ResumoThe Journal of EngineeringVolume 2019, Issue 23 p. 8858-8861 7th International Symposium on Test Automation and Instrumentation (ISTAI 2018)Open Access Establishment of ISO 4037-1 X-ray narrow-spectrum series Deliang Zhang, Deliang Zhang Chengdu University of Technology, Chengdu, People's Republic of China National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorWanchang Lai, Wanchang Lai Chengdu University of Technology, Chengdu, People's Republic of ChinaSearch for more papers by this authorJinjie Wu, Corresponding Author Jinjie Wu wujj@nim.ac.cn National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorHaiyan Du, Haiyan Du Chengdu University of Technology, Chengdu, People's Republic of China National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorRui Zhao, Rui Zhao Chengdu University of Technology, Chengdu, People's Republic of China National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorSong Fan, Song Fan National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this author Deliang Zhang, Deliang Zhang Chengdu University of Technology, Chengdu, People's Republic of China National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorWanchang Lai, Wanchang Lai Chengdu University of Technology, Chengdu, People's Republic of ChinaSearch for more papers by this authorJinjie Wu, Corresponding Author Jinjie Wu wujj@nim.ac.cn National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorHaiyan Du, Haiyan Du Chengdu University of Technology, Chengdu, People's Republic of China National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorRui Zhao, Rui Zhao Chengdu University of Technology, Chengdu, People's Republic of China National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this authorSong Fan, Song Fan National Institute of Metrology, Beijing, People's Republic of ChinaSearch for more papers by this author First published: 03 December 2019 https://doi.org/10.1049/joe.2018.9126Citations: 3AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract In order to calibrate radiation protection instruments and determine radiation dose, it is critical to establish an X-ray narrow-spectrum series recommended by the standard ISO 4037-1 which is published by the International Standardisation Organisation (ISO). By experiment, the qualities of filtered X radiation of narrow-spectrum series in the range from 60 to 300 kV were established. The differences of the first half-value layer (HVL1) and the second HVL (HVL2) between experimental results and the values given in the standard ISO 4037-1 were all within 5%. What is more, the Monte Carlo code EGSnrc was used to simulate the spectra of these radiation qualities, which showed a good agreement with these spectra given in the standard ISO 4037-1. The spectral resolution, mean energy and effective energy of these reference qualities can be obtained, which are all have good agreement with the given values. 1 Introduction With the wide application of ionising radiation in different fields, such as radiotherapy, industry, research, education and so on, all of which are closely related to people's life, more and more people increase emphasis on radiation protection [1]. When measuring the radiation dose, first of all, we need to calibrate dosimeters which are used to detect the radiation dose around the environment. The International Standard ISO 4037-1 specifies the radiation characteristics and production methods [2]. On the basis of ISO 4037-1, filtered X radiation of narrow-spectrum series in the range from 60 to 300 kV was established. Although the quality of a filtered X radiation is characterised by many specifications, for example, mean energy, resolution, half-value layer (HVL), the X-ray beams can be seen as the reference irradiations that can be used to calibrate radiation protection instruments, only if the installation shall comply with following certain conditions for all established radiation qualities by this experiment. (a) The inherent filtration of the tube plus the aluminium filters which are added to obtain a total fixed filtration is equal to 4 mm Al, and the difference of it is within 5%. (b) Other filters, such as copper, tin, lead, have a thickness which is specified with an accuracy of ±5% and the metals should have the purities more than 99.9%. (c) For the attenuator, the absorber used is copper, and the purities are at least 99.9%. (d) The first and second HVLs in copper agree with ±5% between the measured values in this experiment and the values given in the standard ISO 4037-1. The ISO 4037 narrow-spectrum series X-ray qualities are mainly used to calibrate radiation protection detectors of very large dimensions. Existing key comparison for air kerma for the ISO 4037 narrow-spectrum series that cover the range from 30 to 300 kV is not direct comparison, such as BIPM.RI(I)-K2 and -K3, but indirect comparison, such as EUROMET.RI(I)-S3 whose results are available [3-5]. 