A. Harder

Multiparticle-hole states of high spin in N < 50, A ≈ 90 nuclei: 1. The transitional nucleus 4389Tc46

Abstract High spin states in the nucleus 89 Tc have been studied via the fusion evaporation reaction 58 Ni( 40 Ca,2αp) 89 Tc at 180 MeV beam energy. The NORDBALL γ-ray spectrometer equipped with auxiliary detectors for light particle selection was used to measure γγ- and particle-γγ coin-cidences. Some 60 transitions were placed into a level scheme comprising 38 levels reaching up to 9.2 MeV excitation energy and a possible spin of I = 45/2 h . The level scheme is compared to those of neighbouring nuclei and interpreted in terms of the spherical shell model. The calculations were performed with different sets of parameters within a restricted π(p 1 2 ) , π(g 9 2 ) , ν(p 1 2 ) and ν(g 9 2 ) configuration space. States above 2.3 MeV excitation energy are well reproduced by shell model calculations based on an empirical residual interaction, whereas collective excitations are suggested to contribute to the wave functions of lower lying states.

First Identification and Shell Model Structure of 92Rh

Excited states in theN=47 nucleus92Rh were populated via the fusion evaporation reaction58Ni(40Ca,αpn)92Rh at 180 MeV beam energy. A level scheme reaching up to about 7 MeV and probable spins of (19+) and (21−) was established and interpreted with the shell model in the (p1/2,g9/2) model space.

Multiparticle-hole states of high spin in N < 50, A ≈ 90 nuclei: 3. The odd-odd nucleus 88Nb

Abstract High-spin states of the neutron deficient nucleus 88 Nb have been studied following the reaction 56 Fe ( 35 Cl, 2pn) 88 Nb at 120 and 123 MeV bombarding energy. Neutron gated and pure γγ-coincidences were measured with a neutron-γγ-coincidence setup; in addition γγ-coincidences were detected with the OSIRIS-cube at the Cologne tandem accelerator. Via the analysis of γγ-coincidence spectra the level scheme of 88 Nb has been extended up to 9.7 MeV excitation energy. About 88 transitions and 40 new levels have been placed in the level scheme. The experimental level energies and branching ratios are compared to predictions of shell model calculations in the restricted ( p 1/2 , g 9/2 ) configuration space.

Excited States in the Transitional N=45 Nucleus 85Zr

Excited states in the transitional nucleus85Zr were studied via the fusion evaporation reaction56Fe(35Cl,αpn)85Zr at 120 MeV. A level scheme reaching up to probable spins of (33/2+) at 6.2 MeV and (27/2−) at 4.9 MeV was established and compared to neighbouring nuclei.

Double neutron capture in62Ni

The γ-radiation following single and double neutron capture in isotopically enriched62Ni was studied at the high flux reactor of the Institut Laue-Langevin, using a pair and Compton suppressed germanium detector. Measurements before and after 170 d of breeding were performed. The γ-ray fluxes through63Ni and64Ni are discussed; several new levels and spin-parity assignments were found. On the basis of the known discrete levels and the low-energy neutron resonances, level density parameters were determined within the Constant Temperature Fermi Gas model. The neutron binding energies were measured asBn (63Ni)=6837.92(18) keV andBn (64Ni)=9657.64(24) keV. The63Ni (n, γ) cross section for reactor neutrons was measured to be σ=20−2+5 b.

Electromagnetic Decay Strengths in the Isobars 89Nb, 89Mo and 89Tc

Lifetimes of high spin states in the threeA=89 isobars89Nb,89Mo and89Tc have been measured via the Recoil Distance Doppler Shift technique and the fusion evaporation reactions58Ni(35Cl,xnypzα) at 120 MeV beam energy. Reduced transition probabilities for about 50γ transitions were extracted. The experimental branching ratios in89Mo and reduced transition probabilities in all three isobars are compared with the predictions of the spherical shell model based on the restrictedπ(p1/2),π(g9/2), ν(p1/2),ν(g9/2) configuration space with two different types of residual interaction.

Thermal neutron captureγ-ray spectroscopy of59Ni and61Ni

Theγ-radiation emitted after thermal neutron capture in isotopically enriched58Ni and60Ni was measured at the ILL high flux reactor by means of Ge/NaI detectors operated in Compton suppression and pair spectrometer mode. The neutron binding energies were determined asBn (59Ni)=8999.15(23) keV and Bn(61Ni)=7820.07(20) keV; some 95% of the totalγ-ray fluxes through59,61Ni were assigned. Theγ-ray strength functions of the primary transitions and the level densities are discussed.

High-spin spectroscopy near the deformed N ≈ Z ≈ 38 shell gap: The light Rb isotopes

Nuclei near the prolate single-particle energy gap at proton number Z = 38 (epsilon(2) approximate to +0.38) and neutron number N approximate to Z offer unique possibilities to study the pn-interaction at large quadrupole deformation, In the yrast band of the Z = N = 37 nucleus Rb-74, We have identified a crossing of the T = 1 pn-paired band (even spins) with the T = 0 pn-unpaired band (odd spins). In Rb-77, the positive-parity yrast and yrare bands have been followed over large spin ranges and assigned different 1qp-proton 2qp-neutron structures. These band crossings do not follow the usual pattern of two identical particles aligning in high-j orbits, In addition, an aligned g(9/2) proton-neutron negative-parity sequence with K = 11/2 has been identified in Rb-77 Rotational bands with more conventional band crossings have also been found. (Less)

The N=47 Shell-model Nucleus 90Tc

Lifetimes of high spin states in the nucleus90Tc have been measured via the fusion evaporation reactions58Ni(36Ar,3pn)90Tc at 140 MeV and58Ni(35Cl,2pn)90Tc at 120 MeV beam energy. The OSIRIS spectrometer as well as a new neutron-γ-coincidence setup were used to measure lifetimes in the 10−12-10−9s range by the recoil distance Doppler-shift method. By means ofγ-multiplicity and neutron-gated spectra fifteen lifetimes wered-educed. The experimental branching ratios and transition probabilities are compared to predictions of shell model calculations in a restricted π(p1/2), π(g9/2), ν(p1/2), and ν(g9/2) configuration space. In most cases the agreement with the calculations using the Gross-Frenkel parameters is striking but the results for several yrare states very sensitively depend on the residual interaction used.