T. Inomata

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.

Isospin decomposition of the Gamow-Teller strength in Cu-58

Abstract The Gamow-Teller (GT) strength excited by a (p, n)-type reaction on a nucleus with isospin T0 and N > Z is shared by isospin components T0 − 1, T0 and T0 + 1. A good energy resolution (3He, t) reaction on 58Ni revealed the fine structure of the GT strength in 58Cu. The isospin of each level constituting the fine structure was assigned by comparing to results from inelastic electron and proton scatterings and (n, p)-type reactions, thus resolving the isospin structure of the GT strength in 58Cu. The ratio of the summed GT strengths among the three isospin components is well described by a shell-model calculation.

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.

Spin-isospin resonances in nuclei

Spin-isospin excitations in nuclei have been investigated via the (He-3,t) reaction at 450 MeV. The volume integrals of the effective interactions J(sigma tau) and J(tau) for the (He-3,t) reaction at 450 MeV have been empirically determined to be 172+/-17 MeV-fm(3) and 53+/-5 MeV-fm(3), respectively. These values are consistent with those obtained for the (p,n) reaction at the same bombarding energy per nucleon. The Gamow-Teller strength can be deduced with the same reliability as the (p,n) reaction at the bombarding energy above 100 MeV. The neutrino absorption cross sections by Ga-71 is obtained on basis of the present (He-3,t) measurement. The new SNU value obtained for Ga-71 is 130.3+/-1.6(stat.)+/-16.8(syst.). The spin-isospin responses for the Sn isotopes, Cd-116 and Mo-100 are presented and are discussed in relation with double beta-decay. A measurement of decay protons from the spin-isospin resonances in N-13 is presented. A new possibility of studying the spin-isospin responses on the beta(+) side via the (t,He-3) reaction using a dispersion matching technique is discussed.

(3He,t) Charge-Exchange Reactions at E(3He) = 450 MeV, θ = 0°

Spin-isospin excitations in nuclei have been studied by means of the (3He,t) reactions at 450 MeV on the targets sBe, natC, *%ii, 58Ni, 62Ni, seZr, l18Sn, **OSn, 124Sn, and 154Sm. The new spectrometer “Grand Raiden” was employed for the (3He,t) study for the first time. Observed (3He,t) spectra at 0’ show remarkable similarity with those from the (p,n) results at intermediate energies, suggesting a simple direct reaction mechanism for the (3He,t) reaction at 450 MeV. The GamowTeller (GT) resonances and the spin-flip AL=1 resonances are excited very strongly. A fine structure of the GT resonances in medium-heavy nuclei is observed with an energy resolution of 210 keV. It is demonstrated that the (3He,t) reaction at 450 MeV is a powerful tool to study the spin-isospin excitations in nuclei.

Spin-isospin Responses of ^{71}Ga for Solar Neutrinos Studied by ^{71}Ga(^{3}He,t

Abstract The charge-exchange 71Ga(3He,tγ)71Ge reaction was used to study the spin-isospin (Gamow Teller: GT) excitations relevant to the axial-vector charged-weak response for solar neutrinos. High-lying GT states in 71Ge with excitation energies up to one MeV above the neutron threshold were found to have finite γ-decay branches to low-lying states. The GT strengths for relevant states and absorption rates of solar neutrinos through the 71Ga(ν, e)71Ge and 71Ga(ν,eγ)71Ge reactions were derived.

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Abstract Spin-isospin excitations in nuclei have been studied by means of the ( 3 He,t) reactions at 450 MeV. The Gamow-Teller (GT) resonances are found to be strongly excited. A fine structure of the giant Gamow Teller resonances in medium-heavy nuclei is observed with an energy resolution of 130 keV. The volume integrals of the effective interactions J στ and J τ have been determined experimentally. The importance of high resolution observation of the ( 3 He,t) reactions at intermediate energies, both, to study the double β decay processes and to measure the detection sensitivities for solar neutrino experiments is discussed.

)^{71}Ge Reaction

Initial experiments were carried out to study spin-isospin transitions in nuclei using (t,3He) measurements. A triton beam was produced from the breakup reaction (4He,t-p) on a 9.25 g/cm2 Be production target using a 4He beam of 620 MeV. With a beam of 70 enA a yield of 381 MeV tritons with 4.5 × 106 particles/s was achieved. The first half of the A1200 beam transport system at NSCL was used to analyze the triton beam. The energy spread at the target position was estimated to be about 23 MeV. The second half of the A1200 was used to analyze the energy of 3He particles from the (t,3He) reaction. The dispersion matching method was applied to obtain good energy resolution despite the significant energy spread of the incident tritons. The achromatic properties of the A1200 system made it possible to obtain high-resolution (t,3He) spectra at θ = 0° with a resolution of ΔEE = 0.002 (ΔE = 780 keV).

Spin-isospin excitations in nuclei via (3He,t) reactions at 450 MeV

Abstract The microscopic structure of the Gamow-Teller resonance at E x = 15.6 MeV in 208 Bi has been investigated by observing its direct proton decay to the neutron-hole states in 207 Pb following its excitation via the 208 Pb( 3 He,t) reaction at E( 3 He ) = 450 MeV and θ = 0°. The total width of the resonance as well as total and partial escape widths, associated with proton decay, have been determined. The total escape width was found to be only 4.9 ± 1.3%. A re-examination of several recent theoretical estimates becomes desirable in view of the limited agreement with this value.

(t,3He) Reaction; New tool for studying spin-isospin excitations in neutron rich nuclei

Polarization transfer (PT) coefficients in the 12C, 28Si(p,p′) reactions at a scattering angle of 0° are measured at Ep=392 MeV. The strength of the isoscalar central spin-dependent part (Vσ) of the effective nucleon-nucleon interaction is studied by using the sensitivity of the PT coefficients for the excitation of the 1+, T=0 state in 12C to the Vσ strength. It is found that distorted wave impulse approximation (DWIA) calculations employing the Franey and Love effective interaction well reproduce the measured PT coefficients.