Ch. Droste

Experimental test of the polarization direction correlation method (PDCO)

Abstract The study of the polarization direction correlation method (PDCO) for γ quanta emitted from the nuclear states oriented in fusion-evaporation reactions is discussed with emphasis on making unique multipolarity assignments. The method is applied to the data coming from a typical experiment performed with the EUROGAM II array, where polarization-sensitive CLOVER detectors were used. The accuracy obtained in the experiment for the studied transitions was high enough to exclude, using the PDCO method, most of the ambiguities which occur if the assignments are made on the basis of angular correlation measurements alone.

In-beam study of the 128, 130Xe nuclei

Abstract The level structure of 128,130Xe has been studied in the (α, 2nγ) and (3He, 3nγ) reactions on enriched Te targets using in-beam γ-ray spectroscopic methods. For both nuclei the existing information about positive-parity level structure was enriched and many new negative-parity two-quasiparticle states were observed. Isomeric states with the half-lives of 63 ± 12 ns in 128 Xe and 4.8 ± 0.5 ns in 130 Xe were found. For collective positive-parity states the interacting boson model, and calculations based on Bohr hamiltonian were compared with the experimental data.

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.

Collective quadrupole dynamics and the band structure of the nucleus 127Cs

Abstract Excited states of 127 55 Cs were populated in the 127 I(α, 4n) 127 Cs reaction. Singles, prompt and delayed γ-ray spectra, γγ coincidence spectra, angular distributions and excitation functions were measured, and negative and positive parity bands established. The h 11 2 families of excited levels in 127, 129 Cs and 133 La were reproduced by core-particle coupling calculations, regardless of whether the cores were taken to be rigid triaxial rotors or to have all five quadrupole degrees of freedom. The hamiltonians for the latter case were based on microscopic calculations which attribute an important role to the γ-dependence of the mass functions for collective quadrupole motion. From a core-quasiparticle analysis of the positive-parity levels in 127 Cs, indications of a “Coriolis attenuation” anomaly were inferred.

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.

PDCO: Polarizational-directional correlation from oriented nuclei

Abstract A general formula is given for correlation between two polarized gamma rays ( γ 1 and γ 2 ) emitted in a cascade from an oriented (for example, due to a heavy ion reaction) nucleus. It allows us or one to calculate the angular correlation between: (a) Linear polarizations of γ 1 and γ 2 . (b) Polarization of γ 1 and direction of γ 2 or vice versa. (c) Directions of γ 1 and γ 2 (DCO). The formula, discussed in detail for the case (b), can be used in the analysis of data coming from the modern multidetector gamma ray spectrometers that contain new generation detectors (e.g. CLOVER) sensitive to the polarization. The analysis of polarization together with DCO ratio can lead to a unique spin/parity assignment and a mixing ratio determination.

Study of the124Xe and126Xe structure

The level structure of124Xe and126Xe is studied on the basis ofβ+ decay of124Cs and126Cs. The Cs isotopes were produced in the Xe(p, n) Cs reactions at a proton energy ofE≈9.5 MeV. Decay schemes are proposed for these nuclei. The available experimental data are compared with the predictions of various models.

The decay of128Cs to levels in128Xe

The level structure of128Xe has been studied from theβ+ decay of128Cs by observing gamma rays and gamma-gamma coincidences. The128Cs isotope was produced in the128Xe(p, n)128Cs reaction at a proton energy ofE∼9.5 MeV. A decay scheme has been proposed for this nucleus.

From highly to superdeformed shapes: study of 143Gd

Abstract A superdeformed band has been discovered in 143Gd consisting of 15 transitions. It does not show the band crossing observed in the neighbouring heavier Gd isotopes and it is degenerate with the superdeformed band in 143Eu. In contrast to other degenerate bands at superdeformed shape, the configurations of the bands are quite different here. They result from the exchange of a ν64 with a π[404]9/2 configuration. In addition, a collective band has been observed which adopts a well-deformed triaxial shape at high spins according to calculations. The transition from highly to superdeformed shapes proceeds via triaxial shapes.

El, E2, E3 and M1 information from heavy ion coulomb excitation

Abstract The richness of information pertaining to El, E2, E3 and M1 interaction deduced from Coulomb excitation experiments is illustrated. E2 and particularly M1 transition probabilities in 128 Xe are presented. Large set of E3 and E1 additionally to E2 transition probabilities in 226 Ra are shown.