Search

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 (PbWO 4 ). 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.

Properties of the S11(1535) resonance in nuclear medium were investigated through the 12C(γ,η) reaction for photon energies between 0.68 and 1.0 GeV. A broad resonance due to the the S11 excitation in the carbon nucleus was clearly observed for the first time. The data were compared with calculations of the quantum molecular dynamics, and the observed shape being different from the elementary one is essentially explained by the medium effects such as the Fermi motion, the Pauli blocking and effects of N–η and N–N ∗ collisions.

Data of the ηπ− system were obtained in the reaction π−p → ηπ−p at 6.3 GeV/c beam momentum. About 17 k events of ηπ− were collected in the mass range 0.8 ⩽ Mηπ- ⩽ 1.8 GeV/c2 and in the range of the momentum transfer squared 0.075 ⩽ |t′| ⩽ 0.60 (GeV/c)2. A large forward-backward asymmetry was observed around 1.3 GeV/c2 in the Gottfried-Jackson frame of the ηπ− system. A partial wave analysis of the data was performed. A peak of the D+ wave attributed to a2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/c2 in the P+ wave.

Experimental studies on the ωπ 0 and νπ − systems in the π − p reactions have been performed at KEK. The moment analysis of the ωπ 0 system shows a clear peak of b 1 0 (1235) in the IJ pc = 11 +− wave. In the 11 −− wave, no clear peak is seen. The properties of C(1480) with 11 −− and ϱ(1450) are discussed taking into account upper limits of their cross sections. The experiment on the νπ − system was planned to search for an exotic resonance with IJ pc = 11 −+ . The data taking run was finished and an analysis is under way.

The isotope dependence of the imaginary potentials for the Ca nuclide has been derived by taking account of the coupling of the elastic channel with the pick-up channel. Only pick-up of the valence neutrons in 1 f 7 2 shell is considered. The calculated potential describes quite well the experimental behavior of the angular distributions and the absorption cross sections of Ca isotopes.

The effect of 15 N excitation process is studied in the reaction 48 Ca( 16 O, 15 N) 49 Sc. The excitation process is included into a generalized non-local optical potential for a scattersing 15 N- 49 Sc and is found to be responsible for a shift of a grazing peak in the exact finite-range DWBA calculation.