J. Srebrny

Microscopic dynamic calculations of collective states in xenon and barium isotopes

Abstract Dynamic calculations of collective states for neutron-deficient doubly even Xe and Ba isotopes are performed. The collective Hamiltonian is constructed in terms of the cranking inertial functions and the macroscopic-microscopic potential, both generated by the single-particle motion in the modified harmonic oscillator potential. The pairing correlations are included. Reduction of the standard pairing interaction strengths leads to results compatible with experiment. The deformation dependence of the inertial functions is found to play an important role.

Collective quadrupole excitations in the 50 < Z, N < 82 nuclei with the general Bohr Hamiltonian

Abstract The general Bohr Hamiltonian is applied to a description of low-lying collective excitations in even-even isotopes of Te, Xe, Ba, Ce, Nd and Sm. The collective potential and inertial functions are determined by means of the Strutinsky method and the cranking model, respectively. A shell-dependent parametrization of the Nilsson potential is used. An approximate particle-number projection is performed in the treatment of pairing correlations. The effect of coupling with the pairing vibrations is taken into account approximately when determining the inertial functions. The calculation does not contain any free parameter.

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.

The low-lying quadrupole collective excitations of Ru and Pd isotopes☆

Abstract Quadrupole excitations of even-even Ru and Pd isotopes are described within a microscopic approach based on the general collective Bohr model which includes the effect of coupling with the pairing vibrations. The excitation energies and E2 transition probabilities observed in 104–114 Ru and 106–110 Pd are reproduced in the frame of the calculation containing no free parameters. Particularly interesting are 104 Ru and 106–110 Pd where good agreement to very rich information based on Coulomb excitation experiments is achieved.

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.

Electromagnetic structure of 98Mo

Abstract The nucleus 98 Mo was multiply Coulomb excited using 20 Ne, 84 Kr and 136 Xe beams. Eighteen E2 and M1 reduced matrix elements connecting 7 low-lying levels have been determined using the least-squares code GOSIA. The results are compared with the predictions of an extended version of the IBM1 model. The quadrupole sum rules approach was used to determine the shape parameters in two 0 + (ground and first excited) states. The rotational invariants 〈Q 2 〉 and 〈 cos 3δ〉 obtained show the shape coexistence in 98 Mo nucleus: the triaxial ground state and the prolate first excited state.

Nuclei from the barium region: Nonaxial or gamma-soft?

The possibility is studied of describing nuclei from the Ba, Xe region in terms of the quadrupole collective model with theγ-independent potential energy surface. Results show that the nuclei in question can be treated both asγ-soft vibrators and nonaxial rotors.