No abstract available

[en] The Zr isotopes are often used as a test ground for theoretical studies. Their observed properties change smoothly in going from the spherical "9"0Zr to the strongly deformed "1"0"2Zr. A good description of the low lying excited states in this region can be achieved by performing shell model calculations using interactions based on realistic NN forces. We will report preliminary results on the spectrum of "9"1Zr within the Important sampling approximation in the full model space (1f_5_/_2, 2p_1_/_2, 2p_3_/_2, 1g_9_/_2) for protons and (2d_5_/_2, 3s_1_/_2, 2d_3_/_2, 1g_7_/_2, 1h_1_1_/_2) for neutrons. (author)

[en] Rotational bands built on two-quasineutron states have been identified in ¹⁰⁰Zr and ¹⁰²Zr. The level energies and gamma branching ratios were determined from triple-gamma coincidence data obtained with the EUROGAM 1 array and ²⁴⁸Cm source. The energies of the two-quasiparticle bandheads have been used within the BCS model of pairing to deduce the strength of pairing interaction, G. The values of G have been determined to be 0.21 and 0.19 MeV in ¹⁰⁰Zr and ¹⁰²Zr, respectively. These are somewhat smaller than the value of 23/A used in the spherical even-even nuclei in this mass region but in agreement with the value of 21/A used by Chasman to reproduce observed deformations in these nuclei

[en] Rapid shape changes are observed in the region of neutron rich nuclei with a mass around A=100. Precise lifetime measurements are a key ingredient in the systematic study of the evolution of nuclear deformation and the degree of collectivity in this region. Nuclear lifetimes of excited states can be obtained using the fast-timing technique with LaBr₃(Ce)-scintillators. We used neutron induced fission of ²⁴¹Pu in order to study lifetimes of excited states of fission fragments in the A∝100 region. The EXILL-FATIMA array located at the PF1B cold neutron beam line at the Institut Laue-Langevin comprises of 8 BGO-shielded EXOGAM clover detectors and 16 very fast LaBr₃(Ce)-scintillator detectors, which were installed around the fission target. We have studied the lifetimes of low lying states for the nuclei ⁹⁸Zr, ¹⁰⁰Zr and ¹⁰²Zr by applying the generalized centroid difference method. In this contribution we report on the used fast-timing setup and present preliminary results for the studied isotopes.

[en] The population of ¹⁰²Zr following the β decay of ¹⁰²Y produced in the projectile fission of ²³⁸U at the GSI facility in Darmstadt, Germany has been studied. ¹⁰²Y is known to ß decay into ¹⁰²Zr via two states, one of high spin and the other low spin. These states preferentially populate different levels in the ¹⁰²Zr daughter. In this paper the intensities of transitions in ¹⁰²Zr observed are compared with those from the decay of the low-spin level studied at the TRISTAN facility at Brookhaven National Laboratory and of the high-spin level studied at the JOSEF separator at the Kernforschungsanlage Jülich.

No abstract available

[en] A fast-timing experiment was performed at the Argonne National Laboratory between December 2015 and January 2016, with the purpose of measuring the lifetimes of the lowest lying states of nuclei belonging to the deformed regions around mass number A ∼ 110 and A ∼ 150. The lifetimes of the first excited states are the basic ingredients for quadrupole moment calculations, which give information about the structural evolution that occurs in the deformed areas of the nuclear chart. The nuclei of interest were populated in the spontaneous fission of ²⁵²Cf since the maxima of the fragment mass distribution lie approximately in the centre of the regions of interest. The ²⁵²Cf source was placed at the focus of the Gamma-sphere array (51 HPGe) which was coupled with a fast timing array, comprising 25 LaBr₃:Ce scintillator detectors. Each sub-array covered ∼ 2π of the solid angle. Quadruple events (two gamma rays from Gamma-sphere and two from the LaBr₃:Ce array) were collected for a period of 30 days. LaBr₃:Ce scintillator detectors have been extensively used in the past to perform fast-timing measurements thanks to their capability to access the subnanosecond regime. The high energy resolution of HPGe detectors together with the excellent time resolution of LaBr₃:Ce detectors, conferred to this hybrid array the right features to perform both fast-timing and spectroscopy measurements. This was the first time that the Gamma-sphere array was successfully coupled with an array containing such a large number of LaBr₃:Ce detectors. Details of the setup and the digital acquisition system will be given, focusing on the signal processing and the coincidence mechanism. Some preliminary results obtained from ¹⁵²Eu and ¹⁶⁶Ho sources will be shown in order to prove the effectiveness of this arrangement. The status of the analysis for the nuclei ^103,105Zr, lying in the first peak of the ²⁵²Cf fragment mass distribution, will be presented. This document is made up of an abstract, a poster and the slides of the presentation. (authors)

[en] The projected shell model calculations have been carried out in neutron-rich ^100–108Zr and ^98–102Sr isotopes. The shape evolution and electromagnetic properties have been examined in neutron-rich Zr and Sr isotopes around N = 60. The structure of yrast states, backbending phenomena, g-factors and B(E2) transition probabilities are calculated and compared with corresponding observable quantities. The present calculations predict the occurrence of coexistence of prolate-oblate shapes at 0⁺ state in ^100,102Zr and ^98,100Sr. Nuclei beyond N = 62 are predicted to have prolate deformation in the ground-state. (author)

[en] Fragment angular momenta as a function of neutron multiplicity were extracted for the first time for the Mo-Ba and Zr-Ce charge splits of ²⁵²Cf by studying prompt coincident γ-rays. The obtained primary fragment angular momenta do not continuously rise with the increase in the number of neutrons evaporated. In frame of the scission point bending oscillation model such regularity is explained due the decrease of the bending temperature. Adiabatic bending oscillations (T=0) are obtained at large (ν_tot>5) and small (ν_tot=0) scission point elongation. These oscillations are excited to the temperature of 2 - 3 MeV for the most probable scission configurations indicating a weak coupling between collective and internal degrees of freedom. A strong coupling between the collective bending and dipole oscillations was found. copyright 1998 American Institute of Physics

[en] The A∼110 region of neutron-rich nuclei is one containing a rich variety of nuclear structure, with theory suggesting competition between several different shapes. To gain information about these shapes the half-lives of the 2_1"+ states have been measured for "1"0"2"-"1"0"8Zr and the surrounding region. The nuclei of interest were produced through the in-flight fission of a 345 MeV/nucleon "2"3"8U beam by a "9Be target and selected by the BigRIPS separator. At the final focal plane of the separator, the nuclei were implanted into 5 DSSDs (WAS3ABi). Gamma-rays emitted following β-decay, or decay of isomeric states, were detected in an array of 12 clusters of 7 HPGe detectors (EURICA) augmented with 18 LaBr_3(Ce) detectors. Beta-gamma timing, measured between fast scintillators around WAS3ABi and the LaBr_3(Ce) detectors, allowed the measurement of nuclear level half-lives in the nanosecond regime. The efficacy of the β-γ timing was tested by measuring the half-lives of the 2_1"+ level in "1"0"2","1"0"4Zr and "1"0"6","1"0"8Mo. The preliminary results are presented along with experimental details. (author)