2 Experimental device For complying with the ISO 4037-1 standard, it is necessary to fulfil the certain conditions concerning the X-ray unit, the ionising detector used for the measurements and the X-ray beam characterisation. In this paper, we select a bipolar X-ray unit whose model is COMET MXR-320/26 with adjustable X-ray voltage that covers the range from 15 to 320 kV, which is enough to establish X-ray narrow-spectrum series from 60 to 300 kV. As for filtration, it usually stands for the total filtration which is made up of the fixed filtration that is used by aluminium and additional filtration that is used by copper, tin, lead, consequently it is necessary to determine the inherent filtration. In another article, the inherent filtration measured by different ways is 0.12 mm aluminium. The absorber of copper was obtained from GOODFELLOW whose purity is up to 99.999%. The PTW spherical chamber whose model is 32002 was selected to measure ionising radiation, because it is used in the protection-level range from 0.1 to 0.3 Sv/h. The specification of the spherical chamber shown in Fig. 1 is summarised in Table 1. The laser is used to determine the position. We need to ensure that the focus of the X-ray unit and the focus of the ionisation chamber are on the same horizontal line. The set-up used to measure HVLs is shown in Fig. 2. Fig. 1Open in figure viewerPowerPoint PTW chamber (model 32002) Table 1. Specification of ionisation chamber type 32002 Type of product Vented spherical ionisation chamber application radiation protection measurement measuring quantity photon equivalent dose nominal sensitive volume 1 l design not waterproof, vented reference point Chamber centre nominal response 30 μC/Sv chamber voltage 400 V nominal ±500 V maximal energy response ≤±4% leakage current ≤±10 fA Fig. 2Open in figure viewerPowerPoint Set-up used to measure HVLs 3 Measurements by experiment The definition of the first half-value layer (HVL1) given in ISO4037-1 is the thickness of the specified material which attenuates the beam of radiation to an extent such that the air-kerma rate is reduced to half of its original value. The second half-value layer (HVL2) is the thickness of the same material for measuring HVL1 which attenuates the beam of radiation to some extent such that the air-kerma rate is reduced to a quarter of its initial value minus the HVL1. The homogeneity coefficient is the ratio of the HVL1 to the HVL2. We choose the PTW spherical chamber (model 32002) for HVL measurement. It is very important about the chamber that we should validate the energy response of it. National Institute of Metrology (NIM) had joined in the key comparison of measurement of air kerma for medium-energy X-rays, such as APMP.RI(I)-K3, BIPM.RI(I)-K3 [6]. The air-kerma standards of the NIM and the BIPM in the X-ray range from 100 to 250 kV of the reference conditions recommended by the CCRI had been compared. First of all, the exradin ionisation chamber A5 was calibrated by the air-kerma standards of the reference qualities in CCRI from 100 to 250 kV and the protection-level air-kerma rate of Cs-137 by the following equation: (1) We can get the calibration curve of the chamber A5. Then the chamber A5 is used to measure the HVL for the ISO 4037 narrow-spectrum series. By interpolation we can get the calibration coefficients of the chamber A5 of the narrow-spectrum series and the air-kerma standards of narrow-spectrum series are available by the relation (2) In addition, the PTW chamber (model 32002) is used to measure the HVL1 and the HVL2, then we can get the calibration coefficients of the PTW chamber (model 32002) of the narrow-spectrum series, whose calibration coefficient at the protection-level air-kerma rate can be obtained by calibrating at the radiation quality of Cs-137. The correction factor for the narrow-spectrum series, Nk ,Cs, is defined as the ratio of the calibration coefficients at the narrow-spectrum series and the radiation quality of Cs-137. Finally, as seen in Fig. 3, the energy response of the PTW chamber (model 32002) can be available, which is within ±4%. Fig. 3Open in figure viewerPowerPoint Energy response of chamber (model 32002) As shown in Fig. 1, the ionisation chamber placed at a distance of 200 cm from the focus of X-ray unit. The absorber of copper is in the middle between focuses of the X-ray