Differences in synchrotron radiation beamline shielding design between the facilities of 3 GeV class and 8 GeV class are discussed with regard to SLAC SSRL and SPring-8 beamlines. Requirements of beamline shielding as well as the accelerator shielding depend on the stored electron energy, and here some factors in beamline shielding depending on the stored energy in particular, are clarified, namely the effect of build up, the effect of double scattering of photons at branch beamlines, and the spread of gas bremsstrahlung

Asano, Yoshihiro

Liu, James C.

Rokni, Sayed

UNT Digital Library

Work supported in part by US Department of Energy contract DE-AC02-76SF00515Shielding design aspects of SR beamlines for 3 and 8GeV classsynchrotron radiation facilitiesYoshihiro Asanoa,∗, James C. Liub, Sayed RoknibaJapan Synchrotron Radiation Research Institute, Sayo-cho, Hyogo-ken 679-5198, JapanbStanford Linear Accelerator Center, 2575 Stand Hill Road, M/S 48 Menlo Park, CA 94025, USAAbstractDifferences in synchrotron radiation beamline shielding design between the facilities of 3GeV class and 8GeV class are discussed withregard to SLAC SSRL and SPring-8 beamlines. Requirements of beamline shielding as well as the accelerator shielding depend on the storedelectron energy, and here some factors in beamline shielding depending on the stored energy in particular, are clariﬁed, namely the effect ofbuild up, the effect of double scattering of photons at branch beamlines, and the spread of gas bremsstrahlung.Keywords: Shielding design; Synchrotron radiation; Beamline; Build up; Gas bremsstrahlung; Double scattering1. IntroductionRecently, many synchrotron radiation facilities with interme-diate levels of stored electron energy such as Canadian LightSource in Canada and DIAMOND in UK are under construc-tion or design. Some facilities such as SPEAR3 in USA havebeen upgraded. These facilities are required to be shielded moreseverely in keeping with growth of radiation power and the ringenergy of about 3GeV. Furthermore, strong shielding of inser-tion devices for the beamline is strictly required. On the otherhand, large synchrotron radiation facilities with high storedelectron energy such as ESRF in France, APS in USA, andSPring-8 in Japan are currently available, with stored electronenergy of 6, 7, and 8GeV, respectively. The shielding designsof these facilities were made independently. However, thereare points in common as well as points of difference betweenthe intermediate and the high stored electron energy facilitieswith regard to radiation shielding of the beamlines, and thisinformation is very useful. Especially, the differences are veryimportant for future designing. In this paper, therefore, we dis-cuss the characteristics of the beamline shielding as they are∗ Corresponding author. Tel.: +81 791 58 2705.E-mail address: asano@spring8.or.jp (Y. Asano).affected by build up, spread of gas bremsstrahlung and doublescattering of photons at branch beamlines, using the SLACSSRL (Liu et al., 2005b) and SPring-8 (Asano, 2001) beamlinesas examples to clarify the differences between the above twocategories of the synchrotron radiation facilities.2. Shielding calculation for synchrotron radiation2.1. Typical beamlines of SPring-8 and SSRLThe typical beamlines of SPring-8 and SSRL are listed inTable 1 together with key parameters of the light sources andthe hutch shield wall. For SPring-8, one bending beamlineBL02B1, one wiggler beamline, BL08W, and two undula-tor beamlines, BL45XU and BL47XU, are given. For SLACSSRL, we took one bending beamline and one wiggler beam-line, BL11, and summarized the key parameters. The criticalenergy for a SPring-8 bending magnet with the stored electronenergy of 8GeV is 29 keV, and 7.7 keV for a SLAC SSRLbending