Measurements of the 40Ar(n, γ)41Ar radiative-capture cross section between 0.4 and 14.8 MeV

AbstractThe 40Ar(n, γ)41Ar neutron capture cross section has been measured between 0.4 and 14.8 MeV neutron energy using the activation technique. The data are important for estimating backgrounds in argon-based neutrino and dark-matter detectors and in the neutrino-less double-beta decay search GERDA, which uses liquid argon as cooling and shielding medium. For the first time the 40Ar(n, γ)41Ar cross section has been measured for neutron energies above 1 MeV. Our results are compared to the evaluation ENDF/B-VII.1 and the calculated prediction TENDL-2013. The latter agrees very well with the present results

Recent cross-section measurements of neutron-induced reactions of importance for background estimates in 0νββ

We report on cross-section measurements for the reactions 76Ge(n,2n)75Ge, 76Ge(n,n′γ)76Ge, 126,127,128Te(n,γ)127,129,131Te, and 136Xe(n,n′γ)136Xe in the neutron energy range between 0.5 MeV and 15 MeV

Energy dependence of fission product yields from 235

Under a joint collaboration between TUNL-LANL-LLNL, a set of absolute fission product yield measurements has been performed. The energy dependence of a number of cumulative fission product yields (FPY) have been measured using quasi-monoenergetic neutron beams for three actinide targets, 235U, 238U and 239Pu, between 0.5 and 14.8 MeV. The FPYs were measured by a combination of fission counting using specially designed dual-fission chambers and γ-ray counting. Each dual-fission chamber is a back-to-back ionization chamber encasing an activation target in the center with thin deposits of the same target isotope in each chamber. This method allows for the direct measurement of the total number of fissions in the activation target with no reference to the fission cross-section, thus reducing uncertainties. γ-ray counting of the activation target was performed on well-shielded HPGe detectors over a period of two months post irradiation to properly identify fission products. Reported are absolute cumulative fission product yields for incident neutron energies of 0.5, 1.37, 2.4, 3.6, 4.6, 5.5, 7.5, 8.9 and 14.8 MeV. Preliminary results from thermal irradiations at the MIT research reactor will also be presented and compared to present data and evaluations. This work was performed under the auspices of the U.S. Department of Energy by Los Alamos National Security, LLC under contract DE-AC52-06NA25396, Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and by Duke University and Triangle Universities Nuclear Laboratory through NNSA Stewardship Science Academic Alliance grant No. DE-FG52-09NA29465, DE-FG52-09NA29448 and Office of Nuclear Physics Grant No. DE-FG02-97ER41033

The decay pattern of the Pygmy Dipole Resonance of ¹⁴⁰Ce

The decay properties of the Pygmy Dipole Resonance (PDR) have been investigated in the semi-magic N=82 nucleus ¹⁴⁰Ce using a novel combination of nuclear resonance fluorescence and γ–γcoincidence techniques. Branching ratios for transitions to low-lying excited states are determined in a direct and model-independent way both for individual excited states and for excitation energy intervals. Comparison of the experimental results to microscopic calculations in the quasi-particle phonon model exhibits an excellent agreement, supporting the observation that the Pygmy Dipole Resonance couples to the ground state as well as to low-lying excited states. A 10% mixing of the PDR and the [2+1×PDR]is extracted

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

A program is underway at the Triangle Universities Nuclear Laboratory (TUNL) to measure the neutron capture cross section in the 0.5 to 15 MeV energy range on nuclei whose radioactive daughters could potentially create backgrounds in searches for rare events. Here, we refer to neutrino-less double-beta decay and dark-matter searches, and to detectors built for neutrino and/or antineutrino studies. Neutron capture cross-section data obtained by using the activation method are reported for 40Ar, 74,76Ge, 128,130Te and 136Xe and compared to model calculations and evaluations

124Xe(n,γ)125Xe and 124Xe(n,2n)123Xe measurements for National Ignition Facility

The cross section for the 124Xe(n,γ)125Xe reaction has been measured for the first time for neutron energies above 100 keV. In addition, the 124Xe(n,2n)123Xe reaction has been studied between threshold and 14.8 MeV. The results of these measurements provide sensitive diagnostic tools for investigating properties of the inertial confinement fusion plasma in Deuterium-Tritium (DT) capsules at the National Ignition Facility (NIF) located at Lawrence Livermore National Laboratory

Measurement of the neutron-capture cross section of 76Ge and 74Ge below 15 MeV and its relevance to 0νββ decay searches of 76Ge

The neutron radiative-capture cross section of 76Ge was measured between 0.4 and 14.8 MeV using the activation technique. Germanium samples with the isotopic abundance of ∼86%Ge76 and ∼14%Ge74 used in the 0νββ searches by the GERDA and Majorana Collaborations were irradiated with monoenergetic neutrons produced at eleven energies via the H3(p,n)He3, H2(d,n)He3 and H3(d,n)He4 reactions. Previously, data existed only at thermal energies and at 14 MeV. As a by-product, capture cross-section data were also obtained for 74Ge at neutron energies below 8 MeV. Indium and gold foils were irradiated simultaneously for neutron fluence determination. High-resolution γ-ray spectroscopy was used to determine the γ-ray activity of the daughter nuclei of interest. For the 76Ge total capture cross section the present data are in good agreement with the TENDL-2013 model calculations and the ENDF/B-VII.1 evaluations, while for the Ge74(n,γ)Ge75 reaction, the present data are about a factor of two larger than predicted. It was found that the Ge74(n,γ)Ge75 yield in the High-Purity Germanium (HPGe) detectors used by the GERDA and Majorana Collaborations is only about a factor of two smaller than the Ge76(n,γ)Ge77 yield due to the larger cross section of the former reaction. Keywords: Neutron radiative capture, Neutron induced background, Neutrino detectors, Double-beta decay detectors, Dark matter detector