Hisao Ohtsubo

Breakdown of the Siegert theorem and the many-body charge density operators

Abstract The exchange charge density operator is studied in the two-boson exchange model with consistent treatment of the exchange current and nuclear wave functions. We find a non-vanishing exchange charge density operator even in the static limit, which leads to the breakdown of the Siegert theorem.

Average polarization of 12B in polarized muon capture

Abstract A formula is given for the average polarization of the recoil nucleus in polarized muon capture in a spin zero nucleus. This formula includes the correction due to contributions from the excited states which are produced in the muon captures of the same parent nucleus, through γ-transitions. Average polarizations and partial muon capture rates are numerically obtained in the processes μ − + 12 C → 12 B (1 + , 2 + , 2 − , 1 − )+ ν μ . The nuclear wave functions adopted are of the Co Cohen-Kurath type for the postive parity states and of the most general configurations of 1 ħϵ excitations for the negative parity states. The average polarizations are, generally, less dependent on the nuclear structure than the partial muon capture rates. The experimental data on the average polarization of 12B given by the Louvain-Saclay-ETH group is analyzed with the correction from the excited states. This leads to (ɡ p − ɡ T )/ɡ A = 10.3 ± 2.7 for the form factors.

Beta-ray angular distribution in aligned 12B and 12N and G-parity irregular induced tensor current

Abstract We made an explicit formula for beta-ray angular distribution by taking into account the radiative corrections, Coulomb corrections of the finite-size nucleus, weak magnetism, induced pseudoscalar, second-class induced tensor, and contributions of the d-wave leptons. Experimental data on the beta decays of aligned 12 B and 12 N given at Osaka are carefully investigated, and it is shown that these data are compatible with no induced tensor current, ƒ T ƒ A = −(0.44 +-0.88) 2M . The nuclear parameter y is 3.3±0.9 in excellent agreement with the predicted value 3.6.

Longitudinal Polarization of 12B in Muon Capture Reaction

A general formula is given for the longitudinal polarization of the recoil nucleus in polarized muon capture in a spin zero nucleus. The longitudinal polarization of the recoil 12B is studied )

Relativistic effects on electron scattering of the deuteron

Relativistic corrections to the elastic electron scattering and electrodisintegration of a deuteron are studied in the framework of a realistic one-boson-exchange model. Effective generators of the Poincare group for the nuclear system are described in terms of the nucleonic degree of freedom by using the unitary transformations: The hamiltonian H includes the nuclear force and exchange current. The Lorentz boost generator K depends on the interaction. These generators satisfy the commutation relations of the Poincare group and current conservation law up to the order of 1/M3 in the 1/M expansion, with M being the nucleon mass. Numerical calculation revealed the importance of relativistic corrections to the electromagnetic current and state vector.

Effect of meson exchange current on deuteron muon capture

Abstract The effect of meson exchange current was investigated on the energy spectrum of the emitted neutron and the asymmetric angular distribution of the neutrino in muon capture in the deuteron, μ − + d → n + n + v . We adopt the one-pion and one-rho-meson exchange model and the Siegert theorem for electric multipole amplitude in order to satisfy phenomenologically the vector-current conservation relation. We found a large effect of the meson exchange current on the neutron energy spectrum, particularly at high energies, in the muon capture from doublet and quartet hyperfine states. The asymmetry coefficient of the neutrino is also affected significantly by the exchange current in the muon capture from the doublet hyperfine state, but not from the quartet state.

Electron scattering and charged pion photoproduction on12C and13C

Electron scattering and charged pion photoproduction at 200 MeV on12C and13C have been studied by the nuclear shell model to investigateM1 andE2 nuclear form factors of the isovector type. Starting with the Op-shell model of Hauge-Maripuu, the effects of core polarization by theM 3Y force and the one-pion-exchange current are taken into account. The effect of core polarization is found to be essential in both electron scattering and pion photoproduction, while the meson-exchange current, which also improves the calculated results, gives contributions of about 10%–15%.

Beta-ray spectra of 12B and 12N and conserved vector current

Abstract In order to investigate spectral shape factors of 12 B and 12 N, we make a new formalism of β-decay theory, where the radial wave functions of leptons are treated with no approximation and, therefore, the nuclear matrix elements are electron-energy dependent. With this formalism we can show strong support for the conserved vector current hypothesis in analyzing the experimental data which were given by Wu, Lee and Mo in 1963 and revised by them in 1977 using the latest experimental results on the end-point energies and branching ratios of the inner β-groups, in addition to the correct Fermi functions for the positron. In fact, the average slopes of the spectral shape factors for 12 B and 12 N are in excellent agreement with those in our theory. Recent experimental data given by the Heidelberg group are also in good agreement with the theory if we analyze the difference of the average slopes for 12 B and 12 N. There are, however, small discrepancies with the theory in their individual values. The relation of the present formalism with traditional theories of β-decay is discussed.

Muon Capture and Nuclear Structure

We have studied the fundamental muon-nucleon interaction from the muon capture in gaseous and molecular hydrogen and the nuclear structure problem upon the knowledge of the former from muon captures in C12 and O16.

Investigation of radiative pion capture in 16O by the continuum shell model

Abstract The radiative pion capture in 16O with excitation of the states above the threshold of particle emission is investigated by the continuum shell model. For simplicity, the ground state of 16O is assumed to be the double-closed shell, while the states with T = 1 are assumed to be 1p-1h configurations. The calculated widths of the strongly excited resonances (1−, 2−) agree with the experimental data. Beyond the excitation energy of 30 MeV, the photon spectra are dominated by the even parity states. The quasi-free emission of nucleons, in addition to resonances, are well reproduced.