35,819 research outputs found
Correlated Prompt Fission Data in Transport Simulations
Detailed information on the fission process can be inferred from the
observation, modeling and theoretical understanding of prompt fission neutron
and -ray~observables. Beyond simple average quantities, the study of
distributions and correlations in prompt data, e.g., multiplicity-dependent
neutron and \gray~spectra, angular distributions of the emitted particles,
-, -, and -~correlations, can place stringent
constraints on fission models and parameters that would otherwise be free to be
tuned separately to represent individual fission observables. The FREYA~and
CGMF~codes have been developed to follow the sequential emissions of prompt
neutrons and -rays~from the initial excited fission fragments produced
right after scission. Both codes implement Monte Carlo techniques to sample
initial fission fragment configurations in mass, charge and kinetic energy and
sample probabilities of neutron and ~emission at each stage of the
decay. This approach naturally leads to using simple but powerful statistical
techniques to infer distributions and correlations among many observables and
model parameters. The comparison of model calculations with experimental data
provides a rich arena for testing various nuclear physics models such as those
related to the nuclear structure and level densities of neutron-rich nuclei,
the -ray~strength functions of dipole and quadrupole transitions, the
mechanism for dividing the excitation energy between the two nascent fragments
near scission, and the mechanisms behind the production of angular momentum in
the fragments, etc. Beyond the obvious interest from a fundamental physics
point of view, such studies are also important for addressing data needs in
various nuclear applications. (See text for full abstract.)Comment: 39 pages, 57 figure files, published in Eur. Phys. J. A, reference
added this versio
Hot medium effects on J/psi production in p+Pb collisions at sqrt{s_{NN}}=5.02 TeV
Based on a kinetic description of J/psi dissociation and production in an
expanding quark-gluon plasma that is described by a 2+1 dimensional ideal
hydrodynamics, we have studied the hot medium effects on J/psi production in
p+Pb collisions at sqrt{s_{NN}}=5.02 TeV. Including also the cold nuclear
matter effects, we are able to reproduce recent experimental results on the
nuclear modification factor R_{pPb}(J/psi) measured by the ALICE Collaboration.
We have also made predictions for the R_{pPb} of J/psi and the double ratio
R_{pPb}^{pro}(psi')/R_{pPb}^{pro}(J/psi) of prompt quarkonia produced in the
most central 10% p+Pb collisions. We find that different from the cold nuclear
matter effects, the R_{pPb}(J/psi) is slightly smaller than that in the minimum
bias collisions, and the double ratio is significantly less than one at
backward rapidity.Comment: 8 pages, 6 figure
Nonmesonic decay of the Lambda hyperon in nuclear matter - implications on the weak Lambda-N interaction
The lifetime of the Lambda hyperon in heavy hypernuclei as measured by the
COSY-13 Collaboration in proton - Au, Bi and U collisions has been analysed to
yield tau(Lambda) = (145 +- 11) ps. This value for tau(Lambda) is compatible
with the lifetime extracted from antiproton annihilation on Bi and U targets,
however, much more accurate. We find that the dependence of the lifetime
tau(Lambda) on the mass of hypernuclei indicates a violation of the
phenomenological Delta I = 1/2 rule known from the weak mesonic decays of
strange particles. PACS: {13.30.-a}{Decays of baryons}
{13.75.Ev}{Hyperon-nucleon interaction} {21.80}{Hypernuclei}
{25.80.Pw}{Hyperon-induced reactions}Comment: 21 pages, 11 PostScript figures, EPJA in prin
Energy Loss of Leading Hadrons and Direct Photon production in Evolving Quark-Gluon Plasma
We calculate the nuclear modification factor of neutral pions and the photon
yield at high p_T in central Au-Au collisions at RHIC (\sqrt{s}=200 GeV) and
Pb-Pb collisions at the LHC (\sqrt{s}=5500 GeV). A leading-order accurate
treatment of jet energy loss in the medium has been convolved with a physical
description of the initial spatial distribution of jets and a (1+1) dimensional
expansion. We reproduce the nuclear modification factor of pion R_{AA} at RHIC,
assuming an initial temperature T_i=370 MeV and a formation time \tau_i=0.26
fm/c, corresponding to dN/dy=1260. The resulting suppression depends on the
particle rapidity density dN/dy but weakly on the initial temperature. The jet
energy loss treatment is also included in the calculation of high p_T photons.
