Estimation of Synchrotron Radiation Dose Outside The Hutch of SPring-8 Beamline

INTRODUCTION Synchrotron radiation facilities are to get high brilliance and high power density of synchrotron radiation. Especially, the third generation synchrotron radiation facilities such as the European Synchrotron Radiation Facility (ESRF)(1), The Advanced Photon Source (APS)(2), and SPring-8(3) can get extremely high brilliance, high power density, and high energy photons. The shields of the beamlines must be designed for the radiation safety under the severe conditions. The PHOTON II(4) code has actually been used to design the shields in synchrotron radiation beamlines. But the PHOTON II code underestimated doses outside the shield wall of the hutch (an enclosure of the beam, optical elements or experimental instruments) in some cases. The PHOTON II code has been validly created for calculations of the attenuation by filters, the isotropic scattering process by the optical elements without coherent scattering, and the shielding with the walls of the hutches ignoring the buildup effect of the synchrotron radiations emitted from a wiggler and bending magnet. The polarization effect is actually dominant in the synchrotron radiation and the code does not well simulate the scattering process. Furthermore, with the considerably high energy X-rays as generated in the third generation synchrotron radiation facilities, the dose outside the shield wall strongly depends on the scattering angle. A new shielding design code STAC8(5) was developed in order to fill up the deficiencies in the PHOTON II code and to be applicable to the calculations of the radiation emitted from the insertion devices including undulators, the effect of linear polarization of photons on the scattering process, and the angular dependence of both the coherent and incoherent scatterings. The buildup factors were also introduced in the shielding calculations. Comparing with Monte Carlo simulations were performed the validity verifications of the STAC8 code. Verification of the validity of the code by using the actual synchrotron radiation sources is more important to relay on the shielding design of beamlines. However, the shield data of the practical beamline to perform the benchmark are quite insufficient. The shielding designs of the SPring-8 beamlines were performed by STAC8 and the construction of the BL14B1 bending beamline(6) was completed. This beamline is very adequate for the benchmark experiments, because the high power of the radiation can be obtained without so called local shielding and the roof of the hutch were designed to shield in severe conditions in order to reduce the weight. Thus the leakage dose measurements outside the shield wall of the roof were planned to be carried out and compared with the calculations. The dose distribution around the scatterer (first mirror) was also measured to compare the calculations.