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1
Atiyah, M. F. y N. S. Manton. "Complex geometry of nuclei and atoms". International Journal of Modern Physics A 33, n.º 24 (30 de agosto de 2018): 1830022. http://dx.doi.org/10.1142/s0217751x18300223.
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We propose a new geometrical model of matter, in which neutral atoms are modelled by compact, complex algebraic surfaces. Proton and neutron numbers are determined by a surface’s Chern numbers. Equivalently, they are determined by combinations of the Hodge numbers, or the Betti numbers. Geometrical constraints on algebraic surfaces allow just a finite range of neutron numbers for a given proton number. This range encompasses the known isotopes.
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Naghiyev, T. G. "Neutron-alpha reactions in nano α-Si3N4 particles by neutrons". Modern Physics Letters A 36, n.º 24 (10 de agosto de 2021): 2150181. http://dx.doi.org/10.1142/s0217732321501819.
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Computer modeling was applied to the study of [Formula: see text] transmutations in [Formula: see text] nanoparticles under the influence of neutrons at different energies. The modeling was separately performed for each Si and N atoms in the [Formula: see text] nanoparticles and the effect of neutrons on transmutations was investigated. The simulations were conducted individually for each stable isotope due to different effective cross-section of the probability of transmutation in the different types of isotopes of silicon and nitrogen atoms. Effective cross-section spectra of [Formula: see text] transmutation in Si and N atoms were comparatively studied.
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Mason, T. E. y A. D. Taylor. "Neutron Scattering in Materials Research". MRS Bulletin 24, n.º 12 (diciembre de 1999): 14–16. http://dx.doi.org/10.1557/s0883769400053665.
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With materials of ever-increasing complexity becoming key elements of the technologies underpinning industrial and economic development, there is an ongoing need for tools that reveal the microscopic origins of physical, electrical, magnetic, chemical, and biological properties. Neutron scattering is one such powerful tool for the study of the structure and dynamics of materials. Neutrons are well suited to this purpose for several reasons:∎ Neutrons are electrically neutral, leading to penetration depths of centimeters and thereby enabling in situ studies.∎ Neutron cross sections exhibit no regular dependence on atomic number and are similar in magnitude across the periodic table, giving rise to sensitivity to light elements in the presence of heavier ones.∎ Certain large differences in isotopic scattering cross sections (e.g., hydrogen to deuterium, H/D) make neutrons especially useful for the study of light atoms in materials.∎ The range of momentum transfer available allows probing of a broad range of length scales (0.1–105 Å), important in many different materials and applications.∎ Thermal and “cold” (longer-wavelength) neutrons cover a range of energies sufficient to probe a wide range of lattice or magnetic excitations, “slow” dynamic processes such as polymer chain reptation, and so forth.∎ Neutrons have magnetic moments and are thus uniquely sensitive probes of magnetic interactions.∎ Neutrons can be polarized, allowing the cross sections (magnetic and non-magnetic) to be separated.∎ The simplicity of the magnetic and nuclear interactions makes interpretation of results straightforward.
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Morris, Elizabeth M. y J. David Cooper. "Density measurements in ice boreholes using neutron scattering". Journal of Glaciology 49, n.º 167 (2003): 599–604. http://dx.doi.org/10.3189/172756503781830403.
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AbstractThis paper describes the use of a neutron probe to measure detailed stratigraphy in ice and snow. The Wallingford neutron probe, developed for measurement of soil moisture, consists of an annular radioactive source of fast neutrons around the centre of a cylindrical detector for slow (thermal) neutrons. In snow and ice, the fast neutrons lose energy by scattering from hydrogen atoms, and the number of slow neutrons arriving at the detector (the count rate) is related to the density of the medium. Calibration equations for count rate as a function of snow density and borehole diameter have been derived. Snow-density profiles from boreholes obtained using the probe show that, despite the smoothing produced by the neutron-scattering process, annual variations in density can be resolved. The potential contribution of the neutron probe to improvements in mass-balance monitoring is discussed.
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Roberts, Joyce A. "The Manuel Lujan Jr. Neutron Scattering Center". MRS Bulletin 22, n.º 9 (septiembre de 1997): 42–46. http://dx.doi.org/10.1557/s0883769400033996.
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In October 1986, the neutron scattering facility at Los Alamos National Laboratory became a national user facility and a formal user program was initiated in 1988. In July 1989, this facility was dedicated as the Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) in honor of the long-term Congress representative from New Mexico. The Lujan Center, part of the Los Alamos Neutron Science Center (LANSCE), is a pulsed spallation neutron source equipped with time-of-flight neutron-scattering spectrometers for condensed-matter research. Neutron scattering is a powerful technique for probing the microscopic structure of condensed matter. The energies and wavelengths of thermal neutrons closely match typical excitation energies and interatomic distances in solids and liquids. Because neutrons have no charge, they penetrate bulk samples of material to give precise information on the positions and motions of individual atoms. The magnetic moment of a neutron interacts with unpaired electrons, making neutrons ideal for probing microscopic magnetic properties. Because neutron-scattering cross sections do not vary monotonically with the atomic number of the scattering nucleus, neutrons and x-rays can provide complementary structural information. This technique is particularly effective for structural problems in polymer and biological studies because hydrogen and deuterium scatter neutrons strongly but with different cross sections.
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Dlougach, Eugenia, Mikhail Shlenskii y Boris Kuteev. "Neutral Beams for Neutron Generation in Fusion Neutron Sources". Atoms 10, n.º 4 (25 de noviembre de 2022): 143. http://dx.doi.org/10.3390/atoms10040143.
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Neutral beam injection is supposed to be the main source of high-energy particles, driving non-inductive current and generating primary neutrons in fusion neutron sources design based on tokamaks. Numerical simulation of high-energy particles’ thermalization in plasma and fusion neutron emission is calculated by novel dedicated software (NESTOR code). The neutral beam is reproduced statistically by up to 109 injected particles. The beam efficiency and contribution to primary neutron generation is shown to be dependent on the injection energy, input current, and plasma temperature profile. A beam-driven plasma operation scenario, specific for FNS design, enables the fusion rate and neutron generation in plasma volume to be controlled by the beam parameters; the resultant primary neutron yield can be efficiently boosted in plasma maintained at a relatively low temperature when compared to ‘pure’ fusion reactors. NESTOR results are applicable to high-precision nuclear and power balance estimations, neutron power loads distribution among tokamak components, tritium generation in hybrid reactors, and for many other tasks critical for FNS design.
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Pylypchuk, Ie V., V. O. Kovach, Anna V. Iatsyshyn, O. V. Farrakhov, V. N. Bliznyuk y V. O. Kutsenko. "Immobilization of boronic acid derivative onto the magnetic Gd-containing composites". IOP Conference Series: Earth and Environmental Science 1049, n.º 1 (1 de junio de 2022): 012014. http://dx.doi.org/10.1088/1755-1315/1049/1/012014.
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Abstract Aiming to develop new magnetic materials for neutron shielding applications, B- and Gd-containing magnetic nanoparticles were synthesized. Following bottom-up synthetic approach, core-shell Fe 3 O 4/Gd 2 O 3 nanocomposite particles were synthesized at the first stage. In the next stage, magnetic core-shell particles were modified with amino groups followed by grafting onto their surface of the boronic acid derivative. Such a multifunctional material, containing both boron (B) and gadolinium (Gd) atoms is a promising candidate for developing films and membranes, strongly interacting with neutrons. Due to the presence of boronic acids and bound to the indicator (Alizarin Red S), the material can induce color changes while immersed in sugar-containing solutions. Such a feature enables a possibility to estimate the number of boron atoms left after interaction with neutrons, thus allowing to check composite neutron-capture recourse.
