Measurement of gas bremsstrahlung at the SPring-8 insertion device beamline using PWO scintillator

Gas bremsstrahlung, generated by the interaction of stored electrons with residual gas molecules in a storage ring vacuum chamber, was measured at the insertion device beamlines of SPring-8 by using a new-type scintillator PWO (PbWO4). The fine energy resolution for the bremsstrahlung photons was obtained, which is about three times as good as that of lead glass. The measurements were made at the two beamlines, BL11XU (high-betatron function beamline) and BL46XU (low-betatron function beamline), in relation to the characteristics of the stored electron beam. The gas bremsstrahlung was measured as a function of the aperture size of the slits, showing the apparent dependence on the conditions of the stored electron beam, as well as the beam current and the vacuum pressure. The measurements of the aperture size dependency were compared with the calculations by using the Monte Carlo code EGS4, to show a fairly good agreement. The total power of the gas bremsstrahlung was estimated as 25.8±0.8 nW/10−8 Pa/mA and the corresponding equivalent dose rates for a scoring radius of 0.023 cm were calculated to be 15.8 nSv/s/10−8 Pa/mA for BL11XU, 9.22 nSv/s/10−8 Pa/mA for BL46XU. Calculations were also made to obtain 25.9 nSV/s/10−8 Pa/mA neglecting the stored beam conditions at 40 m from the center of the straight section of SPring-8.