M. K. Suzuki

Anomalously hindered E2 strength B(E2;2+(1)-->0+) in 16C.

The electric quadrupole transition from the first 2(+) state to the ground 0(+) state in 16C is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive 16C nuclei. The measured mean lifetime is 77+/-14(stat)+/-19(syst) ps. The central value of mean lifetime corresponds to a B(E2;2+(1)-->0(+)) value of 0.63e(2) fm(4), or 0.26 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.

Lifetime measurements of first excited states in C 16 , 18

The electric quadrupole transition from the first 2{sup +} state to the ground 0{sup +} state in {sup 18}C was studied through a lifetime measurement by an upgraded recoil shadow method applied to inelastically scattered radioactive {sup 18}C nuclei. The measured mean lifetime is 18.9{+-}0.9(stat){+-}4.4(syst) ps, corresponding to a B(E2;2{sub 1}{sup +}{yields}0{sub g.s.}{sup +}) value of 4.3{+-}0.2{+-}1.0 e{sup 2} fm{sup 4}, or about 1.5 Weisskopf units. The mean lifetime of the first 2{sup +} state in {sup 16}C was remeasured to be 18.3{+-}1.4{+-}4.8 ps, about four times shorter than the value reported previously. The discrepancy between the two results was explained by incorporating the {gamma}-ray angular distribution measured in this work into the previous measurement. These transition strengths are hindered compared to the empirical transition strengths, indicating that the anomalous hindrance observed in {sup 16}C persists in {sup 18}C.

REMARKS ON THE SUPERCONDUCTOR MODELS OF ELEMENTARY PARTICLES

It is shown that precise equivalence holds between the energy gap in the superconductor model derived by Bardeen, Cooper, and Schrieffer and the self- consistently generated mass derived by Numbu and Jona-Lasinio only in case of four-fermion interaction. The stability criterion for the elementary particle mass equations is also derived. (C.E.S.)

FOUNDATION OF SPONTANEOUS BREAKDOWN OF SYMMETRIES

It is shown in a simple model that physical masses can split even without particle mixture in a hamiltonian in which bare masses are degenerate and permutation symmetry holds among bare particles. Infinity of the normalization volume is indispensable for proof. In this connection the problem of representation of an operator ring is discussed. A model of quantum number nonconservation is similarly considered. (auth)

Proton-rich nuclear structure and mirror asymmetry investigated by β-decay spectroscopy of 24Si

In order to investigate the characteristic properties of proton-rich nuclei, β-decay spectroscopy was carried out on 24Si. The Gamow-Teller transition strength B(GT) of 24Si to low-lying states in 24Al was determined. Considering in particular the breaking of mirror symmetry for energy levels and B(GT), we discuss the behavior of a weakly-bound s-orbital proton by incorporating a recent experimental result.

Mirror asymmetry for B(GT) of 24Si induced by Thomas‐Ehrman shift

We carried out the β‐decay spectroscopy on 24Si in order to investigate a change in configuration in the wave function induced by Thomas‐Ehrman shift from a perspective of mirror asymmetry of B(GT). We observed two β transitions to low‐lying bound states in 24Al for the first time. In this proceeding, the B(GT) of 24Si is compared with that of the mirror nucleus 24Ne, and the mirror asymmetry of B(GT) is determined. Then the origin of the B(GT) asymmetry is discussed through the comparison with theoretical calculations.

Gamow‐Teller transition of the proton‐rich nucleus 24Si

The Gamow‐Teller transition strength B(GT) of 24Si was measured to investigate characteristic structure of proton‐rich nuclei induced by a weakly‐bound proton. By combining the results of the delayed γ‐ray and proton measurements, the entire decay scheme of 24Si was reconstructed, then the B(GT) of 24Si was deduced. Focusing to the low‐lying states, the B(GT) of 24Si to the 11+ and 12+ states in 24Al were smaller than that of the mirror nucleus 24Ne by 22% and 10%, respectively. The mirror asymmetry of B(GT) indicates the configuration change in the wave function. Through the comparison with theoretical shell‐model calculations, it is implied that the configuration change is attributed to the lowering of the 1s1/2 orbital. The applicability of the theoretical calculations was checked using overall B(GT) distribution.

Low-lying states in {sup 32}Mg studied by proton inelastic scattering

Proton inelastic scattering on the neutron-rich nucleus {sup 32}Mg has been studied at 46.5 MeV/nucleon in inverse kinematics. Populated states were identified by measuring de-excitation {gamma} rays, in which five new states were found by {gamma}-{gamma} coincidence analyses. By analyzing the angular differential cross sections via coupled-channel calculations, their spins and parities were constrained and the amplitudes for each transition were extracted. The spin and parity of the 2321-keV state was assigned as 4{sub 1}{sup +}. The ratio between the energies of the 2{sub 1}{sup +} and 4{sub 1}{sup +} states indicates that {sup 32}Mg is a transitional nucleus rather than an axially deformed rigid rotor. The collectivities in the nucleus {sup 32}Mg with N=20 are discussed based on the results obtained in the present experiment.

Application of Doppler-shift attenuation method to the de-excitation γ rays from the in-flight 12Be beam

The B(E2; ↓) value of the neutron‐rich nucleus 12Be has been determined through the measurement of the lifetime of the first 2+ state using a modified Doppler‐shift attenuation method (DSAM). The first excited state was produced by the inelastic scattering of the intermediate energy 12Be beam off a thick gold target, which played two roles, to excite the beam and to decrease the velocity. The lifetime has been determined to be 2.5±0.7 (stat) ±0.3 (syst) ps, which gives a B(E2) value of 5.0±1.3±0.5 in Weisskopf units. The result shows a large quadrupole strength in the ground state transition. The B(E2) value together with the deformation length measured by proton inelastic scattering yields a neutron quadrupole matrix element two times larger than those for 14C and 16O.

Investigation into behavior of weakly-bound proton via B(GT) measurement for the β decay of 24Si

The β‐decay spectroscopy on 24Si was carried out in order to investigate the behavior of a weakly‐bound s‐wave proton. We observed two β transitions to low‐lying bound states in 24Al for the first time. The Gamow‐Teller transition strengths B(GT) to the 11+ and 12+ states were deduced to be 0.13(2) and 0.14(1), which were smaller than that of mirror nucleus 24Ne by 22% and 10%, respectively. These mirror asymmetries of B(GT) indicate the configuration change in the wave function. By comparing with theoretical shell‐model calculations, it is implied that the configuration change is attributed to the lowering of the 1s1/2 orbital.