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Liebschner, Dorothee, Pavel V. Afonine, Nigel W. Moriarty, Paul Langan y Paul D. Adams. "Evaluation of models determined by neutron diffraction and proposed improvements to their validation and deposition". Acta Crystallographica Section D Structural Biology 74, n.º 8 (24 de julio de 2018): 800–813. http://dx.doi.org/10.1107/s2059798318004588.
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The Protein Data Bank (PDB) contains a growing number of models that have been determined using neutron diffraction or a hybrid method that combines X-ray and neutron diffraction. The advantage of neutron diffraction experiments is that the positions of all atoms can be determined, including H atoms, which are hardly detectable by X-ray diffraction. This allows the determination of protonation states and the assignment of H atoms to water molecules. Because neutrons are scattered differently by hydrogen and its isotope deuterium, neutron diffraction in combination with H/D exchange can provide information on accessibility, dynamics and chemical lability. In this study, the deposited data, models and model-to-data fit for all PDB entries that used neutron diffraction as the source of experimental data have been analysed. In many cases, the reported R work and R free values were not reproducible. In such cases, the model and data files were analysed to identify the reasons for this mismatch. The issues responsible for the discrepancies are summarized and explained. The analysis unveiled limitations to the annotation, deposition and validation of models and data, and a lack of community-wide accepted standards for the description of neutron models and data, as well as deficiencies in current model refinement tools. Most of the issues identified concern the handling of H atoms. Since the primary use of neutron macromolecular crystallography is to locate and directly visualize H atoms, it is important to address these issues, so that the deposited neutron models allow the retrieval of the maximum amount of information with the smallest effort of manual intervention. A path forward to improving the annotation, validation and deposition of neutron models and hybrid X-ray and neutron models is suggested.
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Lucas, G. E., G. R. Odette y A. F. Rowcliffe. "Innovations in Testing Methodology for Fusion Reactor Materials Development". MRS Bulletin 14, n.º 7 (julio de 1989): 29–35. http://dx.doi.org/10.1557/s0883769400062138.
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The successful development of fusion power critically depends on structural materials which can maintain their integrity and dimensional stability in an extremely hostile service environment involving high temperatures and heat fluxes, corrosive media, high stresses, and intense fluxes of neutrons. Neutron irradiation results in a variety of mechanical, physical, and chemical property changes that are collectively referred to as radiation effects. The primary sources of damage are neutron-induced atomic displacements and transmutation products.High-energy neutrons produce primary recoil atoms (PKAs) with energies ranging from less than 1 keV to more than 100 keV. The energetic PKAs create a cascade of additional displacements. About 10% of the displaced atoms survive cascade recombination as isolated vacancies and self-interstitials or small clusters of these defects. The mobile defects migrate to pre-existing sinks such as grain boundaries and dislocations, or cluster to form a variety of extended defects such as voids (vacancies) or faulted dislocation loops (interstitials).
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Meilleur, Flora, Leighton Coates, Matthew Cuneo, Andrey Kovalevsky y Dean Myles. "The Neutron Macromolecular Crystallography Instruments at Oak Ridge National Laboratory: Advances, Challenges, and Opportunities". Crystals 8, n.º 10 (11 de octubre de 2018): 388. http://dx.doi.org/10.3390/cryst8100388.
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The IMAGINE and MaNDi instruments, located at Oak Ridge National Laboratory High Flux Isotope Reactor and Spallation Neutron Source, respectively, are powerful tools for determining the positions of hydrogen atoms in biological macromolecules and their ligands, orienting water molecules, and for differentiating chemical states in macromolecular structures. The possibility to model hydrogen and deuterium atoms in neutron structures arises from the strong interaction of neutrons with the nuclei of these isotopes. Positions can be unambiguously assigned from diffraction studies at the 1.5–2.5 Å resolutions, which are typical for protein crystals. Neutrons have the additional benefit for structural biology of not inducing radiation damage to protein crystals, which can be critical in the study of metalloproteins. Here we review the specifications of the IMAGINE and MaNDi beamlines and illustrate their complementarity. IMAGINE is suitable for crystals with unit cell edges up to 150 Å using a quasi-Laue technique, whereas MaNDi provides neutron crystallography resources for large unit cell samples with unit cell edges up to 300 Å using the time of flight (TOF) Laue technique. The microbial culture and crystal growth facilities which support the IMAGINE and MaNDi user programs are also described.
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Dufour, G., D. B. Cassidy, P. Crivelli, P. Debu, A. Lambrecht, V. V. Nesvizhevsky, S. Reynaud, A. Yu Voronin y T. E. Wall. "Prospects for Studies of the Free Fall and Gravitational Quantum States of Antimatter". Advances in High Energy Physics 2015 (2015): 1–16. http://dx.doi.org/10.1155/2015/379642.
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Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium, and antihydrogen. Among those, the project GBAR at CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs). Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could also be observed in positronium. In this contribution, we report on the status of the ongoing experiments and discuss the prospects of observing gravitational quantum states of antimatter and their implications.
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Zaccai, Nathan Richard y Nicolas Coquelle. "Opportunities and challenges in neutron crystallography". EPJ Web of Conferences 236 (2020): 02001. http://dx.doi.org/10.1051/epjconf/202023602001.
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Neutron and X-ray crystallography are complementary to each other. While X-ray scattering is directly proportional to the number of electrons of an atom, neutrons interact with the atomic nuclei themselves. Neutron crystallography therefore provides an excellent alternative in determining the positions of hydrogens in a biological molecule. In particular, since highly polarized hydrogen atoms (H+) do not have electrons, they cannot be observed by X-rays. Neutron crystallography has its own limitations, mainly due to inherent low flux of neutrons sources, and as a consequence, the need for much larger crystals and for different data collection and analysis strategies. These technical challenges can however be overcome to yield crucial structural insights about protonation states in enzyme catalysis, ligand recognition, as well as the presence of unusual hydrogen bonds in proteins.
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Schröder, Gabriela C., William B. O'Dell, Dean A. A. Myles, Andrey Kovalevsky y Flora Meilleur. "IMAGINE: neutrons reveal enzyme chemistry". Acta Crystallographica Section D Structural Biology 74, n.º 8 (17 de julio de 2018): 778–86. http://dx.doi.org/10.1107/s2059798318001626.
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Neutron diffraction is exquisitely sensitive to the positions of H atoms in protein crystal structures. IMAGINE is a high-intensity, quasi-Laue neutron crystallography beamline developed at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. This state-of-the-art facility for neutron diffraction has enabled detailed structural analysis of macromolecules. IMAGINE is especially suited to resolve individual H atoms in protein structures, enabling neutron protein structures to be determined at or near atomic resolutions from crystals with volumes of less than 1 mm3 and unit-cell edges of less than 150 Å. Beamline features include elliptical focusing mirrors that deliver neutrons into a 2.0 × 3.2 mm focal spot at the sample position, and variable short- and long-wavelength cutoff optics that provide automated exchange between multiple wavelength configurations. This review gives an overview of the IMAGINE beamline at the HFIR, presents examples of the scientific questions being addressed at this beamline, and highlights important findings in enzyme chemistry that have been made using the neutron diffraction capabilities offered by IMAGINE.
