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1
Gorlova, D. A., A. Yu Zavorotny, I. N. Tsymbalov, K. A. Ivanov, S. A. Shulyapov, R. V. Volkov und A. B. Savel’ev. „Neutron Source from (γ,<i>n</i>) Reactions at a Laser-Plasma Accelerator and Its Use for Electron Beam Characterization“. Поверхность. Рентгеновские, синхротронные и нейтронные исследования, Nr. 8 (01.08.2023): 22–31. http://dx.doi.org/10.31857/s1028096023080083.
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Development of compact laboratory-scale neutron sources is of importance both for fundamental physical research and practical applications (for example, neutron radiography and spectroscopy). One of the most promising approaches to the development of such a source is the implementation of laser-plasma accelerated electrons or ions, and the subsequent initiation of nuclear reactions (γ,n), (p,n) or (d,n) with the emission of neutrons. In the present work, a neutron source produced via photodisintegration reactions (γ,n) using an electron beam from a one TW laser-plasma accelerator has been created and characterized. Maximum observed neutron flux was ~105 neutrons/s · srad with a ~106 neutrons per J of laser radiation efficiency. With constant efficiency and 10 times increase in the laser pulse energy the neutron flux will be sufficient for certain applications. Numerical Monte-Carlo simulations of neutron generation by an electron beam with parameters corresponding to those measured experimentally were also carried out. It was demonstrated that the number of generated neutrons can be used to estimate the charge and average energy of accelerated electrons. The obtained values are in good agreement with the values measured by the standard beam diagnostic tools.
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Liu, Yiheng, Kai He, Gang Wang, Guilong Gao, Xin Yan, Yanhua Xue, Ping Chen et al. „Simulation of the impact of using a novel neutron conversion screen on detector time characteristics and efficiency“. AIP Advances 12, Nr. 4 (01.04.2022): 045206. http://dx.doi.org/10.1063/5.0073025.
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To directly measure the DT neutrons from inertial confinement fusion with a high time resolution, a new type of neutron conversion composed of a CH2 conversion layer, a metal moderation layer, and a CsI secondary electron emission layer is proposed. The conversion screen is based on the principle that recoil protons produced by elastic scattering of the neutrons in CH2 interact with CsI to generate secondary electrons. The moderation layer can filter the energy spectrum of protons to prevent low-energy protons from reaching CsI, which shortens the duration of the secondary electron pulse and improves the temporal resolution of the conversion screen. Based on the Monte Carlo method, both the neutron impulse and background γ-rays response of this conversion screen were calculated. The simulation indicates that the temporal resolution of the conversion screen can reach up to 4.9 ps when the thickness of the gold layer is 100 µm. The detection efficiency of secondary electrons/neutrons can reach 7.4 × 10−3. The detection efficiency of the neutron conversion screen for secondary electrons/γ-rays is an order of magnitude lower than the neutron impulse response, and the response time of γ-rays is 20 ps earlier than the neutron pulses. This means that using this conversion screen is beneficial to distinguish between neutrons and γ-rays and has a good signal-to-noise ratio.
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Garibli, A. A., A. A. Garibov und E. M. Huseynov. „Defect formation processes in the silicon nanoparticles under the neutron irradiation“. Modern Physics Letters B 33, Nr. 26 (20.09.2019): 1950315. http://dx.doi.org/10.1142/s0217984919503159.
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Silicon nanoparticles have been irradiated by neutrons up to 20 h. Free electrons and defects in the nanosilicon particles have been comparatively investigated before and after neutron irradiation using electron paramagnetic resonance (EPR) method. The neutron scattering and capture cross-section processes have been calculated for natural [Formula: see text], [Formula: see text], [Formula: see text] isotopes, which are main part of nanosilicon samples when irradiated for 20 h by epithermal neutrons. Particle size, agglomeration and other surface effects of silicon nanoparticles were studied with scanning electron microscope (SEM) before and after neutron irradiation.
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Potera, Piotr. „Analytical Description of Concentration of Radiation Displacement Defects in Oxide Crystals as Function of Electrons or Neutrons Energy“. Advances in Materials Science 22, Nr. 3 (01.09.2022): 41–52. http://dx.doi.org/10.2478/adms-2022-0012.
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Abstract The main purpose of this work is the description of dependence of the concentration of radiation displacements defects (RDD) induced by electrons and neutrons in garnets, perovskites, silicates, germanates, and tungsted bronzes type crystals (Y3Al5O12, Gd3Ga5O12, YAlO3, LiNbO3, Bi4Si3O12, Bi4Ge3O12, Ca0.28Ba0.72Nb2O6) on the energy of particles by analytical function. The dependences were determined on the basis of calculations made using the Monte-Carlo method realized in the Atom Collision Cascade Simulation program. The results of calculations show that the concentrations of RDD reduced to one impinging particle increased initially with the particles energy and they saturates for the electron and neutron energy above 3–36 MeV, depending on crystal, sublattice and kind of irradiation particle. A wide range of energies for which the concentration of RDD is independent of the energy of particles (neutrons, electrons) makes them potential materials for the dosimetry of high-energy particles. The comparison of the concentrations of RDD calculated for different sublattices as well as for the cases of electrons and neutrons is made. In the case of irradiation with electrons, the relative concentration of RDD of the oxygen sublattice strongly depends on the energy of electrons and the crystal and varies in the range of 10–90%. In the case of neutrons, the relative concentration of RDD of the oxygen sublattice does not depend on the neutron energy and is in the range of 66–84% depending on the crystal.
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Ozawa, Naohiro. „The Emergence of Weak Interaction“. Hyperscience International Journals 2, Nr. 3 (September 2022): 108–14. http://dx.doi.org/10.55672/hij2022pp108-114.
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The view of the Standard Model on the β decay of neutrons through weak interaction is that neutrons break down to form protons P and weak bosons W^- and finally into protons, electron and anti-electron neutrinos. The three quarks (U,d,d) that compose neutrons are joined by strong interaction, so bonds formed by strong interaction supposedly cannot be broken by weak interaction, which is far weaker than strong interaction. Nevertheless, neutrons do decay. Further, the three quarks (U,d,d) that form neutrons are fundamental particles, and it should not be possible for other fundamental particles to emerge from these three fundamental particles. Nevertheless, not only does (U,d,d) change into (U,U,d), but electrons and anti-electron-neutrinos, which are fundamental particles, also emerge. This must not have a double meaning. As shown here, there are multiple contradictions in weak interaction of the Standard Model. In this paper, weak interaction is mediated by the π-ons group that results from the working of strong interaction step 1 that was described in a previous paper and acts on the nucleons group (P ,P ̅ ,n,n ̅ ) that resulted from step 2. In other words, at the point immediately prior to the emergence of weak interaction, all the particles that existed in the universe were used in order to make weak interaction emerge. The weak interaction in this paper refers to the strong interaction bonds composed of neutrons and π^±-ons first being dissolved by strong interaction. As such, the reason why neutrons change to protons is just because the d-quark of the neutron is replaced with the U-quark of the π^±-on.
