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with two-dimensional and three-dimensional local environments
摘要： ZnNi(CN)4 is a three-dimensional (3D) framework material consisting of two interpenetrating PtS-type networks in which tetrahedral [ZnN4] units are linked by square-planar [NiC4] units. Both the parent compounds, cubic Zn(CN)2 and layered Ni(CN)2, are known to exhibit 3D and 2D negative thermal expansion (NTE), respectively. Temperature-dependent inelastic neutron scattering measurements were performed on a powdered sample of ZnNi(CN)4 to probe phonon dynamics. The measurements were underpinned by ab initio lattice dynamical calculations. Good agreement was found between the measured and calculated generalized phonon density-of-states, validating our theoretical model and indicating that it is a good representation of the dynamics of the structural units. The calculated linear thermal expansion coefficients are αa = ?21.2 × 10?6 K?1 and αc = +14.6 × 10?6 K?1, leading to an overall volume expansion coefficient, αV of ?26.95 × 10?6 K?1, pointing towards pronounced NTE behavior. Analysis of the derived mode-Grüneisen parameters shows that the optic modes around 12 and 40 meV make a significant contribution to the NTE. These modes involve localized rotational motions of the [NiC4] and/or [ZnN4] rigid units, echoing what has previously been observed in Zn(CN)2 and Ni(CN)2. However, in ZnNi(CN)4, modes below 10 meV have the most negative Grüneisen parameters. Analysis of their eigenvectors reveals that a large transverse motion of the Ni atom in the direction perpendicular to its square-planar environment induces a distortion of the units. This mode is a consequence of the Ni atom being constrained only in two dimensions within a 3D framework. Hence, although rigid-unit modes account for some of the NTE-driving phonons, the added degree of freedom compared with Zn(CN)2 results in modes with twisting motions, capable of inducing greater NTE.
关键词： framework compound,ZnNi(CN)4,negative thermal expansion,lattice dynamics,ab initio calculations,inelastic neutron scattering
更新于2025-09-19 17:15:36
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Effect of neutron irradiation on the structural, electrical and optical properties evolution of RPLD VO2 films
摘要： This study reports on the effect of neutron irradiation at different fluences on the properties of VO2 thin films. The irradiations were performed at NUR research reactor, Algiers at a temperature of about 40 °C, with fast neutron fluence (En > 1 MeV) up to 1.9 × 1018 n.cm?2. The induced defects have been investigated using structural, optical and electrical measurements. Both bulk sensitive characterization techniques, Raman and grazing incident angle X-ray diffraction (GIXRD) analysis, show that no structural transformation is induced by neutron irradiation, although strain induced defect production are generated throughout the films while surface sensitive techniques, X-ray photoelectron spectroscopy (XPS) and work function measurements, show that the charge carrier (electron) concentration at room temperature decreases after irradiation. Potentially due to fast neutron irradiation induced defects, mainly in the form of Frenkel pairs, swelling and color center formation occurs in VO2 thin films without amorphization. This is further corroborated by an increase of the room temperature resistivity through the irradiated films. Temperature-dependent electrical and optical transmission measurements confirm that the characteristic semiconductor-to-metal transition of the VO2 films is preserved upon irradiation. We therefore conclude that VO2 is an excellent candidate for thermal shielding and thermal management of small satellites.
