Fast Neutron Cross Sections and Nuclear Level Density

Abstract

The capture cross sections for unmoderated fission neutrons, effective energy one Mev, are determined by the average properties of nuclear levels at excitation energies equal to neutron binding plus one Mev. The level spacings determined from measured cross sections for 61 isotopes are discussed in connection with the statistical and shell nuclear models. Whereas the discontinuity in neutron binding energy at magic numbers accounts for most of the abnormality of the cross sections of the magic-N nuclei, the effect of shell structure is evident in level spacing even at high (5-7 Mev) excitation energy. The level spacings obtained for nonmagic-number nuclei, on the other hand, are in reasonable agreement with the statistical nuclear model, and in addition are the same for levels of widely different spin.

Neutron radiative capture reactions on nuclei of relevance to 0νββ, dark matter and neutrino/antineutrino searches

“…While the TENDL-2012 calculation gives larger cross-section values, the ENDF/B-VII evaluation agrees with our data up to about 3 MeV and again at 14.8 MeV, but in between the evaluated crosssection data are approximately one order of a magnitude lower than the trend of the present data. The only previously existing datum of Hughes [8] at 1 MeV agrees very well with our data, which are important for the 0QEE decay searches of the EXO-200 [21] and KamLAND-Zen [22] collaborations.…”

“…2 together with the only existing previous results [8,9]. The TENDL-2013 calculation based on the TALYS code [10] gives an excellent description of the present data.…”

Systematic study of direct neutron capture

“…To test the reliability of the potential model, we compare in Fig. 2 our calculated neutron DC (including the E1 + E2 + M1 multipolarities) cross sections (solid lines) with the available experimental data for the nine neutron capture reactions on light nuclei, namely 16 O, 18 O, 22 Ne, 26 Mg, 27 Al, 36 S, 37 Cl, 46 Ca, and 48 Ca. A rather good agreement is found which confirms that the potential model with the adopted nuclear structure ingredients (in particular the average spectroscopic factor), as described in Sec.…”

“…III, can provide a fair prediction of the neutron DC cross section. Note that for the open-shell heavy species like 36 S or 37 Cl the resonant capture already dominates the reaction mechanism, it is therefore not unrealistic to underestimate the experimental cross section. For the closedshell Ca isotopes, the DC is still expected to dominate the reaction mechanism.…”

Measurements of theKr86(n,γ)Kr87Bhike1, Rubino2, Gooden3 et al. 2015Phys. Rev. C3220View full textAdd to dashboardCite

“…With this information at hand, the production rate of 87 Kr via the s-process on 86 Kr can be calculated, if the neutron-capture cross section on this stable N=50 nucleus is known. Unfortunately, between 200 keV and 1 MeV neutron energy only a single datum exists for the 86 Kr(n,γ) 87 Kr capture cross section to guide model calculations from the keV to the MeV energy range [3]. In order to improve the (n,γ) database for 86 Kr, the neutron-capture cross section was measured between 0.37 MeV and 14.…”