T. Morikawa

Electromagnetic structure of 98Mo

Abstract The nucleus 98 Mo was multiply Coulomb excited using 20 Ne, 84 Kr and 136 Xe beams. Eighteen E2 and M1 reduced matrix elements connecting 7 low-lying levels have been determined using the least-squares code GOSIA. The results are compared with the predictions of an extended version of the IBM1 model. The quadrupole sum rules approach was used to determine the shape parameters in two 0 + (ground and first excited) states. The rotational invariants 〈Q 2 〉 and 〈 cos 3δ〉 obtained show the shape coexistence in 98 Mo nucleus: the triaxial ground state and the prolate first excited state.

Superdeformation in asymmetric N>Z nucleus 40Ar

Abstract A rotational band with five γ -ray transitions ranging from 2 + to 12 + states was identified in 40 Ar. This band is linked through γ transitions from the excited 2 + , 4 + and 6 + levels to the low-lying states; this determines the excitation energy and the spin–parity of the band. The deduced transition quadrupole moment of 1.45 − 0.31 + 0.49 ± 0.15 eb indicates that the band has a superdeformed shape. The nature of the band is revealed by cranked Hartree–Fock–Bogoliubov calculations and a multiparticle–multihole configuration is assigned to the band.

High-spin isomer and level structure of 145Sm

Abstract High-spin states of 145 Sm were studied by using the reactions 20 Ne( 136 Xe,α7n), 16 O( 136 Xe,7n), 139 La( 10 B,4n) and 138 Ba( 13 C,6n). The level scheme was extended up to the state at 14.6 MeV. The excitation energy and the spin-parity of the 0.96 μs high-spin isomer were determined to be 8.8 MeV and ( 49 2 + ), respectively. Experimental results were discussed comparing with the deformed independent particle model calculation. High-spin isomers observed in N = 83 isotones were interpreted to be caused by the sudden shape change from near spherical to oblate. The Z = 64 shell gap energy was found to decrease from 2.4 to 2.0 MeV as the proton number decreases from Z = 64 to 61.

Band structures of nuclei around N, Z = 40 selected by charged particle detection

Abstract High-lying and high spin states of nuclei around N,Z=40 have studied using the ( 58 Ni + 28 Si) and ( 58 Ni + 32 S) reactions and NORDBALL Ge-Array equipped with a Silicon Ball for light charged particle detection. Simultaneously complementary experiment have been carried out using in-beam and β decay measurements to establish lifetimes and spin-party values of low-lying and ground states at Kyushu University. Some of results are reported.

High-spin states in148Tb

High-spin states of148Tb were studied by inbeam γ-ray spectroscopic techniques using141Pr(13C,6n)148Tb and27Al(130Te,9n)148Tb reactions. The level scheme of148Tb was established up to the excitation energy of 11.8MeV. The excitation energy of the high-spin isomer reported previously was revised to be 8.620MeV. The excited states below the isomer could be understood as resulted from the weak couplings of πh11/2 and νf7/2 to those of147Gd and147Tb, respectively.

Identification of the K{sup {pi}}=11/2{sup +} isomer in neutron-rich {sup 187}W

Excited states in neutron-rich {sup 187}W have been populated via deep inelastic collisions of a 630-MeV {sup 82}Se beam on a {sup 186}W target. Projectilelike fragments were measured by an annular Si detector for reaction channel selection. Delayed {gamma} rays from target residues were detected by means of the so-called recoil shadow technique. A new isomer at 411 keV, based on the 11/2{sup +}[615] Nilsson configuration, has been identified with a half-life of 1.55(13) {mu}s. The decay rates of the isomers are discussed in terms of the K quantum number by comparison with the systematics from neighboring nuclei.

Superdeformed Band in Asymmetric N > Z Nucleus, 40Ar and High-Spin States in A = 30 ∼ 40 Nuclei

1Center for Nuclear Study, The University of Tokyo, Wako 351-0198, Japan 2Department of Physics, Kyushu University, Fukuoka 812-8581, Japan 3Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 4Chiba Institute of Technology, Narashino 275-0023, Japan 5Institute of Particle and Nuclear Studies, KEK, Tsukuba 305-0801, Japan 6Institute of Natural Sciences, Senshu University, Tokyo 101-8425, Japan

High-spin states in Au-188: Further evidence for nonaxial shape

The high-spin level structure of {sup 188}Au has been investigated via the {sup 173}Yb({sup 19}F,4n{gamma}) reaction at beam energies of 86 and 90 MeV. The previously reported level scheme has been modified and extended significantly. A new I{sup {pi}}=20{sup +} state associated with {pi}h{sub 11/2}{sup -1} x {nu}i{sub 13/2}{sup -2}h{sub 9/2}{sup -1} configuration and two new rotational bands, one of which is built on the {pi}h{sub 9/2} x {nu}i{sub 13/2} configuration, have been identified. The prolate-to-oblate shape transition through triaxial shape has been proposed to occur around {sup 188}Au for the {pi}h{sub 9/2} x {nu}i{sub 13/2} bands in odd-odd Au isotopes. Evidence for {pi}h{sub 11/2}{sup -1} x {nu}i{sub 13/2}{sup -1} structure of nonaxial shape with {gamma}<-70 deg. has been obtained by comparison with total Routhian surface and cranked-shell-model calculations.

SUPERDEFORMED BAND IN ASYMMETRIC N > Z NUCLEUS 40Ar

A rotational band with five cascade γ-ray transitions was newly found in 40Ar. The deduced transition quadrupole moment of

First measurement of the quadrupole moment in the 21+ state of 84Kr

1.45_{-0.31}^{+0.49}\, {\rm eb}