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Hot carrier transfer processes in nonstoichiometric titanium hydride
摘要： The absorber of the hot carrier solar cell (HCSC) needs to have a considerably reduced hot carrier thermalisation rate, in order to maintain the photo-generated hot carriers for enough time such that they can be extracted. The slow carrier cooling effect is predicted in materials in which the phononic band gap is sufficiently large to block the Klemens decay. Binary compounds with a large mass ratio between the constituent elements are likely to have large phononic band gap. Titanium hydride is one of these binary compounds that has the potential to become an absorber of the HCSC. Whilst a large phononic gap has been observed in stoichiometric TiH2, it has not been experimentally confirmed for hydrogen deficient TiHx (where x < 2). In this article, we report the phonon density of states of TiH1.65 measured using inelastic neutron scattering and presented to clearly show the phononic band gap. We also present the carrier thermalisation process of a TiHx (1< x <2) thin film by transient absorption, and estimate the carrier cooling time in this material.
关键词： titanium hydride,hot carrier solar cell,inelastic neutron scattering,transient absorption,phononic band gap
更新于2025-09-10 09:29:36
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Simulation of the ELIGANT-GN array performances at ELI-NP for gamma beam energies larger than neutron threshold
摘要： Performance of the ELIGANT-GN array being developed at ELI-NP was evaluated using dedicated GEANT4 simulation code. The array is designed to consist of 17 LaBr3:Ce and 17 CeBr3 detectors as well as 33 BC501A and 29 6Li-glass detectors. The energy and time responses of the detectors were studied giving information on gamma and neutron absolute detection efficiencies of the array. A planned day-one experiment regarding the gamma and neutron decay from GDR in 208Pb is discussed and, based on simulations, the data analysis procedure is proposed. The detection efficiencies as well as the count rates estimations are presented.
关键词： gamma-ray detection,neutron detection,GEANT4 simulations,gamma beam
更新于2025-09-10 09:29:36
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<i>Ab initio</i> response functions for Cherenkov-based neutron detectors
摘要： Neutron time-of-?ight diagnostics at the NIF were recently out?tted with Cherenkov detectors. A fused silica radiator delivers sub-nanosecond response time and is optically coupled to a microchannel plate photomultiplier tube with gain from ～1 to 104. Capitalizing on fast time response and gamma-ray sensitivity, these systems can provide better than 30 ps precision for measuring ?rst moments of neutron distributions. Generation of ab initio instrument response functions (IRFs) is critical to meet the <1% uncertainty needed. A combination of Monte Carlo modeling, benchtop characterization, and in situ comparison is employed. Close agreement is shown between the modeled IRFs and in situ measurements using the NIF’s short-pulse advanced radiographic capability beams. First and second moments of neutron spectra calculated using ab initio IRFs agree well with established scintillator measurements. Next-step designs offer increased sensitivity and time-response.
关键词： instrument response functions,neutron time-of-flight,NIF,Cherenkov detectors,Geant4 modeling
更新于2025-09-10 09:29:36
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Study of the reflection spectra of SAX J1748.9?2021
摘要： the spectral analysis of accretion powered millisecond X-ray pulsar SAX J1748.9?2021 from the NuSTAR observation made during its 2015 outburst. The spectra displayed a broad emission line at ～6.5 keV with line width of ～0.5 keV and excess above ～20 keV due to Compton hump. The persistent emission of SAX J1748.9?2021 is described by a combination of soft thermal component with kT = 0.62+0.03 ?0.05 keV and thermally Comptonized component with kTe = 2.50+0.06 ?0.03 keV re?ected from the disc with re?ection fraction of 0.30+0.08 ?0.04. We have modelled the re?ection spectrum with self-consistent model relxillCP and have found the inclination of the accretion disc to be 32.?3+4.8 ?4.7 and log ξ is equal to 3.05+0.40 ?0.34. We have obtained an upper limit of 57 km for inner disc radius; and the estimated magnetic ?eld strength at the poles is less than 3.4 × 109 G. This kind of detailed investigation of re?ection spectrum of SAX J1748.9?2021, especially above 10 keV, has been achieved only because of high statistics NuSTAR data of the source.
关键词： X-rays: binaries,accretion,accretion discs,X-rays: individual: SAX J1748.9?2021,stars: neutron
更新于2025-09-10 09:29:36
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The inverse perovskite BaLiF <sub/>3</sub> : single-crystal neutron diffraction and analyses of potential ion pathways
摘要： Doped barium lithium tri?uoride has attracted attention as component for scintillators, luminescent materials and electrodes. With lithium and ?uoride, it contains two possibly mobile species, which may account for its ionic conductivity. In this study, neutron diffraction on oxide-containing BaLiF3 single-crystals is performed at up to 636.2(cid:2)C. Unfortunately, ion-migration pathways could not be mapped by modelling anharmonic ion displacement or by inspecting the scattering-length density that was reconstructed via maximum-entropy methods. However, analyses of the topology and bond-valence site energies derived from the high-temperature structure reveal that the anions can migrate roughly along the edges of the LiF6 coordination octahedra with an estimated migration barrier of (cid:3)0.64 eV (if a vacancy permits), whereas the lithium ions are con?ned to their crystallographic positions. This ?nding is not only valid for the title compound but for ion migration in all perovskites with Goldschmidt tolerance factors near unity.
