O. Wieland

Constraints on the symmetry energy and neutron skins from pygmy resonances in Ni 68 and Sn 132

Correlations between the behavior of the nuclear symmetry energy, the neutron skins, and the percentage of energy-weighted sum rule (EWSR) exhausted by the Pygmy Dipole Resonance (PDR) in 68Ni and 132Sn have been investigated by using different Random Phase Approximation (RPA) models for the dipole response, based on a representative set of Skyrme effective forces plus meson-exchange effective Lagrangians. A comparison with the experimental data has allowed us to constrain the value of the derivative of the symmetry energy at saturation. The neutron skin radius is deduced under this constraint.

Structural Evolution in the Neutron-Rich Nuclei ^{106}Zr and ^{108}Zr

The low-lying states in ¹⁰⁶Zr and ¹⁰⁸Zr have been investigated by means of β-γ and isomer spectroscopy at the radioactive isotope beam factory (RIBF), respectively. A new isomer with a half-life of 620 ± 150 ns has been identified in ¹⁰⁸Zr. For the sequence of even-even Zr isotopes, the excitation energies of the first 2⁺ states reach a minimum at N = 64 and gradually increase as the neutron number increases up to N = 68, suggesting a deformed subshell closure at N = 64. The deformed ground state of ¹⁰⁸Zr indicates that a spherical subshell gap predicted at N = 70 is not large enough to change the ground state of ¹⁰⁸Zr to the spherical shape. The possibility of a tetrahedral shape isomer in ¹⁰⁸Zr is also discussed.

Evidence for the Jacobi shape transition in hot46Ti

The gamma-rays from the decay of the GDR in 46Ti compound nucleus formed in the 18O+28Si reaction at bombarding energy 105 MeV have been measured in an experiment using a setup consisting of the combined EUROBALL IV, HECTOR and EUCLIDES arrays. A comparison of the extracted GDR lineshape data with the predictions of the thermal shape fluctuation model shows evidence for the Jacobi shape transition in hot 46Ti. In addition to the previously found broad structure in the GDR lineshape region at 18-27 MeV caused by large deformations, the presence of a low energy component (around 10 MeV), due to the Coriolis splitting in prolate well deformed shape, has been identified for the first time.

Position sensitivity of large volume LaBr 3 :Ce detectors

The position sensitivity of two large volume (1” × 1” and 3” × 3”) LaBr<inf>3</inf>:Ce crystals has been measured using collimated beams of 662 keV γ-rays. The crystals have been coupled to a Position Sensitive Photo Multiplier Tube (PSPMT) and/or shielded phototube. The results indicate that, in the case of 662 keV γ -rays, both crystals should allow identification of the the position of the γ-ray first interaction with a 1-2 cm resolution. Similar tests have been done in the past using 140 keV γ-rays and no sensitivity was found. Using GEANT4 simulations we confirmed these results.

Probing the Order-to-Chaos Region in Superdeformed {sup 151}Tb and {sup 196}Pb Nuclei with Continuum {gamma} Transitions

The gamma decay associated with the warm rotation of the superdeformed nuclei 151Tb and 196Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the superdeformed well. A Monte Carlo simulation of the gamma decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength for 1-2 MeV gamma rays, which may be related to the evidence for octupole vibrations in both mass regions.

Neutron-skin thickness from the study of the anti-analog giant dipole resonance

The γ-decay of the anti-analog of the giant dipole resonance (AGDR) to the isobaric analog state has been measured following the p( 124Sn,n) reaction at a beam energy of 600 MeV/nucleon. The energy of the transition was also calculated with state-of-the-art self-consistent relativistic random-phase approximation (RPA) and turned out to be very sensitive to the neutronskin thickness (ΔRpn). By comparing the theoretical results with the measured one, the ΔRpn value for 124Sn was deduced to be 0.21 ± 0.07 fm, which agrees well with the previous results. The present method offers new possibilities for measuring the neutron-skin thicknesses of very exotic isotopes.

Active voltage divider for improved estimation of interacting radiation energy with photomultiplier tubes coupled to high light yield scintillators

New materials with very high light yield and short scintillation decay time have been developed in the past few years: e.g. Cerium doped Lanthanum Bromide (LaBr3:Ce), Europium doped Strontium Iodide (SrI2: Eu).

PRE-EQUILIBRIUM EFFECTS IN THE SECONDARY PARTICLE SPECTRA IN THE REACTIONS WITH HEAVY IONS

Theoretical description of the experimentally obtained spectra for protons and α-particles and model calculations for the neutron spectra in the reactions with heavy ions has been presented. The hybrid model of non-equilibrium processes was used. Equilibrium evaporation process was analyzed in the framework of the statistical theory of nuclear reactions with Monte-Carlo simulation including certain dynamical and kinematical characteristics. This approach was included in PACE code, which permits to simulate Monte-Carlo de-excitation nuclear process. The Fermi-gas model and level-density phenomenological model for the variation of the nuclear level density parameters was used. In this approach data on 16O+116Sn reaction with Ebeam = 130, 250 MeV were analyzed. Double-differential light charged particle spectra for this reaction were measured using the GARFIELD apparatus in coincidence with evaporation residues. The experimental data were collected in four angular ranges from 29 to 41, 41 to 53, 53 to 67 and 67 to 82 degrees in the laboratory system. The results of the calculations are shown and discussed for these four angular ranges. The contributions from the evaporative and pre-equilibrium processes were analyzed in connection with different nucleus equilibration mechanisms.

GAMMA-RAY SPECTROSCOPY IN THE VICINITY OF 108 Zr

F. Browne et al.; 4 pags.; 2 figs.; Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane, Poland, August 31–September 7, 2014; PACS numbers: 21.10.Re, 21.10.Tg, 23.20.Js, 27.60.+j

Double-differential spectra of the secondary particles in the frame of pre-equilibrium model

An approach was developed to describe the double-differential spectra of secondary particles formed in heavy-ion reactions. Griffin model of nonequilibrium processes was used to account for the nonequilibrium stage of the compound system formation. Simulation of de-excitation of the compound system was carried out using the Monte-Carlo method. Analysis of the probability of neutron, proton, and α-particle emission was performed both in equilibrium, and in the pre-equilibrium stages of the process. Fission and γ-ray emission were also considered after equilibration. The analysis of the experimental data on the double-differential cross sections of p, α particles for the 16O + 116Sn reaction at the oxygen energy E = 130 and 250 MeV were performed.