S. Nishihara

Status of the cyric neutron TOF facilities upgrade

Abstract We describe progress in the Tohoku neutron time-of-flight (TOF) facilities improved to facilitate high resolution measurements for neutrons in the range 10 ≤ E n ≲ 60 MeV. Efforts have been concentrated on completing the neutron detection system consisting of twelve neutron detectors, in which 23 1 of NE213 liquid scintillator are encapsulated, and a CAMAC-based data acquisition system. A systematic study of the neutron detection efficiency has been performed by Monte Carlo calculation for monochromatic neutrons with E n ≲ 34 MeV. Results have been tested by counting neutrons from the 7 Li(p, n) 7 Be reaction and comparing the yield with the absolute neutron fluence determined by activation.

Isovector deformation parameters from the (p, n) reactions on 54, 56Fe and 58, 60, 62, 64Ni at 35 MeV

Abstract The (p, n) reactions on 54, 56 Fe and 58, 60, 62, 64 Ni have been studied at E p = 35 MeV. Angular distributions of emitted neutrons leading to ground-state analogs and 2 + excited-state analogs were obtained for each target. Differential cross sections have been found to be consistent with the predictions obtained from DWBA calculations in which the Lane potential was employed. It was found that the direct process dominates at E p = 35 MeV for the excitation of 2 + analogs. Their isoveetor deformation parameters are extracted from these isotope sets by comparison with the DWBA calculations. The magnitudes of the isoveetor deformation parameters are larger than the isoscalar parameters by a factor of 3 to 5, and are consistent with the calculated results in terms of the core polarization.

The (p, n) reaction on cadmium isotopes leading to the ground- and excited-state analogs

Abstract The (p, n) reactions to ground- and excited-state analogs on 110,114,116 Cd have been studied at a bombarding energy of 25 MeV. Angular distributions of emitted neutrons leading to ground-state analogs, and 2 + , 3 − and 4 + excited-state analogs were obtained for each target. Angular distributions of differential cross sections to the ground-state analog agree with the predictions obtained from macroscopic DWBA calculations in which a Lane potential is employed. Coupled-channel calculations indicate the importance of two-step processes in the (p, n) transition to an excited-state analog. Further, the calculation using a larger value for the deformation parameter of the isovector part than of the isoscalar one fairly well describes the 2 + excited-state analog.

Direct extraction of the isovector deformation parameter β(1)2 from the (p, n) reaction of 56Fe

Abstract The reaction 56Fe(p, n)56Co leading to the analog of the ground state and the first excited 2+ state of 56Fe has been studied at Ep=20, 28, 32 and35MeV. The direct process dominates at higher energies, thus the direct extraction of the isovector deformation parameter β(1)2 is feasible. It is found that β(1)2 is about three times larger than β(0)2, the isoscalar deformation parameter.

Excitation of the 6.41 MeV, T=14− state in 16F by the 16O(p, n)16F reaction

Abstract The angular distribution for the 16 O(p, n) 16 F (6.41 MeV) reaction at 35 MeV has been measured and analyzed using a distored-wave approximation. With analyses of 99 and 135 MeV data fixing the characteristics of the nuclear structure and direct reaction models required, analysis of the 35 MeV data reveals evidence of higher-order reaction processes, which we suggest involve virtual excitation of giant multipole resonances.

Excitation of ΔL = 1 resonances in the (p,n) reaction on 90Zr, 120Sn, 140Ce and 208Pb at Ep = 41 MeV

Abstract A broad peak was systematically observed at about 10 MeV above the Gamow-Teller resonance in the 90 Zr, 120 Sn, 140 Ce, 208 Pb (p,n) reactions at E p = 41 MeV. The angular distribution shapes of these peaks support the interpretation that they they correspond to ΔL = 1 state. The data are compared with TDA-DWBA calculations.

Observation of isospin mixing for the isobaric analog state in 56Co through the 56Fe(p, n)56Co reaction

Abstract The reaction 56 Fe(p, n) 56 Co has been studied at E p = 17 MeV by employing the time-of-flight technique. Two prominent peaks observed at E x = 3.51 and 3.59 MeV are assigned to be J π = 0 + states from the angular distribution measurement, and interpreted as the splitting of the isobaric analog state into the nearby T , 0 + state through the isospin-mixing Coulomb interaction. A shell-model calculation has been carried out to find such a 0 + state, which may yield a Coulomb matrix element 〈J = 0 2 + (T = 1)¦V coul ¦J = 0 3 + (T = 2, IAS )〉 of the order of 10 keV.

Excitation of giant Gamow-Teller resonances in the reaction 140Ce(p, n)140Pr

Abstract Two broad peaks were observed at E x = 6.5 and 12.1 MeV in the (p, n) reaction on 140 Ce at E p = 38 MeV. They are interpreted as the T = T 0 − 1 Gamow-Teller resonances (GTR). A self-consistent TDA model with a Skyrme type interaction predicts such a splitting of the T = T 0 − 1 GTR, and reproduces the relative energies and strengths of the components. Experimental results are also compared with a recent RPA calculation which includes Δ -hole excitations.