关键词： bond-valence energy landscape,topological analysis,high-temperature neutron diffraction,maximum-entropy methods,fluoroperovskite
更新于2025-09-10 09:29:36
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-ray suppression using artificial neural networks with the liquid scintillators BC-501A and BC-537
摘要： In this work we present a comparison between the two liquid scintillators BC-501A and BC-537 in terms of their performance regarding the pulse-shape discrimination between neutrons and γ rays. Special emphasis is put on the application of artificial neural networks. The results show a systematically higher γ-ray rejection ratio for BC-501A compared to BC-537 applying the commonly used charge comparison method. Using the artificial neural network approach the discrimination quality was improved to more than 95% rejection efficiency of γ rays over the energy range 150 to 1000 keV for both BC-501A and BC-537. However, due to the larger light output of BC-501A compared to BC-537, neutrons could be identified in BC-501A using artificial neural networks down to a recoil proton energy of 800 keV compared to a recoil deuteron energy of 1200 keV for BC-537. We conclude that using artificial neural networks it is possible to obtain the same γ-ray rejection quality from both BC-501A and BC-537 for neutrons above a low-energy threshold. This threshold is, however, lower for BC-501A, which is important for nuclear structure spectroscopy experiments of rare reaction channels where low-energy interactions dominates.
关键词： fast-neutron detection,BC-537,digital pulse-shape discrimination,liquid scintillator,BC-501A,neural networks
更新于2025-09-10 09:29:36
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Small-Angle Neutron Scattering Reveals Energy Landscape for Rhodopsin Photoactivation
摘要： Knowledge of the activation principles for G-protein-coupled receptors (GPCRs) is critical to development of new pharmaceuticals. Rhodopsin is the archetype for the largest GPCR family, yet the changes in protein dynamics that trigger signaling are not fully understood. Here we show that rhodopsin can be investigated by small-angle neutron scattering (SANS) in fully protiated detergent micelles under contrast matching to resolve light-induced changes in the protein structure. In SANS studies of membrane proteins, the zwitterionic detergent [(Cholamidopropyl)dimethylammonio]-propanesulfonate (CHAPS) is advantageous because of the low contrast difference between the hydrophobic core and hydrophilic head groups as compared to alkyl glycoside detergents. Combining SANS results with quasielastic neutron scattering (QENS) reveals how changes in volumetric protein shape are coupled (slaved) to the aqueous solvent. Upon light exposure rhodopsin is swollen by penetration of water into the protein core, allowing interactions with effector proteins in the visual signaling mechanism.
关键词： Detergent,Neutron Scattering,Hydration,GPCR,Protein Dynamics,Vision,Membrane Proteins,Energy landscape,Slaving,Rhodopsin
更新于2025-09-10 09:29:36
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MCP PMT with high time response and linear output current for neutron time-of-flight detectors
摘要： A microchannel plate (MCP) photomultiplier tube (PMT) with a subnanosecond time response and a high linear output current has been developed. PMT is designed for detection of weak pulses of radiation in UV-, visible and nearer-IR ranges and can be used in neutron time-of-flight (nTOF) detectors in experiments on laser compression of thermonuclear fuel. The results of measurements of MCP PMT main parameters are presented: photocathode spectral sensitivity, gain, maximum linear output current, and time response.
关键词： neutron time-of-flight detectors,MCP PMT,thermonuclear fuel,linear output current,time response,laser compression
更新于2025-09-10 09:29:36
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Atomic ordering, magnetic properties, and electronic structure of Mn<sub>2</sub>CoGa Heusler alloy
摘要： The magnetic properties and atomic arrangement of Mn2CoGa Heusler alloy were investigated experimentally and by theoretical calculations. The magnetic moment derived from spontaneous magnetization at 5 K was 2.06 μB/f.u. and was close to the integer number of the expected value from theoretical calculation and the Slater–Pauling rule predicted by Galanakis et al. The Curie temperature and L21-B2 order-disorder phase transition temperature were 741 and 1047 K, respectively. Powder neutron diffraction experiment results suggested that the atomic arrangement prefers an L21b-type structure rather than that of Hg2CuTi, being consistent with our previous results of high-angle annular dark-field-scanning transmission electron microscopic observations. The magnetic moments obtained were in good agreement with the theoretical values in the model of the L21b-type structure. The density of states obtained by the first-principles calculation combined with the coherent potential approximation in Mn2CoGa with the L21b-type crystal structure maintained the half-metallic character, even though disordering by Mn and Co atoms was introduced.
关键词： powder neutron diffraction,magnetic moment,Half-metal-type ferromagnets,order-disorder phase transition,atomic ordering,Curie temperature
更新于2025-09-09 09:28:46
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Resonant enhancement of an oscillating electric field in an atom
摘要： When an atom is placed into an oscillating electric ?eld with frequency far from atomic resonances, the atomic electrons partly shield this ?eld at the nucleus. It is conjectured that when the frequency of an electric ?eld reaches an atomic resonance, the electric ?eld at the nucleus may be signi?cantly enhanced. In this paper we systematically study the mechanisms of this enhancement and show that it may reach ?ve orders in magnitude in particular cases. As an application, we consider laser-assisted neutron capture in 139-lanthanum nucleus and screening and resonance enhancement of nuclear electromagnetic transitions by electrons.
关键词： nuclear electromagnetic transitions,atomic resonance,laser-assisted neutron capture,oscillating electric ?eld,enhancement
更新于2025-09-09 09:28:46