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Honma, M

Publications and source records attributed to Honma, M.

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

THE KCAL VERA 22 GHz CALIBRATOR SURVEY

We observed a sample of 1536 sources with correlated flux densities brighter than 200 mJy at 8 GHz with the very long baseline interferometry (VLBI) array VLBI Exploration of Radio Astrometry at 22 GHz. One half of the target sources has been detected. The detection limit was around 200 mJy. We derived the correlated flux densities of 877 detected sources in three ranges of projected baseline lengths. The objective of these observations was to determine the suitability of given sources as phase calibrators for dual-beam and phase-referencing observations at high frequencies. Preliminary results indicate that the number of compact extragalactic sources at 22 GHz brighter than a given correlated flux density level is two times less than that at 8 GHz.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Electron Capture Reactions and Beta Decays in Steller Environments

Electron capture reactions on Ni and Co isotopes are investigated by shell model calculations in steller environments. The capture rates depend sensitively on the distribution of the Gamow-Teller (GT) strength. The capture rates obtained by using GXPF1J Hamiltonian for fp-shell are found to be consistent with the rates obtained from experimental GT strength in {sup 58}Ni and {sup 60}Ni. Capture rates in Co isotopes, where there were large discrepancies among previous calculations, are also investigated. Beta decays of the N = 126 isotones are studied by shell model calculations taking into account both the GT and first-forbidden (FF) transitions. The FF transitions are found to be important to reduce the half-lives by twice to several times of those by the GT contributions only. Implications of the short half-lives of the waiting point nuclei on the r-process nucleosynthesis are discussed for various astrophysical conditions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Single-particle and collective structures in {sup 55}Cr and {sup 55}V

Excited states in {sup 55}V and {sup 55}Cr have been populated via pn and 2n evaporation channels, respectively, following the fusion of a {sup 48}Ca beam at 172 MeV with a {sup 9}Be target. Level schemes have been deduced for the two nuclides to excitation energies of 7467 ({sup 55}V) and 12226 keV ({sup 55}Cr), with spins of 27/2{sup +} and 33/2{sup +}, respectively. Negative-parity states are compared with shell-model calculations using three different effective interactions in the full fp model space. Negative-parity levels of {sup 55}Cr are explained in terms of single-particle fp-shell configurations outside N=28 and N=32 cores. Positive-parity states in both isotopes show evidence for the involvement of neutron g{sub 9/2} configurations. In the case of {sup 55}Cr, a quasirotational structure based on the 1/2{sup +}[440] Nilsson orbital is observed up to the terminating state. In {sup 55}V, positive-parity states do not exhibit well-developed collective features, and the observation of octupole decays is an indication of their importance in transitions from neutron g{sub 9/2} configurations to the fp shell. Experimental results are compared with the predictions of a traditional shell model, the projected shell model, and total-Routhian-surface calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Nuclear spins, magnetic moments, and quadrupole moments of Cu isotopes from N=28 to N=46: Probes for core polarization effects

Measurements of the ground-state nuclear spins and magnetic and quadrupole moments of the copper isotopes from {sup 61}Cu up to {sup 75}Cu are reported. The experiments were performed at the CERN online isotope mass separator (ISOLDE) facility, using the technique of collinear laser spectroscopy. The trend in the magnetic moments between the N=28 and N=50 shell closures is reasonably reproduced by large-scale shell-model calculations starting from a {sup 56}Ni core. The quadrupole moments reveal a strong polarization of the underlying Ni core when the neutron shell is opened, which is, however, strongly reduced at N=40 due to the parity change between the pf and g orbits. No enhanced core polarization is seen beyond N=40. Deviations between measured and calculated moments are attributed to the softness of the {sup 56}Ni core and weakening of the Z=28 and N=28 shell gaps.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Experimental determination of an I{sup {pi}=}2{sup -} ground state in {sup 72,74}Cu

This article reports on the ground-state spin and moments measured in {sup 72,74}Cu using collinear laser spectroscopy at the CERN On-Line Isotope Mass Separator (ISOLDE) facility. From the measured hyperfine coefficients, the nuclear observables {mu}({sup 72}Cu)=-1.3472(10){mu}{sub N}, {mu}({sup 74}Cu)=-1.068(3){mu}{sub N}, Q({sup 72}Cu)=+8(2) efm{sup 2}, Q({sup 74}Cu)=+26(3) efm{sup 2}, I({sup 72}Cu)=2, and I({sup 74}Cu)=2 have been determined. Through a comparison of the measured magnetic moments with different models, the negative moment reveals a strong {pi}f{sub 5/2} x {nu}g{sub 9/2} component in the ground-state wave function. Consequently, a negative parity has been assigned to the ground states of {sup 72,74}Cu. Large-scale shell-model calculations illustrate the strong sensitivity of the nuclear moments to configuration mixing and to the effective interaction employed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