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Chen, Zekun, Konstantin Kouzakov, Yu-Feng Li, Vadim Shakhov, Konstantin Stankevich und Alexander Studenikin. „Collective neutrino oscillations in moving and polarized matter“. Journal of Physics: Conference Series 2156, Nr. 1 (01.12.2021): 012180. http://dx.doi.org/10.1088/1742-6596/2156/1/012180.
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Abstract We consider neutrino evolution master equations in dense moving and polarized matter consisted of electrons, neutrons, protons and neutrinos. We also take into account the neutrino magnetic moment interaction with a magnetic field. We point out the mechanisms responsible for the neutrino spin precession and provide the expressions for the corresponding interaction Hamiltonians that should be taken into account in theoretical treatments of collective neutrino oscillations.
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Papp, Daniel, Ales Necas, Nasr Hafz, Toshiki Tajima, Sydney Gales, Gerard Mourou, Gabor Szabo und Christos Kamperidis. „Laser Wakefield Photoneutron Generation with Few-Cycle High-Repetition-Rate Laser Systems“. Photonics 9, Nr. 11 (03.11.2022): 826. http://dx.doi.org/10.3390/photonics9110826.
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Simulations of photoneutron generation are presented for the anticipated experimental campaign at ELI-ALPS using the under-commissioning e-SYLOS beamline. Photoneutron generation is a three-step process starting with the creation of a relativistic electron beam which is converted to gamma radiation, which in turn generates neutrons via the γ,n interaction in high-Z material. Electrons are accelerated to relativistic energies using the laser wakefield acceleration (LWFA) mechanism. The LWFA process is simulated with a three-dimensional particle in cell code to generate an electron bunch of 100s pC charge from a 100 mJ, 9 fs laser interaction with a helium gas jet target. The resultant electron spectrum is transported through a lead sphere with the Monte Carlo N-Particle (MCNP) code to convert electrons to gammas and gammas to neutrons in a single simulation. A neutron yield of 3×107 per shot over 4π is achieved, with a corresponding neutron yield per kW of 6×1011 n/s/kW. The paper concludes with a discussion on the attractiveness of LWFA-driven photoneutron generation on high impact, and societal applications.
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HO, CHOON-LIN, V. R. KHALILOV und CHI YANG. „EFFECT OF STRONG MAGNETIC FIELDS ON THE EQUILIBRIUM OF A DEGENERATE GAS OF NUCLEONS AND ELECTRONS“. Modern Physics Letters B 10, Nr. 23 (10.10.1996): 1141–49. http://dx.doi.org/10.1142/s0217984996001309.
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We obtain the equations that define the equilibrium of a homogeneous relativistic gas of neutrons, protons and electrons in a constant magnetic field as applied to the conditions that probably occur near the center of neutron stars. We compute the relative densities of the particles at equilibrium and the Fermi momentum of electrons in the strong magnetic field as function of the density of neutrons and the magnetic field induction. Novel features are revealed as to the ratio of the number of protons to the number of neutrons at equilibrium in the presence of large magnetic fields.
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Ghosh, Sayan, Abhijit Bandyopadhyay, Pijushpani Bhattacharjee, Sovan Chakraborty, Kamales Kar und Satyajit Saha. „Simulation of Nuclear Recoils due to Supernova Neutrino-induced Neutrons in Liquid Xenon Detectors“. Journal of Physics: Conference Series 2156, Nr. 1 (01.12.2021): 012135. http://dx.doi.org/10.1088/1742-6596/2156/1/012135.
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Abstract Neutrinos from supernova (SN) bursts can give rise to detectable number of nuclear recoil (NR) events through the coherent elastic neutrino-nucleus scattering (CEυNS) process in large scale liquid xenon detectors designed for direct dark matter search, depending on the SN progenitor mass and distance. Here we show that in addition to the direct NR events due to CEvNS process, the SN neutrinos can give rise to additional nuclear recoils due to the elastic scattering of neutrons produced through inelastic interaction of the neutrinos with the xenon nuclei. We find that the contribution of the supernova neutrino-induced neutrons (υIn) can significantly modify the total xenon NR spectrum at large recoil energies compared to that expected from the CEυNS process alone. Moreover, for recoil energies ≳ 20 keV, dominant contribution is obtained from the (υIn) events. We numerically calculate the observable S1 and S2 signals due to both CEvNS and vIn processes for a typical liquid xenon based detector, accounting for the multiple scattering effects of the neutrons in the case of υIn, and find that sufficiently large signal events, those with S1≳50 photo-electrons (PE) and S2≳2300 PE, come mainly from the υIn scatterings.
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Spence, J. C. H., U. Weierstall und J. Fries. „On Lensless Imaging of Organics with Neutrons, X-Rays, Helium Atoms and Low Energy Electrons: Damage and Iterative Phase Retrieval“. Microscopy and Microanalysis 7, S2 (August 2001): 268–69. http://dx.doi.org/10.1017/s1431927600027410.
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Recent experiments with X-rays and high energy electrons have shown that image recovery from diffracted intensities is possible for non-periodic objects using iterative algorithms. Application of these methods to biological molecules raises the crucial problem of radiation damage, which may be quantified by Q = ΔE σi/σe, the amount of energy deposited by inelastic events per elastic event. Neutrons, helium atoms and low energy electrons below most ionization thresholds produce the smallest values of Q (see for TMV imaged at 60 eV). For neutrons (λ = 10-2Å, and deuterated, 15N-abelled molecules) Q is ∼3000 times smaller (∼50 times for λ = 1.8Å) than for electrons (80- 500keV) and about 4x 106 times smaller than for soft X-rays (1.5Å). Since σe for neutrons is about 105 times smaller than for electrons (and about 10 times smaller than for soft X-rays), a 105 times higher neutron dose is required to obtain the same S/N in a phase contrast image compared with electrons, if other noise sources are absent.
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Kasilov, V. I., S. P. Gokov, A. N. Dovbnya, S. A. Kalenik, K. S. Kokhnyuk, S. S. Kochetov, A. A. Khomich und O. A. Shopen. „Thermal and Epithermal Neutron Generation for Nuclear Medicine Using Electron Linear Accelerator“. East European Journal of Physics 3, Nr. 3 (14.12.2016): 64–72. http://dx.doi.org/10.26565/2312-4334-2016-3-05.
