M. Kidera

A γ-ray detector array for joint spectroscopy experiments at the JAERI tandem–booster facility

Abstract A compact array for γ-ray spectroscopy developed for the joint experiment at the Japan Atomic Energy Research Institute is described. It consists of an array of 11 Compton suppressed Ge detectors, a 4π silicon detector array for charged particle measurements, a position-sensitive silicon detector for experiments on Coulomb excitation and a conversion-electron spectrometer. The details of the detectors and new experimental results obtained with the compact array are also described.

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.

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.

Anomalous Q EC-Values of Tz=1 Nuclei, 80Y, 84Nb and 88Tc

Beta decay end point energies of the T z =1 odd-odd nuclei, 80 Y, 84 Nb, 88 Tc were measured by using βγ-coincidences. The Q EC -values were deduced to be 6.2±0.6, 7.2±0.3 and 7.8±0.6 MeV for 80 Y, 84 Nb and 88 Tc, respectively. These values are more than 2 MeV lower than those predicted by most of the mass formulae. It is suggested that these anomalies may be partly attributed to residual p-n interactions of odd-odd nuclei.

Coulomb excitation of 174Hf K-isomer. γ-ray spectroscopy with high-spin isomer beam

Abstract A new experimental technique utilizing a high-spin isomer beam (HSIB) has been developed. The HSIB of 174Hf was produced by the 9Be(170Er, 5n)174Hf reaction in inverse kinematics. By using the HSIB, the Coulomb excitation of the Kπ = 8− isomer in 174Hf was measured. The γ-rays from the 9− level, which is the first excited state built on the isomer, were observed as well as the cascade γ-rays of the ground-state rotational band. From the measured γ-ray yield, a value of 2 ± 1 e2b2 was extracted for the B(E2: 8− → 9−). This is the first experiment of γ-ray spectroscopy by means of the HSIB-induced secondary reactions.

Theβ+ decay of the new isotope86Mo and the first observation of86mNb

Theβ+ decay of86Mo has been firstly investigated by means ofβγ spectroscopy. The86Mo nuclei were produced by fusion-evaporation reactions of54Fe (35Cl, 1 p2n) and58Ni (32S,2p 2n) at beam energies of 103 and 120 MeV, respectively. Threeγ rays of 47.3, 49.8 and 187.0 keV were unambiguously identified to follow theβ+ decay of86Mo by results ofXγ andβγ coincidence and cross-bombardment. A half life and a maximumβ+-ray energy of86Mo were determined to be 19.6±1.1 s and 3.9±0.4 MeV, respectively. A decay scheme of86Mo is proposed in this article. Furthermore, a decay of86Nb has been studied using the same combinations of projectiles and targets, and a newβ-decaying isomer86mNb was observed with a half life of 56.3±8.3 s.

Coulomb Excitation of 155Gd

The high-spin states of 155 Gd were investigated by means of multiple Coulomb excitation with a 390-MeV 90 Zr beam. The members of the ground-state rotational band of 155 Gd were assigned up to (31/2 - ). The members of a positive-parity side band were also strongly excited up to high spins (33/2 + ) with populations comparable to those of ground-band members. The experimental population is compared with Coulomb-excitation calculations taking account of the recommended upper limits for E 1 and E 3 strengths compiled in the whole mass region. It turns out that an E 1 and/or an E 3 strength larger than those limits would be necessary to account for the experiment.

High-spin states of145Sm

High-spin states of145Sm were studied by using the20Ne(136Xe, α7n),139La (10B, 4n) and138Ba(13C,6n) reactions. The decay scheme of a high-spin isomer of145Sm was established. The excitation energy and the spin-parity of the isomer were determined to be 8.8 MeV and (49/2+), respectively. The level scheme was extended up to the (65/2) state at 14.6 MeV. The experimental results were discussed comparing with the deformed independent particle model (DIPM) calculation.

High-spin isomers and high-spin isomer beams

Yrast traps were found in N=83 isotones, 144Pm and 145Sm, by using inverse kinematic reactions, 14N(136Xe, 6n)144Pm and 16O(136Xe, 7n)145Sm. Their probable spin-parities are (27+) and (492+), respectively. Excitation energies of these isomers are 7.5 and 8.7 MeV Reaction products were transported by a gas filled recoil ion separation system and collected at 6 m down stream of the primary target position . The possible utilization of these high-spin isomers as secondary beams are discussed.