DISTANCE AND PROPER MOTION MEASUREMENT OF THE RED SUPERGIANT, S PERSEI, WITH VLBI H{sub 2}O MASER ASTROMETRY

We have conducted Very Long Baseline Array phase-referencing monitoring of H{sub 2}O masers around the red supergiant, S Persei, for six years. We have fitted maser motions to a simple expanding-shell model with a common annual parallax and stellar proper motion, and obtained the annual parallax as 0.413 {+-} 0.017 mas and the stellar proper motion as (-0.49 {+-} 0.23 mas yr{sup -1}, -1.19 {+-} 0.20 mas yr{sup -1}) in right ascension and declination, respectively. The obtained annual parallax corresponds to the trigonometric distance of 2.42{sup +0.11}{sub -0.09} kpc. Assuming a Galactocentric distance of the Sun of 8.5 kpc, the circular rotational velocity of the local standard of rest at a distance of the Sun of 220 km s{sup -1}, and a flat Galactic rotation curve, S Persei is suggested to have a non-circular motion deviating from the Galactic circular rotation for 15 km s{sup -1}, which is mainly dominated by the anti-rotation direction component of 12.9 {+-} 2.9 km s{sup -1}. This red supergiant is thought to belong to the OB association, Per OB1, so that this non-circular motion is representative of a motion of the OB association in the Milky Way. This non-circular motion is somewhat larger than that explained by the standard density-wave theory for a spiral galaxy and is attributed to either a cluster shuffling of the OB association, or to non-linear interactions between non-stationary spiral arms and multi-phase interstellar media. The latter comes from a new view of a spiral arm formation in the Milky Way suggested by recent large N-body/smoothed particle hydrodynamics numerical simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

New measurement of the {sup 68}Zn(4{sub 1}{sup +}) g factor combined with a reanalysis of previous data

We have remeasured and have redetermined the g factor for the 4{sub 1}{sup +} state in {sup 68}Zn following inconsistencies between earlier measurements and a recent result. We have reanalyzed several former measurements by applying an alternative analysis procedure, which allows for determining the precession effect separately for each gamma detector implying less uncertainties in the background subtraction for the relevant spectra. In addition, all measured g-factor and B(E2) data for the first 2{sup +} and 4{sup +} states in all stable even-A Zn isotopes and the radioactive {sup 62}Zn, are compared with new large-scale shell model calculations based on the most advanced effective interaction in the fpg-shell model space.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Nuclear Spins and Moments of Ga Isotopes Reveal Sudden Structural Changes between N=40 and N=50

Collinear laser spectroscopy was performed on Ga (Z=31) isotopes at ISOLDE, CERN. A gas-filled linear Paul trap (ISCOOL) was used to extend measurements towards very neutron-rich isotopes (N=36-50). A ground state (g.s.) spin I=1/2 is measured for {sup 73}Ga, being near degenerate with a 3/2{sup -} isomer (75 eV < or approx. E{sub ex} < or approx. 1 keV). The {sup 79}Ga g.s., with I=3/2, is dominated by protons in the {pi}f{sub 5/2} orbital and in {sup 81}Ga the 5/2{sup -} level becomes the g.s. The data are compared to shell-model calculations in the f{sub 5/2}pg{sub 9/2} model space, calling for further theoretical developments and new experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Collectivity at N=50: {sup 82}Ge and {sup 84}Se

The neutron-rich N=50 isotones {sup 82}Ge and {sup 84}Se were investigated using intermediate-energy Coulomb excitation on a {sup 197}Au target and inelastic scattering on {sup 9}Be. As typical for intermediate-energy Coulomb excitation with projectile energies exceeding 70 MeV/nucleon, only the first 2{sup +} states were excited in {sup 82}Ge and {sup 84}Se. However, in the inelastic scattering on a {sup 9}Be target, a strong population of the first 4{sup +} state was observed for {sup 84}Se, while there is no indication of a similarly strong excitation of the corresponding state in the neighboring even-even isotone {sup 82}Ge. The results are discussed in the framework of systematics and shell-model calculations using three different effective interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Recent Progress in Shell-Model Calculations for pfg-shell Nuclei

The structure of upper pf-shell nuclei is studied by the nuclear shell model, taking a model space consisting of four spherical single-particle orbits p{sub 3/2}, f{sub 5/2}, p{sub 1/2} and g{sub 9/2}. The effective interaction JUN45 is used, which is obtained by modifying empirically the renormalized G-matrix interaction. The oblate-prolate shape coexistence in {sup 68}Se is predicted consistently with the experimental observations, indicating the applicability of the shell model to the cases with moderate deformation. The calculated high-spin band structure highlights the important role played by the g{sub 9/2} orbit. The appearance of the j{sub p}-j{sub n} multiplets in {sup 88}Y is successfully described except for a few cases such as the 1{sub 1}{sup +} state, suggesting the good property of the effective proton-neutron interaction inherited from the renormalized G-matrix.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