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In this paper, to obtain streams of thermal and epithermal neutrons are used delayed neutrons emitted from the target with a fissile material. The target preliminarily activated with help of electron beam from linear accelerator with an energy of 20 MeV and a power of 9 Watts. At the same time to obtain a stream of thermal as well as epithermal neutron density 6 10^-5 n / (cm^2 s) The results of experiment are presented where half-decay curves have been measured of emitting delayed neutrons radioactive nuclei produced in the fission process. It has been shown that the activated target, which contains the fissile material, presents a compact small size source of delayed neutrons. It can be delivered to the formator where thermal and epithermal neutrons are formed during a certain time period with help of the moderator, absorber and collimator. Then this target is moved to the activator being replaced with another target. Thus, pulsed neutron flux is produced. The duration of neutron pulse corresponds to the presence time of the activated target in the formator, and time interval between pulses is determined by the delivery time of the target from the activator to the formator. Given that the yield of neutrons from the target is directly proportional to the power of the beam of accelerated electrons, shows that the beam power of 1.5 - 3 kW, the flux density of thermal and epithermal neutrons can reach the values of (2-3) 10^9 n / (cm^2 s). Such a neutron beam can be used in nuclear medicine, in particular, in neutron capture therapy of oncologic diseases.
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Kotila, Jenni. „Rare weak decays and neutrino mass“. Journal of Physics: Conference Series 2453, Nr. 1 (01.03.2023): 012012. http://dx.doi.org/10.1088/1742-6596/2453/1/012012.
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Abstract The question whether neutrinos are Majorana fermions (i.e., their own anti-particles) remains among the most fundamental open questions of subatomic physics. If neutrinos are Majorana particles it would revolutionize our understanding of physics. Although neutrinoless double beta decay, 0νββ, was proposed more than 80 years ago to establish the nature of neutrinos, it remains the most sensitive probe into the non-conservation of lepton number. 0νββ-decay is a postulated extremely slow and yet unobserved radioactive process in which two neutrons (or protons) inside a nucleus transform into two protons (or neutrons) emitting two electrons (or positrons), respectively, but no neutrinos. Its observation would be a breakthrough in the description of elementary particles and would provide fundamental information on the neutrino masses, their nature, and origin. In this paper double beta decay, its connection to neutrino mass, and mechanisms beyond the standard mass mechanism are discussed from a theoretical point of view. The current situation is then addressed by combining theoretical results with recent experimental limits.
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Zaccai, Nathan Richard, und 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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Gaganov, V. V., E. V. Ryabeva, D. A. Molodtsev, R. F. Ibragimov, I. S. Vershinin, Y. A. Kokorev und I. V. Urupa. „Experimental characterisation of diamond-based neutron spectrometer“. Journal of Instrumentation 17, Nr. 09 (01.09.2022): T09001. http://dx.doi.org/10.1088/1748-0221/17/09/t09001.
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Abstract The results of testing and characterisation of the neutron spectrometer based on a diamond detector are presented. It is shown that spectrometer calibration with monoenergetic electrons and alpha-particles leads to different results. The energy resolution of the spectrometer is estimated based on the experiments with alpha-particles and with DT-neutrons from NG-150M neutron generator. It has been shown experimentally that for neutrons with an energy of 14 MeV the energy resolution of a diamond-based spectrometer is 0.6%.
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Roberts, Joyce A. „The Manuel Lujan Jr. Neutron Scattering Center“. MRS Bulletin 22, Nr. 9 (September 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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Ranjbaran, Mohammad, Mohammad Mehdi Firoozabadi und Mahdi Zangian. „Optimization of photoneutron source for use in subcritical reactors“. Journal of Instrumentation 19, Nr. 05 (01.05.2024): T05014. http://dx.doi.org/10.1088/1748-0221/19/05/t05014.
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Abstract This work is an effort to maximize the number of output neutrons of a photoneutron target for 100 MeV incident electrons. The work steps were; to select the appropriate material, select the appropriate shape, and find the optimized dimensions. The simulations of this work were done with MCNPX2.6 simulation code. At first, U-235 was selected as the best material for the target, among some heavy atoms from the number of outlet neutron point of view. Then the best shape for the target was selected from geometric shapes that have been considered for the target and the dimensions of the target were optimized. After these parts, the energy spectrum of outlet neutrons was estimated and after that, the deposited energy of neutrons, electrons, and photons in the target was estimated and drowned with Tec plot.
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Zhang, Liyuan, Rihua Mao und Ren-Yuan Zhu. „Fast Neutron Induced Nuclear Counter Effect in Hamamatsu Silicon PIN Diodes and APDs“. IEEE Transactions on Nuclear Science 58, Nr. 5 (Juni 2011): 1249–56. http://dx.doi.org/10.1109/tns.2011.2132144.
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Neutron induced nuclear counter effect in Hamamatsu silicon PIN diodes and APDs was measured by irradiating fast neutrons from a pair of252Cf sources directly to these devices. It was found that the entire kinetic energy of these neutrons may be converted into electron signals in these devices, leading to anomalous signals of up to a few million electrons in a single isolated calorimeter readout channel. Signals of such amplitude represent equivalent energy of several hundred GeV and a few GeV for PWO and LSO/LYSO crystals respectively assuming the corresponding light yields of 4 and 800 p.e./MeV. The overall rate of the neutron induced nuclear counter effect in APDs is found to be more than an order of magnitude less than that in PIN diodes. Increasing the APD gain was also found to reduce the neutron induced nuclear counter effect. An intelligent front-end chip capable of selecting un-contaminated signal is proposed to eliminate completely the nuclear counter effect without significant cost increase.
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Castillo, F., A. Reisenegger und J. A. Valdivia. „Two-fluid simulations of the magnetic field evolution in neutron star cores in the weak-coupling regime“. Monthly Notices of the Royal Astronomical Society 498, Nr. 2 (21.08.2020): 3000–3012. http://dx.doi.org/10.1093/mnras/staa2543.
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ABSTRACT In a previous paper, we reported simulations of the evolution of the magnetic field in neutron star (NS) cores through ambipolar diffusion, taking the neutrons as a motionless uniform background. However, in real NSs, neutrons are free to move, and a strong composition gradient leads to stable stratification (stability against convective motions) both of which might impact on the time-scales of evolution. Here, we address these issues by providing the first long-term two-fluid simulations of the evolution of an axially symmetric magnetic field in a neutron star core composed of neutrons, protons, and electrons with density and composition gradients. Again, we find that the magnetic field evolves towards barotropic ‘Grad–Shafranov equillibria’, in which the magnetic force is balanced by the degeneracy pressure gradient and gravitational force of the charged particles. However, the evolution is found to be faster than in the case of motionless neutrons, as the movement of charged particles (which are coupled to the magnetic field, but are also limited by the collisional drag forces exerted by neutrons) is less constrained, since neutrons are now allowed to move. The possible impact of non-axisymmetric instabilities on these equilibria, as well as beta decays, proton superconductivity, and neutron superfluidity, are left for future work.
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Baring, Matthew G. „Synchrotron Radiation from Energetic Electrons Emitted by AGN: A Probe for Magnetic Fields in External Galaxies“. Symposium - International Astronomical Union 140 (1990): 399. http://dx.doi.org/10.1017/s0074180900190631.
