Status of standard data on shielding calculation in standard committee of the Atomic Energy Society of Japan

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1 DOI:.5669/pnst Progress in Nuclear Science and Technology Volue 4 (204) pp REVIEW Status of standard data on shielding calculation in standard coittee of the Atoic Energy Society of Japan Yukio Sakaoto a*, Hideo Hirayaa b and the ebers of the Subcoittee a ATOX Co., Ltd.,20 Takata, Kashiwa-shi, Chiba, , Japan; b High Energy Accelerator Research Organization, - Oho, Tsukuba, Ibaraki , Japan The two standard data on shielding calculation was published or has been prepared by the Standard Coittee of the Atoic Energy Society of Japan. One provides dose conversion coefficients fro fluence rate to effective dose rate of photons and neutrons for use in radiation shielding calculations. The other provides gaa-ray buildup factors for use in gaa-ray shielding calculations. Keywords: standard data; dose conversion coefficients; effective dose; gaa-ray buildup factors; Invariant Ebedding ethod; Geoetrical-Progression fitting forula. Introduction In radiation shielding calculations, fluence-to-dose conversion coefficients are necessary to estiate dose rate. This standard gives effective dose conversion coefficients based largely on the ICRP recoendations in 990. However, original values based on research conducted in Japan have been retained priarily with respect to the extension of energy range and ultigroup-wise data. The gaa-ray buildup factor is defined by the ratio of gaa-ray dose included scattered gaa-ray contribution to dose of unscattered gaa-ray which has no experience of collision fro source point to evaluation point. 20 years have passed since publication of standard data by the standard coittee of Aerica Nuclear Society at 99, the extension of data is needed for the evaluation of effective dose and abient dose equivalent in the shielding calculations, and the codes were also advanced for the evaluation of buildup factors. In the new report, buildup factors obtained by the Invariant Ebedding (IE) ethod and its Geoetrical-Progression (GP) fitting forula paraeters appeared for 28 aterials. 2. Standard coittee in Atoic Energy Society of Japan The Radiation Shielding Subcoittee is under Advanced and Fundaental Systes Technical Coittee of the Standard Coittee in Atoic Energy Society of Japan. Its issions is standardization of ethods and data used in shielding calculations, for *Corresponding author. Eail: yukio_sakaoto@atox.co.jp exaples, dose conversion coefficients data, gaa-ray buildup factors and typical coposition of shielding aterials. The two standard data on shielding calculation was published or has been prepared. One is Radiation dose conversion coefficients for radiation shielding calculations: 20 []. The other is Gaa-ray buildup factors: 20X. 3. Dose conversion coefficient standard 3.. Status of dose conversion coefficient data The International Coission of Radiation Protection published three reports on the dose conversion coefficients for external radiation in recent 30 years. Publication 5 [2] provided the data of abient dose equivalent at depth of ICRU phanto. Publication 74 [3] provided the data of effective dose at various irradiation geoetries of anthropoorphic phantos of MIRD-5 odel. Publication 6 [4] provided the new data of effective dose of VOXEL phanto. The standard coittee of Aerican Nuclear Society also published two reports on dose conversion coefficients. ANSI/ANS-6..(977) [5] and ANSI/ANS-6..(99) [6] provided the energy fitting paraeters for axiu dose equivalent in slab phanto and for effective dose equivalents, respectively. In Japan, the standard data on dose conversion coefficients is needed in the view points of following ites, high-energy data over the energy region shown by ICRP reports, group-wise data and energy fitting paraeters for effective dose. The standard coittee in the Atoic Energy Society of Japan published standard 204 Atoic Energy Society of Japan. All rights reserved.

