589 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
A shell-model study of the light Cd isotopes
In an attempt to describe the excitation spectra and transitions strengths of light even-even Cd-isotopes (A = 98 - 108), large-scale shell-model calculations in the proton (2p(1/2), 1g(9/2)) and the neutron (2d(5/2), 1g(7/2), 2d(3/2), 3s(1/2), 1h(11/2)) model space were performed. Preliminary results are presented and discussed
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
High-precision measurement of the half-life of Ga
The beta-decay half-life of 62Ga has been studied with high precision using
on-line mass separated samples. The decay of 62Ga which is dominated by a 0+ to
0+ transition to the ground state of 62Zn yields a half-life of T_{1/2} =
116.19(4) ms. This result is more precise than any previous measurement by
about a factor of four or more. The present value is in agreement with older
literature values, but slightly disagrees with a recent measurement. We
determine an error weighted average value of all experimental half-lives of
116.18(4) ms.Comment: 9 pages, 5 figures, accepted for publication in PR
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
Evolution of E2 transition strength in deformed hafnium isotopes from new measurements on Hf, Hf, and Hf
The available data for E2 transition strengths in the region between
neutron-deficient Hf and Pt isotopes are far from complete. More and precise
data are needed to enhance the picture of structure evolution in this region
and to test state-of-the-art nuclear models. In a simple model, the maximum
collectivity is expected at the middle of the major shell. However, for actual
nuclei, this picture may no longer be the case, and one should use a more
realistic nuclear-structure model. We address this point by studying the
spectroscopy of Hf. We remeasure the 2^+_1 half-lives of 172,174,176Hf, for
which there is some disagreement in the literature. The main goal is to
measure, for the first time, the half-lives of higher-lying states of the
rotational band. The new results are compared to a theoretical calculation for
absolute transition strengths. The half-lives were measured using \gamma-\gamma
and conversion-electron-\gamma delayed coincidences with the fast timing
method. For the determination of half-lives in the picosecond region, the
generalized centroid difference method was applied. For the theoretical
calculation of the spectroscopic properties, the interacting boson model is
employed, whose Hamiltonian is determined based on microscopic energy-density
functional calculations. The measured 2^+_1 half-lives disagree with results
from earlier \gamma-\gamma fast timing measurements, but are in agreement with
data from Coulomb excitation experiments and other methods. Half-lives of the
4^+_1 and 6^+_1 states were measured, as well as a lower limit for the 8^+_1
states. We show the importance of the mass-dependence of effective boson charge
in the description of E2 transition rates in chains of nuclei. It encourages
further studies of the microscopic origin of this mass dependence. New data on
transition rates in nuclei from neighboring isotopic chains could support these
studies.Comment: 16 pages, 16 figures, 7 tables; Abstract shortened due to character
limi
High-spin structure of Xe 134
A. Vogt et al. ; 12 págs.; 9 figs.; 1 tab.Detailed spectroscopic information on the N∼82 nuclei is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in Xe134 is investigated after multinucleon transfer (MNT) and actinide fission. Xenon-134 was populated as (i) a transfer product in Xe136+U238 and Xe136+Pb208 MNT reactions and (ii) as a fission product in the Xe136+U238 reaction employing the high-resolution Advanced Gamma Tracking Array (AGATA). Trajectory reconstruction has been applied for the complete identification of beamlike transfer products with the magnetic spectrometer PRISMA. The Xe136+Pt198 MNT reaction was studied with the γ-ray spectrometer GAMMASPHERE in combination with the gas detector array Compact Heavy Ion Counter (CHICO). Several high-spin states in Xe134 on top of the two long-lived isomers are discovered based on γγ-coincidence relationships and information on the γ-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of Xe134 is extended up to an excitation energy of 5.832 MeV with tentative spin-parity assignments up to 16+. Previous assignments of states above the 7- isomer are revised. Latest shell-model calculations employing two different effective interactions reproduce the experimental findings and support the new spin and parity assignments.The research leading to these results has received funding
from the German BMBF under Contract No. 05P12PKFNE
TP4, from the European Union Seventh Framework Programme
FP7/2007–2013 under Grant Agreement No. 262010 -
ENSAR, from the Spanish Ministerio de Ciencia e Innovación
under Contract No. FPA2011-29854-C04, from the Spanish
Ministerio de Economía y Competitividad under Contract No.
FPA2014-57196-C5, from the Bonn-Cologne Graduate School
of Physics and Astronomy (BCGS), from the UK Science
and Technology Facilities Council (STFC), and from the US
National Science Foundation (NSF). One of the authors (A.
Gadea) has been supported by the Generalitat Valenciana,
Spain, under Grant No. PROMETEOII/2014/019 and EU
under the FEDER program.Peer Reviewe
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
Low-energy Coulomb excitation of Fe and Mn following in-beam decay of Mn
Sub-barrier Coulomb-excitation was performed on a mixed beam of Mn and
Fe, following in-trap decay of Mn at REX-ISOLDE,
CERN. The trapping and charge breeding times were varied in order to alter the
composition of the beam, which was measured by means of an ionisation chamber
at the zero-angle position of the Miniball array. A new transition was observed
at 418~keV, which has been tentatively associated to a
transition. This fixes the relative
positions of the -decaying and states in Mn for
the first time. Population of the state was observed in Fe
and the cross-section determined by normalisation to the Ag target
excitation, confirming the value measured in recoil-distance lifetime
experiments.Comment: 9 pages, 10 figure
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