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Shock acceleration of protons in the central region of active galaxies can energize them to Lorentz factors as high as 108 (Sikora et al., 1987), and these can subsequently produce a host of other relativistic particles including pions, e+e– pairs and neutrons. The luminosities of each species are expected to be of the same order of magnitude. Rapid decay of the pions leads to the secondary production of photons and pairs with energies of around 109 − 1011 MeV. The electrons and positrons can escape the compact central region and interact with the microwave background forming a pair cascade, and can also emit synchrotron radiation in the magnetic field. The neutrons do not interact with the field, and a significant fraction of them can escape the central region of a galaxy (Kirk and Mastichiadis, 1989). They can travel until they decay, producing protons and electrons in outer regions of the galaxy. Their decay time of γnτn gives a typical length for decay of about 1 kpc for the most energetic neutrons. The synchrotron radiation of these decay product electrons is examined in Baring (1989, in preparation), and it produces definite signatures of galactic magnetic fields. Magnetic fields of 1μG imply synchrotron emission in the X-ray and soft gamma-ray range for maximum Lorentz factors of γe = 1010, with a continuum extending down to much lower energies. It is observed that cooler neutrons deposit electrons at smaller radii, and these electrons are cooler (in a decay γe ~ γn). Hence the radiation would be cooler at smaller radii. This provides a diagnostic for the magnetic field: estimates of the field strength are possible from cut-offs that are expected in spectra from galactic halos. The injection of energetic electrons via neutron decay is found to yield a sharp cut-off in the injection distribution at γm = γe ~ r/τnc at radius r. Below this, no electrons are injected since they are produced in decays at smaller radii. This implies a low energy cutoff of ωm = γ2mBmec2 in the spectrum at given radius. Typically for r = 10 pc and a field of 1μG, the cutoff is at 10−8mec2 in the far infra-red. At larger radii, this low energy cutoff rapidly increases to X-ray energies. This cut-off provides a good way to measure the magnetic field strength and obtain its spatial dependence. In practice the situation is complicated by the superposition of different regions within the galaxy along the line of sight. Ways in which the observations could be deconvolved are discussed in Baring (1989, in preparation). A real possibility exists for detecting these signatures of energetic neutron emission from central regions of nearby galaxies and using the electron synchrotron spectra to spatially map galactic fields.
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Ivanov, Andrey N., Roman Höllwieser, Nataliya I. Troitskaya, Markus Wellenzohn und Yaroslav A. Berdnikov. „Electrodisintegration of Deuteron into Dark Matter and Proton Close to Threshold“. Symmetry 13, Nr. 11 (12.11.2021): 2169. http://dx.doi.org/10.3390/sym13112169.
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We discuss an investigation of the dark matter decay modes of the neutron, proposed by Fornal and Grinstein (2018–2020), Berezhiani (2017, 2018) and Ivanov et al. (2018) for solution of the neutron lifetime anomaly problem, through the analysis of the electrodisintegration of the deuteron d into dark matter fermions χ and protons p close to threshold. We calculate the triple-differential cross section for the reaction e−+d→χ+p+e− and propose to search for such a dark matter channel in coincidence experiments on the electrodisintegration of the deuteron e−+d→n+p+e− into neutrons n and protons close to threshold with outgoing electrons, protons, and neutrons in coincidence. An absence of neutron signals should testify to a detection of dark matter fermions.
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Sikora, Marek, Bronisław Rudak und Mitchell Begelman. „Relativistic Neutrons in Active Galactic Nuclei“. Symposium - International Astronomical Union 134 (1989): 215–16. http://dx.doi.org/10.1017/s0074180900140902.
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A substantial fraction of the radiation from an active galactic nucleus (AGN) is apparently nonthermal in origin, and is probably produced by ultrarelativistic electrons. How much energy goes into relativistic protons is uncertain, but it is likely to be comparable to the electron energy or larger. Indeed, several authors (Sikora et al. 1987; Kazanas and Ellison 1986; Zdziarski 1986) have shown that proton-photon and proton-proton collisions can be efficient sources of relativistic pairs in the central engine of an AGN. Thus it is not necessary for electrons to be accelerated directly in AGNs, provided that protons are accelerated with high enough efficiency.
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Liu, Yang, Tengfei Zhu, Jianxi Yao und Xiaoping Ouyang. „Simulation of Radiation Damage for Silicon Drift Detector“. Sensors 19, Nr. 8 (13.04.2019): 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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ANDREEV, A. A., und K. Yu PLATONOV. „Hard X-ray generation and particle production via the relativistic-intensity laser pulse interaction with a solid target“. Laser and Particle Beams 18, Nr. 1 (Januar 2000): 81–86. http://dx.doi.org/10.1017/s0263034600181091.
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This paper considers various channels of electron–positron pair, neutron, and γ-quantum generation via the ultrashort high-power laser pulse interaction with targets made from different materials. The positron yields in materials with different Z are estimated for the positron production by high-speed electrons and γ-photons. It is shown that a picosecond 100-TW laser pulse gives rise to formation of about 1010 positrons, possible channels of the neutron production in light- and heavy-atom materials being studied as well. It is ascertained that the formation of up to 107 laser neutrons per shot is possible when the laser intensity is ∼1021 W/cm2 on a heavy-atom target.
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Kondrik, A. I., und G. P. Kovtun. „Influence of radiation defects on the electrophysical and detector properties of CdTe:Cl irradiated by neutrons“. Технология и конструирование в электронной аппаратуре, Nr. 1-2 (2020): 22–29. http://dx.doi.org/10.15222/tkea2020.1-2.22.
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A promising material for semiconductor detectors of ionizing radiation is CdTe:Cl which allows obtaining detectors with high resistivity ρ and electron mobility μn. During operation, the detector materials may be exposed to neutron irradiation, which causes radiation defects to form in crystal lattice and deep levels to appear in the band gap, acting as centers of capture and recombination of nonequilibrium charge carriers, thus reducing the detection capability. The aim of this study was to use computer simulation to investigate the mechanisms of the influence of such radiation defects on the electrophysical properties (ρ, μn) of CdTe:Cl and the charge collection efficiency η of radiation detectors based on this material. The simulations were based on the models tested for reliability. It was found that the increase of the CdTe:Cl resistivity ρ during low-energy neutrons bombardment and at the initial stages of high-energy neutrons bombardment is caused by an increase in the concentration of radiation donor defect Z (with an energy level EC – 0.47 eV), presumably interstitial tellurium, which shifts the Fermi level into the middle of the band gap. The sharp rise of ρ observed at high-energy neutron bombardment is probably caused by the restructuring of the crystalline structure of the detector material with a change in the lattice constant and with an increase of the band gap, accompanied by a change in the conductivity properties. The degradation of the detector properties of CdTe:Cl during neutron irradiation is due to the capture and recombination of nonequilibrium electrons at radiation defects: Te interstitial, Te substitutional at the cadmium site, on tellurium vacancies and cadmium vacancies. The degradation of electron mobility μn can be caused by the scattering of electrons at microscopic areas of radiation defect clusters. The increase in concentration of the defects over the volume of the crystal at their uniform distribution of up to 1016 cm–3 does not significantly affect the electron mobility at room temperature.
