R. Schubart

The shell model at 100Sn—An experimental status report

The present status of the shell model structure at .t = Z = 50 is giken. On the basis of recent and previous experimental work a shell model description of known nuclei is given resulting in predictions for single particle energies for the doubly magic Sn core. Various approaches for the residual (two-body) interaction (empirical, realistic. schematic) were used (and combined), to test their influence on the extrapolated single particle energies. A comparison with the lighter .V = Z doubly magic nuclei 0. and 40Ca and Ni reveals consistent results for Coulomb shifts, spin-orbit splitting and proton-neutron symmetry. There are first indications for dripline effects breaking the isospin symmetry. The results are used to discuss future experiments and their relevance for the determination of the OSn shell model parameters.

Shears bands in 201Pb and 202Pb

Abstract High-spin states in 201 Pb and 202 Pb have been investigated using in-beam γ-ray spectroscopic techniques. Seven regular sequences of enhanced dipole transitions, with weak E2 crossovers in some cases, have been found, one of which is firmly connected to low-lying levels in 201 Pb. These bands are interpreted to be built on high-spin proton-particle neutron-hole excitations. Tilted-axis cranking calculations show that the angular momentum along the bands is predominantly generated by a continuous and simultaneous reorientation of the proton and neutron spins into the direction of the total angular momentum (shears effect).

Excited states built on the 6[sup [minus]] isomer in [sub 37][sup 86]Rb[sub 49]

High-spin states of the doubly-odd nucleus[sup 86]Rb containing 37 protons and 49 neutrons have been investigated via the reaction [sup 82]Se([sup 7]Li,3[ital n]) using [sup 7]Li ions with energies between 30 and 35 MeV. The new level scheme is based on prompt [gamma][gamma] coincidences, angular distributions and directional correlation orientation ratios of [gamma] rays as well as on linear polarizations of some strong [gamma] rays and contains levels with excitation energies up to 7.9 MeV and tentative spins up to 16[h bar]. For fifteen of the levels lifetimes in the ps region have been determined by analyzing the Doppler shift of [gamma] rays. Several fast [ital M]1 transitions with [ital B]([ital M]1)[approx gt]0.3W.u. have been identified. The new high-spin level scheme of [sup 86]Rb is interpreted on the basis of shell-model calculations in the configuration space 1[ital p][sub 3/2], 0[ital f][sub 5/2], 1[ital p][sub 1/2], and 0[ital g][sub 9/2] for the protons and 1[ital p][sub 1/2], 0[ital g][sub 9/2], and 1[ital d][sub 5/2] for the neutrons. The energies of the observed levels with [ital I][gt]5 as well as most of the observed electromagnetic transition probabilities could be well described. The excitation of a 0[ital g][sub 9/2] neutron over the [italmorexa0» N]=50 shell gap into the [ital d][sub 5/2] orbital is predicted to cause remarkable alterations only for states with [ital I][sup [pi]][ge]15[sup +]. Some of the reduced [ital M]1 transition probabilities calculated within the shell model are found to depend critically on the parametrization used to describe the residual interaction.«xa0less

High-spin States in the Transitional Nucleus 88Mo

The reaction58Ni(36Ar,α qρ)88Mo has been studied at 145 MeV beam energy. A detector array consisting of the OSIRIS spectrometer, four charged-particleΔE detectors and seven NE213 neutron detectors has been used to meaure the gamma radiation inγγ- and particle-γγ-coincidence mode. The level scheme of88Mo has been extended up to 11.6 MeV excitation energy and probable spin 23ħ; some 70 transitions and 40 levels have been identified. Spin assignments have been proposed on the basis of measured DCO ratios. Hartree Fock cranking calculations of the Total Routhians and shell model calculations of the high spin states are presented which imply near-sphericity of the yrast line up to the highest spins found. A classification of the high spin states according to their leading seniority is proposed.

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

High spin states in the nucleus Tc-89 have been studied via the fusion evaporation reaction Ni-58(Ca-40,2 alpha p)Tc-89 at 180 MeV beam energy. The NORDBALL gamma-ray spectrometer equipped with auxiliary detectors for light particle selection was used to measure gamma gamma- and particle-gamma gamma coincidences. 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 = 45/2HBAR 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 pi(p(1/2)), pi(g(9/2)), nu(p(1/2)) and nu(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. (Less)

The decay of theIπ=8+ isomer in100Cd-neutron particle and proton hole states

The γ-decay and half life of the t1/2=60(3) ns Iπ=8+ isomer in100Cd have been studied with a recoil catcher setup inside the multidetector π-array OSIRIS. Evaporation neutrons and charged particles from the reaction58Ni+46Ti were measured in coincidence with delayed γ-rays. Six new γ-ray transitions with intensities of 1–10% of the main γ-ray cascade were found, two new states established and firm spin-parity assignments were made to all states below the isomer. The new states were identified as the 4+ and 6+ members of the proton πg9/2−2 multiplet.

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.

High spin structure in127Xe and125Xe

Excited states of the nuclei127Xe and125Xe have been investigated in the inverse kinematic reactions48Ca(82Se,(3.5)n) at 275 MeV beam energy with the OSIRIS multidetector system at the VICKSI-accelerator of the HMI Berlin. The level scheme of127Xe was extended up to a level of tentative spin (51/2−). Two excited bands of 3QP-character were observed. For125Xe these structures were extended towards higher spins. Experimental Routhians of selected bands are presented.