Masaru Yosoi

9Be(α, p)12B reaction and primordial nucleosynthesis

Abstract The high-lying levels of 12 B have been studied via the 9 Be(α, p) 12 B reaction using 65 MeV α-particles. The reaction protons were analyzed with a quadrupole-dipole-dipole spectrograph, yielding a resolution of about 40 keV. Angular distributions were measured for 20 states ranging in excitation energy from 7.55 to 13.31 MeV. Results of DWBA calculations were compared to the angular distributions to attempt to set limits on the angular momentum transfers. The states seen at excitation energies of 10.57 and 13.31 MeV have potential significance to models of primordial nucleosynthesis via their possible importance to the 8 Li(α, n) 11 B and 9 Be(t, p) 11 B reactions respectively. A new reaction rate for the latter reaction was obtained.

Key resonant states in the8Li(α,n)11B reaction in the inhomogeneous big bang models

The resonant states in the key reaction8Li(α,n)11B for the inhomogeneous Big Bang Models were studied experimentally through the9Be(α,p)12B reaction at 64 MeV. This reaction is found to excite all the resonances of interest in12B. The most crucial resonant state at 10.572 MeV in12B (0.572 MeV above the α threshold) was found to have Γtot≤20±10 keV and Jπ=(1−), suggesting that the S-factor of the (α,n) process should be larger than that obtained before.

Decay properties of the key resonant states in8Li(α, n)11B for primordial nucleosynthesis

The particle decay property of the key resonant states in the reaction8Li(α,n)11B for the inhomogeneous big bang models was studied experimentally. The sum of the branching ratios of the 10.572 MeV state for the neutron decays to the excited states in11B is as large as for the ground state, indicating that the neutron decays to excited states are crucial and enhance the reaction rate for heavy element synthesis considerably.

Development of polarized HD target for SPring-8/LEPS experiment.

A polarized solid HD (Hydrogen - Deuteride) has been developed for near future photoproduction experiment at SPring-8/LEPS. The solid HD target is polarized by the static method in a strong magnetic field of 17 T and low temperature of about 15 mK at RCNP Osaka university. The solid HD target is transported from RCNP to SPring-8, under the condition of a magnetic field larger than 0.1 T for holding the polarization and low temperature lower than 4 K, in which we use five cryostats. We have achieved a polarization degree of 44 % and a relaxation time of 8 months for H. We have recently succeeded in the connection among three cryostats used at SPring-8. After succeeding all the target transportations, we will start the physics experiment at SPring-8.

Electric dipole response in Sn-120

In high-resolution (,) experiments under 0° the complete B(E1) strength distribution can be studied in stable nuclei. At the Research Center of Nuclear Physics in Osaka, Japan, the cross sections and observables for the polarization transfer of E1 and M1 excitations in 120Sn were measured for scattering angles Θ = 0° − 4° in an excitation energy range of 5 - 25 MeV. From the present measurement the complete B(E1) strength distribution and the branching ratios of the PDR to the ground state can be extracted. The experimental setup, the principle of backgound subtraction and first results on the E1 strength are presented.

Experimental Study of the Key Reaction to the Nucleosynthesis in the Inhomogeneous Big Bang Models

Inhomogeneous Big Bang models1-4), which introduced inhomogeneities in baryon density in the quark-hadron phase transition, have succeeded in predicting synthesis of finite metallicity. Among the postulated dominant flow path3), which bypasses the A = 8 gap in the inhomogeneous models, the most unknown process is 8Li(α,n)1 1B. An experiments) for this process was recently reported which used the reverse reaction 11B(n,α)8Li. Some resonances were clearly observed, although crucial physical parameters such as total level widths and the spin-parities were not determined for the resonances. We have studied the property of these resonant states in 12B by using the direct reaction 9Be(α,p)12B.