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Plaster, B., E. Adamek, B. Allgeier, J. Anaya, H. O. Back, Y. Bagdasarova, D. B. Berguno et al. „Final results for the neutron β-asymmetry parameter A0 from the UCNA experiment“. EPJ Web of Conferences 219 (2019): 04004. http://dx.doi.org/10.1051/epjconf/201921904004.
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The UCNA experiment was designed to measure the neutron β-asymmetry parameter A0 using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for A0 was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in 2007, 2008–2009, 2010, and 2011–2013, which ultimately culminated in a 0.67% precision result for A0.
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SZPIKOWSKI, STANISŁAW. „40 YEARS OF THE DYNAMICAL PROTON-NEUTRON PAIRING SYMMETRIES“. International Journal of Modern Physics E 16, Nr. 02 (Februar 2007): 199–209. http://dx.doi.org/10.1142/s021830130700534x.
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In the years 1964-66 several physicists from several groups were searching quite independently for new symmetries related to the proton-neutron pairing interaction. They exploited the so-called quasi-spin method introduced earlier to apply to the system of electrons and then to identical nucleons (only protons or only neutrons). In what follows, a short introduction to the quasi-spin method is presented and then its application to the pairing interaction of neutrons (protons) is given. With the help of the quasi-spin method, the orthogonal symmetry groups SO(5) and SO(8) are shown to deal with proton-neutron pairing interaction in j - j and L - S coupling schemes, respectively. Comments about chronology of published papers related to the symmetry of pairing interaction written by inventors of the new symmetries are also made.
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Hasselbach, F., und M. Nicklaus. „Phase Shift of Electron Waves in A Rotating Frame of Reference“. Proceedings, annual meeting, Electron Microscopy Society of America 48, Nr. 1 (12.08.1990): 212–13. http://dx.doi.org/10.1017/s0424820100179816.
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After the first matter wave version of Sagnac’s classical light optical experiment of 1913, performed by Mercereau and Zimmermann with electron Cooper pairs in 1965, and the Sagnac experiment realized with neutrons by Werner et al. in 1979 , we report here on the first observation of the rotational phase shift of electron waves in vacuum.Theory. The Sagnac effect links classical physics, quantum physics and relativity. Using the special theory of relativity it can be derived that coherent waves, e.g. of light, neutrons or electrons, travelling around a finite area A experience a relative phaseshift
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Shkolnikov, P. L., und A. E. Kaplan. „Laser-Induced Particle Production and Nuclear Reactions“. Journal of Nonlinear Optical Physics & Materials 06, Nr. 02 (Juni 1997): 161–67. http://dx.doi.org/10.1142/s0218863597000149.
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We show that electrons accelerated in plasma generated by available, or within reach, terawatt lasers can initiate positron and neutron production and a host of nuclear reactions. We propose and evaluate the environments and processes favorable for this phenomenon, which can be used to develop a practical table-top source of intense short pulses of positrons, gamma-photons, neutrons, and fission fragments.
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Evans, Alan C., Jerry Mayers, David N. Timms und Malcolm J. Cooper. „Deep Inelastic Neutron Scattering in the Study of Atomic Momentum Distributions“. Zeitschrift für Naturforschung A 48, Nr. 1-2 (01.02.1993): 425–32. http://dx.doi.org/10.1515/zna-1993-1-271.
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Abstract The electron-volt spectrometer (EVS) at the pulsed neutron source facility (ISIS) is being developed for the study of atomic momentum distributions. Neutrons with energies in the range 1 to 100 eV are incident on the sample, and the time-of-flight (TOF) spectrum of the scattered beam is measured by an array of fixed detectors. A resonant foil difference technique is used to yield a set of TOF spectra for those neutrons scattered into a fixed energy and through fixed angles. Information on the momentum distribution of the target nuclei can be deduced within an impulse approximation in a procedure analogous to that in Compton scattering of electrons by photons.Crystalline compounds containing aligned hydrogen bonds and other hydrogenous compounds are of particular interest owing to the high cross-section of the proton at these neutron energies. With improved statistical accuracy of the data it is anticipated that deviations of the proton's potential from a harmonic potential may be determined. Non-hydrogenous systems have also been investigated. A description is given of the basic theory and interpretive method. Data obtained on numerous systems are presented and discussed.
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Baláž, J., A. V. Dmitriev, M. A. Kovalevskaya, K. Kudela, S. N. Kuznetsov, I. N. Myagkova, Yu I. Nagornikh, J. Rojko und S. P. Ryumin. „Solar Flare Energetic Neutral Emission Measurements in the Project Coronas-I“. International Astronomical Union Colloquium 144 (1994): 635–39. http://dx.doi.org/10.1017/s0252921100026208.
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AbstractThe experiment SONG (SOlar Neutron and Gamma rays) for the low altitude satellite CORONAS-I is described. The instrument is capable to provide gamma-ray line and continuum detection in the energy range 0.1 – 100 MeV as well as detection of neutrons with energies above 30 MeV. As a by-product, the electrons in the range 11 – 108 MeV will be measured too. The pulse shape discrimination technique (PSD) is used.
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DIMITRAKOUDIS, STAVROS, MARIA PETROPOULOU und APOSTOLOS MASTICHIADIS. „THE TIME-DEPENDENT ONE-ZONE HADRONIC MODEL: FIRST PRINCIPLES“. International Journal of Modern Physics: Conference Series 08 (Januar 2012): 19–24. http://dx.doi.org/10.1142/s2010194512004369.
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We present some results on the radiative signatures of the one zone hadronic model. For this we have solved five spatially averaged, time-dependent coupled kinetic equations which describe the evolution of relativistic protons, electrons, photons, neutrons and neutrinos in a spherical volume containing a magnetic field. Protons are injected and lose energy by synchrotron, photopair and photopion production. We model photopair and photopion using the results of relevant MC codes, like the SOPHIA code in the case of photopion, which give accurate description for the injection of secondaries which then become source functions in their respective equations. This approach allows us to calculate the expected photon and neutrino spectra simultaneously in addition to examining questions like the efficiency and the temporal behaviour of the hadronic models.
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Biswal, S. K., Bharat Kumar und S. K. Patra. „Effects of isovector scalar meson on neutron star both with and without hyperon“. International Journal of Modern Physics E 25, Nr. 11 (November 2016): 1650090. http://dx.doi.org/10.1142/s0218301316500907.
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We study the effects of isovector-scalar ([Formula: see text])-meson on neutron and hyperon stars. Influence of [Formula: see text]-meson on both static and rotating stars is discussed. The [Formula: see text]-meson in a neutron star consisting of protons, neutrons and electrons, makes the equations of states (EOS) stiffer at higher density, and consequently increases the maximum mass of the star. But induction of [Formula: see text]-meson in the hyperon star decreases the maximum mass. This is due to the early evolution of hyperons in presence of [Formula: see text]-meson.
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Weick, Sarah, und Mirco Grosse. „Investigating Hydrogen in Zirconium Alloys by Means of Neutron Imaging“. Materials 17, Nr. 4 (06.02.2024): 781. http://dx.doi.org/10.3390/ma17040781.
