Y. Arimoto

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 The relaxation rates of the polarized rubidium (Rb) vapor were measured by using a chopped pumping laser to investigate the depolarization mechanism of a high density Rb vapor in a strong magnetic field. The measurement was carried out in a range of the magnetic field from 1 to 5 T and the Rb cell temperature from 90 to 130 °C which corresponds to the Rb vapor density from 0.2 to 2.0×10 13 at./cm 3 . The position dependence of the relaxation rates was also measured along the Rb cell axis. The experimental results showed that two components, i.e. a fast component with the relaxation rate of ∼ 65 ms −1 and a slow component with the relaxation rate of ∼ 1 ms −1 contribute. The observed relaxation rates were analyzed by the wall relaxation model, the effusion model and the radiation trapping model. It was found that the slow component was well explained by the wall relaxation and the effusion effect. On the other hand, the fast component is due to a formation of the localized Rb polarization around the pumping laser by a radiation trapping effect and a subsequent relaxation process due to an effusion.

)^{71}Ge Reaction

A novel type of polarized 3He ion source based on “electron pumping” was recently proposed. This ion source requires multiple electron capture and stripping collisions of 3He+ ions with polarized alkali atoms under a strong magnetic field (2–3 T). Since these processes may induce a serious increase in the emittance and reduction of polarized beam intensity, we investigated them in detail by using the Monte Carlo simulation. It was found that there is (1) increase in the emittance results not from angular broadening but from a beam size enlargement, (2) the phenomena under magnetic field B are simplified by a collisionless phenomenon under a weaker magnetic field (effective magnetic field) Beff defined by Beff≃(λ+0/(λ+0+λ0+))B, where λ+0 and λ0+ are mean free paths for 3He+ ions and 3He0 atoms traveling in the alkali vapor.

Relaxation mechanism of optically pumped Rb vapor of high density in strong magnetic fields

Abstract We investigated the spatial distribution of a polarization in 3He beam expected from a novel polarized 3He ion source based on electron pumping, i.e., multiple electron capture and stripping collisions of an incident fast 3He+ ion with a polarized Rb vapor in a strong axial magnetic field. For this purpose, a Monte Carlo simulation was carried out for 19 keV 3He+ ions with varying Rb vapor thickness, magnetic field, and beam emittance. The calculated results showed a distribution of the 3He polarization that we call a “polarization hole”, which has a low polarization area around the beam axis. The parameters characterizing the polarization hole, i.e., the polarization and radius of the hole, were found to depend on the Rb vapor thickness, the magnetic field, the beam size, and the angular divergence of the initial beam. These parameters were successfully reproduced with analytical functions deduced from a probability density function prescription. This provides a powerful tool to treat complex phenomena of multiple collisions in strong magnetic fields without performing time-consuming Monte Carlo calculations.