Photons coming from primordial hard N-N scattering are the dominant
contribution at RHIC for p_T > 5 GeV, while at the LHC, the range 8<p_T<14 GeV
is dominated by jet-photon conversion in the plasma.Comment: 21 pages, 16 figures. Discussions and references added. New figure
includind photon dat
Photonuclear reactions with Zinc: A case for clinical linacs
The use of bremsstrahlung photons produced by a linac to induce photonuclear
reactions is wide spread. However, using a clinical linac to produce the
photons is a new concept. We aimed to induce photonuclear reactions on zinc
isotopes and measure the subsequent transition energies and half-lives. For
this purpose, a bremsstrahlung photon beam of 18 MeV endpoint energy produced
by the Philips SLI-25 linac has been used. The subsequent decay has been
measured with a well-shielded single HPGe detector. The results obtained for
transition energies are in good agreement with the literature data and in many
cases surpass these in accuracy. For the half-lives, we are in agreement with
the literature data, but do not achieve their precision. The obtained accuracy
for the transition energies show what is achievable in an experiment such as
ours. We demonstrate the usefulness and benefits of employing clinical linacs
for nuclear physics experiments
First observation of two hyperfine transitions in antiprotonic He-3
We report on the first experimental results for microwave spectroscopy of the
hyperfine structure of antiprotonic He-3. Due to the helium nuclear spin,
antiprotonic He-3 has a more complex hyperfine structure than antiprotonic He-4
which has already been studied before. Thus a comparison between theoretical
calculations and the experimental results will provide a more stringent test of
the three-body quantum electrodynamics (QED) theory. Two out of four
super-super-hyperfine (SSHF) transition lines of the (n,L)=(36,34) state were
observed. The measured frequencies of the individual transitions are
11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current
theoretical values, but still within their estimated errors. Although the
experimental uncertainty for the difference of these frequencies is still very
large as compared to that of theory, its measured value agrees with theoretical
calculations. This difference is crucial to be determined because it is
proportional to the magnetic moment of the antiproton.Comment: 8 pages, 6 figures, just published (online so far) in Physics Letters
Search for Solar Axions Produced by Primakoff Conversion Using Resonant Absorption by Tm Nuclei
The search for resonant absorption of the Primakoff solar axions by
Tm nuclei have been performed. Such an absorption should lead to the
excitation of low-lying nuclear energy level: Tm Tm
Tm (8.41 keV). The Si(Li) detector and Tm target
placed inside the low-background setup were used for that purpose. As a result,
a new restriction on the axion-photon coupling and axion mass was obtained:
(90% c.l.). In model
of hadronic axion this restriction corresponds to the upper limit on axion mass
- 191 eV for 90% c.l.Comment: 6 pages, 5 figures, submitted to Physics Letters
Nuclear Matter and Nuclear Dynamics
Highlights on the recent research activity, carried out by the Italian
Community involved in the "Nuclear Matter and Nuclear Dynamics" field, will be
presented.Comment: Proceedings of the 12th Conference on Problems in Theoretical Nuclear
Physics, to appear in Journal of Physics, Conference Serie
Recommended from our members
Analysis of 83mKr prompt scintillation signals in the PIXeY detector
Prompt scintillation signals from 83mKr calibration sources are a useful metric to calibrate the spatial variation of light collection efficiency and electric field magnitude of a two phase liquid-gas xenon time projection chamber. Because 83mKr decays in two steps, there are two prompt scintillation pulses for each calibration event, denoted S1a and S1b. We study the ratio of S1b to S1a signal sizes in the Particle Identification in Xenon at Yale (PIXeY) experiment and its dependence on the time separation between the two signals (Δ t), notably its increase at low Δ t. In PIXeY data, the Δ t dependence of S1b/S1a is observed to exhibit two exponential components: one with a time constant of 0.05 ± 0.02 μ s, which can be attributed to processing effects and pulse overlap and one with a time constant of 10.2 ± 2.2 μs that increases in amplitude with electric drift field, the origin of which is not yet understood
Dynamics of Coulomb fission
A general formalism is described for the treatment of Coulomb fission, within the framework of the semiquantal theory. We develop a model for the fission probabilities of levels excited in Coulomb excitation. This model contains penetration of the double-humped fission barrier, competition from gamma and neutron emission, and the spreading of the collective states into noncollective compound states. For 74184W + 92238U, the fission probability at θc.m.=180° is increased by a factor of 3.9, 3.3, and 2.0 at E/ECoul=0.77, 0.85, and 0.935, respectively, compared to the simplified sharp cutoff model used in earlier model calculations. The enhancement comes from barrier penetration. The damping of the fission probability due to spreading into noncollective compound states is small. Prompt Coulomb fission (near the distance of closest approach) is studied in a one-dimensional model. The results clearly imply that prompt fission is negligible. We have also studied the sudden approximation for collective rotational levels in connection with Coulomb fission. At high spins (I≈20), it leads to significant errors. Contrary to the basic assumption of the sudden approximation that the nuclear symmetry axis remains fixed during the collision, it is shown that Coulomb excitation results in a strong alignment of the nuclear symmetry axis perpendicular to the beam axis at small internuclear distances. NUCLEAR REACTIONS, FISSION Semiquantal theory of prompt and asymptotic Coulomb fission, study of double-humped barrier penetration, damping effects, neutron and γ emission. Calculated σ(Ep, θc.m.=180°)
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