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Neutrons interact with the magnetic moment of the atomic shell of an atom, as is common for X-rays, but mainly they interact directly with the nucleus. Therefore, the atomic number and the related number of electrons does not play a role in the strength of an interaction. Instead, hydrogen that is nearly invisible for X-rays has a higher attenuation for neutrons than most of the metals, e.g., zirconium, and thus would be visible through dark contrast in neutron images. Consequently, neutron imaging is a precise, non-destructive method to quantify the amount of hydrogen in materials with low attenuation. Because nuclear fuel cladding tubes of light water reactors are made of zirconium (98%), the hydrogen amount and distribution in metallic claddings can be investigated. Even hydrogen concentrations smaller than 10 wt.ppm can be determined locally with a spatial resolution of less than 10 μm (with a high-resolution neutron microscope). All in all, neutron imaging is a very fast and precise method for several applications. This article explains the basics of neutron imaging and provides samples of investigation possibilities, e.g., for hydrogen in zirconium alloy cladding tubes or in situ investigations of hydrogen diffusion in metals.
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ESPOSITO, SALVATORE. „THE ACTION OF NEUTRINO PONDEROMOTIVE FORCE ON SUPERNOVA DYNAMICS“. Modern Physics Letters A 14, Nr. 26 (30.08.1999): 1763–73. http://dx.doi.org/10.1142/s0217732399001863.
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Collective interactions of a beam of neutrinos/antineutrinos traversing a dense magnetized plasma of electrons/positrons, protons and neutrons are studied with particular reference to the case of a supernova. We find that the ponderomotive force exerted by neutrinos gives, contrary to expectations, a negligible contribution to the revival of the shock for a successful supernova explosion, although new types of convection and plasma cooling processes induced by the ponderomotive force could be, in principle, relevant for the dynamics itself.
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Ashkar, Rana, P. Stonaha, A. L. Washington, V. R. Shah, M. R. Fitzsimmons, B. Maranville, C. F. Majkrzak, W. T. Lee, W. L. Schaich und Roger Pynn. „Dynamical theory calculations of spin-echo resolved grazing-incidence scattering from a diffraction grating“. Journal of Applied Crystallography 43, Nr. 3 (30.04.2010): 455–65. http://dx.doi.org/10.1107/s0021889810010642.
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Neutrons scattered or reflected from a diffraction grating are subject to a periodic potential analogous to the potential experienced by electrons within a crystal. Hence, the wavefunction of the neutrons can be expanded in terms of Bloch waves and a dynamical theory can be applied to interpret the scattering phenomenon. In this paper, a dynamical theory is used to calculate the results of neutron spin-echo resolved grazing-incidence scattering (SERGIS) from a silicon diffraction grating with a rectangular profile. The calculations are compared with SERGIS measurements made on the same grating at two neutron sources: a pulsed source and a continuous wave source. In both cases, the spin-echo polarization, studied as a function of the spin-echo length, peaks at integer multiples of the grating period but there are some differences between the two sets of data. The dynamical theory explains the differences and gives a good account of both sets of results.
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Gottlieb, Ore, und Abraham Loeb. „Electromagnetic signals from the decay of free neutrons in the first hours of neutron star mergers“. Monthly Notices of the Royal Astronomical Society 493, Nr. 2 (07.02.2020): 1753–60. http://dx.doi.org/10.1093/mnras/staa363.
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ABSTRACT The first hours following a neutron star merger are considered to provide several ultraviolet (UV)/optical/near-infrared signals: β-decay emission from free neutrons, radioactive decay of shocked heavy elements in the cocoon and cocoon’s cooling emission. Here, we consider two additional emission sources: β-decay of free neutrons in the cocoon and synchrotron by the β-decay electrons. We present three-dimensional relativistic hydrodynamic simulations of jets that propagate in a multi-layer ejecta from the merger and calculate semi-analytically the resulting light curves. We find that the free neutrons emission at high latitudes is enhanced by the cocoon by a factor of a few to power a wide (≲60°) and brief (∼1 h) UV signal that can reach an absolute magnitude of ≳−15, comparable with the cooling emission. If the ejected neutron matter mass is $M_{\rm n} \gtrsim 10^{-4}\, {\rm M_{\odot }}$, the synchrotron emission may yield a long (∼8 h) quasi-isotropic UV/optical signal with an absolute magnitude between −12 and −15, depending on the magnetic field. Such a high mass of a mildly relativistic component may partly obscure the cocoon’s shocked r-process elements, thereby attenuating its radioactive decay emission. Future observations on these time-scales, including null detections, may place constraints on the ejected neutron matter mass and shed light on the ejecta and jet-cocoon characteristics.
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Pfeifer, Kent B., Komandoor E. Achyuthan, Matthew Allen, Michele L. B. Denton, Michael P. Siegal und Ronald P. Manginell. „Microfabrication of a gadolinium-derived solid-state sensor for thermal neutrons“. Journal of Radiation Research 58, Nr. 4 (25.03.2017): 464–73. http://dx.doi.org/10.1093/jrr/rrx010.
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Abstract Neutron sensing is critical in civilian and military applications. Conventional neutron sensors are limited by size, weight, cost, portability and helium supply. Here the microfabrication of gadolinium (Gd) conversion material–based heterojunction diodes for detecting thermal neutrons using electrical signals produced by internal conversion electrons (ICEs) is described. Films with negligible stress were produced at the tensile-compressive crossover point, enabling Gd coatings of any desired thickness by controlling the radiofrequency sputtering power and using the zero-point near p(Ar) of 50 mTorr at 100 W. Post-deposition Gd oxidation–induced spallation was eliminated by growing a residual stress-free 50 nm neodymium-doped aluminum cap layer atop Gd. The resultant coatings were stable for at least 6 years, demonstrating excellent stability and product shelf-life. Depositing Gd directly on the diode surface eliminated the air gap, leading to a 200-fold increase in electron capture efficiency and facilitating monolithic microfabrication. The conversion electron spectrum was dominated by ICEs with energies of 72, 132 and 174 keV. Results are reported for neutron reflection and moderation by polyethylene for enhanced sensitivity, and γ- and X-ray elimination for improved specificity. The optimal Gd thickness was 10.4 μm for a 300 μm-thick partially depleted diode of 300 mm2 active surface area. Fast detection (within 10 min) at a neutron source-to-diode distance of 11.7 cm was achieved with this configuration. All ICE energies along with γ-ray and Kα,β X-rays were modeled to emphasize correlations between experiment and theory. Semi-conductor thermal neutron detectors offer advantages for field-sensing of radioactive neutron sources.
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Muškinja, Miha, John Derek Chapman und Heather Gray. „Geant4 performance optimization in the ATLAS experiment“. EPJ Web of Conferences 245 (2020): 02036. http://dx.doi.org/10.1051/epjconf/202024502036.