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Hajihoseini, H., N. Brenning, M. Rudolph, M. A. Raadu, D. Lundin, J. Fischer, T. M. Minea y J. T. Gudmundsson. "Target ion and neutral spread in high power impulse magnetron sputtering". Journal of Vacuum Science & Technology A 41, n.º 1 (enero de 2023): 013002. http://dx.doi.org/10.1116/6.0002292.
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In magnetron sputtering, only a fraction of the sputtered target material leaving the ionization region is directed toward the substrate. This fraction may be different for ions and neutrals of the target material as the neutrals and ions can exhibit a different spread as they travel from the target surface toward the substrate. This difference can be significant in high power impulse magnetron sputtering (HiPIMS) where a substantial fraction of the sputtered material is known to be ionized. Geometrical factors or transport parameters that account for the loss of produced film-forming species to the chamber walls are needed for experimental characterization and modeling of the magnetron sputtering discharge. Here, we experimentally determine transport parameters for ions and neutral atoms in a HiPIMS discharge with a titanium target for various magnet configurations. Transport parameters are determined to a typical substrate, with the same diameter (100 mm) as the cathode target, and located at a distance 70 mm from the target surface. As the magnet configuration and/or the discharge current are changed, the transport parameter for neutral atoms [Formula: see text] remains roughly the same, while transport parameters for ions [Formula: see text] vary greatly. Furthermore, the relative ion-to-neutral transport factors, [Formula: see text], that describe the relative deposited fractions of target material ions and neutrals onto the substrate, are determined to be in the range from 0.4 to 1.1.
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Mechetin, Grigory V. y Dmitry O. Zharkov. "DNA Damage Response and Repair in Boron Neutron Capture Therapy". Genes 14, n.º 1 (2 de enero de 2023): 127. http://dx.doi.org/10.3390/genes14010127.
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Boron neutron capture therapy (BNCT) is an approach to the radiotherapy of solid tumors that was first outlined in the 1930s but has attracted considerable attention recently with the advent of a new generation of neutron sources. In BNCT, tumor cells accumulate 10B atoms that react with epithermal neutrons, producing energetic α particles and 7Li atoms that damage the cell’s genome. The damage inflicted by BNCT appears not to be easily repairable and is thus lethal for the cell; however, the molecular events underlying the action of BNCT remain largely unaddressed. In this review, the chemistry of DNA damage during BNCT is outlined, the major mechanisms of DNA break sensing and repair are summarized, and the specifics of the repair of BNCT-induced DNA lesions are discussed.
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Fleming, Nina C. y Ayman I. Hawari. "Structure-Dependent Doppler Broadening Using a Generalized Thermal Scattering Law". Journal of Nuclear Engineering 2, n.º 2 (8 de abril de 2021): 124–31. http://dx.doi.org/10.3390/jne2020013.
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The thermal scattering law (TSL), i.e., S(α,β), represents the momentum and energy exchange phase space for a material. The incoherent and coherent components of the TSL correlate an atom’s trajectory with itself and/or with other atoms in the lattice structure. This structural information is especially important for low energies where the wavelength of neutrons is on the order of the lattice interatomic spacing. Both thermal neutron scattering as well as low energy resonance broadening involve processes where incoming neutron responses are lattice dependent. Traditionally, Doppler broadening for absorption resonances approximates these interactions by assuming a Maxwell–Boltzmann distribution for the neutron velocity. For high energies and high temperatures, this approximation is reasonable. However, for low temperatures or low energies, the lattice structure binding effects will influence the velocity distribution. Using the TSL to determine the Doppler broadening directly introduces the material structure into the calculation to most accurately capture the momentum and energy space. Typically, the TSL is derived assuming cubic lattice symmetry. This approximation collapses the directional lattice information, including the polarization vectors and associated energies, into an energy-dependent function called the density of states. The cubic approximation, while valid for highly symmetric and uniformly bonded materials, is insufficient to capture the true structure. In this work, generalized formulation for the exact, lattice-dependent TSL is implemented within the Full Law Analysis Scattering System Hub (FLASSH) using polarization vectors and associated energies as fundamental input. These capabilities are utilized to perform the generalized structure Doppler broadening analysis for UO2.
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Michael, A. T., M. Opher, G. Tóth, V. Tenishev y D. Borovikov. "The Solar Wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) Code: A Self-consistent Kinetic–Magnetohydrodynamic Model of the Outer Heliosphere". Astrophysical Journal 924, n.º 2 (1 de enero de 2022): 105. http://dx.doi.org/10.3847/1538-4357/ac35eb.
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Abstract Neutral hydrogen has been shown to greatly impact the plasma flow in the heliosphere and the location of the heliospheric boundaries. We present the results of the Solar Wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model, a new, self-consistent, kinetic–MHD model of the outer heliosphere within the Space Weather Modeling Framework. The charge exchange mean free path is on the order of the size of the heliosphere; therefore, the neutral atoms cannot be described as a fluid. The numerical code SHIELD couples the MHD solution for a single plasma fluid to the kinetic solution for neutral hydrogen atoms streaming through the system. The kinetic code is based on the Adaptive Mesh Particle Simulator, a Monte Carlo method for solving the Boltzmann equation. The numerical code SHIELD accurately predicts the increased filtration of interstellar neutrals into the heliosphere. In order to verify the correct implementation within the model, we compare the results of the numerical code SHIELD to those of other, well-established kinetic–MHD models. The numerical code SHIELD matches the neutral hydrogen solution of these studies as well as the shift in all heliospheric boundaries closer to the Sun in comparison with the multi-fluid treatment of neutral hydrogen atoms. Overall the numerical code SHIELD shows excellent agreement with these models and is a significant improvement to the fluid treatment of interstellar hydrogen.
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Jorgensen, James D. y John M. Newsam. "Neutron Powder Diffraction". MRS Bulletin 15, n.º 11 (noviembre de 1990): 49–55. http://dx.doi.org/10.1557/s088376940005836x.
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For many classes of materials, neutron diffraction is the best way to obtain detailed atomic-level structural information. Diffraction experiments on single crystals provide the most precise data, but sufficiently large specimens (>0.1–0.5 mm3) are often not available. Steady development of instrumentation and data analysis techniques, however, has now made it possible to obtain comparably precise structural information from neutron diffraction experiments on powder samples. Such studies have played a prominent role in solid state physics, chemistry, and materials science in recent years. The special capabilities that have contributed to the success of this technique include atomic cross sections that are often favorable for a particular structural problem, high neutron penetrating power, the excellent resolution achieved with state-of-the-art diffractometers, and steadily advancing analysis techniques that facilitate obtaining structural information from a diverse range of polycrystalline materials.As Axe, Pynn, and Hayter note in their introductory article in this issue of the MRS BULLETIN, atomic scattering cross sections for neutrons are not simply a function of atomic number, as is the case for x-rays. The scattering is predominantly from the nuclei (thus avoiding the form factor diminution observed for x-ray scattering), and coherent neutron scattering cross sections can, generally, be as large for light atoms as for heavy atoms. Light atoms, such as hydrogen (deuterium), oxygen, nitrogen, carbon, or lithium, can therefore be located in the presence of heavier atoms. This advantage has led to the widespread use of neutron powder diffraction for studing metal hydrides and, more recently, oxide superconductors.
