Investigation of the fundamental constants stability based on the reactor Oklo burn-up analysis

The burn-up for SC56-1472 sample of the natural Oklo reactor zone 3 was calculated using the modern Monte Carlo codes. We reconstructed the neutron spectrum in the core by means of the isotope ratios: $^{147}$Sm/$^{148}$Sm and $^{176}$Lu/$^{175}$Lu. These ratios unambiguously determine the spectrum index and core temperature. The effective neutron absorption cross section of $^{149}$Sm calculated using this spectrum was compared with experimental one. The disagreement between these two values allows to limit a possible shift of the low laying resonance of $^{149}$Sm even more . Then, these limits were converted to the limits for the change of the fine structure constant $\alpha$. We found that for the rate of $\alpha$ change the inequality $|\delta \dot{\alpha}/\alpha| \le 5\cdot 10^{-18}$ is fulfilled, which is of the next higher order than our previous limit.Comment: 16 pages, 7 figure

Nuclear model tests with neutron resonance data

Previous determinations of the level density parameters, a, as derived from analyses of resonance parameter data, were carried out on the basis of the Gilbert-Cameron theoretical relation for the spin dispersion parameter, {sigma}. However, other different theoretical expressions for {sigma} have been derived previously on the basis of various nuclear models, such as the Fermi gas model, the unified Bohr-Mottelson model with and without inclusion of nucleon pairing correlations, and the Hartree-Fock model. The different expressions for {sigma} would impact the derivation of the a parameter. Because of these considerations, a new examination of the level density parameter, devoid of a reliance on a theoretical expression for {sigma}, is of great importance in various computations in the fields of reactor physics, astrophysics, and spallation neutrons. Here, the spin dispersion parameter of the level density formula, {sigma}, as determined from the spin dependent level spacings of neutron resonances, is compared with theoretical expressions and found to be in agreement with the results of Ericson. On the basis of the present results, the level density parameters, a, for a few nuclides were then derived and found to be lower than previous determinations by about 20%. The impact of the present findings on the LAHET calculations of neutron yields from thick targets of W is discussed

Nuclear Reaction and Structure Databases of the National Nuclear Data Center

We discuss nuclear data resources of the National Nuclear Data Center (NNDC) of relevance to nuclear astrophysics applications. These resources include databases, tools and powerful web service at www.nndc.bnl.gov. Our objective is to provide an overview of nuclear databases, related products and demonstrate nuclear astrophysics potential of the ENDF/B-VII beta2 library. A detailed discussion on the Maxwellian neutron capture cross sections obtained from the ENDF/B-VII beta2 library is presented

Test of nuclear level density inputs for Hauser-Feshbach model calculations

The energy spectra of neutrons, protons, and alpha-particles have been measured from the d+59Co and 3He+58Fe reactions leading to the same compound nucleus, 61$Ni. The experimental cross sections have been compared to Hauser-Feshbach model calculations using different input level density models. None of them have been found to agree with experiment. It manifests the serious problem with available level density parameterizations especially those based on neutron resonance spacings and density of discrete levels. New level densities and corresponding Fermi-gas parameters have been obtained for reaction product nuclei such as 60Ni,60Co, and 57Fe

Enhanced radiative strength in the quasi-continuum of 117Sn

Radiative strength functions of 117Sn has been measured below the neutron separation energy using the (3He,3He'gamma) reactions. An increase in the slope of the strength functions around E_gamma= 4.5 MeV indicates the onset of a resonance-like structure, giving a significant enhancement of the radiative strength function compared to standard models in the energy region 4.5 <= E_gamma <= 8.0 MeV. For the first time, the functional form of this resonance-like structure has been measured in an odd tin nucleus below neutron threshold in the quasi-continuum region.Comment: 4 pages, 3 figure

Evidence for the pair-breaking process in 116,117Sn

The nuclear level densities of 116,117Sn below the neutron separation energy have been determined experimentally from the (3He,alpha gamma) and (3He,3He gamma') reactions, respectively. The level densities show a characteristic exponential increase and a difference in magnitude due to the odd-even effect of the nuclear systems. In addition, the level densities display pronounced step-like structures that are interpreted as signatures of subsequent breaking of nucleon pairs.Comment: 7 pages, 5 figures, accepted for publication in Phys. Rev. C, 22 December 200

Precision Measurement of the n-3He Incoherent Scattering Length Using Neutron Interferometry

We report the first measurement of the low-energy neutron-$^3$He incoherent scattering length using neutron interferometry: $b_i' = (-2.512\pm 0.012{statistical}\pm0.014{systematic})$ fm. This is in good agreement with a recent calculation using the AV18+3N potential. The neutron-$^3$He scattering lengths are important for testing and developing nuclear potential models that include three nucleon forces, effective field theories for few-body nuclear systems, and neutron scattering measurements of quantum excitations in liquid helium. This work demonstrates the first use of a polarized nuclear target in a neutron interferometer.Comment: 4 figure

The damping width of giant dipole resonances of cold and hot nuclei: a macroscopic model

A phenomenological macroscopic model of the Giant Dipole Resonance (GDR) damping width of cold- and hot-nuclei with ground-state spherical and near-spherical shapes is developed. The model is based on a generalized Fermi Liquid model which takes into account the nuclear surface dynamics. The temperature dependence of the GDR damping width is accounted for in terms of surface- and volume-components. Parameter-free expressions for the damping width and the effective deformation are obtained. The model is validated with GDR measurements of the following nuclides, $^{39,40}$K, $^{42}$Ca, $^{45}$Sc, $^{59,63}$Cu, $^{109-120}$Sn,$^{147}$Eu, $^{194}$Hg, and $^{208}$Pb, and is compared with the predictions of other models.Comment: 10 pages, 5 figure

Parity violation in n+3He→3H+pn + ^3He \rightarrow ^3H + p reaction: resonance approach

The method based on microscopic theory of nuclear reactions has been applied for the analysis of parity violating effects in a few-body systems. Different parity violating and parity conserving asymmetries and their dependence on neutron energy have been estimated for $n + ^3He \rightarrow ^3H + p$ reaction. The estimated effects are in a good agreement with available exact calculations

Direct radiative capture of p-wave neutrons

The neutron direct radiative capture (DRC) process is investigated, highlighting the role of incident p-wave neutrons. A set of calculations is shown for the 12-C(n,gamma) process at incoming neutron energies up to 500 keV, a crucial region for astrophysics. The cross section for neutron capture leading to loosely bound s, p and d orbits of 13-C is well reproduced by the DRC model demonstrating the feasibility of using this reaction channel to study the properties of nuclear wave functions on and outside the nuclear surface. A sensitivity analysis of the results on the neutron-nucleus interaction is performed for incident s- as well as p-waves. It turned out that the DRC cross section for p-wave neutrons is insensitive to this interaction, contrary to the case of incident s-wave neutrons. PACS number(s): 25.40Lw,21.10Gv,23.40.HcComment: 16 pages, REVTeX file, PostScript file, .dvi fil