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Software improvements in the ATLAS Geant4-based simulation are critical to keep up with evolving hardware and increasing luminosity. Geant4 simulation currently accounts for about 50% of CPU consumption in ATLAS and it is expected to remain the leading CPU load during Run 4 (HL-LHC upgrade) with an approximately 25% share in the most optimistic computing model. The ATLAS experiment recently developed two algorithms for optimizing Geant4 performance: Neutron Russian Roulette (NRR) and range cuts for electromagnetic processes. The NRR randomly terminates a fraction of low energy neutrons in the simulation and weights energy deposits of the remaining neutrons to maintain physics performance. Low energy neutrons typically undergo many interactions with the detector material and their path becomes uncorrelated with the point of origin. Therefore, the response of neutrons can be efficiently estimated only with a subset of neutrons. Range cuts for electromagnetic processes exploit a built-in feature of Geant4 and terminate low energy electrons that originate from physics processes including conversions, the photoelectric effect, and Compton scattering. Both algorithms were tuned to maintain physics performance in ATLAS and together they bring about a 20% speed-up of the ATLAS Geant4 simulation. Additional ideas for improvements, currently under investigation, will also be discussed in this paper. Lastly, this paper presents how the ATLAS experiment utilizes software packages such as Intel’s VTune to identify and resolve hot-spots in simulation.
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Bell, David C., Anthony J. Garratt-Reed und Linn W. Hobbs. „RDF Analysis of Radiation-Amorphized SiC using a field Emission Scanning Electron Microscope“. Microscopy and Microanalysis 4, S2 (Juli 1998): 700–701. http://dx.doi.org/10.1017/s143192760002362x.
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AbstractFast electrons are a particularly useful chemical and structural probe for the small sample volumes associated with ion- or fast electron-irradiation-induced amorphization, because of their much stronger interaction with matter than for X-rays or neutrons, and also because they can be readily focused to small probes. Three derivative signals are particularly rich in information: the angular distribution of scattered electrons (which is utilized in both diffraction and imaging studies); the energy loss spectrum of scattered electrons (electron energy loss spectroscopy, or EELS); and the emission spectrum of characteristic X-rays resulting from ionization energy losses (energy dispersive X-ray spectroscopy, or EDXS). We have applied the first two to the study of three amorphized compounds (AIPO4, SiO2, SiC) using MIT's Vacuum Generators HB603 field-emission (FEG) scanning transmission electron microscope (STEM), operating at 250 kV and equipped with a Gatan digital parallel-detection electron energy-loss spectrometer (digiPEELS).
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BELVEDERE, RICCARDO, JORGE A. RUEDA und REMO RUFFINI. „NEUTRON STAR CORES IN THE GENERAL RELATIVISTIC THOMAS-FERMI TREATMENT“. International Journal of Modern Physics: Conference Series 23 (Januar 2013): 185–92. http://dx.doi.org/10.1142/s2010194513011288.
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We introduce a new set of equations to describe the equilibrium of the core of neutron stars, composed by self-gravitating degenerate neutrons, protons and electrons in β-equilibrium. We take into account strong, weak, electromagnetic and gravitational interactions within the framework of general relativity. We extend the conditions of equilibrium based on the constancy of the Klein potentials to the strongly interactive case. The strong interactions between nucleons are modeled through the exchange of the σ, ω and ρ virtual mesons. The equations are solved numerically in the case of zero temperatures and for a non-rotating spherically symmetric neutron stars in the mean-field approximation.
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Escobar, G. J., L. J. Pellizza und G. E. Romero. „Cosmic-ray production from neutron escape in microquasar jets“. Astronomy & Astrophysics 650 (Juni 2021): A136. http://dx.doi.org/10.1051/0004-6361/202039860.
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Context. The origin of Galactic cosmic rays remains a matter of debate, but supernova remnants are commonly considered to be the main place where high-energy cosmic rays are accelerated. Nevertheless, current models predict cosmic-ray spectra that do not match observations and the efficiency of the acceleration mechanism is still undetermined. On the other hand, the contribution of other kinds of sources to the Galactic cosmic-ray population is still unclear, and merits investigation. Aims. In this work we explore a novel mechanism through which microquasars might produce cosmic rays. In this scenario, microquasar jets generate relativistic neutrons, which escape and decay outside the system; protons and electrons, created when these neutrons decay, escape to the interstellar medium as cosmic rays. Methods. We introduce the relativistic neutron component through a coupling term in the transport equation that governs the jet proton population. We compute the escape rate and decay distribution of these neutrons, and follow the propagation of the decay products until they escape the system and become cosmic rays. We then compute the spectra of these cosmic rays. Results. Neutrons can drain only a small fraction of the jet power as cosmic rays. The most promising scenarios arise in extremely luminous systems (Ljet ∼ 1040 erg s−1), in which the fraction of jet power deposited in cosmic rays can reach ∼0.001. Slow jets (Γ ≲ 2, where Γ is the bulk Lorentz factor) favour neutron production. The resulting cosmic-ray spectrum is similar for protons and electrons, which share the power in the ratio given by neutron decay. The spectrum peaks at roughly half the minimum energy of the relativistic protons in the jet; it is soft (spectral index ∼3) above this energy, and almost flat below. Conclusions. The proposed mechanism produces more energetic cosmic rays from microquasars than those presented by previous works in which the particles escape through the jet terminal shock. Values of spectral index steeper than 2 are possible for cosmic rays in our model and these indeed agree with those required to explain the spectral signatures of Galactic cosmic rays, although only the most extreme microquasars provide power comparable to that of a typical supernova remnant. The mechanism explored in this work may provide stronger and softer cosmic-ray sources in the early Universe, and therefore contribute to the heating and reionisation of the intergalactic medium.
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Parenteau, M., C. Carlone, M. Aubin, S. M. Khanna, W. T. Anderson und J. W. Gerdes Jr. „Effects of neutron and electron irradiation on the absorption edge of GaAs“. Canadian Journal of Physics 69, Nr. 3-4 (01.03.1991): 324–28. http://dx.doi.org/10.1139/p91-054.
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Semi-insulating liquid encapsulated Czochralski GaAs wafers were submitted to irradiation with 1 MeV neutrons, thermal neutrons, 7 MeV electrons, and white electrons (up to 7 MeV). The direct absorption edge was then studied by means of transmission (T = 15 K) and thermoreflectance (T = 35 and 51 K) measurements. Thermoreflectance spectra showed that the position of the exciton does not shift after irradiation with 1 MeV neutrons, but that its broadening parameter Γ increases as the fluence increases. Transmission measurements have revealed the presence of two acceptor levels (C and Zn) in the unirradiated samples. The absorption associated with these impurities increased by a factor of 10 after irradiation with 1 MeV neutrons. This effect was not produced by the three other types of radiation. However, an absorption tail extending well below the direct edge is seen after irradiation with all four types of particles. A model proposed by Toyozawa fits this continuum quite well, suggesting that irradiation causes amorphization of the crystal. The rate of introduction of defects and its dependence on irradiation fluence is different for each type of radiation.
