Search

The proton shell structure in neutron-rich fluorine 23F was investigated using the in-beam γ-ray spectroscopy technique via the proton transfer reaction onto the 22O nucleus. We also measured the α inelastic scattering on 23F, the neutron knockout from 24F, and the two-nucleon knockout from 25Ne using a cocktail secondary beam. The excited states were identified by de-excitation γ-rays coincident with outgoing 23F, and we found the proton single-particle states at 2268 and 4059 keV by comparison of the population strengths among these reactions. These states were respectively assigned to have and by the angular distributions obtained in the transfer reaction, and therefore they were considered to have the configurations of and . The excitation energies of these states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which may indicate that the centroid energy gaps between and are wider than predictions. [Copyright &y& Elsevier]

In the first half of the paper, the nuclear astrophysics activities in Japan, especially in experimental studies are briefly overviewed. A variety of beams have been developed and used for nuclear astrophysics experiments in Japan. The activities include the RI beam facilities at low energies by the in-flight method at the Center for Nuclear Study (CNS), University of Tokyo and by the ISOL-based method at the JAERI tandem facility, and the RI beam facility at intermediate energies at RIKEN. Other activities include a study of the 12C(α,γ)16O reaction exclusively at the tandem accelerator at the Kyushu University, and studies at the neutron facility at Tokyo Institute of Technology and at the photon facility at AIST (Sanso-ken). Research opportunities in the future at RIBF, J-PARC, and SPRING8 are also discussed. A discussion on the research activities at CNS has been specifically extended in the latter half, including various possibilities in collaboration at the RI beam factory at RIKEN. [ABSTRACT FROM AUTHOR]

The proton shell structure in neutron-rich fluorine 23F was investigated using the in-beam γ-ray spectroscopy technique via the proton transfer reaction onto the unstable nucleus 22O, in addition to α inelastic scattering on 23F, and the neutron-knockout reaction from 24F. The level and γ-decay scheme in 23F was deduced from de-excitation γ-ray-particle coincidence events. We found that a single-particle state at 4.061MeV has a large contribution from the d shell by the analysis of population strengths and the angular distribution for the state. We reported here the present experiment and the preliminary results. [ABSTRACT FROM AUTHOR]

We report on the first detailed study of intruder configurations in the ground state of 30 Ne by means of the 12 C( 30 Ne,  29 Ne+ γ )X one-neutron knockout reaction at 228 MeV/nucleon. Using a combined analysis of individual parallel momentum distributions and partial cross sections we find: (a) comparable p - and d -wave removal strength to 29 Ne final states with excitation energies below 200 keV, and (b) significant p -wave removal strength to the 620 keV state of 29 Ne, and (c) no evidence for f -wave intruder strength leading to bound 29 Ne final states. The SDPF-U-MIX shell model calculation in the s d – p f model space provides a better overall agreement with the measured energy levels of 29 Ne and the fp -intruder amplitudes in 30 Ne than the SDPF-M prediction, suggesting that the refinement of the s d – p f cross shell interaction and extension of the model space to include the 2 p 1 / 2 and 1 f 5 / 2 levels are important for understanding the island of inversion. [ABSTRACT FROM AUTHOR]

Isoscalar monopole and dipole responses in unstable nucleus 14O have been studied for a wide excitation energy range by inelastic α scattering at 60 A MeV in inverse kinematics. In order to deduce isoscalar compressional strengths, the multipole decomposition analysis was carried out and the DWBA calculation for isoscalar excitation was studied. Result from the multipole decomposition analysis, isoscalar monopole and dipole strengths were identified corresponding to 63±12% and 109±15% of energy-weighted sum rule in , respectively, for the measured decay channels of , , , , and . [Copyright &y& Elsevier]

Abstract: A low-energy in-flight type RI beam separator, called CRIB, has been installed for nuclear physics and nuclear astrophysics by the Center for Nuclear Study, the University of Tokyo in the RIKEN Accelerator Research Facility. It consists of a double achromatic system and an Wien filter. It is capable of providing RI beams at 5–10MeV/nucleon. Since CRIB has been developed in the end of 2000, many proton-rich RI beams were successfully produced via the (p,n), (d,t), and (,n) reactions in inverse kinematics. In this paper, the design of the separator and its performance are discussed including the method of RI-beam production at low energies. [Copyright &y& Elsevier]

The 1H(27F, 25,26,27F) reactions have been studied at average energy using a liquid hydrogen target. For 25F, 26F and 27F nuclei, we have observed two γ-ray peaks each originating from the decay of two bound excited states. This is the first sign of the existence of bound excited states in 26,27F. The presence of a single bound excited state in 27F is a clear indication of a substantial change in the structure of the fluorine isotopes approaching the neutron dripline. The proposed second excited states in 25,26,27F nuclei have no counterparts in either the or the shell model calculations suggesting the appearance of nuclear structure effects lying out of these model spaces. [Copyright &y& Elsevier]

The neutron and proton excitations in 16C nucleus have been investigated by use of the Coulomb-nuclear interference method applied to the 208Pb+16C inelastic scattering. Angular distribution of the 16C nuclei in the inelastic channel populating the first 2+ state has been measured. The neutron and proton transition matrix elements, Mn and Mp, have been determined from the “Coulomb” and “matter” deformation-length parameters obtained by distorted wave calculations. The Mp or its corresponding B(E2;2+1→0+) value was found to be extremely small: 0.28±0.06 Weisskopf units consistent with a recent lifetime measurement. Furthermore, the extracted Mn/Mp ratio has an unexpectedly large value of 7.6±1.7. These results suggest that the 2+1 state in 16C is a nearly pure valence neutron excitation. [Copyright &y& Elsevier]

The energy of the first excited state in the very neutron-rich nucleus 30Ne was determined via proton inelastic scattering. A liquid hydrogen target was bombarded by a radioactive 30Ne beam, and energies of the de-excitation γ rays emitted from excited 30Ne nuclei were measured. The observed transition is likely to be the one from the first 2+ state to the ground state of 30Ne. The excitation energy, 791 (26) keV, is lower than that of 32Mg, indicating an enhancement of deformation as the neutron excess increases in the N = 20 isotones. [Copyright &y& Elsevier]