unit and the ionisation chamber, which is different with the ways wrote by ED Trout and JM Boone [7, 8]. Since the nominal sensitive volume of the chamber (model 32002) used in this experiment is too big to place it at a distance of 100 cm from the focus of X-ray unit. The radiation field of X-ray unit cannot completely cover the ionisation chamber. Before each measurement, it is necessary to ensure that the leakage is so small that we can neglect it by a micro-current measuring system. For the measurements of the HVLs, we obtained five different datum every time when the thickness of the absorber copper was changed. By interpolation calculation and exponential function fitting, the HVLs can be obtained. The actually added filtrations including inherent filtration and additional filtration are all within ±5% compared with the given values in the standard ISO 4037-1. The measured attenuation curves are shown in Fig. 4, whose exponential correlation coefficient R 2 are all more than 99.9% [9]. The measurement results of HVLs are shown in Table 2 and whose deviations are all within ±5% compared with the given values in the standard ISO 4037-1 shown in Table 3. Fig. 4Open in figure viewerPowerPoint Attenuation curves for narrow-spectrum series Table 2. Measurement results of HVLs Radiation quality Filtrations HVL1, mm HVL2, mm Pb Sn Cu Al N60 — — 0.601 3.958 0.232 0.266 N80 — — 1.987 3.9 0.586 0.634 N100 — — 4.981 3.9 1.128 1.190 N120 — 0.997 4.973 3.939 1.739 1.808 N150 — 2.493 — 3.952 2.424 2.545 N200 1.029 2.972 2.015 3.913 4.097 4.221 N250 2.998 1.991 — 3.935 5.316 5.440 N300 4.977 2.991 — 3.894 6.232 6.392 Table 3. Deviations of HVLs Radiation quality HVL1, mm Deviation, % HVL2, mm Deviation, % ISO NIM ISO NIM N60 0.24 0.232 −3.40 0.26 0.266 2.42 N80 0.58 0.586 0.98 0.62 0.634 2.34 N100 1.11 1.128 1.63 1.17 1.190 1.68 N120 1.71 1.739 1.72 1.77 1.808 2.17 N150 2.36 2.424 2.72 2.47 2.545 3.03 N200 3.99 4.097 2.69 4.05 4.221 4.21 N250 5.19 5.316 2.44 5.23 5.440 4.02 N300 6.12 6.232 1.83 6.15 6.392 3.93 4 Simulation of X-ray spectra The energy spectrum of the radiation quality is one of the important characteristics to characterise the radiation quality. It is a common way to simulate spectra by Monte Carlo codes, such as EGSnrc, MCNP, ETRAN, which are widely used in solving radiation transport problems [10-12]. In this paper, the Monte Carlo code EGSnrc was used to simulate the spectra of the radiation qualities included in the ISO 4037-1 narrow-spectrum series. The EGSnrc code system is used for the coupled transport of electrons and photons with arbitrary geometry for particles, whose energies cover the range from a few keV to several hundreds of GeV. BEAMnrc is built on the EGSnrc Code System used to simulated spectra, the data of which are stored in phase-space files [13]. With the help of the BEAM Data Processor computer program which is used for analysing the phase-space files, the data of spectral distribution can be derived [14]. By data processing, we can get the corresponding spectra which are all shown in Fig. 5. Compared with the recommended spectra given in the standard ISO 4037-1, there are good agreement between simulated and given spectra. Fig. 5Open in figure viewerPowerPoint X-ray spectra simulated by EGSnrc From the spectral distribution data, the spectral resolution, RE, of the X radiation quality can be derived, which is defined by the relation (3) where ▵E is the spectrum width that is corresponding to the maximum ordinate. The results of the spectral resolution of the narrow-spectrum series are listed in Table 4, from which we can find the resolutions are all better than the values given in the standard ISO 4037-1, except the radiation quality N250, whose deviation is also within ±15% that comply with the given value. Table 4. Results of the spectral resolution Radiation quality Spectral resolution, % Deviation ISO4037-1 Simulation N60 36 33.90 −2.10 N80 32 17.04 −14.96 N100 28 25.24 −2.76 N120 27 24.78 −2.22 N150 37 34.48 −2.52 N200 30 27.52 −2.48 N250 28 31.31 3.31 N300 27 25.52 −1.48 The mean energy is the ratio defined by the following formula: (4) where is the derivative of the fluence Φ(E), which is a function of energy E, defined by the formula: (5) From the data of spectral distribution and the formula (3) and formula (4), the mean energy of these radiation qualities can be derived, which is shown in Table 5, where we can find that there is a good agreement between the values simulated by EGSnrc with the values given by the standard ISO 4037-1. Table 5. Results of the mean energy Radiation quality Mean energy, keV Deviation ISO4037-1 Simulation N60 48 47.6 −0.4 