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Henderson, Richard. „The potential and limitations of neutrons, electrons and X-rays for atomic resolution microscopy of unstained biological molecules“. Quarterly Reviews of Biophysics 28, Nr. 2 (Mai 1995): 171–93. http://dx.doi.org/10.1017/s003358350000305x.
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SummaryRadiation damage is the main problem which prevents the determination of the structure of a single biological macromolecule at atomic resolution using any kind of microscopy. This is true whether neutrons, electrons or X-rays are used as the illumination. Forneutrons, the cross-section for nuclear capture and the associatedenergy deposition and radiation damage could be reduced by using samples that are fully deuterated and15N-labelled and by using fast neutrons, but single molecule biological microscopy is still not feasible. For naturally occurring biological material,electronsat present provide the most information for a given amount of radiation damage. Using phase contrast electron microscopy on biological molecules and macromolecular assemblies of ˜ 105molecular weight and above, there is in theory enough information present in the image to allow determination of the position and orientation of individual particles: the application of averaging methods can then be used to provide an atomic resolution structure. The images of approximately 10000 particles are required. Below 105molecular weight, some kind of crystal or other geometrically ordered aggregate is necessary to provide a sufficiently high combined molecular weight to allow for the alignment. In practice, the present quality of the best images still falls short of that attainable in theory and this means that a greater number of particles must be averaged and that the molecular weight limitation is somewhat larger than the predicted limit. ForX-rays, the amount of damage per useful elastic scattering event is several hundred times greater than for electrons at all wavelengths and energies and therefore the requirements on specimen size and number of particles are correspondingly larger. Because of the lack of sufficiently bright neutron sources in the foreseeable future, electron microscopy in practice provides the greatest potential for immediate progress.
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Chatel, Carole, Ludovic Mathieu, Mourad Aïche, Maria Diakaki und Olivier Bouland. „Development of a small Time-Projection-Chamber for the quasi-absolute neutron flux measurement“. EPJ Web of Conferences 284 (2023): 01012. http://dx.doi.org/10.1051/epjconf/202328401012.
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Accurate actinides fission cross sections around 1 MeV are of primary importance for the safety of generation IV reactors. To have accurate measurements, the neutron flux must also be accurately estimated. This is usually done with respect to the 235U(n,f) cross section. It is however possible to measure the neutron flux with respect to the 1H(n,n)p cross section which is a primary standard, providing an independent and precise measurement. Typically, the usual proton recoil technique uses a silicon detector for neutrons of energy between 1 and 70 MeV. However, the high electron and gamma background due to neutron production under irradiation makes the use of this or any other detector not suitable for an accurate measurement below 1 MeV. To this end, the Gaseous Proton Recoil Telescope is developed and characterized. The goal is to provide quasi-absolute neutron flux measurements with an accuracy better than 3%. It consists of a double ionization chamber with a Micromegas segmented detection plane and the gaseous pressure can be adjusted to protons – and hence neutron – energy. The sensitivity to gamma and electrons background, the intrinsic efficiency as well as the resolution of this detector have been investigated.
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LAMOREAUX, STEVE K. „A REVIEW OF THE EXPERIMENTAL TESTS OF QUANTUM MECHANICS“. International Journal of Modern Physics A 07, Nr. 27 (30.10.1992): 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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Chandler, GS, D. Jayatilaka und SK Wolff. „Electronic Structure from Polarised Neutron Diffraction“. Australian Journal of Physics 49, Nr. 2 (1996): 261. http://dx.doi.org/10.1071/ph960261.
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The polarised neutron diffraction experiment is described and the nature of the information obtained is outlined. In many cases interpretation of the experiment assumes that the crystal is made up of non-interacting molecular or ionic units. The soundness of this assumption is examined in the case of copper Tutton salt. Polarised neutrons are scattered by the crystal magnetisation density which has a contribution from the orbital motion of electrons. A method for including the spin-orbit contribution to this effect is described for the particular example of the CoCI24− ion.
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Majkrzak, Charles F., und Gian P. Felcher. „Neutron Scattering Studies of Surfaces and Interfaces“. MRS Bulletin 15, Nr. 11 (November 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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Moodie, A. F., und J. C. H. Spence. „John Maxwell Cowley 1923 - 2004“. Historical Records of Australian Science 17, Nr. 2 (2006): 227. http://dx.doi.org/10.1071/hr06012.
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John Cowley contributed significantly to all of the fields that relate to electron diffraction and electron microscopy, and helped to found not a few of them. His name is associated in particular with n-beam dynamical theory, high-resolution electron microscopy, scanning transmission electron microscopy, instrumental design, and the application of the techniques of electron scattering to structure analysis. His experimental work was not, however, confined to the scattering of electrons: to take but one instance, his seminal work on the theory of short-range order was stimulated initially by his experiments using X-rays, and it was only later that he extended the technique to include electron diffraction. Finally, to all those who practise the techniques of scattering electrons, X-rays, or neutrons in the study of solids, liquids or gases, his book Diffraction Physics remains not only eminently readable but authoritative.
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Ankele, Jürgen, Joachim Mayer, Peter Lamparter, Peter Lamparter und Siegfried Steeb. „Investigation of the Structure of Amorphous Substances by Means of Electron Diffraction“. Zeitschrift für Naturforschung A 49, Nr. 7-8 (01.08.1994): 771–75. http://dx.doi.org/10.1515/zna-1994-7-807.
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Abstract The structure factor of amorphous germanium was determined using 120 kV electrons, an Ω-filter for the elimination of inelastically scattered electrons and a correction procedure for multiple scattering. The structure factor thus obtained is in good accordance to that obtained with X-rays and neutrons, respectively.
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Guinan, M. W. „Fundamental Studies of Irradiation Effects in Fusion Materials“. MRS Bulletin 14, Nr. 7 (Juli 1989): 20–28. http://dx.doi.org/10.1557/s0883769400062126.
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Fusion is the energy production process which drives the universe. Controlled utilization of this process for the benefit of man has been the illusive goal of the world's fusion power research since the 1950s. The most easily utilized fusion reaction is the fusion of deuterium and tritium. Every major fusion power research program is directed toward utilization of the energy released from this reaction.When the hydrogen isotopes deuterium (D) and tritium (T) are fused, 80% of the energy released is carried by a single neutron. This neutron moves at 5 × 107 m/s and a kinetic energy of 14 MeV, so the designer of a magnetically confined reactor is faced with the reality that 80% of the power produced will impinge on the structure facing the burning plasma as a “current” of 14 MeV neutrons. The D-T reaction is illustrated in Figure 1.Neutrons are not charged and do not interact with electrons in material through which they move. They collide with nuclei. The result of these collisions is always some combination of the in-situ creation of one or more energetic ions, alteration of chemistry through transmutation, and the introduction of radioactivity. Each changes material properties.Nearly all the present experimental data base of neutron irradiation effects has come from fission reactor irradiations.