Total prompt γ

The total prompt γ-ray energy distributions for the neutron-induced fission of 235U, 239,241Pu at incident neutron energy of 0.025 eV ‒ 100 keV, and the spontaneous fission of 252Cf were measured using the Detector for Advanced Neutron Capture Experiments (DANCE) array in coincidence with the detection of fission fragments by a parallel-plate avalanche counter. DANCE is a highly segmented, highly efficient 4π γ-ray calorimeter. Corrections were made to the measured distribution by unfolding the two-dimension spectrum of total γ-ray energy vs multiplicity using a simulated DANCE response matrix. The mean values of the total prompt γ-ray energy, determined from the unfolded distributions, are ~ 20% higher than those derived from measurements using single γ-ray detector for all the fissile nuclei studied. This raises serious concern on the validity of the mean total prompt γ-ray energy obtained from the product of mean values for both prompt γ-ray energy and multiplicity

A high precision n-p scattering measurement at 14.9 MeV

The n-p scattering angular distribution was measured with 14.9 MeV incident neutrons using the traditional time-of-flight technique with neutron-gamma discrimination. The scattering angle varied from 20o to 65o (laboratory system) in 5o incremental steps. The efficiency of the neutron detectors was measured in the energy range 2–9 MeV relative to the 252Cf-standard, and was calculated using Monte Carlo methods in the 2–14 MeV energy range. Two methods of analysis were applied for experimental and simulated data: a traditional approach with a fixed threshold, and a dynamic threshold approach. The present data agree with the ENDF/B-VII evaluation for the shape of n-p angular distribution within about 1.5%

Nuclear data research at the Los Alamos Neutron Science Center

The Los Alamos Neutron Science Center is based on an 800-MeV high current proton linear accelerator, which is used to produce intense pulses of neutrons over 16 orders of magnitude in energy from ultra-cold neutrons to neutrons with energies up to 800 MeV. The four separate neutron production areas and the neutron energy ranges at each are: (1) the Weapons Neutron Research facility (0.1 to 800 MeV); (2) the Lujan Center with moderated neutrons (cold - 500 keV); (3) the Lead Slowing-Down Spectrometer (0.1 eV to 200 keV); and (4) the Ultracold Neutron Research facility (ultracold). Because of the flexibility of the accelerator, a wide range of neutron source intensities, pulse widths, and intensities is possible. Nuclear data measurements are conducted with the first three of these sources. Present research activities include experiments (with the instruments used) on high-resolution gamma-ray production by neutrons (GEANIE), neutron capture (DANCE), neutron and gamma-ray emission from fission and other reactions (FIGARO), charged-particle emission (NZ), neutron-induced fission (FISSION), and fission on small samples with a Lead Slowing Down Spectrometer (LSDS). With these capabilities, new approaches to studying neutron-induced reactions are yielding information on a wide range of nuclear data: gamma-ray emission including multiplicity and energy distributions, capture-to-fission ratios, transmutation reactions, emission probabilities for charged particles and neutrons, and cross sections on nuclides off the valley of stability. For some of the instruments, reactions can be studied on very small or short-lived samples. Analysis of the accuracy and precision of experiments is now being carried out in cooperation with data evaluators in order to improve the files of data covariances. Furthermore, the data are providing stringent tests of nuclear reaction models. Researchers from other laboratories in the US and from other countries collaborate in or lead many of these studies. The overview, presented here, of recent and on-going nuclear data research highlights several of the unique research opportunities made possible by the LANSCE neutron sources and specialized instrumentation. Possibilities for future advances are outlined

Comments on (n, charged particle) reactions at E/sub n/ = 14 MeV

The study of charged particles produced by bombarding materials with 14 MeV neutrons is important for the development of fusion reactors and for biomedical applications as well as for the basic understanding of nuclear reactions. Several experimental techniques for investigating these reactions are discussed here. The interpretation of the data requires the consideration of several possible reaction mechanisms including equilibrium and preequilibrium particle emission and, for light nuclei, sequential particle emission, final state interactions, and the effect of resonances. 17 references

Hydrogen and helium production in structural materials by neutrons

Hydrogen and helium are produced when energetic neutrons interact with materials, and these gases can lead to significant changes in materials properties such as embrittlement and swelling. Such effects have been seen in fission reactors and a significant effort has been made for the development of fusion reactors where the effects are expected to be larger because of the higher neutron energy. For the Advanced Fuel Cycle Initiative, new structural materials are proposed, and the amount of gas production must be known to assess the properties of these materials under radiation damage. We are measuring the production cross sections for these gases by neutrons in the energy range from threshold to 100 MeV at the Los Alamos Neutron Science Center/Weapons Neutron Research (LANSCE/WNR) spallation source of fast neutrons. We measure the light charged particles (protons, deuterons, tritons, 3He and alpha particles) emitted as a function of incident energy and angle and then integrate the angular distributions to obtain production cross sections. Results for the higher neutron energies are relevant to accelerated radiation damage facilities based on spallation neutron sources. The data measured for tantalum show a monotonic increase in the production cross sections of hydrogen and helium with neutron energy, whereas for iron and chromium, the cross sections flatten out above 50 MeV. Nuclear data evaluations often do not account well for the excitation functions

Office of Basic Energy Sciences program to meet high priority nuclear data needs of the Office of Fusion Energy 1983 review

This review was prepared during a coordination meeting held at Oak Ridge National Laboratory on September 28-29, 1983. Participants included research scientists working for this program, a representative from the OFE's Coordination of Magnetic Fusion Energy (MFE) Nuclear Data Needs Activities, and invited specialists

Status of (n, charged particle) measurements at LLL. [14 MeV]

A charged-particle magnetic-quadrupole spectrometer was used to study (n, charged particle) reactions on materials bombarded with 14- to 15-MeV neutrons. Charged-particle production cross sections, angular distributions, and spectra were measured. The materials investigated to date include most of those proposed for fusion reactor structures, Al, Ti, Cr, V, Fe, Ni, Cu, Nb, and stainless steels 304 and 316. Isotopic data on /sup 46/ /sup 48/Ti, /sup 50/ /sup 52/Cr, /sup 54/ /sup 56/Fe, /sup 58/ /sup 60/Ni, and /sup 63/ /sup 65/Cu and on the monoisotopic elements /sup 27/Al, /sup 51/V, and /sup 93/Nb provided stringent tests of reaction model calculations. Equilibrium and pre-equilibrium reaction mechanisms were identified and quantified. Preliminary data on /sup 92/ /sup 94/ /sup 95/ /sup 96/Mo and on light nuclides including /sup 12/C and /sup 7/Li were obtained recently. 8 figures, 1 table