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"Neutrons"
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Neutrino
Discusses the development of the theory of the existence of neutrinos, and examines the struggle to detect and understand the tiny particles.
Book
Neutron Imaging at LANSCE—From Cold to Ultrafast
In recent years, neutron radiography and tomography have been applied at different beam lines at Los Alamos Neutron Science Center (LANSCE), covering a very wide neutron energy range. The field of energy-resolved neutron imaging with epi-thermal neutrons, utilizing neutron absorption resonances for contrast as well as quantitative density measurements, was pioneered at the Target 1 (Lujan center), Flight Path 5 beam line and continues to be refined. Applications include: imaging of metallic and ceramic nuclear fuels, fission gas measurements, tomography of fossils and studies of dopants in scintillators. The technique provides the ability to characterize materials opaque to thermal neutrons and to utilize neutron resonance analysis codes to quantify isotopes to within 0.1 atom %. The latter also allows measuring fuel enrichment levels or the pressure of fission gas remotely. More recently, the cold neutron spectrum at the ASTERIX beam line, also located at Target 1, was used to demonstrate phase contrast imaging with pulsed neutrons. This extends the capabilities for imaging of thin and transparent materials at LANSCE. In contrast, high-energy neutron imaging at LANSCE, using unmoderated fast spallation neutrons from Target 4 [Weapons Neutron Research (WNR) facility] has been developed for applications in imaging of dense, thick objects. Using fast (ns), time-of-flight imaging, enables testing and developing imaging at specific, selected MeV neutron energies. The 4FP-60R beam line has been reconfigured with increased shielding and new, larger collimation dedicated to fast neutron imaging. The exploration of ways in which pulsed neutron beams and the time-of-flight method can provide additional benefits is continuing. We will describe the facilities and instruments, present application examples and recent results of all these efforts at LANSCE.
Journal Article
14 MeV neutrons : physics and applications
\"Despite the often difficult and time-consuming effort of performing experiments with fast (14 MeV) neutrons, these neutrons can offer special insight into nucleus and other materials because of the absence of charge. 14 MeV neutrons: physics and applications explores fast neutrons in basic science and applications to problems in medicine, the environment, and security. Drawing on his more than 50 years of experience working with 14 MeV neutrons, the author focuses on: Sources of 14 MeV neutrons, including laboratory size accelerators, small and sealed tube generators, well logging sealed tube accelerators, neutron generators with detection of associated alpha particles, plasma devices, high flux sources, and laser-generated neutron sources ; Nuclear reactions with 14 MeV neutrons, including measurements of energy spectra, angular distributions, and deductions of reaction mechanism ; Nuclear reactions with three particles in the final state induced by neutrons and the identification of effects of final state interaction, quasi-free scattering, and charge-dependence of nuclear forces ; Charged particle and neutron detection methods, particularly position-sensitive detectors ; Industrial applications of nuclear analytical methods, especially in the metallurgy and coal industries ; Quality assurance and quality control measures for nuclear analytical methods ; Nuclear and atomic physics-based technology for combating illicit trafficking and terrorism ; and Medical applications, including radiography, radiotherapy, in vivo neutron activation analysis, boron neutron therapy, collimated neutron beams, and dosimetry. This book reflects the exciting developments in both fundamental nuclear physics and the application of fast neutrons to many practical problems. The book shows how 14 MeV neutrons are used in materials detection and analysis to effectively inspect large volumes in complex environments.\"--Back cover.
Book
Heavy-element production in a compact object merger observed by JWST
The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs)
1
, sources of high-frequency gravitational waves (GWs)
2
and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (the
r
-process)
3
. Here we present observations of the exceptionally bright GRB 230307A. We show that GRB 230307A belongs to the class of long-duration GRBs associated with compact object mergers
4
–
6
and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs.
7
–
12
). We obtained James Webb Space Telescope (JWST) mid-infrared imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns, which we interpret as tellurium (atomic mass
A
= 130) and a very red source, emitting most of its light in the mid-infrared owing to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create
r
-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe.
Observations from the JWST of the second brightest GRB ever detected, GRB 230307A, indicate that it belongs to the class of long-duration GRBs resulting from compact object mergers, with the decay of lanthanides powering the longlasting optical and infrared emission.
Journal Article
The basis and advances in clinical application of boron neutron capture therapy
Boron neutron capture therapy (BNCT) was first proposed as early as 1936, and research on BNCT has progressed relatively slowly but steadily. BNCT is a potentially useful tool for cancer treatment that selectively damages cancer cells while sparing normal tissue. BNCT is based on the nuclear reaction that occurs when
10
B capture low-energy thermal neutrons to yield high-linear energy transfer (LET) α particles and recoiling
7
Li nuclei. A large number of
10
B atoms have to be localized within the tumor cells for BNCT to be effective, and an adequate number of thermal neutrons need to be absorbed by the
10
B atoms to generate lethal
10
B (n, α)
7
Li reactions. Effective boron neutron capture therapy cannot be achieved without appropriate boron carriers. Improvement in boron delivery and the development of the best dosing paradigms for both boronophenylalanine (BPA) and sodium borocaptate (BSH) are of major importance, yet these still have not been optimized. Here, we present a review of this treatment modality from the perspectives of radiation oncology, biology, and physics. This manuscript provides a brief introduction of the mechanism of cancer-cell-selective killing by BNCT, radiobiological factors, and progress in the development of boron carriers and neutron sources as well as the results of clinical study.
Journal Article
Spin–isospin excitation of 3He with three-proton final state
Abstract
Spin–isospin excitation of the ^3$He nucleus by a proton-induced charge exchange reaction, ^3\\mathrm{He}(p,n)ppp$, at forward neutron scattering angle is studied in a plane wave impulse approximation (PWIA). In PWIA, cross sections of the reaction are written in terms of proton–neutron scattering amplitudes and response functions of the transition from ^{3}$He to the three-proton state by spin–isospin transition operators. The response functions are calculated with realistic nucleon–nucleon potential models using a Faddeev three-body method. Calculated cross sections agree with available experimental data in substance. Possible effects arising from the uncertainty of proton–neutron amplitudes and three-nucleon interactions in the three-proton system are examined.
Journal Article
Local structure determination in helimagnetic${\\mathrm{Co}}_{8}{\\mathrm{Zn}}_{8}{\\mathrm{Mn}}_{4-x}{\\mathrm{Fe}}_{x}
We have carried out a structural and magnetic characterization of Co8Zn8+y Mn4−y−x Fe x by means of bulk techniques, powder neutron scattering and Mössbauer spectroscopy. From our data, we derive the main magnetic parameters and carry out a detailed structural characterization. We observe that disorder is present in our samples in various forms and that this seems to be generic for this class of materials. However, the disorder appears to have little impact on the character of the magnetic phases, and thus seems to be of no relevance for the skyrmionic phases established for these types of materials.
Journal Article