The 10B + n system has been studied by measuring charged particles from neutron-induced reactions in the 1 to 20 MeV energy range. Protons, deuterons, tritons, and α particles were measured at four ...angles using the pulsed white neutron spectrum at the Los Alamos Neutron Science Center Weapons Neutron Research facility. Differential cross sections for each species are reported. These new data are combined with literature data in an R-matrix analysis of the 11B compound system. Furthermore, a comparison is made to the molecular and cluster states candidates observed in these reactions.
The 10B + n system has been studied by measuring charged particles from neutron-induced reactions in the 1 to 20 MeV energy range. Protons, deuterons, tritons, and α particles were measured at four ...angles using the pulsed white neutron spectrum at the Los Alamos Neutron Science Center Weapons Neutron Research facility. Differential cross sections for each species are reported. These new data are combined with literature data in an R-matrix analysis of the 11B compound system. Furthermore, a comparison is made to the molecular and cluster states candidates observed in these reactions.
Measuring prompt fission neutrons to high precision is an experimental challenge, especially for radioactive fissioning nuclides. However, accurate average multiplicities, ν¯p, and kinetic energy ...distributions of prompt fission neutrons are essential for fundamental and applied nuclear physics. We present here a recent measurement of the 239Pu (n,f) ν¯p as a function of the incident-neutron energy, over the range 1-700 MeV. The measurement was performed with a cutting-edge setup and an innovative technique, which allowed to minimize and account for the main sources of bias. An unprecedented precision was therefore achieved. Our data are compared to GEF predictions as well as to evaluated libraries. For the first time, at low energies, the ENDF/B-VIII.0 nuclear data evaluation is validated with an independent measurement and the evaluated uncertainty reduced by up to 60%. This work paves the way to precisely measure prompt fission neutron multiplicities on highly radioactive nuclei.
The increasing economic and environmental losses caused by non-native invasive species amplify the value of identifying and implementing optimal management options to prevent, detect, and control ...invasive species. Previous literature has focused largely on preventing introductions of invasive species and post-detection control activities; few have addressed the role of detection. By increasing resources to detect invasive species, managers may increase their chances of finding a species at a smaller population level, lessening the extent of damages and making subsequent control potentially less expensive and more effective. However, detecting new invasive species is difficult and uncertain; many factors reduce the likelihood of successful detection, such as low population densities which are prevalent in invasive species management. This paper presents a model that captures the stochastic and dynamic aspects of this trade-off by incorporating a detection stage in which the agency managers choose search effort prior to the post-detection control stage. The analysis of the model illustrates that the optimal detection strategy depends primarily on the ‘detectability’, or ease of detection, and the biological relationships of each distinct species.
Prompt fission neutron spectra (PFNS) are crucial to any neutronic simulation of critical nuclear systems. An experimental setup dedicated to the measurements of PFNS of very high accuracy was ...developed at the Los Alamos Neutron Science Center (LANSCE) some ten years ago. It allows for the measurement of PFNS for neutron induced fission at the Weapon Neutron Research (WNR) neutron source of the LANSCE. A measurement of the PFNS from the 235U(n,f) reaction was realized recently and is currently analyzed. Preliminary results are presented here and are compared to present nuclear data evaluations.
Fast-neutron detectors are used in a wide range of nuclear physics experiments including studies of elastic and inelastic neutron scattering, charge-exchange reactions, photonuclear reactions, ...neutron-induced fission, and, especially recently, reactions of radioactive nuclei. Although many of the detectors being developed now are based on technologies that are several decades old, new physics is now accessible due to the advent of advanced accelerators, and these facilities present challenging opportunities for detecting fast neutrons. The choice of detectors, their appropriateness for particular measurements and how they are integrated into experiments will be discussed. Detector arrays are of particular importance these days to study angular distributions or simply to increase the solid angle coverage to increase the data rate. Modeling the response of the detectors has become much more important in order to understand better their response and to calculate effects of neutron scattering in the experimental area, including detector-to-detector scattering. Data acquisition through waveform digitizers is now common and leads to more information from each event as well as significant reductions in dead time and in the complexity of the electronics. At the same time, analyzing waveforms in real time presents challenges in terms of handling large amounts of information. Examples of significant improvements in the utilization of neutron detectors in physics experiments, in the characterization of the detector response, and in signal processing will be presented.
Accurate multiplicities of prompt fission neutrons emitted in neutron-induced fission on a large energy range are essential for fundamental and applied nuclear physics. Measuring them to high ...precision for radioactive fissioning nuclides is, however, an experimental challenge. In this work, we extract the average prompt-neutron multiplicity emitted in the 239 Pu (n, f) reaction as a function of the incident-neutron energy, over the range 0.7-700 MeV. We used a novel technique, which allowed us to minimize and correct for the main sources of bias and thus achieve unprecedented precision. At low energies, our data validate, for the first time, the ENDF/B-VIII.0 nuclear data evaluation with an independent measurement and reduce the evaluated uncertainty by up to 60%. This work opens up the possibility of measuring, with high precision, prompt fission neutron multiplicities on highly radioactive nuclei relevant for energy production.
In the commissioning phase of the DANCE project (Detector for Advanced Neutron Capture Experiments) measurements have been performed with special emphasis on the identification and suppression of ...possible backgrounds for the planned (n,γ) experiments. This report describes several background sources, observed in the experiment or anticipated from simulations, which will need to be suppressed in this and in similar detectors that are planned at other facilities. First successes are documented in the suppression of background from scattered neutrons captured in the detector as well as from the internal radiation. Experimental results and simulations using the GEANT code are compared.
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