2 Progress in Nuclear Science and Technology, Volue 4, data of dose conversion coefficients [] Basic data on dose conversion coefficients Table shows the energy range and irradiation geoetries of dose conversion coefficients in various reports. ICRP Publication 74 shows data in 6 geoetries in the energy range of 0.0 MeV and ev 80 MeV, for photons and neutrons, respectively. Japanese doestic laws on radiation protection requires the data of Anterior-Posterior irradiation geoetry (irradiation geoetry fro front side of phanto odel to back side) in the energy range of 0.0 MeV and ev 20 MeV, for photons and neutrons, respectively. In the shielding calculations in the high energy accelerators, data for high energy photons and neutrons are required. Standard data extend the energy region up to GeV for photons and 5 GeV for neutrons, respectively. Standard data include the data at specific energy and corresponding to group averaged, and fitting paraeters of polynoial expressions. Table. Energy range and irradiation geoetries of dose conversion coefficients in various reports. Photons Neutrons ICRP MeV 6 Geoetries ev 80 MeV 6 Geoetries Doestic Law(Japan) 0.0 MeV ev 20 MeV High Energy EGS4: MeV GeV HETC-3STEP: Data FLUKA: 0.05MeV-0GeV 20MeV GeV FLUKA: ev - 0GeV Scope 3.3. Data for photons 0.0 GeV ev 5 GeV Figure shows the data for AP irradiation of high-energy photons. In the high-energy region, the transportation of produced charge particles affects dose conversion coefficients. ICRP Publication 74 adopted Kera approxiation where the produced electrons deposit the energy within near region of produced position. The adoption of Kera approxiation for high energy photos reveals the overestiation of dose conversion coefficients because electrons have large range. E/ (psv c 2 ) Phot on AP irradiation E this work,with electron transport E this work,kera approx. E ICRP Photon energy (MeV) Figure. Effective dose at AP irradiation of high-energy photons. Effective dose, E/ (psv c 2 ) Figure 2. Effective dose at various irradiation geoetries of high-energy photons. Figure 2 shows the data of effective dose at various irradiation geoetries for high-energy photons. Above few MeV, data for AP irradiation geoetry is not axiu value of effective dose. But data for AP irradiation geoetry were adopted in the standard data in the view point of the consistency to the low energy region where doestic law adopted the data for AP irradiation geoetry Data for neutrons Figure 3 shows radiation weighting factor shown by ICRP Publication 60 and the average quality factors obtained by the calculations of effective dose equivalents for high-energy neutrons. The value of 5 for radiation weighting factor of high-energy neutrons is conservative copared to average quality factors of three irradiation geoetries for high-energy neutrons. avarage Q or wr Photon energy (MeV) Neutron AP PA RLAT LLAT ROT ISO w R,ICRP60 Q AP Q PA Q ISO Neutron Energy (MeV) Figure 3. Radiation weighting factor and average of quality factors for high-energy neutrons. Figure 4 shows the data of effective dose at various irradiation geoetries for high-energy neutrons. The data for AP irradiation geoetry were also adopted in the standard data by the sae reason in the case of photons. The degree of underestiation was studied by

3 540 Y. Sakaoto et al. using the concrete transitted neutron spectra produced in iron targets by the irradiation of 0.6, and.5 GeV protons and eitted to 90 degree direction. The difference of total effective dose between dose conversion coefficient at AP irradiation geoetry and the axiu dose conversion coefficient is below about 20 % [7]. Effective dose, E/ (psv c 2 ) Figure 4. Effective dose at AP irradiation of high-energy neutrons Fitting forula expressed by polynoial function For effective dose conversion coefficient at desired energy point, the following fitting forula expressed by polynoial function is shown in standard report for photons and neutron, respectively. 4 E photon exp M (ln E ) 0 5 E neutron exp M n (ln En) ICRP Pub.74 AP PA RLAT LLAT ROT ISO Neutron energy (MeV) () (2) Fitting errors for photons are below 3 %, and those for neutrons are below 6 % except 0 MeV data Group averaged data for typical shielding group constants Table 2. Group averaged effective dose and abient dose equivalent for energy group structure. Energy Group Effective dose Abient Dose Structure (n/g) Equivalent DLC23/CASK (22n/8g) BUGL-96 (47n/20g) JSD-J2 (0n/20g) VITAMIN-B6 (99n/42g) High Energy - (78n/22g Extended HILO86 Up to 3GeV) Group average effective dose and abient dose equivalent for 5 energy group structures, DLC23/CASK (22 neutron and 8 gaa-ray groups), BUGL-96 (47n, 20g), JSD-J2 (0n, 20g), VITAMIN-B6 (99n, 42g) and high energy group constant (78n, 22g), were prepared as standard data shown in Table Gaa-ray buildup factor standard 4.. Status of gaa-ray buildup factors The gaa-ray buildup factors of ANSI/ANS (99) [8] are widely used in the shielding calculation for RI gaa-ray sources. This standard includes the Japanese contributions, which are buildup factors for high-atoic-nuber aterials evaluated by PALLAS code with consideration of Bresstrahlung and fluorescence, data checking for low-atoic-nuber aterials and GP fitting paraeters. Over 20 yeas passed after publication of ANSI/ANS-6.4.3, we have the otivation of revision of gaa-ray buildup factors in the following reasons, ) data produced by sae evaluation code and sae cross section data, 2) data corresponding to deep penetration up to 0 fp of shielding thickness, 3) introduction of ore accurate Bresstrahlung atrix, 4) data of effective dose for AP and ISO irradiation geoetries and abient dose equivalent, and 5) revision of GP forula Coparison of buildup factor standard between ANS and AESJ The data in AESJ standard were prepared by the IE ethod coupled with Bresstrahlung atrix calculated by EGS4 code. ANS data were prepared for low-z aterials by the oents ethod and for high-z aterials by PALLAS code. Table 3 shows the coparison of gaa-ray buildup factors between ANS and AESJ standard. The data of effective dose for AP and PA irradiation geoetries, and abient dose equivalent were added to those for exposure and absorbed dose in AESJ standard. The data for rubidiu (atoic nuber Z: 37) and bisuth (Z: 83) were added to those of 23 eleents fro berylliu to uraniu, and water, concrete and air. Energy range of gaa-ray is fro 0.05 to 5 MeV, sae as ANS standard. The thickness of shielding aterial is extended to 0 fp. The treatent of scattering and fluorescence in photon transport is sae as that in ANS standard. The contribution of Bresstrahlung is considered in all aterials, and the production atrix of Bresstarlung is prepared with gaa shower code EGS4. In ANS standard, the contribution of Bresstrahlung was liited to high-z aterials fro olybdenu to uraniu, and the production of Bresstrahlung is approxiated by forward direction eission. Photon cross section and energy absorption coefficients in IE ethod were based on PHOTX. Gaa-ray buildup factor data obtained by IE ethod were evaluated by the coparison with