N80 65 64.7 −0.3 N100 83 82.9 −0.1 N120 100 99.8 −0.2 N150 118 117.8 −0.2 N200 164 164.2 0.2 N250 208 207.5 −0.5 N300 250 248.4 −1.6 5 Calculation of effective energy The definition of effective energy given in ISO4037-1 is the monoenergetic X-rays which have the same HVL. Effective energy is one of the important parameters to characterise the X-ray reference radiation. The X-ray mass attenuation coefficients given by National Institute of Standards and Technology lists the values of the mass attenuation coefficient, μ /ρ, and the mass energy-absorption coefficient, μ en /ρ, as a function of photon energy, for 92 elements [15]. As shown in Fig. 6, we can get the relation curve between mass attenuation coefficient and effective energy by fitting the given datum. Fig. 6Open in figure viewerPowerPoint Mass attenuation coefficient curve For a narrow-beam single-energy X-ray, the intensity of the X-ray satisfies the exponential decay law as shown in formula (6) when passing through an attenuator with thickness d and a density ρ(6) When the thickness of the attenuator is the HVL of the radiation quality, the formula (6) can be transformed into formula (7) (7) The density of elemental copper is 8.96 g/cm3. According to the density and HVL, including experimental HVL and recommended HVL given in ISO4037-1 into the formula (7), we can derive the corresponding mass attenuation coefficient. By interpolation calculation, we can obtain the corresponding effective energy, the results of which is shown in Table 6. Table 6. Results of the effective energy Radiation quality Effective energy, keV Deviation ISO4037-1 Simulation N60 46.72 46.13 −0.58 N80 63.25 64.31 1.06 N100 81.09 83.90 2.81 N120 100.65 101.57 0.92 N150 121.99 118.94 −3.05 N200 165.54 168.29 2.75 N250 197.79 201.55 3.76 N300 229.13 233.75 4.62 6 Conclusion From this paper, the reference qualities of narrow-spectrum series given by ISO 4037-1 were established with the energy from 60 to 300 kV. The results of the measurements are all comply with the values given by the standard ISO 4037-1. The other reference qualities that cover the energy from 10 to 40 kV will be established as soon as possible. Then the absolute measurement methods of air kerma for reference qualities of narrow-spectrum series will be researched. It lays the foundation for the follow-up comparison of air kerma conducted by APMP. 7 Acknowledgments This work was supported by the National Key R&D Plan of China under grant no. 2017YFF0205100, Research Fund for the Research on key technology of measurement of low dose rate X-rays and γ-rays. 8 References 1Đurđica M.: 'Ionizing radiation protection', 2009 2 International Organization for Standardization: 'X and gamma reference radiation for calibrating dose meters and dose rate meters and for determining their response as a function of photon energy Part1: Radiation characteristics and production methods', ISO4037-1:1996, 1996 3Burns D.T.: 'Key comparison: degrees of equivalence for the key comparison BIPM.RI(I)-K2 between national primary standards for low-energy x-rays', Metrologia, 2003, 40, (1A), p. 06036 4Burns D.T., Zhongqing T., Yazhu L. et al.: 'Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the NIM and the BIPM in medium-energy x-rays', Radiographic Image Analysis, 2007, 44, (1A), p. 06008 5Büermann L., O'Brien M., Butler D. et al.: 'Supplementary comparison: comparison of national air Kerma standards for ISO 4037 narrow spectrum series in the range 30kV to 300 kV', Metrologia, 2008, 45, (1A), p. 06013 6Lee J.H., Hwang W.S., Kotler L.H. et al.: 'Key comparison: APMP/TCRI key comparison report of measurement of air kerma for medium-energy x-rays (APMP.RI(I)-K3)', Metrologia, 2008, 45, (1A), p. 06012 7Trout E.D., Kelley J.P., Lucas A.C.: 'Determination of half-value layer', Am. 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NRC Report Pirs, 2011 14Ma C.M, Rogers D.W.O.: ' BEAMDP users manual', NRC Report Pirs, 2009 15Hubbell J.H.: ' Table of X-ray mass attenuation coefficients and mass energy absorption coefficients from 1 keV to 20 MeV for elements Z = 1 to 92 and 48 additional substances of dosimetric interest' ( U.S. Department of Commerce, Gaithersburg, MD, USA, 1996). Available at https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir5632.pdf, accessed November 2019 16Burns D.T., Kessler C., Jinjie W. et al.: 'Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the NIM and the BIPM in medium-energy x-rays', Metrologia, 2017, 44, (1), p. 06008 Citing Literature Volume2019, Issue23December 2019Pages 8858-8861 FiguresReferencesRelatedInformation
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