537 research outputs found
Neutron-skin thickness of Pb, and symmetry-energy constraints from the study of the anti-analog giant dipole resonance
The Pb(,) Pb reaction at a beam energy of
30 MeV has been used to excite the anti-analog of the giant dipole resonance
(AGDR) and to measure its -decay to the isobaric analog state in
coincidence with proton decay of IAS. The energy of the transition has also
been calculated with the self-consistent relativistic random-phase
approximation (RRPA), and found to be linearly correlated to the predicted
value of the neutron-skin thickness (). By comparing the
theoretical results with the measured transition energy, the value of 0.190
0.028 fm has been determined for of Pb, in
agreement with previous experimental results. The AGDR excitation energy has
also been used to calculate the symmetry energy at saturation (
MeV) and the slope of the symmetry energy ( MeV), resulting in
more stringent constraints than most of the previous studies.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1205.232
Scissors resonance in the quasi-continuum of Th, Pa and U isotopes
The gamma-ray strength function in the quasi-continuum has been measured for
231-233Th, 232,233Pa and 237-239U using the Oslo method. All eight nuclei show
a pronounced increase in gamma strength at omega_SR approx 2.4 MeV, which is
interpreted as the low-energy M1 scissors resonance (SR). The total strength is
found to be B_SR = 9-11 mu_N^2 when integrated over the 1 - 4 MeV gamma-energy
region. The SR displays a double-hump structure that is theoretically not
understood. Our results are compared with data from (gamma, gamma') experiments
and theoretical sum-rule estimates for a nuclear rigid-body moment of inertia.Comment: 11 pages, 9 figure
Completing the nuclear reaction puzzle of the nucleosynthesis of 92Mo
One of the greatest questions for modern physics to address is how elements
heavier than iron are created in extreme, astrophysical environments. A
particularly challenging part of that question is the creation of the so-called
p-nuclei, which are believed to be mainly produced in some types of supernovae.
The lack of needed nuclear data presents an obstacle in nailing down the
precise site and astrophysical conditions. In this work, we present for the
first time measurements on the nuclear level density and average strength
function of Mo. State-of-the-art p-process calculations systematically
underestimate the observed solar abundance of this isotope. Our data provide
stringent constraints on the NbMo reaction rate,
which is the last unmeasured reaction in the nucleosynthesis puzzle of
Mo. Based on our results, we conclude that the Mo abundance
anomaly is not due to the nuclear physics input to astrophysical model
calculations.Comment: Submitted to PR
Level densities and thermodynamical properties of Pt and Au isotopes
The nuclear level densities of Pt and Au below the
neutron separation energy have been measured using transfer and scattering
reactions. All the level density distributions follow the constant-temperature
description. Each group of isotopes is characterized by the same temperature
above the energy threshold corresponding to the breaking of the first Cooper
pair. A constant entropy excess and is observed in
Pt and Au with respect to Pt and Au,
respectively, giving information on the available single-particle level space
for the last unpaired valence neutron. The breaking of nucleon Cooper pairs is
revealed by sequential peaks in the microcanonical caloric curve
Statistical properties of Pu, and Pu(n,) cross section calculation
The level density and gamma-ray strength function (gammaSF) of 243Pu have
been measured in the quasi-continuum using the Oslo method. Excited states in
243Pu were populated using the 242Pu(d,p) reaction. The level density closely
follows the constant-temperature level density formula for excitation energies
above the pairing gap. The gammaSF displays a double-humped resonance at low
energy as also seen in previous investigations of actinide isotopes. The
structure is interpreted as the scissors resonance and has a centroid of
omega_{SR}=2.42(5)MeV and a total strength of B_{SR}=10.1(15)mu_N^2, which is
in excellent agreement with sum-rule estimates. The measured level density and
gammaSF were used to calculate the 242Pu(n,gamma) cross section in a neutron
energy range for which there were previously no measured data.Comment: 9 pages, 8 figure
A beam monitor detector based on doped silica and optical fibres
A beam monitor detector prototype based on doped silica fibres coupled to
optical fibres has been designed, constructed and tested, mainly for
accelerators used in medical applications. Scintillation light produced by Ce
and Sb doped silica fibres moving across the beam has been measured, giving
information on beam position, shape and intensity. Mostly based on commercial
components, the detector is easy to install, to operate and no electronic
components are located near the beam. Tests have been performed with a 2 MeV
proton pulsed beam at an average current of 0.8 {\mu}A. The response
characteristics of Sb doped silica fibres have been studied for the first time
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