S. Shimoura

Large deformation of the very neutron-rich nucleus 32Mg from intermediate-energy Coulomb excitation

Abstract The Coulomb excitation of a very neutron-rich nucleus 32Mg to its 2+ state was studied using an unstable nuclear beam of 32Mg at 49.2 MeV/u with a 208Pb target. The B(E2) value of 454±78 e2fm4 was extracted by a coupled channel analysis. The value is in good agreement with recent predictions. It confirms a large deformation for 32Mg suggested by the low excitation energy of the 2+ state, and points to the vanishing of the N = 20 shell gap.

Coulomb Dissociation of B-8 and the Be-7(p, Gamma)b-8 Reaction At Low Energies

The cross section for Coulomb dissociation of [sup 8]B---the [sup 208]Pb([sup 8]B,[sup 7]Be [ital p])[sup 208]Pb reaction---was measured using a [sup 8]B radioactive beam of 46.5 MeV/nucleon energy, and the cross section for the [sup 7]Be([ital p],[gamma])[sup 8]B capture reaction was deduced at low energies; [ital E][sub c.m.]=0.6[minus]1.7 MeV. The extracted astrophysical [ital S][sub 17] factors were found to be consistent with the values measured by Vaughn [ital et] [ital al]. and Filippone [ital et] [ital al]. This result encourages further experimental studies extended to lower relative energies for a new determination of the [ital S][sub 17] value relevant to the [sup 8]B solar neutrino flux.

Quadrupole deformation of 12Be studied by proton inelastic scattering

Abstract Inelastic proton scattering exciting the 2 + 1 states in the neutron-rich beryllium isotopes 10,12 Be has been studied in inverse kinematics. From a coupled-channel analysis, the deformation lengths for the 2 + 1 states in 10 Be and 12 Be were determined to be 1.80±0.25 fm and 2.00±0.23 fm respectively, indicating that a tendency towards strong quadrupole deformation is preserved for these nuclei and that the singly-closed shell structure does not prevail in 12 Be. A quantitative analysis based on shell model calculations supports this picture.

Coulomb dissociation reaction and correlations of two halo neutrons in 11Li

Abstract We have performed an exclusive measurement for the Coulomb dissociation reaction, Pb( 11 Li, 9 Li+2n) X at an incident energy of 43 A MeV. The deduced excitation energy spectrum of the 11Li nucleus shows a prominent peak at 1 MeV with a large tail towards higher excitation energies. The relative energy spectra for the n-n and 9Li−2n sub-systems show that the excitation is dominated by the relative motion between 9Li and the center-of-mass of the two neutrons. The above characteristics are explained by a direct Coulomb breakup mechanism with an extended ‘di-neutron’ model.

Coulomb excitation of 11Be

Abstract The Coulomb excitation of a halo nucleus 11 Be to its first bound excited state (E1: 1 2 + → 1 2 − ) has been studied using a 64 MeV/u 11 Be radioactive beam incident on a 208 Pb target. The electric dipole strength deduced by a first-order perturbation analysis is in good agreement with the result of previous life-time measurements of the 11 Be 1 2 − state.

Isobaric analog state of 11Li

The isobaric analog state (IAS) of the halo nucleus 11Li has been investigated using the charge exchange reaction 11Li(p,n)11Be∗ in inverse kinematics at E(11Li) = 64A MeV. The IAS was observed in 11Be, for the first time, at an excitation energy of 21.16 ± 0.02 MeV with a width of 0.49 ± 0.07 MeV (FWHM). The unit cross section, distortion factor and effective N-N interaction associated with the Fermi transition are extracted. Coulomb displacement energy, decay width, reaction variables and their relation to the halo structure are discussed.

Radiation damage factor for ion-implanted silicon detectors irradiated with heavy ions

Ion-implanted silicon detectors were irradiated with 18-150 MeV /sup 16/O, 20 MeV /sup 40/Ar, and 53 MeV /sup 110/Xe. A linear increase of the leakage current was observed as a function of the particle fluence up to 2.2/spl times/10/sup 8/ cm/sup -2/. Extracted damage factors are proportional to the averaged nuclear stopping power over five orders of magnitude covering heavy ions studied in the present work and also protons of 25-800 MeV energies. >

Study of the 7Be(p, γ)8B Reaction with the Coulomb Dissociation Method

The Coulomb-dissociation cross section for the process B-8 --> Be-7 + p in the field of Pb-208 was measured at E(B-8) = 46.5 A MeV. The Be-7(p,gamma)B-8 cross section relevant to the high-energy B-8 solar-neutrino production was extracted at E(C.M.) = 0.6 - 1.7 MeV. Two theoretical models on the structure of 8B were used to evaluate possible corrections due to M1 and E2 admixtures to the dominant E1 cross sections. Their overall effect is shown to be small regardless of the choice of the models. The present result is consistent with the results of the direct measurements of Filippone et al. and Vaughn et al. within errors. This result suggests further studies with the Coulomb-dissociation method to extract astrophysical S-17 factor at similar to 20 keV relevant to the high-energy solar-neutrino flux.

Hindered proton collectivity in 16(28)S12: possible magic number at Z=16.

The reduced transition probability B(E2;0(gs)(+)→2(1)(+)) for (28)S was obtained experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2) value 181(31) e(2)fm(4) is smaller than the expectation based on empirical B(E2) systematics. The double ratio |M(n)/M(p)|/(N/Z) of the 0(gs)(+)→2(1)(+) transition in (28)S was determined to be 1.9(2) by evaluating the M(n) value from the known B(E2) value of the mirror nucleus (28)Mg, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z=16 in the |T(z)|=2 nucleus (28)S.

Proton-proton correlations in distinguishing the two-proton emission mechanism of 23Al and 22Mg

The proton-proton momentum correlation functions (