magnet with 3GeV stored energy. The “distance” inthe table refers to the distance from the synchrotron beam axisto the hutch side wall. Making the thicknesses of the side wall(T0) sufﬁcient to prevent leakage due to scattered photons is apractical consideration for the shielding design of each opticshutch. The thicknesses given for SLAC SSRL beamlinesSLAC-PUB-12824Submitted to Radiat.Meas.Table 1Key parameters for build up calculation of the light sources of SPring-8 and SSRLBeamline Light source Period Period Magnetic Critical Distance Side wall thicknesslength ﬁeld energy (cm) (optics hutch, T0),(cm) (Tesla) (keV) (cm)SPring-8 Bending (0.5) 3930 0.69 29.0 60 Pb 1.3BL02B1 (bending Fe 1.0radius)SPring-8 Wiggler 37 12 1.0 42.66 235 Pb 3.0BL08W Fe 1.0SPring-8 Undulator 74 3.7 0.5 (21.33) 103 Pb 1.0BL45XU (tandem) Fe 1.0SPring-8 Undulator 140 3.2 0.78 (33.27) 170 Pb 2.0BL47XU (in vacuum) Fe 1.0SSRL Bending (0.5) 785 1.2772 7.70 100 Pb 0.3SLM (bendingradius)SSRL Wiggler 13 17.5 2.02 12.2 100 Pb 0.7Target of the scatterer-SPring-8: Cu 1 cm disk; SLAC-SSRL: Si 2 cm thick disk, inclined 2◦.0 50 10010810101012Photon energy (keV)Total flux (photons/s/eV/mA)Undulator(In–vacuum)Wiggler(BL08W)UndulatorBendingWiggler(SSRL,BL11)Bending magnet(SSRL,SLM) magnet(BL45XU)Fig. 1. Angle integrated photon ﬂux for SPring-8 and SSRL typical beamlines.are tentative thicknesses for the upgraded SPEAR3 ring. Theangle integrated photon spectra calculated by STAC8 (Asanoand Sasamoto, 1994) are shown in Fig. 1 for each beamline,and it is clear that the SPring-8 beamlines have high intensitiesof high energy components in comparison with those of SSRLbeamlines.2.2. Shielding design code STAC8A shielding design code, STAC8, was developed for syn-chrotron radiation beamlines at SPring-8. This code calculatesthe synchrotron radiation spectrum including angle integratedradiation from an undulator source, angular dependent coher-ent and incoherent scattering taking into consideration polar-10000.010.020.03Scattering angle (degrees)Dose equivalent H∗( microSv/h/mA)BL47XUBL02B1BL08WBL45XUFig. 2. Leakage dose distribution outside the hutches with and without con-sideration of build up effect. Solid and dashed lines are the dose distributionswith and without consideration of the build up effect, respectively. The calcu-lation conditions are those indicated in Table 1 for each beamline of SPring-8.ization effect and self-shielding of the scatterer, and the amountof leakage outside the hutch considering buildup effect, usingthe G-P method (Harima et al., 1984), with consistent accu-racy. Now this code has been upgraded in the new STAC8V2.1,so that it can calculate both the double scattering process ofcoherent and incoherent, and the specular reﬂection process.To verify the STAC8 calculations, several comparisons withresults of experiments using beamlines of practical use wereperformed, and the calculations showed good agreement withthese results. In addition, Monte Carlo simulations were per-formed and compared with the calculation of STAC8, showingreasonable agreement (Liu et al., 2005a; Asano and Liu, 2002).In case of a thick shield to reduce the leakage dose outside thehutch to the allowable level, the STAC8 calculations consider-ing the build up effect also show fairly good agreement withthe Monte Carlo simulations (Prinz et al., 2003).0 2100101102103Wall thickness (T/T0)Ratio of maximum leakage dose ratewith and without considering build up effect: SPring–8 BL02B1:SSRL BL11:SSRL SLM:SPring–8 BL08W:SPring–8 BL45XU:SPring–8 BL47XU1 3Fig. 3. Dependence of build up effect on the shield thickness of hutch sidewall. T0 means the thickness of the actual facility as indicated in Table 1. Solidcircles, open circles, double circles and open squares are for SPring-8 BL02B1,BL08W, Bl45Xu, and Bl47XU beamlines, respectively. Solid diamonds anddouble diamonds are for SSRL SLM and BL-11 beamlines, respectively.SR BEAMHUTCHTARGET VECTORSTORAGERINGIDSCATTERE RTARGET VECTOR2SCATTERER2HUTCH2ESTIMATION POINTHOLE(OPENINGANGLE)SCATTERED SR BEAMRing; 3GeV, 500mAID: Wiggler, Magnetic field:1.8T    Period:13, Critical energy;10.77keV     Period length;7.85 cmFig. 