U. Kaup

Description of even-even Krypton isotopes by the Interacting Boson Approximation

Energy spectra andB(E2) values of the even-even Kr isotopes74–82Kr have been analyzed in terms of the IBA-2 model of Otsuka, Arima and Iachello [6, 7]. We can reproduce the variation of collectivity along the isotope chain by means of a consistent set of 5 parameters, essentially only one of them has been varied with neutron number. The low lying 02+ states have been found to be strongly influenced by shell effects. Predictions are given for the not yet observed gamma bands of74,76Kr.

Excited states in124Xe

Excited states of124Xe have been investigated via the122Te(α, 2n),114Cd(13C, 3n) and108Pd(19F, p2n) reactions using in-beam gamma-ray and electron spectroscopy methods. 36 new levels and several spin and parity assignments were established, revealing the existence of at least one positive parity superband and two negative parity bands, one of them showing backbending.

Prealignment B(E2)-anomaly in 124Xe

Lifetimes of 17 levels of 124Xe were measured using the Recoil Distance Doppler Shift method. An anomalous E2-reduction was observed, starting at Iπ = 8+ and Iπ = 5+ in the groundstate and in the quasi-gamma band respectively. This anomaly is discussed in terms of the Interacting Boson Model.

Excited states in 130Ba

Abstract Excited states of 130Ba have been studied by means of in-beam γ-ray spectroscopy and electron-spectroscopy via the reaction 120Sn(13C, 3n). Spin and parity assignments have been made for 28 new levels. A comparison with a cranking-model calculation shows that the negative-parity band based on the 5− state is a two-quasiproton band.

Band structure of even-even selenium isotopes in the proton-neutron interacting Boson model

Available systematic IBM calculations [1-6] for Krypton and Strontium isotopes have been extended to Selenium. The analysis in terms of the IBM is complicated by the interplay of collective and noncollective degrees of freedom. However, satisfactory agreement has been obtained forN≦42.

Band structure of 78Kr

Abstract Lifetimes of fifteen states of the ground-state, octupole and gamma-band in 78Kr have been measured; energies and E2 transition strengths have been interpreted in terms of the neutron-proton boson model.

A TEST OF THE INTERACTING BOSON FERMION MODEL AND ITS MICROSCOPIC BASIS IN TRANSITIONAL TC AND AG NUCLEI

Abstract Parameters of the interacting boson fermion model obtained by fitting the model to the spectra of four nuclei in the 1g 9 2 shell have been compared with the values given by microscopic formulas taking into account the two-particle structure of the bosons.

E2-transition probabilities in 77Br+

Abstract77Br has been investigated by the reaction64Ni(16O,p2nγ) at 60 MeV. The following mean lives (in parentheses) have been determined by the recoil distance Doppler shift method (energies in keV): 161.9 (718±50 ps), 575.2 (14.2±2.1 ps), 639.0 (14.1±0.8 ps), 782.0 (4.3±0.9 ps), 790.1 (6.2±0.8 ps), 1,273.2 (4.0±1.0 ps), 1,303.0 (4.0±1 ps), 1,480.8 (0.6 ±0.2 ps). The resultingB(E2) values are compared with rotor plus particle calculations. Nuclear reaction64Ni(16O,p2nγ)E0=60 MeV; measuredEγ, recoil distance Doppler shift; deducedT1/2. Enriched target, Ge(Li).

High-spin states in97Tc

The level scheme of97Tc was studied by gamma ray spectroscopy using the94Zr(6Li, 3nγ)97Tc reaction. New levels and spins and parities were established.97Tc is compared with the neighbouring even-even nucleus and with the results of an IBFM calculation.

Description of Odd Medium Mass Nuclei in the Interacting Boson-Fermion Model

In this paper we will discuss the application of the new Interacting Boson Fermion Model (IBFM)1 to low lying positive parity levels in Rb, Tc and Ag nuclei. We restrict the discussion on the positive parity levels, because the odd particle is then predominantly in the g9/2 shell only, thus providing a rather pure case.