S. Törmänen

High-spin spectroscopy of the 142Eu, 143Eu and 144Eu nuclei

Abstract High-spin level schemes of the 142Eu, 143Eu and 144Eu nuclei have been investigated by in-beam γ-ray spectroscopic methods using the NORDBALL Compton-suppressed multi-detector array. The previously known schemes have been extended to considerably higher spin and excitation energy, up to I ≈ 30, Ex ⩾ 9 MeV in 142Eu, I = 75 2 , Ex = 15.6 MeV in 143Eu and I ≈ 40, Ex ⩾ 16 MeV in 144Eu. The level schemes are very complicated, characteristic of spherical or slightly oblate nuclei. Also, long cascades of stretched E2 transitions have been observed in all three nuclei. Plunger and DSAM lifetime results demonstrate high collectivity values up to ∼100 W.u. (up to ∼200 W.u. in 142Eu) in these E2 cascades and they are proposed to represent several crossing collective bands with the nucleus at triaxial shape of β2 ≈ 0.25 and γ ≈ 30°. Low parts of the level schemes have been discussed within the spherical shell model. Below 5.5 MeV excitation in 144Eu and 3.5 MeV in 143Eu practically all the observed levels are interpreted with shell model configurations of respectively two or four, and one or three quasiparticles.

Competing T=0 and T=1 structures in the N=Z nucleus 6231Ga

Abstract The low-lying levels in the odd-odd N = Z nucleus 62 Ga have been identified for the first time. These data reveal a cascade of stretched-E2 transitions based on a T =0, 1 + bandhead which decays directly to the T =1, 0 + ground state. The observed levels are interpreted in the context of theshell model, using as a basis, the pf 5/2 g 9/2 orbits with a 56 Ni core.

Stability of 10050Sn50 deduced from excited states in 9948Cd51.

Excited states of neutron deficient nuclei close to Sn-100 were investigated in an in-beam spectroscopic experiment using the NORDBALL detector array. Excited states in Cd-99 were identified for the first time. The measured half-life of an isomeric state in Cd-99 indicates that the stability with respect to quadrupole shape changes is as large in Sn-100 as for other heavy doubly magic nuclei.Excited states of neutron deficient nuclei close to {sup 100}Sn were investigated in an in-beam spectroscopic experiment using the NORDBALL detector array. Excited states in {sup 99}Cd were identified for the first time. The measured half-life of an isomeric state in {sup 99}Cd indicates that the stability with respect to quadrupole shape changes is as large in {sup 100}Sn as for other heavy doubly magic nuclei. {copyright} {ital 1996 The American Physical Society.}

Gamma-ray spectroscopy of 110Cd

Abstract The nucleus 110Cd has been studied using the 13C and 18O induced reactions and the NORDBALL multi-detector array. The yrast band was observed to Iπ = 28+ and a large number of side bands were identified. The h 11 2 neutrons were found to play a dominant role in the observed rotational structures. The weakly populated yrast 3187 keV 8+ state is interpreted as arising from the proton g 9 2 −2 configuration. Collective bands, where the band members are connected by ΔI = 1 transitions and where the ΔI = 2 transitions are not observed, are also reported. These bands are interpreted to have prolate configurations involving both the h 11 2 neutrons and the g 9 2 protons. The experimental data are discussed in terms of the total routhian surface and cranked shell model calculations.

Lifetimes of yrast states in 110Cd

Abstract Lifetimes or lifetime limits of 20 yrast levels in 110 Cd have been measured using the recoil-distance method and the NORDBALL array of Compton-suppressed Ge detectors. From the reduced transition probabilities competing rotational and vibrational behaviour of 110 Cd is revealed. Also non-collective states, associated with proton configurations, have been observed.

Transition probabilities in negative parity bands of the 119I nucleus

Abstract Lifetimes in four negative-parity bands of 119 I were measured using DSAM and RDM. 119 I nuclei were produced in the 109 Ag( 13 C,3n) reaction, γγ coincidences were collected using the NORDBALL array. RDDSA — a new method of RDM analysis — is described. This method allowed for the self-calibration of stopping power. From 31 measured lifetimes, 39 values of B (E2) were established. Calculations in the frame of the Core Quasi Particle Coupling (CQPC) model were focused on the problem of susceptibility of the nucleus to γ -deformation. It was established that nonaxial quadrupole deformation of 119 I plays on important role. The Wilets–Jean model of a γ -soft nucleus describes the 119 I nucleus in a more consistent way then the Davydov–Filippov model of a γ -rigid nucleus.

Coexisting structures in 119I

Abstract High-spin structures of 119 I have been studied by using 13 C and 15 N induced reactions. In all, fifteen ΔI = 1 or 2 bands belonging to 119 I were found. No evidence was found for bands with collective oblate shape, instead, all the observed rotational bands were interpreted to possess a collective prolate shape. A rich tapestry of noncollective states of both negative and positive parity was observed. Based on TRS calculations various configurations at β 2 ≈ 0.17 and γ = 60° were assigned to these states.

The role of the shape driving h12 neutron orbital in 108Cd

Abstract The nucleus 108Cd has been studied using a heavy-ion reaction and the NORDBALL multi-detector array. The yrast band has been extended to Ip = 24+, and nine quasi-rotational side bands have been identified. The n h 11 2 negative-parity orbital is found to play a dominant role both in the low-spin as well as in the high-spin structure of 108Cd. The first band crossing in the yrast band is caused by the h 11 2 neutrons. The 10+ state of the aligned n( h 11 2 ) 2 configuration decays strongly into a low-lying low-spin intruder-like positive-parity band. It is suggested that this intruder structure is dominated by a non-aligned n( h 11 2 ) 2 configuration. For the first time in this mass region, we report a collective, possibly prolate, M1 band built on the p( g 9 2 ) −2 configuration. The experimental results are discussed in terms of total-routhian-surface and cranked-shell-model calculations.

Competing proton and neutron alignments in neutron-deficient Xe-nuclei

Abstract High-spin structures of the neutron-deficient 117,118,120 Xe isotopes have been studied by in-beam γ-ray spectroscopic techniques. The final nuclei have been identified by means of charged-particle detectors. Collective rotational bands based on the neutron d 5 2 , g 7 2 and h 11 2 configurations have been identified in 117 Xe. In the even 118 Xe and 120 Xe nuclei several new side bands were observed and the previously known bands were extended. The present level schemes include two positive-parity bands constructed to high spin in 118 Xe, whereas in 120 Xe three such bands were observed. In order to explain these bands, both proton and neutron ( h 11 2 ) 2 alignments, as well as the shape degree of freedom, have to be invoked. The possible occurrence of a γS-band is addressed and a pronounced structural change for more heavy Xe-isotopes is discussed. All negative-parity side bands are interpreted in terms of proton two-quasiparticle excitations. The experimental data are compared with total routhian surface calculations.

In-beam study of 102In, 104In and 106In

Proton-rich odd-odd In isotopes have been investigated by in-beam spectroscopic methods using the NORDBALL detector array. A Ni-58 beam with an energy of 270 MeV was used to bombard a Fe-54 target. ...