4. Illustration of the SSRL BL-11 beamline with a branch beamline created using a mirror.2.3. The need for consideration of build up effectFor hutch shielding design, one of the most important factorsis the scattered synchrotron radiation. In case of the calcula-tion of leakage dose due to scattered synchrotron radiation, theleakage dose outside the optics hutch is normally estimatedconsidering the polarization effect, build up effect, and self-shielding effect of the scatterer. These effects depend stronglyon photon energy, however, the build-up effect has the poten-tial to cause misleading indications of serious conditions. Forthe SPring-8 beamline, leakage dose distributions outside thehutches are shown in Fig. 2 with and without consideration ofbuild up effects. In comparing the SSRL with SPring-8 beam-lines, the effect of the build up on the SSRL BL-11 beamlineis obviously higher than that on SPring-8. In order to ﬁnd themechanism of the differences, the dependence of the build upeffect on the wall thickness was investigated and the results areshown in Fig. 3 as the respective ratio of maximum leakagedose with and without consideration of build up effect. In thisﬁgure, the horizontal axis shows the shield thickness of thehutch wall relative to T0 indicated in Table 1, and on this axisare the shield thickness of the actual facility of each beamline.The vertical axis shows the ratio of the maximum leakage doseconsidering the build up effect and the maximum leakage dosenot considering the build up effect, calculated by using STAC8.It is clear that there are some build up effect in the SPring-8beamline, but the effect is less than twice the dose calculatedwithout considering the build up effect. However, the build upeffect is obviously important in the SSRL beamline cases. Thismeans that serious consequences may occur if the shielding0 1001081010Energy (keV)Photon spectrum (photon.eV–1 .s–1 .mrad.–1 .mA–1 ) SourceFiltered spectrum (C:1.6mm)Fig. 5. Synchrotron radiation light source spectrum and spectrum ﬁlteredthrough graphite of 1.6mm in thickness.100 101 1021001010Energy (keV)Photon spectrum (photon.eV–1 .s–1 .mrad.–1 .mA–1 )ReflectionAu coated Si 0.5degSi 1.0deg.Si 12.1deg.ScatteringSi 12.1 deg.Si 1.0degAu +Si 0.5deg.Fig. 6. Spectrum of specular reﬂected and scattered photons by the ﬁrstscatterer in Fig. 7. Solid lines indicate the spectra from a silicon mirror withthe glancing angle of 12.1◦. Dashed lines are for the silicon mirror withthe glancing angle of 1.0◦, and dotted lines are for a gold coated siliconmirror with glancing angle of 0.5◦. The aperture size which is deﬁned bythe beam transport pipe is 4.9mrad. The lines with and without diamondsare the spectra of specular reﬂected and scattered photons, respectively.designs of 3GeV class beamlines are performed without con-sidering the build up effect.0 50 100 15010–1010–5100Scattering angle (degrees)Leakage dose rate outside the hutch2 wall (uSv/h)Pb(double scattering)Pb(reflection)Hutch 2       Lead 1mm ShieldSi 12.1degSi 1deg.Au coated Si 0.5degSi 12.1degSi 1deg.Au coated Si 0.5deg.Fig. 7. Leakage dose outside the hutch 2 due to double scattering and dueto specular reﬂected photons. The lines with and without diamonds indicatethe leakage doses due to the specular reﬂected and double scattered photons.2.4. Double scattering photonsUsing a mirror, some beamlines are split