H. Tomura

The silicon ball: a 4π Si detector array for reaction channel selection

Abstract A 4π array of seventeen charged particle detectors (Si Ball) has been dessigned and constructed to provide selection of reaction channels for in-beam spectroscopy. The detector array, which consists of ΔE Si detectors of 170 μm thickness, is very compact to allow insertion into Inner Ball or Neutron Wall which may be a part of the NORDBALL γ-ray spectrometer. High spin states of neutron deficient nuclei around A = 80 have been studied using the Si Ball, and it has been proven that the Si Ball is a powerful tool in the in-beam spectroscopy of nuclei far from the β-stability line.

New neutron-deficient isotopes 83Nb and 85Nb

Abstract New neutron-deficient isotopes of 83,85 Nb were identified with the aid of results of the in-beam spectroscopic studies of 83,85 Zr. The activities were generated by the 58 Ni( 28 Si, p2n) 83 Nb, 60 Ni( 28 Si, p2n) 85 Nb and 58 Ni( 32 S, αp) 85 Nb, reactions, and the radiations were measured by means of βγ-coincidence. Then the half-lives of 83 Nb and 85 Nb were found to be 4.1 ± 0.3 and 20.9 ± 0.7 sec, and the Q EC values were determined to be 7.5 ± 0.3 and 6.0 ± 0.2 MeV for 83 Nb and 85 Nb, respectively, which are noticeably lower than predicted values from mass formulae.

A charged particle multiplicity filter for nuclidic identification of the specific gamma rays

Abstract A charged particle multiplicity filter was developed to investigate excited states in neutron-deficient nuclei far from the β-stability line. This system enabled the determination of the atomic numbers of γ-emitting nuclei for many of the γ-rays produced by the compound nuclear reactions. Details and performance of the system are described and an application is demonstrated for the 60 Ni+ 28 Si reaction.

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.

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.

High-spin states in the odd-odd nucleus 82Y

Abstract High-spin states in 82 Y have been studied by the 58 Ni( 28 Si,3pn) reaction at 128 MeV. Low-lying states were investigated by the same reaction but at a lower bombarding energy and the band heads of the high-spin sequences have been characterized. Four rotational bands forming two sets of signature partners were established. The yrast band was observed up to j π = 27 + and shows (large signature splitting, while a negative-parity yrare band, observed up to spin 22 shows a much smaller splitting. The yrast band structure was very similar to the g 9 2 proton band in 79 Rb.

The ? decay of the new isotope79Y

The neutron deficient isotope79Y has been firstly identified and the decay properties were studied fromΒ-decay measurements in the reaction of54Fe(28Si,p2n at 92 MeV. Threeγ rays of 152.5, 177.4, and 1106 keV were observed concerning theΒ decay. The half life and QEC value were determined to be 14.9 ± 0.6 s and 7.12 ± 0.45 MeV, respectively. The decay scheme including spin-parity is discussed, and 5/2+ assignment for the ground state is proposed.

Particle identification by modified Bragg-curve centroid detection

Abstract A new particle identification method based on the measurement of Bragg-curve centroids using a gas-filled ionization chamber has been improved for detection of low-energy particles around 1 MeV per nucleon by introducing a nonuniform distribution of resistance on the anode electrode. Almost the same quality of Z-resolutions as in the conventional ΔE−E method could be obtained up to Z = 19.

A rotational band in82Zr

The neutron deficient nucleus82Zr has been studied through the reaction58Ni(28Si, 2p 2n)82Zr with a calculated cross section of 0.3% of the total fusion cross section atE(28Si)=128 MeV. Gamma rays from excited states of82Zr were measured and identified using the NORDBALL escape-suppression array at the Niels Bohr Institute. Reaction channel selection was performed by use of neutron and charged particle detector arrays in conjunction with the germanium detectors. A rotational band in82Zr has been identified with spins up to 20 ħ by analysis of reaction channel selectedγ-γ coincidence matrices. Band crossings were identified at frequencies 0.57 and 0.69 MeV.

The β -decay of 88 Tc

Decay scheme, half life andQEC value of88Tc were deduced from aβ-decay study. The neutron deficient nucleus88Tc was produced by the58Ni(32S,pn)88Tc reaction using beam energies of 100, 101 and 105 MeV. The ground- and isomeric states of88Tc were found to decay to88Mo with similar half lives of 5.8±0.2 and 6.4±0.8 sec. The most probable spins and parities of these states are 3+ and 6+, respectively, though the order in energy could not be determined. TheQEC value was deduced to be 8.6±1.3 MeV.