A single crystal chemical vapor deposited (sCVD) diamond detector is used as an active target to measure neutron-induced reactions on natural carbon using the neutrons produced by spallation, with a ...broad energy spectrum at LANSCE. Additionally, the neutron-induced reactions are detected in the diamond as low as E n=400 keV and up to approximately 100 MeV. Relative cross sections for C 12(n,α0), C 12(n,p0), C 12(n,d0+p1), and C 13 (n,α0) are reported up to E n=22 MeV and comparisons on detected pulse-height spectra and detector response of scattering reactions are made with GEANT4 simulations using the ENDF/B-VIII.0 evaluated nuclear data library up to 20 MeV. The results are compared with past experimental data, including other works that incorporate diamond detectors as an active carbon target. In addition, R-matrix calculations for the C 13 + n system are presented.
Neutron-induced reactions with charged particle emission play an important role in a variety of research fields ranging from fundamental nuclear physics and nuclear astrophysics, to applications of ...nuclear technologies, to energy production, and material science. Recently, the capability to study reactions with radioactive targets has become important to significantly advance research in explosive nucleosynthesis and nuclear applications. To achieve the relevant research goals and study (n, x) reactions over a broad neutron beam energy range, the Low Energy Neutron-induced charged-particle (Z) chamber (LENZ) at Los Alamos Neutron Science Center (LANSCE) was developed, along with varied ancillary instrumentation, to enable the aforementioned research program. For the (n, x) reactions of interest at low energies, a precise simulation of the discrete spectrum of emitted charged particles is essential. In addition, since LANSCE is a user facility, a simulation of the LENZ setup easily accessible by users has a high value. With these goals in mind, we have developed a detailed simulation using the Geant4 toolkit. In this work, we present the implementation and the validation of the simulation using experimental data from recent campaigns with the LENZ apparatus. Specifically, we benchmark the simulation against a similar MCNP-based application, and determine the realistic range of applicability for the utilized probability biasing technique. We describe the implementation of an evaluated library with angular distribution and partial cross-section data, and we perform a validation of the simulation based on comparisons of simulated spectra with experimental ones for a number of targets used in previous experimental campaigns. Lastly, we discuss the limitations, caveats, and assets of the simulation code and techniques used.
The recent discovery and spectroscopic measurements of O 27 and O 28 suggests the disappearance of the N = 20 shell structure in these neutron-rich oxygen isotopes. We measured one- and two-proton ...removal cross sections from F 27 and Ne 29 , respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations. The invariant mass technique was used to reconstruct the two-body ( O 24 + n ) and three-body ( O 24 + 2 n ) decay energies from knockout reactions of F 27 (106.2 MeV/u) and Ne 29 (112.8 MeV/u) beams impinging on a Be 9 target. The one-proton removal from F 27 strongly populated the ground state of O 26 and the extracted cross section of 3 . 4 − 1.5 + 0.3 mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from Ne 29 an upper limit of 0.08 mb was extracted for populating states in O 27 decaying though the ground state of O 26 . The measured upper limit for the population of the ground state of O 26 in the two-proton removal reaction from Ne 29 indicates a significant difference in the underlying nuclear structure of F 27 and Ne 29 . Published by the American Physical Society 2024
An advanced neutron beam collimation system has been developed as part of an effort to optimize neutron beam transport at the Weapons Neutron Research (WNR) Facility 1, located within the Los Alamos ...Neutron Science Center (LANSCE). The goal of this work was to develop and demonstrate techniques to tailor neutron delivery in order to provide maximum available flux on sample with a specific beam profile, while simultaneously reducing unwanted background. A holistic approach was taken, upgrading the facility spallation target, facility metrology infrastructure, and flight path shutter insert to support the implementation of this advanced collimation system. Modern instruments and software were employed to conduct facility surveys, characterization of as-built geometry of critical components, 3D ray tracing and neutron transport calculations. Beam images and flux measurements were acquired after installation to evaluate the performance of the collimation system and to demonstrate consistent agreement with MCNP simulations which showed an 87% increase of flux on sample while providing suppression of background neutron impingement on the sample frame by 103.
The electromagnetic form factors of the proton and neutron encode information on the spatial structure of their charge and magnetization distributions. While measurements of the proton are relatively ...straightforward, the lack of a free neutron target makes measurements of the neutron's electromagnetic structure more challenging and more sensitive to experimental or model-dependent uncertainties. Various experiments have attempted to extract the neutron form factors from scattering from the neutron in deuterium, with different techniques providing different, and sometimes large, systematic uncertainties. We present results from a novel measurement of the neutron magnetic form factor using quasielastic scattering from the mirror nuclei ^{3}H and ^{3}He, where the nuclear effects are larger than for deuterium but expected to largely cancel in the cross-section ratios. We extracted values of the neutron magnetic form factor for low-to-modest momentum transfer, 0.6<Q^{2}<2.9 GeV^{2}, where existing measurements give inconsistent results. The precision and Q^{2} range of these data allow for a better understanding of the current world's data and suggest a path toward further improvement of our overall understanding of the neutron's magnetic form factor.
New segmented target for studies of neutron unbound systems Redpath, T.; Baumann, T.; Brown, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Letnik:
977, Številka:
C
Journal Article
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The study of neutron-unbound systems using invariant mass spectroscopy is often performed using low-intensity radioactive ion beams. Low reaction yields can be countered by using thick targets but at ...the expense of larger uncertainties in the reconstructed invariant mass. We present a new segmented target designed to address this trade-off. It is composed of three ∼4 mm thick passive beryllium targets interleaved between four 140μm thick position sensitive silicon detectors. In the first experiment to use this new system the half-life of two-neutron unbound 26O was measured to be T1∕2=5.0−2.2+1.7 (stat)±1.7 (syst) ps, which agrees with a previous measurement made by the MoNA Collaboration.
Here, a mass spectroscopy experiment with a pair of nearly identical high resolution spectrometers and a tritium target was performed in Hall A at Jefferson Lab. Utilizing the (e,e'K+) reaction, ...enhancements, which may correspond to a possible $\Lambda$nn resonance and a pair of ΣNN states, were observed with an energy resolution of about 1.21 MeV (σ), although greater statistics are needed to make definitive identifications. An experimentally measured Λnn state may provide a unique constraint in determining the Λn interaction, for which no scattering data exist. In addition, although bound A = 3 and 4 Σ hypernuclei have been predicted, only an A = 4 Σ hypernucleus ($^4_Σ$He) was found, utilizing the (K-,π-) reaction on a 4He target. The possible bound ΣNN state is likely a Σ0nn state, although this has to be confirmed by future experiments.
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