to produce a branchbeamline in order to perform synchrotron radiation experi-ments simultaneously or alternately. Fig. 4 is an illustration ofthe SSRL Bl-11 beamline with one branch beamline producedusing a mirror. The spectrum of a synchrotron radiation beamﬁltered through graphite 1.6mm in thickness is shown in Fig. 5.This beam hits the inclined ﬁrst scatterer corresponding to theﬁrst mirror, and then specular reﬂected photons and scatteredphotons are collimated onto the second scatterer by the trans-port pipe. The leakage dose outside the hutch 2 due to the scat-tered photons of both the specular reﬂected and the scatteredphotons by second scatterer can be calculated accurately fromthe light source considering build up effect and polarization,by using STAC8. The specular reﬂected photons can be calcu-lated based on the glancing angle and mirror material. Fig. 6shows the specular reﬂected and scattered photon spectra usingvarious materials for the mirror. The leakage dose distributionsoutside the hutch 2 due to photons specular reﬂected and scat-tered by each mirror material and the glancing angle are shownin Fig. 7 by using silicon scatterer 2 whose target angle inclines89.9◦ and the shield wall of lead, 1mm in thickness. The leak-age dose due to the double scattering photons is dominant, asshown in this graph. The reason is that the scattered photons aredominant in the high energy regions in comparison with thatof specular reﬂected photons, as shown in Fig. 6. The ratios ofthe maximum leakage dose due to the double scattering pho-tons and maximum leakage due to specular reﬂected photonsare indicated in Table 2 for each mirror material and glancingangle. In the table, the geometries and calculation conﬁgura-Table 2Ratio of the maximum leakage dose due to double scattering photons and that due to specular reﬂected photonsMirror Ratio of maximum leakage dose (double scattering/specular reﬂection)(material, glancing angle)SLAC SSRL SPring-8 SP8/SSRLBL11 bendingSilicon 12.1◦ 3.75E6 4.75E6 1.27Silicon 1.0◦ 8.19E3 1.40E4 1.71Gold coated Silicon 0.5◦ 1.45E1 2.32E1 1.600.0 2.0 4.0 6.0 8.0 10.010–1310–1110–910–710–5Emission angle (mrad)Photon(sr–1 e–1 m–1  at 10–9 Torr)8GeV5GeV3GeV1GeV500MeV100MeVFig. 8. Emission angle distribution of photons for various stored electronenergies with path length of 1m and gas pressure of 0.1 atm, allowing onlya single interaction of the electrons.tions are those of SSRL BL11, and “SPring-8 bending” meansthat the light source assumed the SPring-8 dipole magnet andothers such as conﬁgurations assumed the same as SSRL BL-11 geometries and components. Table 2 shows that double scat-tering photons are the dominant consideration for the design ofbranch beamline shielding in all cases.3. Distribution of gas bremsstrahlungInformation on gas bremsstrahlung intensity and its distri-bution is very important for synchrotron radiation beamlineshielding. However, this intensity distribution has not beengiven much attention. In the case of a compact beamline, thedistribution of gas bremsstrahlung has a critical impact onaspects of shielding design such as using a beam transportpipe. Therefore, dependence of the intensity distribution of gasbremsstrahlung on the stored electron beam conditions andmagnetic ﬁeld strength of insertion devices was investigated(Asano, 2002). As a result, it was clariﬁed that the distribu-tion of gas bremsstrahlung depends strongly on the stored elec-10–1 100 101102104106108Emission angle (mradian)Photons(sr–1mA–1 m–1 10nPa–1 )sigma U (mradi.): 0.0: 0.1: 0.3: 0.5Fig. 9. Emission angle distribution of photons for various 8GeV storedelectron divergence distributions. Sigma U : 1 means the sigma of the Gaussiandistribution of the divergence is one, and solid, dotted, dot-dashed, and