1,343 research outputs found
ENDF-6 compatible evaluation of neutron induced reaction cross sections for 182,183,184,186W
An ENDF-6 compatible evaluation for neutron induced reactions in the resonance region has been completed for 182,183,184,186W. The parameters are the result of an analysis of experimental data available in the literature together with a parameter adjustment on transmission and capture data obtained at the time-of-flight facility GELINA. Complete evaluated data files in ENDF-6 format have been produced by joining the evaluations in the resonance region with corresponding files from the JEFF-32T1 and ENDF/B-VII.1 library. The evaluated files have been processed with the latest updates of NJOY.99 to test their format and application consistency as well as to produce a continuous-energy data library in ACE format for use in Monte Carlo codes. The evaluated files will be implemented in the next release of the JEFF-3 library which is maintained by the Nuclear Energy Agency of the OECD. The evaluated files will be implemented in the next release of the JEFF-3 library which is maintained by the Nuclear Energy Agency of the OECD.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard
Two-neutron overlap functions for 6He from a microscopic structure model
A fully antisymmetrized microscopic model is developed for light two-neutron
halo nuclei using a hyper-spherical basis to describe halo regions. The
many-body wavefunction is optimized variationally. The model is applied to 6He
bound by semi realistic Minnesota nucleon-nucleon forces. The two-neutron
separation energy and the radius of the halo are reproduced in agreement with
experiment. Antisymmetrization effects between 4He and halo neutrons are found
to be crucial for binding of 6He. We also properly extract two-neutron overlap
functions and find that there is a significant increase of 30%-70% in their
normalization due to microscopic effects as compared to the results of
three-body models.Comment: To be published in Nucl. Phys.
Evaluation of neutron induced reaction cross sections in the resolved and unresolved resonance region at EC-JRC-IRMM
Recent efforts made at the EC-JRC-IRMM to produce evaluated cross section data files for neutron induced reactions are described as well as the methodology applied in both the resolved and unresolved resonance. For the resolved resonance region the paper focuses on a recent evaluation of isotopes present in natural cadmium. For the unresolved resonance region results for gold are presented.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard
Holographic analysis of diffraction structure factors
We combine the theory of inside-source/inside-detector x-ray fluorescence
holography and Kossel lines/x ray standing waves in kinematic approximation to
directly obtain the phases of the diffraction structure factors. The influence
of Kossel lines and standing waves on holography is also discussed. We obtain
partial phase determination from experimental data obtaining the sign of the
real part of the structure factor for several reciprocal lattice vectors of a
vanadium crystal.Comment: 4 pages, 3 figures, submitte
ENDF-6 compatible evaluation of neutron induced reaction cross sections for 106,108,110,111,112,113,114,116Cd
An ENDF-6 compatible evaluation for neutron induced reactions in the resonance region has been completed for 106,108,110,111,112,113,114,116Cd. The parameters are the result of an analysis of experimental data available in the literature together with a parameter adjustment on transmission and capture data obtained at the time-of-flight facility GELINA. Complete evaluated data files in ENDF-6 format have been produced by joining the evaluations in the resonance region with corresponding files from the JEFF-3.1.2 nuclear data library (or with the JEFF-Beta-CAD proposed evaluation in case of 113Cd). These files were produced for use in the JEFF32T2 library. For neutron induced reactions in the unresolved resonance region the JENDL-4.0 evaluation for 111Cd and 113Cd was adopted. The evaluated files have been processed with the latest updates of NJOY.99 to test their format and application consistency as well as to produce a continuous-energy data library in ACE format for use in Monte Carlo codes. The ACE files have been utilized to study the effect of the evaluated resonance parameters on results of integral experiments. The evaluated files will be implemented in the next release of the JEFF-3 library which is maintained by the Nuclear Energy Agency of the OECD.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard
Evaluation of neutron induced reaction cross sections on gold
