K. Ishibashi

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.

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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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).

)^{71}Ge Reaction

A γ-ray detector system “NYMPHS” was built for 7Be-γ coincidence measurements to separate (7Li, 7Beg.s.) and (7Li, 7Be0.43MeV) channels in the (7Li, 7Be) reaction at intermediate energies. NYMPHS is composed of 22 GSO scintillators, each with a volume of about 30 cm3. A typical energy resolution was about 9% at Eγ = 0.66 MeV. The absolute detection efficiency of NYMPHS was 0.200 ± 0.005 for the 0.43 MeV 7Be γ-ray. NYMPHS combined with a magnetic spectrograph showed good performance for 7Be-γ coincidence measurements in the (7Li, 7Be) reactions on 12C and 90Zr targets at EL = 65A MeV.

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

Abstract The ( 7 Li, 7 Be) reaction was found to be used to separate ΔS = 0 and ΔS = 1 transitions through the coincidence measurement of the γ-ray from deexcitation of the 0.43 MeV state of 7 Be at an incident energy of 65 A MeV on 6 Li, 7 Li, 12 C and 90 Zr nuclei. The reaction was shown to proceed predominantly via one-step reaction process. Predominance of one-step process means utility for derivation of spin-flip and non spin-flip strengths for isovector excitations in medium heavy nuclei at intermediate incident energies. The relative nuclear spin-strength P sf was deduced for isovector excitations.

GSO-detector system “NYMPHS” for (7Li, 7Be-γ) reaction at intermediate energies

Decay via proton emission of isobaric analog states (IAS’s) in 91 Nb was studied using the 90 Zr(α, t) reaction at E�=180 MeV. This study provides information about the damping mechanism of these states. Decay to the ground state and low-lying phonon states in 90 Zr was observed. The experimental data are compared with theoretical predictions wherein the IAS ‘single-particle’ proton escape widths are calculated in a continuum RPA approach. The branching ratios for decay to the phonon states are explained using a simple model.