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Mohanmurthy, Prajwal, Albert R. Young, Jeff A. Winger y Geza Zsigmond. "A Search for Neutron to Mirror Neutron Oscillation Using Neutron Electric Dipole Moment Measurements". Symmetry 14, n.º 3 (28 de febrero de 2022): 487. http://dx.doi.org/10.3390/sym14030487.
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Baryon number violation is a key ingredient of baryogenesis. It has been hypothesized that there could also be a parity-conjugated copy of the standard model particles, called mirror particles. The existence of such a mirror universe has specific testable implications, especially in the domain of neutral particle oscillation, viz. the baryon number violating neutron to mirror-neutron (n−n′) oscillation. Consequently, there were many experiments that have searched for n−n′ oscillation, and imposed constraints upon the parameters that describe it. Recently, further analysis on some of these results have identified anomalies which could point to the detection of n−n′ oscillation. All the previous efforts searched for n−n′ oscillation by comparing the relative number of ultracold neutrons that survive after a period of storage for one or both of the two cases: (i) comparison of zero applied magnetic field to a non-zero applied magnetic field, and (ii) comparison where the orientation of the applied magnetic field was reversed. However, n−n′ oscillations also lead to variations in the precession frequency of polarized neutrons upon flipping the direction of the applied magnetic field. Precession frequencies are measured, very precisely, by experiments searching for the electric dipole moment. For the first time, we used the data from the latest search for the neutron electric dipole moment to constrain n−n′ oscillation. After compensating for the systematic effects that affect the ratio of precession frequencies of ultracold neutrons and cohabiting 199Hg-atoms, chief among which was due to their motion in non-uniform magnetic field, we constrained any further perturbations due to n−n′ oscillation. We thereby provide a lower limit on the n−n′ oscillation time constant of τnn′/|cos(β)|>5.7s,0.36T′<B′<1.01T′ (95% C.L.), where β is the angle between the applied magnetic field and the ambient mirror magnetic field. This constraint is the best available in the range of 0.36T′<B′<0.40T′.
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Schwarzschild, Bertram M. "Accelerating neutral atoms". Physics Today 62, n.º 12 (diciembre de 2009): 21. http://dx.doi.org/10.1063/1.3273005.
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KADAR-KALLEN, M. A. y K. D. BONIN. "FOCUSING NEUTRAL ATOMS". Optics News 14, n.º 12 (1 de diciembre de 1988): 41. http://dx.doi.org/10.1364/on.14.12.000041.
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Liu, Yang, Tengfei Zhu, Jianxi Yao y Xiaoping Ouyang. "Simulation of Radiation Damage for Silicon Drift Detector". Sensors 19, n.º 8 (13 de abril de 2019): 1767. http://dx.doi.org/10.3390/s19081767.
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Silicon drift detector with high sensitivity and energy resolution is an advanced detector which is suitable to be used in deep space detection. To study and reveal the radiation damage of the silicon drift detector (SDD) in a deep-space environment, which will degrade the detector performance, in this paper, the SDD radiation damage effects and mechanics, including displacement damage and ionization damage, for irradiations of different energy of neutrons and gammas are investigated using Geant4 simulation. The results indicate the recoil atoms distribution generated by neutrons in SDD is uniform, and recoil atoms’ energy is mainly in the low energy region. For secondary particles produced by neutron irradiation, a large energy loss in inelastic scattering and fission reactions occur, and neutron has a significant nuclear reaction. The energy deposition caused by gammas irradiation is linear with the thickness of SDD; the secondary electron energy distribution produced by gamma irradiation is from several eV to incident particle energy. As the scattering angle of secondary electron increases, the number of secondary electrons decreases. Therefore, a reasonable detector epitaxial thickness should be set in the anti-irradiation design of SDD.
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Goldhagen, Paul. "Cosmic-Ray Neutrons on the Ground and in the Atmosphere". MRS Bulletin 28, n.º 2 (febrero de 2003): 131–35. http://dx.doi.org/10.1557/mrs2003.41.
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AbstractNeutrons from collisions of cosmic rays with the nuclei of atoms in the atmosphere are an irremovable external radiation that causes single-event upsets in microelectronic devices. Predicting soft error rates requires knowledge of the flux and energy distribution of the cosmic-ray-induced neutrons. This article reviews cosmic-ray neutrons in the atmosphere and on the ground, the factors that determine their intensity, and recent calculations and state-of-the-art measurements of neutron spectra covering 12 decades of energy, from the thermal energy range up to 10 GeV.
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Jeffries, Cy M., Zuzanna Pietras y Dmitri I. Svergun. "The basics of small-angle neutron scattering (SANS for new users of structural biology)". EPJ Web of Conferences 236 (2020): 03001. http://dx.doi.org/10.1051/epjconf/202023603001.
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Small-angle neutron scattering (SANS) provides a means to probe the time-preserved structural state(s) of bio-macromolecules in solution. As such, SANS affords the opportunity to assess the redistribution of mass, i.e., changes in conformation, which occur when macromolecules interact to form higher-order assemblies and to evaluate the structure and disposition of components within such systems. As a technique, SANS offers scope for ‘out of the box thinking’, from simply investigating the structures of macromolecules and their complexes through to where structural biology interfaces with soft-matter and nanotechnology. All of this simply rests on the way neutrons interact and scatter from atoms (largely hydrogens) and how this interaction differs from the scattering of neutrons from the nuclei of other ‘biological isotopes’. The following chapter describes the basics of neutron scattering for new users of structural biology in context of the neutron/hydrogen interaction and how this can be exploited to interrogate the structures of macromolecules, their complexes and nano-conjugates in solution.
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Troev, T., N. Nankov, L. Petrov y E. Popov. "Computer Modeling of Displacement Cascades in Beryllium Irradiated with Intensive Neutron Flux". Research Letters in Physics 2008 (7 de febrero de 2008): 1–4. http://dx.doi.org/10.1155/2008/746892.
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Computer simulations of the radiation defects created in beryllium irradiated by fast neutrons (E>0.1 MeV) using the Geant4 and SRIM packages were carried out. The atom cascade displacements in Be at a neutron fluence of 1.6×1020 n/cm2 were determined to be 0.06 dpa and the helium concentration was calculated to be 168 appm. The concentration of 6Li has been estimated to be 5% in comparison to the He concentration. Nanoscale calculations were done in 30×30×30 nm cube of fast neutron-irradiated Be. A correlation between the Be primary knock-on atom (PKA) energies and the damage cascades has been established. The final defect distributions of single vacancies, divacancies, and small vacancy clusters were examined. Our results indicate that the damages caused by He atoms are about 3 times less than damages caused by Be primary knock-on atoms (PKAs).
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Dzhimak, S. S., G. F. Kopytov, E. N. Tumaev, V. A. Isaev, A. V. Moiseev, V. V. Malyshko, A. A. Elkina y M. G. Baryshev. "Influence on the energy of covalent link of the isotopic composition forming its nuclei". Izvestiya vysshikh uchebnykh zavedenii. Fizika, n.º 11 (2020): 81–89. http://dx.doi.org/10.17223/00213411/63/11/81.
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In this paper, on the basis of the classical quantum-mechanical approach, an explanation is considered of the physical mechanism of isotope fractionation associated with the predominance of a certain number of neutrons among nucleons and explaining the nonequilibrium accumulation of certain forms of stable isotopes of biogenic elements in heterogeneous systems. The reasons for the detected neutron effect can be: the interaction of the magnetic moments of atomic nuclei and valence electrons, leading to a change in the distance between them, including the effect of the changed distance between atoms on the energy of the covalent bond between the resonant pairs of atoms.
