T. Kuroyanagi

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.

The level structure of 87Nb

Abstract The level structure of 87 Nb has been studied through β-decay of 87 Mo activity produced by the 58 Ni( 32 S, 2pn) reaction and through in-beam γ-ray measurements in the 58 Ni( 32 S, 3pγ) 87 Nb reaction. In the β-decay study, the decay scheme of 87 Mo is constructed firstly from γ-ray energies, intensities of γ-rays and conversion electrons, and γ-, βγ- and γ(ce)-coincidence relations. Spins and parities of the low-lying statesof 87 Nb and 87 Zr were also investigated. In the in-beam study, intensities, coincidence relations and angular distributions of γ-rays were measured in coincidence with charged particles evaporated from the compound nuclei. Then high-spin states of J π ⩽ ( 33+ 2 ) in 87 Nb were established in this study. Systematic behavior in the level structures of N = 46 isotones, and the comparison between those of 85 Y and 87 Nb, are discussed.

The nuclear structure of 83Zr

Abstract High-spin states in 83Zr have been studied via the 58Ni(28Si, 2pn)83 reaction using in-beam gamma-ray spectroscopy techniques. Measurements of multiple (charged-particle)γ-coincidence, nγγ-coincidence, gamma-ray excitation function and gamma-ray angular distribution were performed. These experimental results established a positive-parity band based on the g 9 2 neutron shell and two negative-partity bands built on the 1 − 2 and 5 − 2 states. The existence of the two low-lying isomeric states with the half-lives of 1.8 ±0.1 and 0.50 ±0.25 μs was also revealed. It was found that each band exhibits a rotational-like character and the structures are similar to those of neighboring N=43 isotones, whereas change of neutron number leads to abrupt change at N = 43 ∼45 with regard to the level structure of odd-Zr isotopes.

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.

Half-lives andQβ measurements for new nuclei of89Tc and89mTc

Neutron deficient isotopes of89Tc and89mTc have been produced through the60Ni(32S,p 2n)89Tc at 95 MeV and the58Ni(35Cl, 2p 2n)89Tc reaction at 135 MeV. A rotating catcher foil system was used to collect the activities and transfer them to a measuring position forβ-γ spectroscopy. The half-lives of89Tc and89mTc were measured to be 12.8±0.9 s and 12.9±0.8 s, respectively. The total decay energy, QEC, for89Tc was determined to be 7.51±0.21 MeV.