关键词： Smart radiator device,Vanadium dioxide,Neutron irradiation,Phase transition,Pulsed laser deposition
更新于2025-09-19 17:15:36
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High-efficiency neutron source generation from photonuclear reactions driven by laser plasma accelerator
摘要： We experimentally demonstrate the generation of an electron beam with the charge of about 200 pC, the divergence of about 7 mrad and the maximum energy of about 320 MeV from helium gas via self-injection induced by self-evolved laser pulses (3 J, 30 fs) in the plasma channel. Based on the experimental electron beam parameters, the Monte Carlo simulation code Geant4 was used to optimize the thicknesses of converters for high yield neutrons. The Monte Carlo simulation results show that the simulation neutron number can reach as high as 107 with a 5-cm-thick Pb converter, and the corresponding energy range was about 100 keV~ 1 MeV. In this work, the neutrons were detected by four bubble detectors, and the neutron yield was measured to be 3.2×107/shot and distributed isotropically. Moreover, the neutron generation efficiency is about 1.1×107/J which to best of our knowledge, is the highest compared with other laser neutron generation methods with the same laser energy. Such a laser driven pulsed neutron source could be applied to different fields like the neutron absorption spectroscopy, material science, and nuclear physics, etc.
关键词： laser plasma accelerator,fast neutron,photonuclear reaction
更新于2025-09-19 17:13:59
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Radiology, Lasers, Nanoparticles and Prosthetics || 2. Nuclei and isotopes
摘要： In Chapters 5 to 12 nuclear methods in medicine are discussed either for imaging (scintigraphy, SPECT, PET) or for radiation treatment of cancerous tissues (proton and neutron irradiation, brachytherapy). It is therefore appropriate to first introduce some basic properties of nuclides and isotopes, and in particular of radioactive isotopes which are used in nuclear medicine. This chapter is not intended to replace a textbook on nuclear physics. But it provides sufficient background information for better understanding the subsequent chapters. Handling of radiation in general and application of radioactive isotopes also requires a detailed knowledge of radiation dose and radiation safety, which are topics of Chapter 4.
关键词： scintigraphy,medicine,SPECT,neutron irradiation,PET,brachytherapy,radiation safety,proton irradiation,nuclides,cancerous tissues,isotopes,radioactive isotopes,radiation dose,imaging,nuclear medicine,nuclear methods,radiation treatment
更新于2025-09-19 17:13:59
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Radiology, Lasers, Nanoparticles and Prosthetics || 11. Neutron radiotherapy
摘要： Neutrons like protons are hadrons, however neutrons are uncharged. They are more difficult to produce, and because they are neutral, accelerators and magnets cannot be used for tuning their energy or steering the beam. Neutron irradiation requires a neutron source and a radiological shielding environment that are very different to those for charged particles. Among the various external radiation treatments of cancer, neutron radiation therapy is presently not often prescribed.
关键词： fast neutrons,RBE,Boron Neutron Capture Therapy,BNCT,linear energy transfer,Neutron radiotherapy,LET,relative biological effectiveness
更新于2025-09-16 10:30:52
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Measurements of Neutrons from Photonuclear Reactions Using Laser Compton Scattering Gamma Rays
摘要： The laser Compton scattering gamma ray beamline at the synchrotron light facility NewSUBARU supplies a quasi-monochromatic, polarized, high-energy photon beam. A gamma ray ?ux of more than 107 photons/s is generated at a photon energy range of 1 - 73 MeV. Emission distributions of the fast neutrons generated from di?erent target materials were measured as a function of the polarization angle of the linear polarized gamma-ray beam using a time-of-?ight method with fast plastic scintillators. The neutron distributions were consistent with a previous theoretical result. The relatively slow neutrons were measured via an activation method. The result demonstrated the small anisotropy of the slow neutron emission.