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Lu, Xun, Brinda Selvaraj, Sudipa Ghimire-Rijal, Gregory S. Orf, Flora Meilleur, Robert E. Blankenship, Matthew J. Cuneo y Dean A. A. Myles. "Neutron and X-ray analysis of the Fenna–Matthews–Olson photosynthetic antenna complex from Prosthecochloris aestuarii". Acta Crystallographica Section F Structural Biology Communications 75, n.º 3 (20 de febrero de 2019): 171–75. http://dx.doi.org/10.1107/s2053230x19000724.
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The Fenna–Matthews–Olson protein from Prosthecochloris aestuarii (PaFMO) has been crystallized in a new form that is amenable to high-resolution X-ray and neutron analysis. The crystals belonged to space group H3, with unit-cell parameters a = b = 83.64, c = 294.78 Å, and diffracted X-rays to ∼1.7 Å resolution at room temperature. Large PaFMO crystals grown to volumes of 0.3–0.5 mm3 diffracted neutrons to 2.2 Å resolution on the MaNDi neutron diffractometer at the Spallation Neutron Source. The resolution of the neutron data will allow direct determination of the positions of H atoms in the structure, which are believed to be fundamentally important in tuning the individual excitation energies of bacteriochlorophylls in this archetypal photosynthetic antenna complex. This is one of the largest unit-cell systems yet studied using neutron diffraction, and will allow the first high-resolution neutron analysis of a photosynthetic antenna complex.
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Piotrowski, Tomasz, Dariusz B. Tefelski, Michał Mazgaj, Janusz Skubalski, Andrzej Żak y Joanna Julia Sokołowska. "Polymers in Concrete – The Shielding against Neutron Radiation". Advanced Materials Research 1129 (noviembre de 2015): 131–38. http://dx.doi.org/10.4028/www.scientific.net/amr.1129.131.
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Concrete has been used as a shield against high-energy photons (gamma) and neutrons since the beginning of use of nuclear reaction in energy, medicine and research. State of knowledge in shielding concrete technology is that while in case of protection against gamma radiation an increase in density caused by change of aggregate type for heavy-weight one is usually an efficient solution, the protection against neutrons is more complex. It is due to the differences in interactions of neutrons with the matter, depending on their kinetic energy and cross-sections for different reactions of the component atoms of the cement paste and the aggregate. The paper presents the results of the project NGS-Concrete - New-Generation Shielding Concrete. The aim is to design the composition of concrete against ionizing radiation, achieved by the use of experiment based on multi-criteria optimization of materials supported by the Monte Carlo simulations. Better concrete is the one that absorbs more thermal neutrons and slows down more fast neutrons at the same time. In the paper both results of Monte Carlo simulations and experimental studies on ordinary and heavyweight concrete containing epoxy polymer additive are presented. Close values of thermal neutron attenuation coefficients proved good accordance between simulation and experiment. The final conclusion is that epoxy resin is an efficient additive for neutron shielding concretes improving its ability to protect mainly against low energy neutrons. In experimental measurement there has not been observed an improvement of fast neutron attenuation due to increase of hydrogen atom content introduced with epoxy.
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Mustafakulov, A. "Radiation modification of quartz and its spectral characteristics". E3S Web of Conferences 508 (2024): 07011. http://dx.doi.org/10.1051/e3sconf/202450807011.
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The nature of the structural phase transition of quartz under neutron irradiation was studied by X-ray diffraction analysis. The kinetics of gamma luminescence (GL) bands in quartz crystals grown on seeds irradiated with neutrons with a dose of 5-1018..1019 and 5-1019 n/sm2 after additional neutron irradiation of 1016- 8.1020 n/sm2 in the temperature range 77-300 K. Based on experimental data, it is shown that all the structural characteristics of the seed are transferred to the grown crystal. This opens up the possibility of obtaining quartz crystals with predetermined properties. Diffraction parameters of quartz irradiated with neutrons and grown on neutron-irradiated seeds (n/sm2). Based on the results of studies of GL, the redistribution of the intensities of photoluminescence bands under illumination (λw = 300-340 nm) without heating and with heating in the temperature range 300-720 K, the dependence of the intensities of luminescence bands on the neutron fluence, it was assumed that the luminescence centers are at 550 and 660 nm are, respectively, peroxide radicals and non-bridging oxygen atoms located at the interfaces between the α- and β-phases of quartz.
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GOLDBERG, HAIM. "TEV ANTINEUTRINOS FROM CYGNUS OB2". International Journal of Modern Physics A 20, n.º 06 (10 de marzo de 2005): 1132–39. http://dx.doi.org/10.1142/s0217751x05024006.
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High energy cosmic ray experiments have identified an excess from the region of the Galactic Plane in a limited energy range around 1018 eV ( EeV ). This is very suggestive of neutrons as candidate primaries, because the directional signal requires relatively-stable neutral primaries, and time-dilated neutrons can reach Earth from typical Galactic distances when the neutron energy exceeds an EeV . We here point out that if the Galactic messengers are neutrons, then those with energies below an EeV will decay in flight, providing a flux of cosmic antineutrinos above a TeV which is observable at a kilometer-scale neutrino observatory. The expected event rate per year above 1 TeV in a detector such as IceCube, for example, is 20 antineutrino showers (all flavors) and a 1° directional signal of [Formula: see text] events. A measurement of this flux can serve to identify the first extraterrestrial point source of TeV antineutrinos.
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Lakhina, Gurbax S. y Bruce T. Tsurutani. "Satellite drag effects due to uplifted oxygen neutrals during super magnetic storms". Nonlinear Processes in Geophysics 24, n.º 4 (15 de diciembre de 2017): 745–50. http://dx.doi.org/10.5194/npg-24-745-2017.
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Abstract. During intense magnetic storms, prompt penetration electric fields (PPEFs) through E × B forces near the magnetic equator uplift the dayside ionosphere. This effect has been called the dayside super-fountain effect. Ion-neutral drag forces between the upward moving O+ (oxygen ions) and oxygen neutrals will elevate the oxygen atoms to higher altitudes. This paper gives a linear calculation indicating how serious the effect may be during an 1859-type (Carrington) superstorm. It is concluded that the oxygen neutral densities produced at low-Earth-orbiting (LEO) satellite altitudes may be sufficiently high to present severe satellite drag. It is estimated that with a prompt penetrating electric field of ∼ 20 mV m−1 turned on for 20 min, the O atoms and O+ ions are uplifted to 850 km where they produce about 40-times-greater satellite drag per unit mass than normal. Stronger electric fields will presumably lead to greater uplifted mass.
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Fraternale, F., N. V. Pogorelov y R. K. Bera. "The Role of Electrons and Helium Atoms in Global Modeling of the Heliosphere". Astrophysical Journal 946, n.º 2 (1 de abril de 2023): 97. http://dx.doi.org/10.3847/1538-4357/acba10.
