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We provide an update on the development of an experiment at TUNL for determining the 1S0 neutron-neutron (nn) scattering length (ann) from differential cross-section measurements of three-body photodisintegration of the triton. The experiment will be conducted using a linearly polarized gamma-ray beam at the High Intensity Gamma-ray Source (HIγS) and tritium gas contained in thin-walled cells. The main components of the planned experiment are a 230 Ci gas target system, a set of wire chambers and silicon strip detectors on each side of the beam axis, and an array of neutron detectors on each side beyond the silicon detectors. The protons emitted in the reaction are tracked in the wire chambers and their energy and position are measured in silicon strip detectors. The first iteration of the experiment will be simplified, making use of a collimator system, and silicon detectors to interrogate the main region of interest near 90° in the polar angle. Monte-Carlo simulations based on rigorous 3N calculations have been conducted to validate the sensitivity of the experimental setup to ann.

We are developing an experiment to measure the two and three-body (γ, p) differential cross sections (DCS) for 3H and 3He. These data will be used to determine the 1S0 nn scattering length (ann) and np scattering length (anp) respectively. This paper describes features of the Monte-Carlo (MC) simulation that will aid in the optimization of the experimental design and the data analysis approach.

Using dual-fission chambers each loaded with a thick (200-400-mg/cm²) actinide target of 235,238U or 239Pu and two thin (~10-100-μg/cm²) reference foils of the same actinide, the cumulative yields of fission products ranging from 92Sr to 147Nd have been measured at En = 8.9MeV. The ²H(d,n)³He reaction provided the quasimonoenergetic neutron beam. The experimental setup and methods used to determine the fission product yield (FPY) are described, and results for typically eight high-yield fission products are presented. Our FPYs for 235U(n,f), 238U(n,f), and 239Pu(n,f) at 8.9 MeV are compared with the existing data below 8 MeV from Glendenin et al. [Phys. Rev. C 24, 2600 (1981)], Nagy et al. [Phys. Rev. C 17, 163 (1978)], Gindler et al. [Phys. Rev. C 27, 2058 (1983)], and those of Mac Innes et al. [Nucl. Data Sheets 112, 3135 (2011)] and Laurec et al. [Nucl. Data Sheets 111, 2965 (2010)] at 14.5 and 14.7 MeV, respectively. This comparison indicates a negative slope for the energy dependence of most fission product yields obtained from 235U and 239Pu, whereas for 238U the slope issue remains unsettled. [ABSTRACT FROM AUTHOR]

Measurements of the neutron radiative-capture cross section of 124Xe have been performed for the first time for neutron energies above 100 keV. In addition, data for the 124Xe(n,2n)123Xe reaction cross section have been obtained from threshold to 14.8 MeV to cover the entire energy range of interest, while previous data existed only at around 14 MeV. The results of these measurements provide the basis for an alternative and sensitive diagnostic tool for investigating properties of the inertia! confinement fusion plasma in deuterium-tritium (DT) capsules at the National Ignition Facility located at Lawrence Livermore National Laboratory. Here, areal density pR (density x radius) of the fuel, burn asymmetry, and fuel-ablator mix are of special interest. The 124Xe(n,γ)125Xe reaction probes the down-scattered neutrons, while the 124Xe(n,2n)123Xe reaction provides a measure of the 14 MeV direct neutrons. [ABSTRACT FROM AUTHOR]

The 40 Ar(n,  γ ) 41 Ar 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 40 Ar(n,  γ ) 41 Ar 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. [ABSTRACT FROM AUTHOR]

This paper reports the results of the first measurements of the differential cross section of the 80Se(γ,n)79Se reaction with a linearly polarized gamma-ray (γ-ray) beam. The cross section was measured at three incident γ-ray beam energies: 15.6, 15.8, and 16.0 MeV, with a beam energy spread of 3.0% full width at half-maximum (FWHM). The differential cross section for the excitation spectrum in 79Se was measured at two scattering angles in the plane of the beam polarization: θ=90° and 135°, and at one angle in the plane perpendicular to the plane of polarization: θ=90°. The total photoneutron cross sections determined from these data are between 0.8 and 1.3 standard deviations smaller than previously published results. The excitation spectra measured in this work were fit with a Hauser-Feshbach model. Better fits to the data were obtained with a constant-temperature formulation of the nuclear level density (NLD) than with a Fermi-gas NLD model. The parameters for the constant-temperature NLD model obtained in this work are consistent with those obtained for medium-mass nuclei in previous studies. [ABSTRACT FROM AUTHOR]

The 76Ge(n,p)76Ga reaction and the subsequent β decay of 76Ga to 76Ge has been used to excite the 3951.89-keV state of 76Ge, which decays by the emission of a 2040.70-keV γ ray. Using high-purity germanium detectors, the associated pulse-height signal may be undistinguishable from the potential signal produced in neutrinoless double-β decay of 76Ge with its Q value of 2039.0 keV. At 20-MeV neutron energy the production cross section of the 2040.70-keV γ ray is approximately 0.1 mb. [ABSTRACT FROM AUTHOR]

Cross-section measurements have been made at 16 and 19 MeV in two exit-channel configurations of neutrondeuteron breakup: the space star and coplanar star. In this kinematically complete measurement, the outgoing proton and one of the neutrons were detected in coincidence and their energies were determined via timeof- flight techniques. Monte Carlo simulations based on rigorous three-nucleon Faddeev calculations using the charge-dependent-Bonn (CD-Bonn) nucleon-nucleon potential were used to compare the experimental results with theory. Large discrepancies between data and theory were found in both breakup configurations measured at both energies, suggesting deficiencies in current theoretical treatment of three-nucleon forces or in present knowledge of the neutron-neutron 1So force. [ABSTRACT FROM AUTHOR]

Neutron elastic-scattering angular distributions were measured at beam energies of 11.9 and 16.9 MeV on 40,48Ca targets. These data plus other elastic-scattering measurements, total and reaction cross-sections measurements, (e, e' p) data, and single-particle energies for magic and doubly magic nuclei have been analyzed in the dispersive optical-model (DOM), generating nucleon self-energies (optical-model potentials) that can be related, via the many-body Dyson equation, to spectroscopic factors and occupation probabilities. It is found that, for stable nuclei with N ⩾ Z, the imaginary surface potential for protons exhibits a strong dependence on the neutron-proton asymmetry. This result leads to a more modest dependence of the spectroscopic factors on asymmetry. The measured data and the DOM analysis of all considered nuclei clearly demonstrate that the neutron imaginary surface potential displays very little dependence on the neutron-proton asymmetry for nuclei near stability (N ⩾ Z). [ABSTRACT FROM AUTHOR]

New measurements of the neutron-neutron quasifree scattering cross section in neutron-deuteron breakup at an incident neutron energy of 10.0 MeV are reported. The experiment setup was optimized to evaluate the technique for determining the integrated beam-target luminosity in neutron-neutron coincidence cross-section measurements in neutron-deuteron breakup. The measurements were carried out with a systematic uncertainty of ±5.6%. Our data are in agreement with theoretical calculations performed using the CD-Bonn nucleon-nucleon potential in the Faddeev formalism. The measured integrated cross section over the quasifree peak is 20.5±0.5(stat)±1.1(sys)mb/sr² in comparison with the theory prediction of 20.1mb/sr². These results validate our technique for determining the beam-target luminosity in neutron-deuteron breakup measurements. [ABSTRACT FROM AUTHOR]