关键词： laser Compton scattering,neutron,gamma ray,photonuclear reaction,time-of-?ight,activation,synchrotron light,electron storage ring
更新于2025-09-16 10:30:52
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Residual stress in laser cladded heavy-haul rails investigated by neutron diffraction
摘要： Residual stress is one of the critical parameters affecting the fatigue behaviour of tribological components, which can be introduced by a thermo-mechanical process such as laser cladding. In this study, the residual stress distribution of laser cladded rails was evaluated using a neutron diffraction technique. The substrate rail for the laser cladding was hypereutectoid rail steel used in Australian heavy-haul railway track, and the cladding materials were 410L (a low carbon content stainless steel alloy) and Stellite 6 (a Co-based alloy). The cladding materials were selected based on their high wear, corrosion and fatigue resistance properties. This study measured the residual stress in full-scale laser cladded rails where the residual stresses were measured in the cladding layer, heat affected zone (HAZ) and substrate zone of the railhead. A new sample preparation strategy was developed to quantify the residual stresses in the full-scale rails with high spatial resolution. Higher compressive residual stress was found in the cladding layer, which may have resulted from the martensitic transformation occurred in that region. Tensile stresses occurred in the HAZ to a depth of 4 mm, which might be mainly caused by thermal contraction and volumetric change in the microstructure. The addition of a second cladding layer did not significantly affect the magnitude of the residual stresses, but the peak tensile residual stress shifted to a deeper location from the surface, which is beneficial in resisting wear. Post-cladding heat treatment significantly reduced the undesirable high residual stress from the cladding layer and HAZ.
关键词： Post-cladding heat treatment,Residual stress,Neutron diffraction,Laser cladding,Heavy-haul rail
更新于2025-09-16 10:30:52
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On the issue of neutron source development for a laser-driven nuclear-thermonuclear reactor
摘要： We discuss the feasibility of developing a high-power thermonuclear neutron source driven by laser pulses. Using one-dimensional numerical simulations for targets made in the form of double-sided cones, for an absorbed Nd-laser energy of ~ 1 MJ (at the second and third harmonics) and pulse duration of 10 – 20 ns it is possible to achieve a neutron yield at a level of 1016 – 1017 per shot. This neutron yield is a prerequisite to the commencement of work to develop a hybrid nuclear-thermonuclear reactor.
关键词： numerical simulations,conic target,neutron source
更新于2025-09-16 10:30:52
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The donor of Aquila X-1 revealed by high-angular resolution near-infrared spectroscopy
摘要： The low-mass X-ray binary Aquila X-1 is one of the most active neutron star X-ray transients. Despite its relatively bright quiescent optical counterpart, the detection of its companion has been hampered by the presence of a nearby interloper star. Using the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) on the Very Large Telescope-8.2m telescope, we unambiguously single out Aquila X-1 from the interloper. Phase-resolved near-infrared spectroscopy reveals absorption features from a K4 ± 2 companion star moving at a projected velocity of K2 = 136 ± 4 km s?1. We here present the ?rst dynamical solution and associated fundamental parameters of Aquila X-1, imposing new constraints on the orbital inclination (36? < i < 47?) and the distance (d = 6 ± 2 kpc) to this prototypical neutron star transient.
关键词： accretion,stars: neutron,accretion discs,X-rays: binaries
更新于2025-09-16 10:30:52
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Neutron production from thermonuclear reactions in laser-generated plasmas
摘要： The production of intense neutron beams via thermonuclear reactions in laser-generated plasmas is investigated theoretically. So far, state-of-the-art neutron beams are produced via laser-induced particle acceleration leading to high-energy particle beams that subsequently interact with a secondary target. Here, we show that neutron beams of two orders of magnitude narrower bandwidth can be obtained from thermonuclear reactions in plasmas generated by Petawatt-class lasers. The intensity of such neutron beams is about one or two orders of magnitude lower than the one of the state-of-the-art laser-driven neutron beams. We study to this end the reaction 2H(d, n)3He in plasmas generated by Petawatt-class lasers interacting with D2 gas jet targets and CD2 solid-state targets. The results also show the possibility of direct measurements of reaction rates at low temperatures of astrophysical interest. In addition, the use of CD2 solid-state targets can also lead to great enhancements of the plasma screening compared to the case of D2 gas jet targets, opening new possibilities to study this so far unsolved issue in the field of astrophysics.
关键词： laser-generated plasmas,neutron production,Petawatt-class lasers,plasma screening effects,thermonuclear reactions
更新于2025-09-16 10:30:52