4 Progress in Nuclear Science and Technology, Volue 4, oents ethod data in ANS standard and EGS4 results, and checked by sensitivity analyses to spatial esh, angular esh and nuber of energy group. Table 3. Coparison of gaa-ray buildup factors between ANS and AESJ standard. Ite ANSI/ANS-6.4.3(99) AESJ-SC -A00X:20X Dose Exposure, Absorbed Dose Added E(AP), E(ISO), H*() Material Be-U (23 eleents), water, Added Rb and Bi concrete, air Energy MeV sae Thickness fp (6 points) fp (29 points) Scattering Copton Scattering by Free Electron Fluorescence With consideration BresstarlungOnly high-z Materials (forward eission) X-sec NBS29 / PHOTX Energy NISTIR 5632 Absorption Sae Sae All Materials (EGS4 Results) PHOTX Sae Code Moents / PALLAS IE Method Fitting Forula GP Methods and Taylor s Revised Forula Method 4.3. Fitting function to gaa-ray buildup factors In the shielding calculation of gaa-ray source by point kernel code, the buildup factors at desired shielding thickness were required. For such purposes, fitting function of Geoetrical-Progression (GP) forula is prepared in AESJ standard. The gaa-ray buildup factors at X fp of shielding thickness is obtained by Eq. (3) and (4) for K and K=, respectively, where paraeters b and K are corresponding to a buildup factor at fp and a ultiplication factor of dose through fp photon penetration, respectively. Paraeter K is obtained by Eq. (5) for X below X using paraeters c, a, d and X k. For X above X, K is obtained by Eqs. (6) and (7), where K and K - are paraeters K at X and X -, respectively. In forer forula, was fixed to 0.. X K B( X ) ( b ) K B ( X ) ( b ) X K( X ) cx a tanh( X / X 2) tanh( 2) k d tanh( 2) GP for K ( 3 ) for K= (4) for 0 X X and X =40 fp (5) where K K( X ) ( K ) K for X>X and X <0 fp (6) ( X / X ) ( X ) (7) 0. ( X / X ) The detail of GP fittings to JAES standard is written in Haria s paper of this proceedings. 5. Conclusion ( X ) Dose conversion coefficients standard gives data to obtain effective dose for photons having energies up to GeV, where secondary electron transport is taken into consideration in the energy range above 5 MeV. Also the dose conversion coefficients standard to obtain effective dose for neutrons having energies up to 5 GeV are given in preparation for construction planning of iddle and high energy proton accelerators in the near future. In the new report of gaa-ray buildup factors, data obtained by the IE ethod and its GP fitting forula paraeters appeared for 28 aterials, with the energy range fro 0.05 MeV to 5 MeV, up to 0 fp, 5 dose quantities of exposure, effective dose with AP and ISO irradiation geoetries, absorbed dose and abient dose equivalents. In the future plan, standard data of dose conversion coefficient will adopt ICRP Pub.6 data. After public coents, gaa-ray buildup factor standard will be published, and introduced into point kernel code. English version will be published near future. There is another plan to ake up the standard of aterial copositions for shielding calculations and activation analyses. References [] Standard Coittee of Atoic Energy Society of Japan, Radiation dose conversion coefficients for radiation shielding calculations: 20, AESJ-SC-R [in Japanese] [2] International Coission on Radiological Protection, Data for Use in Protection against External Radiation: ICRP Publication 5, Annals of the ICRP, 7(2-3) (Pergaon Press) (987). [3] International Coission on Radiological Protection, Conversion Coefficients for Use in Radiological Protection Against External Radiation: ICRP Publication 74, Annals of the ICRP, 26(3/4) (Oxford: Elsevier Science) (996). [4] International Coission on Radiological Protection, Conversion Coefficients for Radiological Protection Quantities for External

5 542 Y. Sakaoto et al. Radiation Exposures: ICRP Publication 6, Annals of the ICRP, 40(2/5) (Oxford: Elsevier Science) (202). [5] Aerican National Standard, Neutron and Gaa-Ray Flux-to-Dose Rate Factors, ANSI/ANS (977). [6] Aerican National Standard, Neutron and Gaa-Ray Flux-to-Dose Rate Factors, ANSI/ANS (99). [7] Y. Sakaoto and Y. Yaaguchi, Dose Conversion Coefficients in the Shielding Design Calculation for High Energy Proton Accelerator Facilities, JAERI-Tech , Japan Atoic Energy Research Institute,(200). [8] Aerican National Standard, Gaa-Ray Attenuation Coefficients and Buildup Factors for Engineering Materials, ANSI/ANS (99).