dashedlines indicate U of 0.0, 0.1, 0.3, and 0.5, respectively.tron beam divergence, and that the alternating magnetic ﬁeldstrength of the insertion device affects the intensity distribu-tion. In addition to these inﬂuences, the dependence on thestored electron energy was investigated. The emission angledistributions of photons for stored electrons of various energiesare shown in Fig. 8 by using the EGS4 (Nelson et al., 1985)Monte Carlo code. These simulations were performed withoutconsidering the stored electron beam divergence distributionsor any ﬂuctuations of the stored electrons. As shown in theﬁgure, the gas bremsstrahlung due to 3GeV electrons is morewidely distributed than that of 8GeV. Figs. 9 and 10 show theemission angle distributions as a function of the stored electronenergy divergence distributions of 8 and 3GeV stored electrons,respectively. In these cases, the parameter U is the sigma of theGaussian distribution of the electron beam divergence. In theseﬁgures, the emission angle distributions of gas bremsstrahlungof 8GeV electrons are sharper than that of 3GeV. Besides, theemission angle distribution of 8GeV electron beam is more10–1 100 101102104106108Emission angle (mradian)Photons(sr–1mA–1 m–1 10nPa–1 )sigma U (mradi.): 0.0: 0.1: 0.3: 0.53 GeV electronFig. 10. Emission angle distribution of photons for various 3GeV storedelectron divergence distributions. Lines mean the same as in Fig. 8.easily affected by the beam divergence distribution in compar-ison with that of 3GeV case.4. ConclusionsWe investigated the differences between the intermediateand the high stored electron energy facilities with regard to thebeamline shielding, using SLAC SSRL and SPring-8 as exam-ples. As the results: (1) For the synchrotron radiation shielding,the build up effect is very important for an intermediate en-ergy facility such as SSRL. (2) Double scattering photons havemore effect than specular reﬂective photons on requirementsof the branch beamline shielding. (3) For gas bremsstrahlung,the intensity distribution of intermediate facilities is wider, butthe effect of the stored beam conditions is smaller than in an8GeV class facility.ReferencesAsano, Y., Sasamoto, N., 1994. Development of shielding design code ofsynchrotron radiation beamline. Radiat. Phys. Chem. 44.Asano, Y., 2001. A study on radiation shielding and safety analysis fora synchrotron radiation beamline. JAERI-Research 2001–2006. JAERI(2001).Asano, Y., Liu, J.C., 2002. Comparison of synchrotron radiation calculationbetween EGS4, FLUKA, PHOTON and STAC8. Proceedings of the 10thEGS4 Workshop on KEK Proceedings 2002–2018, Tukuba, SLAC-PUB-9507 (2002), pp. 48–54.Asano, Y., 2002. Intensity distributions of gas bremsstrahlung depending onthe stored beam conditions at SPring-8. Second Workshop of RadsynchESRF France (2002).Harima, Y., et al., 1984. Validity of the geometric-progression formula inapproximating gamma ray build up factors. Nucl. Sci. Eng. 94.Liu, J.C., Fasso, A., Prinz, A., Rokni, S., Asano, Y., 2005a. Comparisonof synchrotron radiation calculations between analytic codes (STAC8,PHOTON) and Monte Carlo codes (FLUKA, EGS4). Radiat. Prot. Dosim.116, 658–661.Liu, J.C., Fasso A., Khater H., Prinz A., Rokni S., 2005b. Generic radiationsafety design for SSRL synchrotron radiation beamlines, in this journal(2005).Nelson, W.R., Hirayama, H., Rogers, D.W.O., 1985. The EGS4 code system,SLAC-265 (1985).Prinz, A., et al., 2003. Private communication (2003).

Shielding Design Aspects of SR Beamlines for 3-GeV And 8-GeV Class Synchrotron Radiation Facilities

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Shielding Design Aspects of SR Beamlines for 3-GeV And 8-GeV Class Synchrotron Radiation Facilities

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