12 research outputs found
Symmetries at and Near Critical Points of Quantum Phase Transitions in Nuclei
We examine several types of symmetries which are relevant to quantum phase
transitions in nuclei. These include: critical-point, quasidynamical, and
partial dynamical symmetries.Comment: 5 pages, 4 figures, Proc. 13th Int. Conf. on "Capture Gamma-Ray
Spectroscopy and Related Topics", August 25-29, 2008, Cologne, German
The 85$Rb(p,n)85Sr reaction and the modified proton optical potential
The cross sections of the astrophysically relevant 85$Rb(p,n)85Srg,m reaction
have been measured between Ec.m. = 2.16 and 3.96 MeV. The cross sections have
been derived by measuring the gamma radiation following the beta decay of the
reaction products. A comparison with the predictions of Hauser-Feshbach
calculations using the NON-SMOKER code confirms a recently derived modification
of the global optical proton potential.Comment: CGS XIII conferenc
Non-Statistical Effects in Neutron Capture
There have been many reports of non-statistical effects in neutron-capture
measurements. However, reports of deviations of reduced-neutron-width
distributions from the expected Porter-Thomas (PT) shape largely have been
ignored. Most of these deviations have been reported for odd-A nuclides.
Because reliable spin (J) assignments have been absent for most resonances for
such nuclides, it is possible that reported deviations from PT might be due to
incorrect J assignments. We recently developed a new method for measuring spins
of neutron resonances by using the DANCE detector at LANSCE. Measurements made
with a 147Sm sample allowed us to determine spins of almost all known
resonances below 1 keV. Furthermore, analysis of these data revealed that the
reduced-neutron-width distribution was in good agreement with PT for resonances
below 350 eV, but in disagreement with PT for resonances between 350 and 700
eV. Our previous (n,alpha) measurements had revealed that the alpha strength
function also changes abruptly at this energy. There currently is no known
explanation for these two non-statistical effects. Recently, we have developed
another new method for determining the spins of neutron resonances. To
implement this technique required a small change (to record pulse-height
information for coincidence events) to a much simpler apparatus: A pair of C6D6
gamma-ray detectors which we have employed for many years to measure
neutron-capture cross sections at ORELA. Measurements with a 95Mo sample
revealed that not only does the method work very well for determining spins,
but it also makes possible parity assignments. Taken together, these new
techniques at LANSCE and ORELA could be very useful for further elucidation of
non-statistical effects.Comment: 8 pages, 3 figures, for proceedings of CGS1
New supersymmetric quartet of nuclei: 192Os, 193Os, 193Ir, 194Ir
We present evidence of the existence of a new supersymmetric quartet of
nuclei in the A=190 mass region. The analysis is based on new experimental
information on the odd-odd nucleus 194Ir from transfer and capture reactions.
The new data allow the identification of a new supersymmetric quartet,
consisting of the 192,193Os and 193,194Ir nuclei. We make explicit predictions
fo r193Os, and suggest that its spectroscopic properties be measured in
dedicated experiments. Finally, we study correlations between different
transfer reactions.Comment: 5 pages, 2 figures, invited talk at CGS 13, Cologne, Germany, to be
published in AIP Conference Proceeding
Neutron Induced Capture Reaction Studies in the Resonance Region at GELINAAIP Conference Proceedings
The neutron time-of-flight facility GELINA installed at the IRMM Geel (13) has been designed to study neutron-induced reactions in the resonance region. It is a multi-user facility, providing a pulsed white neutron source, with a neutron energy range between 10 meV and 20 MeV and a time resolution of 1 ns. The research program concentrates on cross section data needs for nuclear energy applications. In this paper efforts to improve the quality of cross section data for neutron induced capture reactions in the resolved and unresolved resonance region are presented together with examples of cross section data to support the development of advanced reactor concepts and to optimize the use of present nuclear power plants
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New insights into the structure of exotic nuclei using the RISING active stopper
This conference paper outlines the operation and some of the preliminary physics results using the GSI RISING active stopper. Data are presented from an experiment using combined isomer and betaâdelayed gammaâray spectroscopy to study lowâlying spectral and decay properties of heavyâneutronârich nuclei around AâŒ190 produced following the relativistic projectile fragmentation of 208Pb primary beam. The response of the RISING active stopper detector is demonstrated for both the implantation of heavy secondary fragments and inâsitu decay of betaâparticles. Betaâdelayed gammaâray spectroscopy following decays of the neutronârich nucleus 194Re is presented to demonstrate the experimental performance of the setâup. The resulting information inferred from excited states in the W and Os daughter nuclei is compared with results from Skyrme HartreeâFock predictions of the evolution of nuclear shape
Structure of Nâ„126 nuclei produced in fragmentation of
The nuclear structure of neutron-rich Nâ„126 nuclei have been investigated following their production via relativistic projectile fragmentation of a E/A=l GeV 238U beam on a Be target. The cocktail of secondary beam products were separated and identified using the GSI FRagment Separator (FRS). The nuclei of interest were implanted in a high-granularity active stopper detector set-up consisting of 6 double sided silicon strip detectors. The associated gamma-ray transitions were detected with the RISING array, consisting of 15 Euroball cluster Ge-detectors. Time-correlated gamma decays from individually identified nuclear species have been recorded, allowing the clean identification of isomeric decays
Deformation and mixing of coexisting shapes in neutron-deficient polonium isotopes
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Studying Gamow-Teller transitions and the assignment of isomeric and ground states at NâŻ=âŻ50
Direct mass measurements of neutron-deficient nuclides around the N=50 shell closure below 100Sn were performed at the FRS Ion Catcher (FRS-IC) at GSI, Germany. The nuclei were produced by projectile fragmentation of 124Xe, separated in the fragment separator FRS and delivered to the FRS-IC. The masses of 14 ground states and two isomers were measured with relative mass uncertainties down to 1Ă10â7 using the multiple-reflection time-of-flight mass spectrometer of the FRS-IC, including the first direct mass measurements of 98Cd and 97Rh. A new QEC=5437±67 keV was obtained for 98Cd, resulting in a summed Gamow-Teller (GT) strength for the five observed transitions (0+â¶1+) as B(GT)=2.94â0.28+0.32. Investigation of this result in state-of-the-art shell model approaches accounting for the first time experimentally observed spectrum of GT transitions points to a perfect agreement for N=50 isotones. The excitation energy of the long-lived isomeric state in 94Rh was determined for the first time to be 293±21 keV. This, together with the shell model calculations, allows the level ordering in 94Rh to be understood