A new evaluation of neutron induced reactions on 197Au nucleus in the energy regions below 500 eV and from 4 keV and 100 keV is presented. Complete evaluated data files in ENDF-6 format have been produced by joining the evaluation with corresponding files from the ENDF/B-VII.1 library. The evaluation in the unresolved resonance region between 4 keV and 100 keV is based on a generalized single-level representation compatible with the energy-dependent option of the ENDF-6 format. The average partial cross sections have been expressed in terms of transmission coefficients by applying the Hauser-Feshbach statistical reaction theory including width fluctuations. The transmission coefficients have been obtained from a combined analysis of the capture cross section resulting from the cross section standards evaluation project and theoretical non-fluctuating cross sections derived from a dispersive coupled channel optical model. The evaluated cross sections have been validated by a comparison with transmission and capture data obtained at the time-of-flight facility GELINA. The evaluated files have been processed with the latest updates of NJOY.99 to test their format and application consistency as well as to produce a continuous-energy data library in ACE format for use in Monte Carlo codes. The ACE files have been utilized to study the effect of the evaluated resonance parameters on results of lead slowing-down experiments. The evaluated files will be implemented in the next release of the JEFF-3 library which is maintained by the Nuclear Energy Agency of the OECD.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard
Gamma-ray strength function and pygmy resonance in rare earth nuclei
The gamma-ray strength function for gamma energies in the 1-7 MeV region has
been measured for 161,162-Dy and 171,172-Yb using the (3-He,alpha gamma)
reaction. Various models are tested against the observed gamma-ray strength
functions. The best description is based on the Kadmenskii, Markushev and
Furman E1 model with constant temperature and the Lorentzian M1 model. A
gamma-ray bump observed at E_gamma=3 MeV is interpreted as the so-called pygmy
resonance, which has also been observed previously in (n,gamma) experiments.
The parameters for this resonance have been determined and compared to the
available systematics.Comment: 11 pages, including 4 figures and 2 table
Neutron capture cross section measurements for 197Au from 3.5 to 84 keV at GELINA
Cross section measurements have been performed at the time-of-flight facility GELINA to determine the average capture cross section for 197Au in the energy region between 3.5 keV and 84 keV. Prompt gamma-rays, originating from neutron induced capture events, were detected by two C6D6 liquid scintillators. The sample was placed at about 13 m distance from the neutron source. The total energy detection principle in combination with the pulse height weighting technique was applied. The energy dependence of the neutron flux was measured with a double Frisch-gridded ionization chamber based on the 10B(n,alpha)reaction. The data have been normalized to the well-isolated and saturated 197Au resonance at 4.9 eV. Special care was taken to reduce bias effects due to the weighting function, normalization, dead time and background corrections. The total uncertainty due to normalization, neutron flux and weighting function is 1.0%. An additional uncertainty of 0.5% results from the correction for self-shielding and multiple interaction events. Fluctuations due to resonance structures have been studied by complementary measurements at a 30 m flight path station. The results reported in this work deviate systematically by more than 5% from the cross section that is recommended as a reference for astrophysical applications. They are about 2% lower compared to an evaluation of the 197Au(n,gamma) cross section, which was based on a least squares fit of experimental data available in the literature prior to this work. The average capture cross section as a function of neutron energy has been parameterized in terms of average resonance parameters. Maxwellian average cross sections at different temperatures have been calculated.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard
Neutron charge radius and the Dirac equation
We consider the Dirac equation for a finite-size neutron in an external
electric field. We explicitly incorporate Dirac-Pauli form factors into the
Dirac equation. After a non-relativistic reduction, the Darwin-Foldy term is
cancelled by a contribution from the Dirac form factor, so that the only
coefficient of the external field charge density is , i. e. the
root mean square radius associated with the electric Sachs form factor . Our
result is similar to a recent result of Isgur, and reconciles two apparently
conflicting viewpoints about the use of the Dirac equation for the description
of nucleons.Comment: 7 pages, no figures, to appear in Physical Review
Baryon Charge Radii and Quadrupole Moments in the 1/N_c Expansion: The 3-Flavor Case
We develop a straightforward method to compute charge radii and quadrupole
moments for baryons both with and without strangeness, when the number of QCD
color charges is N_c. The minimal assumption of the single-photon exchange
ansatz implies that only two operators are required to describe these baryon
observables. Our results are presented so that SU(3) flavor and isospin
symmetry breaking can be introduced according to any desired specification,
although we also present results obtained from two patterns suggested by the
quark model with gluon exchange interactions. The method also permits to
extract a number of model-independent relations; a sample is r^2_Lambda / r_n^2
= 3/(N_c+3), independent of SU(3) symmetry breaking.Comment: 30 pages, no figures, REVTeX
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