M. Fujiwara

Gamow-Teller strengths from (t,3He) charge-exchange reactions on light nuclei

Abstract Zero-degree cross sections have been measured for (t, 3 He) reactions on the light target nuclei 9 Be, 10 B, 11 B, 12 C, and 13 C at a bombarding energy of 127 MeV/A. The triton beam was produced by ( 4 He,t+p) breakup on a Be production target using a 4 He beam of 155 MeV/A. Dispersion matching was applied to obtain good energy resolution ( Δ E/E=0.002, Δ E=780 keV). The zero-degree (t, 3 He) cross sections are used to discuss Gamow-Teller strengths in 10 Be and 11 Be.

The Giant Monopole Resonance in the Sn Isotopes: Why is Tin so "Fluffy"?

The isoscalar giant monopole resonance (GMR) has been investigated in a series of Sn isotopes (A=112-124) using inelastic scattering of 400-MeV a particles at extremely forward angles (including 0 degrees). The primary aim of the investigation has been to explore the role of the symmetry-energy term in the expression for nuclear incompressibility. It is found that the excitation energies of the GMR in the Sn isotopes are significantly lower than those expected from the nuclear incompressibility previously extracted from the available data on the compressional-mode giant resonances.

2α+t cluster structure in 11B

Abstract The cluster structures of the excited states in 11B are studied by analyzing the isoscalar monopole and quadrupole strengths in the B 11 ( d , d ′ ) reaction at E d = 200 MeV . The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. The large monopole strength for the 3 / 2 3 − state at E x = 8.56 MeV is well described by the AMD calculation and is suggested to be an evidence for a well developed 2 α + t cluster structure.

The (t,He-3) and (He-3, t) reactions as probes of Gamow-Teller strength

It is shown via a study on a {sup 26}Mg target that the (t,{sup 3}He) reaction at 115 MeV/nucleon reaction is an accurate probe for extracting Gamow-Teller transition strengths. To do so, the data are complemented by results from the {sup 26}Mg({sup 3}He, t) reaction at 140 MeV/nucleon that allows for a comparison of T=2 analog states excited via the mirror reactions. Extracted Gamow-Teller strengths from {sup 26}Mg(t,{sup 3}He) and {sup 26}Mg({sup 3}He, t) are compared with those from {sup 26}Mg(d,{sup 2}He) and {sup 26}Mg(p,n) studies, respectively. A good correspondence is found, indicating probe independence of the strength extraction. Furthermore, we test shell-model calculations using the new USD-05B interaction in the sd-model space and show that it reproduces the experimental Gamow-Teller strength distributions well. In anticipation of further (t,{sup 3}He) experiments on medium-heavy nuclei aimed at determining weak-interaction rates of relevance for stellar evolution, a second goal of this work is to improve the understanding of the (t,{sup 3}He) and ({sup 3}He, t) reaction mechanisms at intermediate energies because detailed studies are scarce. The distorted-wave Born approximation is employed, taking into account the composite structures of the {sup 3}He and triton particles. The reaction model provides the means to explainmorexa0» systematic uncertainties at the 10%-20% level in the extraction of Gamow-Teller strengths as being because of interference between Gamow-Teller {delta}L=0,{delta}S=1 and {delta}L=2,{delta}S=1 amplitudes that both contribute to transitions from 0{sup +} to 1{sup +} states.«xa0less

Polarization transfer observables for proton inelastic scattering from 12C at 0

Abstract Polarization transfer (PT) observables in the 12 C (p,p′) reaction at 0° for 392 MeV protons have been measured. The excitation strengths are decomposed into the spin-flip part and the non-spin-flip part by using the obtained PT observables. The PT observables for excitation of the 1+, T=0 and 1+, T=1 states are compared with distorted wave impulse approximation calculations. The strength ratios of the isoscalar spin-dependent term to the isovector tensor term and the isovector tensor term to the isovector spin-dependent term are reasonably consistent with the Franey and Love interaction.