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Abstract We present a new three-dimensional, MHD-plasma/kinetic-neutrals model of the solar wind (SW) interaction with the local interstellar medium (LISM), which self-consistently includes neutral hydrogen and helium atoms. This new model also treats electrons as a separate fluid and includes the effect of Coulomb collisions. While the properties of electrons in the distant SW and in the LISM are mostly unknown due to the lack of in situ observations, a common assumption for any global, single-ion model is to assume that electrons have the temperature of the ion mixture, which includes pickup ions. In the new model, electrons in the SW are colder, which results in a better agreement with New Horizons observations in the supersonic SW. In the LISM, however, ions and electrons are almost in thermal equilibrium. As for the plasma mixture, the major differences between the models are in the inner heliosheath, where the new model predicts a charge-exchange-driven cooling and a decrease of the heliosheath thickness. The filtration of interstellar neutral atoms at the heliospheric interface is discussed. The new model predicts an increase in the H density by ∼2% at 1 au. However, the fraction of pristine H atoms decreases by ∼12%, while the density of atoms born in the outer and inner heliosheath increases by 5% and ∼35%, respectively. While at 1 au the density of He atoms remains unchanged, the contribution from the “warm breeze” increases by ∼3%.
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Swanson, Terry W. y Marc L. Caffee. "Determination of 36Cl Production Rates Derived from the Well-Dated Deglaciation Surfaces of Whidbey and Fidalgo Islands, Washington". Quaternary Research 56, n.º 3 (noviembre de 2001): 366–82. http://dx.doi.org/10.1006/qres.2001.2278.
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AbstractThe 36Cl dating method is increasingly being used to determine the surface-exposure history of Quaternary landforms. Production rates for the 36Cl isotopic system, a critical component of the dating method, have now been refined using the well-constrained radiocarbon-based deglaciation history of Whidbey and Fidalgo Islands, Washington. The calculated total production rates due to calcium and potassium are 91±5 atoms 36Cl (g Ca)−1 yr−1 and are 228±18 atoms 36Cl (g K)−1 yr−1, respectively. The calculated ground-level secondary neutron production rate in air, Pf(0), inferred from thermal neutron absorption by 35Cl is 762±28 neutrons (g air)−1 yr−1 for samples with low water content (1–2 wt.%). Neutron absorption by serpentinized harzburgite samples of the same exposure age, having higher water content (8–12 wt.%), is ∼40% greater relative to that for dry samples. These data suggest that existing models do not adequately describe thermalization and capture of neutrons for hydrous rock samples. Calculated 36Cl ages of samples collected from the surfaces of a well-dated dacite flow (10,600–12,800 cal yr B.P.) and three disparate deglaciated localities are consistent with close limiting calibrated 14C ages, thereby supporting the validity of our 36Cl production rates integrated over the last ∼15,500 cal yr between latitudes of 46.5° and 51°N. Although our production rates are internally consistent and yield reasonable exposure ages for other localities, there nevertheless are significant differences between these production rates and those of other investigators.
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Wang, Li-Min, Bing-Huang Duan, Xian-Guo Xu, Hao Li, Zhi-Jun Chen, Kun-Jie Yang y Shuo Zhang. "Simulation of neutron irradiation damage in lead lanthanum zirconate titanate by Monte Carlo method". Acta Physica Sinica 71, n.º 7 (2022): 076101. http://dx.doi.org/10.7498/aps.71.20212041.
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Lead lanthanum zirconate titanate (PLZT) has a broad application prospect for energy storage devices with high energy density, since it possesses excellent dielectric and energy storage properties. To investigate the irradiation damage to the PLZT induced by neutrons with different energy, the primary energetic recoil spectra of each kind of element are first extracted from the transportation simulations of neutrons with energy ranging from 1 to 14 MeV, respectively. Then, the displacement damages (including vacancies and interstitial atoms) induced by each type of recoil with different energy are simulated based on the binary collision approximation method. Finally the number of defects in PLZT produced by neutrons with an energy range from 1 to 14 MeV is calculated based on the recoil energy spectra and the defect number produced by the recoils. The results show that the number of defects produced in the PLZT material with a thickness of 3 cm is approximately independent of the neutron energy for the fast neutrons with energy in a range from 1 to 14 MeV, even though the primary recoil energy spectra from neutrons with different energy are completely different. The average number of defects produced in 3-cm-thick PLZT is about 460 ± 120 vacancies/neutrons. For neutrons with energy ranging from 1 to 14 MeV, the produced defect concentration in PLZT decreases slightly with the depth increasing within a thickness of 3 cm. The difference in defect concentration in this 3 cm is in a range of 50%. This decrease is caused mainly by the fact that some of neutrons are back-scattered during transport. The average defect concentration produced by neutron irradiation in the PLZT with a thickness of 3 cm is slightly(～20%) higher than that in the PLZT with a thickness of 1 mm. The reason for the higher defect concentration in a thicker (3 cm) PLZT can be attributed to the following facts: (i) the (n, 2n) reactions between neutron and material can make the number of neutrons increase during transport; (ii) the scattering can make the path of neutron longer; (iii) the inelastic scattering can lead to a smallnumber of moderated neutrons, which have a slightly larger interaction cross section with materials. This indicates the damage produced in thick PLZT is quite complicated and closely related to the process of neutron transport. This work presents a method of calculating the displacement damage of neutrons in materials, and the simulation results can provide guidance for studying the neutron irradiation effects of PLZT-based electronic devices.
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Jánský, Jaroslav, Jiří Janda, Michal Košťál, Zdeněk Matěj, Tomáš Bílý, Věra Mazánková, Filip Mravec y František Cvachovec. "Response to Mono-Energetic Neutrons and Light Output Function for Liquid Organic Scintillators PYR5/DIPN and THIO5/DIPN". Quantum Beam Science 6, n.º 2 (12 de mayo de 2022): 18. http://dx.doi.org/10.3390/qubs6020018.
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Liquid organic scintillators are important devices for measurements of neutron radiation. Currently, large-scale liquid organic scintillators have capabilities of detecting neutrons, but the determination of the neutron energy spectra is a challenge. This work aims to measure the responses of two liquid two-component scintillators to mono-energetic neutron radiation and to determine their light output function, which is necessary for proper neutron energy spectra determination. Both scintillators are composed of the solvent di-iso-propyl-naphthalene (DIPN) mixed isomers. The first scintillator, labeled PYR5/DIPN, contains the luminophore 1-phenyl-3-(2,4,6-trimethyl-phenyl)-2-pyrazoline with a concentration of 5 g/L. The second scintillator labeled THIO5/DIPN contains the luminophore 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene also with a concentration of 5 g/L. The responses to neutron energies of 1.5 MeV, 2.5 MeV, and 19 MeV are measured at PTB in Braunschweig. The responses to neutron energies of 2.45 MeV and 14 MeV were measured at CTU in Prague using DD and DT reactions. The responses to a silicon filtered beam were measured at Research Centre Řež. The measurements were processed using a two-parameter spectrometric system NGA-01 to discriminate neutrons from gamma rays. The obtained responses are dominated by recoil protons from elastic collisions of neutrons with hydrogen atoms. The edge of the response of recoil protons gives information about the light output of neutrons, compared to gamma rays for the same radiation energy. The light output function for protons in the PYR5/DIPN scintillator is L(Ep)=0.6294Ep−1.00(1−exp(−0.4933Ep0.95)). The light output function for protons in the THIO5/DIPN scintillator is L(Ep)=0.6323Ep−1.00(1−exp(−0.4986Ep0.9883)). The light output functions well resemble the standard shape, and they are quite similar to each other. That suggests a weak influence of the luminophore on the light output function. The light output functions are ready to be incorporated to the response matrix for the neutron energy spectra determination.
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Tugrul, Taylan. "Investigation of photon doses reaching healthy tissues in the use of different neutron energies in boron neutron capture therapy". Nuclear Technology and Radiation Protection 37, n.º 4 (2022): 334–39. http://dx.doi.org/10.2298/ntrp2204334t.