Charge-Exchange Reactions with a Secondary Triton Beam

A secondary triton beam from fragmentation of 560-MeV alpha-particles has been used in a high-resolution (t,He-3) charge-exchange experiment at intermediate bombarding energies. The experiment was carried out at the National Superconducting Cyclotron Laboratory using a He-4 beam from the K1200 cyclotron. The radioactive triton beam of (0.5-1.0)x 10(6) particles/s with a mean energy of 350 MeV was produced in a production target of the A1200 fragment separator and transported to the target position of the S800 magnetic spectrometer. Ray-tracing and dispersion matching techniques were employed to detect He-3 particles from the C-12(t,He-3)B-12 reaction near 0 degrees. An energy resolution of Delta E approximate to 160 keV or Delta E/E approximate to 4.6 x 10(-4) (FWHM) was achieved. This is an improvement over our previous results and opens the possibility for studying high-resolution (n,p)-type reactions at intermediate bombarding energies

Line broadening and Coulomb displacement energies of the hole-state analogs in the A = 111−123 odd-mass Sn isotopes

Abstract Line broadening and orbit dependence of the Coulomb displacement energy have been observed for the 1g 9/2 , 2p 1/2 and 2p 3/2 hole-state analogs in a series of odd- A Sn isotopes. The observed widths are discussed in terms of spreading width with main contributions from mixing with the isovector monopole state as well as the escape width.

Measurement of the Gamow-Teller strength distribution in Co-58 via the Ni-58(t,He-3) reaction at 115 MeV/nucleon

Electron capture and beta decay play important roles in the evolution of presupernovae stars and their eventual core collapse. These rates are normally predicted through shell-model calculations. Experimentally determined strength distributions from charge-exchange reactions are needed to test modern shell-model calculations. We report on the measurement of the Gamow-Teller strength distribution in Co-58 from the Ni-58(t,He-3) reaction with a secondary triton beam of an intensity of similar to 10(6) pps at 115 MeV/nucleon and a resolution of similar to 250 keV. Previous measurements with the Ni-58(n,p) and the Ni-58(d,He-2) reactions were inconsistent with each other. Our results support the latter. We also compare the results to predictions of large-scale shell-model calculations using the KB3G and GXPF1 interactions and investigate the impact of differences between the various experiments and theories in terms of the weak rates in the stellar environment. Finally, the systematic uncertainties in the normalization of the strength distribution extracted from Ni-58(He-3, t) are described and turn out to be nonnegligible due to large interferences between the Delta L=0,Delta S=1 Gamow-Teller amplitude and the Delta L=2,Delta S=1 amplitude.

Compressional-mode giant resonances in deformed nuclei

Abstract Background-free inelastic scattering spectra have been obtained for the Sm isotopes with 400xa0MeV α particles at forward angles (including 0°) to investigate the effect of deformation on the compressional-mode giant resonances. The strength distributions for the isoscalar giant resonances ( L ⩽3) have been extracted for the spherical nucleus 144 Sm and the deformed nucleus 154 Sm. We have observed that the effects of deformation are different for the low- and high-excitation-energy components of the isoscalar giant dipole resonance in 154 Sm. Evidence for the theoretically predicted coupling between the isoscalar dipole resonance and the high-energy octupole resonance is reported.

DWBA analysis of (3He, d) reactions at 90MeV and contributions from the nuclear interior

Abstract Differential cross sections of 3He elastic scatterings and (3He, d) reactions have been measured at 90 MeV for 28Si, 54Fe, 58Ni, 90Zr and 124Sn. From the optical-model analysis of the elastic scattering, both shallow ( V ⋍ 105 MeV ) and deep ( V ⋍ 150 MeV ) potentials of 3He were obtained. The shallow potentials correspond to the ones which were determined uniquely from other measurements extended to more backward angles. The (3He, d) reactions have been analyzed with the DWBA using the shallow and deep potentials for 3He. The calculations using the deep potentials reproduced the data well, but those using the shallow ones did not. The contributions from the nuclear interior were investigated through the radial cutoff in the DWBA. The calculations using the shallow potentials reproduced the data well when the radial cutoffs were introduced. The effects of the radial cutoff were very small when the deep potentials were used. It was found that a much greater reduction of the contributions from the nuclear interior was needed when the shallow potentials were used in the DWBA calculations.