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Boron neutron capture therapy is a unique treatment method that aims to kill the tumor cells with the help of heavy particles. Particles resulting from the interaction of the tumor region containing 10B atoms with thermal or epithermal neutrons have the most important role in this treatment method. In this study, gamma radiation reaching healthy tissues, which is the result of 10B(n,a)7Li reaction, was investigated. A simulation suitable for boron neutron capture therapy treatment, including the human head model, was created by the Monte Carlo N-Particle (MCNP) program. By using five different neutron energies, the gamma radiations resulting from the 10B(n,a)7Li reaction in the determined regions, close to the tumor tissue, were investigated. It was observed that the healthy tissue between the tumor area and the surface is exposed to the highest gamma flux and the highest gamma radiation absorption. It was also observed that these values increase as neutron energy decreases. It was found that the gamma doses received by some regions outside the neutron irradiation area could be significant. It has been understood that the change in neutron energy may cause significant changes in gamma radiation values reaching healthy tissues, especially in regions close to the surface. In boron neutron capture therapy treatments, the neutrons sent to the tumor should be selected depending on the location of the tumor and the size of the tumor area. This study contains significant data about photon doses in healthy tissues around the brain region treated using different neutron energies with the boron neutron capture therapy technique.
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Dey, Ritu, Malay B. Chowdhuri, Joydeep Ghosh, Ranjana Manchanda, Nandini Yadava, Umeshkumar C. Nagora, Parveen K. Atrey, Jayesh V. Raval, Y. Shankara Joisa y Rakesh L. Tanna. "Modeling of the Hα Emission from ADITYA Tokamak Plasmas". Atoms 7, n.º 4 (5 de octubre de 2019): 95. http://dx.doi.org/10.3390/atoms7040095.
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The spatial profile of Hα spectrum is regularly measured using a high-resolution multi-track spectrometer in ADITYA tokamak to study the neutral particle behavior. The Monte Carlo neutral particle transport code DEGAS2 is used to model the experimental Hα spectral emissions. Through the modeling of the spectral line profile of Hα, it is found that the neutral hydrogen, which is produced from molecular hydrogen and molecular hydrogen ion dissociation processes contributes 56% to the total Hα emission, and the atoms which are produced from charge-exchange process have 30% contribution. Furthermore, the experimentally measured spatial profile of chord integrated brightness was modeled for the two plasma discharges having relatively high and low density to understand the neutral particle penetration. The presence of neutrals inside the core region of the ADITYA tokamak is mainly due to the charge-exchange process. Furthermore, it is observed that neutral particle penetration is lower in higher density discharge.
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Sasaki, Toshihiko, Nobuaki Minakawa, Yukio Morii, Nobuo Niimura y Yukio Hirose. "OS04W0158 A fundamental study on neutron stress measurement using neutron image plate (NIP) at Japan Atomic Energy Research Institute(JAERI) : Observation of neutron diffraction ring". Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics 2003.2 (2003): _OS04W0158. http://dx.doi.org/10.1299/jsmeatem.2003.2._os04w0158.
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Sagatova, Andrea, Bohumir Zatko, Katarina Sedlackova, Marius Pavlovic, Vladimir Necas, Marko Fulop, Michael Solar y Carlos Granja. "Semi-insulating GaAs detectors with HDPE layer for detection of fast neutrons from D–T nuclear reaction". International Journal of Modern Physics: Conference Series 44 (enero de 2016): 1660233. http://dx.doi.org/10.1142/s2010194516602337.
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Bulk semi-insulating (SI) GaAs detectors optimized for fast-neutron detection were examined using mono-energetic neutrons. The detectors have an active area of 7.36 mm2 defined by a multi-pixel structure of a AuZn Schottky contact allowing a relatively high breakdown voltage (300 V) sufficient for full depletion of the detector structure. The Schottky contact is covered by a HDPE (high density polyethylene) conversion layer, where neutrons transfer their kinetic energy to hydrogen atoms through elastic nuclear collisions. The detectors were exposed to mono-energetic neutrons generated by a deuterium (D)–tritium (T) nuclear reaction at a Van de Graaff accelerator. Neutrons reached a kinetic energy of 16.8 MeV when deuterons were accelerated by 1 MV potential. The influence of the HDPE layer thickness on the detection efficiency of the fast neutrons was studied. The thickness of the conversion layer varied from 50 [Formula: see text]m to 1300 [Formula: see text]m. The increase of the HDPE layer thickness led to a higher detection efficiency due to higher conversion efficiency of the HDPE layer. The effect of the active detector thickness modified by the detector reverse bias voltage on the detection efficiency was also evaluated. By increasing the detector reverse voltage, the detector active volume expands to the depth and also to the sides, slightly increasing the neutron detection efficiency.
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Andrievsky, S. M. "AN ENIGMA OF THE PRZYBYLSKI STAR". Odessa Astronomical Publications 35 (14 de diciembre de 2022): 13–17. http://dx.doi.org/10.18524/1810-4215.2022.35.268673.
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A new scenario to explain the Przybylski star phenomenon is proposed. It is based on the supposition that this star is a component of a binary system with a neutron star (similar to the hypothesis proposed earlier by Gopka, Ul’yanov & Andrievskii). The main difference with previous scenario is as following. The orbits of the stars of this system lie in the plane of the sky (or very close to this plane). Thus, we see this star (and its companion) nearly polar-on, and therefore we cannot detect the orbital motion (spectral line based) from the Przybylski star spectrum. In relation to the Przybylski star, the neutron star is a γ-ray pulsar for it. A neutron star is a source of relativistic particles and radiation emitted from the certain parts of its surface. The topology of this radiation strongly depends on the the magnetic field configuration of the neutron star. Existing models suppose that 1) high-energy electronpositron pairs and hard radiation are produced in the (magnetic) polar zones. Accelerated charge particles that move along magnetic lines emit electromagnetic quanta. In this model the radio-emission is genetically linked with the emission of the γ-quanta. 2) Another model of the outer gap is based on the assumption that there is a vacuum gap in the outer magnetosphere of the neutron star, which arises due to the constant escape of charged particles through the light cylinder along the open magnetic field lines. The direction of such escape may be roughly orthogonal to the rotation axis. If the rotational axes of the Przybylski star and the neutron star are close in direction (or even aligned), charged particles and hard radiation ejected in the approximately orthogonal direction at a large solid angle can enter the Przybylski star atmosphere, causing there different physical processes. As a possible source of the free neutrons could be the nuclear reactions between high-energy γ-quanta and nuclei of some atoms in the Przybylski star atmosphere gas. As a result, photoneutrons can be generated. Large enough neutron flux can be produced in the reactions with quite abundant element of the atmosphere gas (for example, helium). The photoneutrons produced in these reactions are rapidly thermalized and, as resonant neutrons, react with seed nuclei in the s-process. It should be also noted that together with s-process elements, the deuterium nuclei could be formed as a result of the interactions of the free resonant neutrons with the hydrogen atoms, but this issue has not yet been worked out.
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Lalazissis, G. A. y C. P. Panos. "Phenomenological nuclear density distributions". HNPS Proceedings 4 (19 de febrero de 2020): 85. http://dx.doi.org/10.12681/hnps.2877.
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A recently proposed semiphenomenological density distribution for neutrons and protons in nuclei is discussed. This density was derived using the separation energies of the last neutron or proton. A comparison is made with the symmetrised Fermi density distribution with parameters determined by fitting electron scattering experimental data and with a Fermi density with parameters coming from a recent analysis of pionic atoms. Theoretical expressions for rms radii for neutron, proton and matter distributions are proposed, which give the average trend of the variation of these quantities as functions of Ν, Ζ and A respectively. To facilitate the use of the new density all the parameters needed in a practical application are tabulated for a series of nuclei. Some applications of the new density are also discussed.
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Balykin, V. I. y V. S. Letokhov. "Laser optics of beams of neutral atoms". Uspekhi Fizicheskih Nauk 153, n.º 10 (1987): 354. http://dx.doi.org/10.3367/ufnr.0153.198710g.0354.
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Abdul Amir, Haider F. y Fuei Pien Chee. "Transport Characteristics of Secondary Charged Particles Resulting from High Energy Neutron in Silicon". Advanced Materials Research 1108 (junio de 2015): 79–84. http://dx.doi.org/10.4028/www.scientific.net/amr.1108.79.
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Silicon is always the dominant semiconductor material of the modern semiconductor industry. This is as silicon can retain its semiconductor characteristics even at a higher temperature while the other semiconductor materials can't. However, when a silicon device is exposed to a flux of energetic radiation or particles, the effects from the radiation and the induced secondary particles can cause several degradation of the device performance. For the purpose of investigate the resultant effects from the bombardment of neutrons and the behavior of secondary charged particles in the silicon model, the neutron displacement defect was measured in situ and then followed by the simulation based on Monte Carlo method. The bombardment of neutron in the silicon model produce at least three secondary particles, which are alpha ˸α˹ particles, proton (p) particles and silicon recoil atoms, through the reactions of ˸̾˼α˹˼˰˸̾˼̀˹˰and neutron scattering respectively. The kinetic energy and range of these charged particles are different among themselves, and thus the probability of hitting and degradation effects in the silicon materials are varies. The simulation calculation showed that ˸̾˼α˹˰reaction induced soft error cross section of about 8.7 x 10-14 cm2 and for recoil atoms, it is about 2.9 x 10-15 cm2. There was no error of the silicon device configuration induced by proton particles until 1010 n/cm2.neutron fluence. It can be concluded that the largest portion of error in the silicon model is induced by the secondary alpha ˸α˹ particles.
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Chapurin, O., A. I. Smolyakov, G. Hagelaar, J. P. Boeuf y Y. Raitses. "Fluid and hybrid simulations of the ionization instabilities in Hall thruster". Journal of Applied Physics 132, n.º 5 (7 de agosto de 2022): 053301. http://dx.doi.org/10.1063/5.0094269.
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Low-frequency axial oscillations in the range of 5–50 kHz stand out as a pervasive feature observed in many types of Hall thrusters. While it is widely recognized that the ionization effects play the central role in this mode, as manifested via the large-scale oscillations of neutral and plasma density, the exact mechanism(s) of the instabilities remain unclear. To gain further insight into the physics of the breathing mode and evaluate the role of kinetic effects, a one-dimensional time-dependent full nonlinear low-frequency model describing neutral atoms, ions, and electrons is developed in full fluid formulation and compared to the hybrid model in which the ions and neutrals are kinetic. Both models are quasi-neutral and share the same electron fluid equations that include the electron diffusion, mobility across the magnetic field, and the electron energy evolution. The ionization models are also similar in both approaches. The predictions of fluid and hybrid simulations are compared for different test cases. Two main regimes are identified in both models: one with pure low-frequency behavior and the other one, where the low-frequency oscillations coexist with high-frequency oscillations in the range of 100–200 kHz, with the characteristic time scale of the ion channel fly-by time, 100–200 kHz. The other test case demonstrates the effect of a finite temperature of injected neutral atoms, which has a substantial suppression effect on the oscillation amplitude.
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LAMOREAUX, STEVE K. "A REVIEW OF THE EXPERIMENTAL TESTS OF QUANTUM MECHANICS". International Journal of Modern Physics A 07, n.º 27 (30 de octubre de 1992): 6691–762. http://dx.doi.org/10.1142/s0217751x92003082.
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A review of the experimental tests of quantum mechanics is presented. Tests of the wave-particle duality of matter for atoms, electrons, and neutrons are discussed. Also covered are applications of neutron interferometry to a variety of quantum mechanics tests. Tests of the topological nature of quantum mechanics (Aharonov-Bohm effect, Aharonov-Casher effect, Berry’s phase, Aharonov-Anandan phase) are reviewed. Other topics reviewed include the experimental tests of the Bell inequality, nonlinear additions to the Schrödinger equation, the Pauli exclusion principle, the Zeno effect, and the uniqueness of ħ.
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Majkrzak, Charles F. y Gian P. Felcher. "Neutron Scattering Studies of Surfaces and Interfaces". MRS Bulletin 15, n.º 11 (noviembre de 1990): 65–72. http://dx.doi.org/10.1557/s0883769400058383.
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During the past decade, scientific and technological interest in the properties of surfaces and interfaces has grown at an astounding rate. On first thought, one might not consider a neutron or even an x-ray photon to be a particularly sensitive surface probe given their relatively weak interactions with matter compared to that of a low-energy electron or atom. Indeed, low-energy electron diffraction and atomic beam scattering techniques have contributed significantly to our understanding of surface phenomena. Nonetheless, the very fact that electrons and atoms are so strongly interacting makes quantitative analysis of their scattering data difficult. The interaction of neutrons or x-rays with matter, on the other hand, is weak enough that the potential can be characterized by a relatively simple scattering amplitude. Presently attainable neutron intensities, though not yet comparable to those of x-ray synchrotron sources, are still of sufficient strength to permit a variety of surface or near surface reflectivity and grazing angle diffraction experiments. Because neutrons can distinguish between different isotopes of the same element, most notably hydrogen and deuterium, as well as couple to atomic magnetic moments via a dipolar interaction, they can be indispensable and complementary probes.More conventional neutron diffraction techniques can also be applied to the study of interfacial phenomena and the effects of reduced dimensionality and compositional modulation in super-lattice structures grown by a variety of thin film deposition methods. In this article we will differentiate between reflectivity and diffraction measurements as follows: if the scattering occurs at a wavevector transfer low enough that the scattering medium appears as a continuum, so that amorphous and crystalline states are indistinguishable, then it will be considered to be in the reflectivity regime whereas diffraction will be taken to correspond to higher wavevector transfer where the precise arrangement of atoms is discernible.
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Weiss, David S. y Mark Saffman. "Quantum computing with neutral atoms". Physics Today 70, n.º 7 (julio de 2017): 44–50. http://dx.doi.org/10.1063/pt.3.3626.
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Briegel, H. J., T. Calarco, D. Jaksch, J. I. Cirac y P. Zoller. "Quantum computing with neutral atoms". Journal of Modern Optics 47, n.º 2-3 (febrero de 2000): 415–51. http://dx.doi.org/10.1080/09500340008244052.
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Nieddu, Thomas, Vandna Gokhroo y Síle Nic Chormaic. "Optical nanofibres and neutral atoms". Journal of Optics 18, n.º 5 (14 de marzo de 2016): 053001. http://dx.doi.org/10.1088/2040-8978/18/5/053001.
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Zwierlein, Martin. "Neutral atoms put in charge". Nature 462, n.º 7273 (diciembre de 2009): 584–85. http://dx.doi.org/10.1038/462584a.
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