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1
SAHU, SARIRA. « MULTI-GeV NEUTRINOS DUE TO $n\bar n$ OSCILLATION IN GAMMA-RAY BURST FIREBALLS ». Modern Physics Letters A 22, no 40 (28 décembre 2007) : 3065–72. http://dx.doi.org/10.1142/s021773230702378x.
Texte intégralRésumé :
The long and short gamma-ray bursts are believed to be produced due to collapse of massive stars and merger of compact binaries respectively. All these objects are rich in neutron and the jet outflow from these objects must have a neutron component in it. By postulating the [Formula: see text] oscillation in the gamma-ray burst fireball, we show that, 19–38 GeV neutrinos and anti-neutrinos can be produced due to annihilation of anti-neutrons with the background neutrons. These neutrinos and anti-neutrinos will be produced before the 5–10 GeV neutrinos due to dynamical decoupling of neutrons from the rest of the fireball. Observation of these neutrinos will shed more light on the nature of the GRB progenitors and also be a unique signature of physics beyond the standard model. A possible way of detecting these neutrinos in future is also discussed.
2
Daywitt, William C. « The Neutrino Decay of the Free Neutron and the Neutrino Structure According to the Planck Vacuum Theory ». European Journal of Engineering and Technology Research 6, no 5 (27 juillet 2021) : 73–75. http://dx.doi.org/10.24018/ejers.2021.6.5.2524.
Texte intégralRésumé :
The Planck vacuum (PV) theory derives equations for the neutrino and antineutrino, and relates them to the unstable free neutron and antineutron. Remarkably, these neu- trons and neutrinos share the same wavefunction solutions that describe the proton and electron and their antiparticle cores.
The neutrino and antineutrino are chargeless and massless; so their propagation through matter goes unnoticed, making these neutrinos invisible. The equations to follow that describe these pseudo-particles are the theoretical embodiment of the circa 1930 Pauli neutrino hypothesis.
Finally, depending on one’s perspective, the neutrons can be viewed as decaying meta-particles or as stable nuclear particles.
3
Daywitt, William C. « The Neutrino Decay of the Free Neutron and the Neutrino Structure According to the Planck Vacuum Theory ». European Journal of Engineering and Technology Research 6, no 5 (27 juillet 2021) : 73–75. http://dx.doi.org/10.24018/ejeng.2021.6.5.2524.
Texte intégralRésumé :
The Planck vacuum (PV) theory derives equations for the neutrino and antineutrino, and relates them to the unstable free neutron and antineutron. Remarkably, these neu- trons and neutrinos share the same wavefunction solutions that describe the proton and electron and their antiparticle cores.
The neutrino and antineutrino are chargeless and massless; so their propagation through matter goes unnoticed, making these neutrinos invisible. The equations to follow that describe these pseudo-particles are the theoretical embodiment of the circa 1930 Pauli neutrino hypothesis.
Finally, depending on one’s perspective, the neutrons can be viewed as decaying meta-particles or as stable nuclear particles.
4
Bondar, Aleksandr, Alexey Buzulutskov, Aleksandr Burdakov, Evgeny Grishnyaev, Aleksandr Dolgov, Aleksandr Makarov, Sergey Polosatkin, Andrey Sokolov, Sergey Taskaev et Lev Shekhtman. « Proposal for Neutron Scattering Systems for Calibration of Dark Matter Search and Low-Energy Neutrino Detectors ». Siberian Journal of Physics 8, no 3 (1 octobre 2013) : 27–38. http://dx.doi.org/10.54362/1818-7919-2013-8-3-27-38.
Texte intégralRésumé :
The proposal of two neutron scattering systems for calibration of two-phase cryogenic avalanche detectors with high sensitivity being developed at Budker INP is presented. This kind of detectors is designed for the search of dark matter and low energy neutrino detection, in particular, coherent neutrino scattering on nuclei. Detector calibration is made with a measurement of ionization yield and scintillation quenching factor for low energy recoiling nuclei (in 0.5 to 100 keV range) originating from elastic scattering of neutrons. To provide wide range of recoiling nuclei energies two systems of neutron scattering are proposed. The first one is based on small-sized DD generator of fast (2.45 MeV) monoenergetic neutrons operating on sealed neutron tube. The second one is based on tandem proton accelerator and lithium target and capable of generation of monoenergetic epithermal neutrons with energy up to 100 keV
5
Chakraborty, Sabyasachi, Aritra Gupta et Miguel Vanvlasselaer. « Anomaly induced cooling of neutron stars : a Standard Model contribution ». Journal of Cosmology and Astroparticle Physics 2023, no 10 (1 octobre 2023) : 030. http://dx.doi.org/10.1088/1475-7516/2023/10/030.
Texte intégralRésumé :
Abstract Young neutron stars cool via the emission of neutrinos from their core. A precise understanding of all the different processes producing neutrinos in the hot and degenerate matter is essential for assessing the cooling rate of such stars. The main Standard Model processes contributing to this effect are ν bremsstrahlung, mURCA among others. In this paper, we investigate another Standard Model process initiated by the Wess-Zumino-Witten term, leading to the emission of neutrino pairs via Nγ → Nνν̅. We find that for proto-neutron stars, such processes with degenerate neutrons can be comparable and even dominate over the typical and well-known cooling mechanisms.
6
Aitkulov, M. T., D. S. Dyussambayev, N. K. Romanova, Sh H. Gizatulin, A. A. Shaimerdenov, Zh T. Bugybay, K. S. Kisselyov et A. O. Beisebayev. « Measurement of the spatial-energy distribution of neutrons in the irradiation channel of the critical facility ». Journal of Physics : Conference Series 2155, no 1 (1 janvier 2022) : 012021. http://dx.doi.org/10.1088/1742-6596/2155/1/012021.
Texte intégralRésumé :
Abstract One of the basic installations of the Republican State Enterprise “Institute of Nuclear Physics” of the Ministry of Energy of the Republic of Kazakhstan is a critical assembly, which is a zero-power reactor. Desalinated water and beryllium serve as moderators and neutrons reflectors. The energy spectrum of neutrons in the core is thermal. The main purpose and area of application is the modeling and study of the neutronic characteristics of the cores of water-moderated research reactors of various types. The paper presents the results of experimental measurements of the spatial-energy distribution of neutrons in the dry, central channel of the critical assembly. Measurements of the neutron flux were carried out using activation foils for three energy groups of neutrons: thermal, epithermal, and fast. The measured thermal neutrons flux in the irradiation channel is ~ 3·108 cm‒2s‒1, and fast neutrons flux (with energies above 0.7 MeV) is ~ 8·108 cm‒2s‒1. The fraction of thermal neutrons in the integral flux was 0.23%, and the fraction of fast neutrons was 0.62%. In the axial distribution of thermal and fast neutrons, the maximum value of the neutron flux is 50 mm below the midplane of the core.
7
Hargrove, C. K., et D. J. Paterson. « Solar-neutrino neutral-current detection methods in the Sudbury neutrino observatory ». Canadian Journal of Physics 69, no 11 (1 novembre 1991) : 1309–16. http://dx.doi.org/10.1139/p91-196.
Texte intégralRésumé :
The Sudbury Neutrino Observatory will study the solar-neutrino problem through the detection of charged-current (CC), neutral-current (NC), and elastic-scattering (ES) interactions of solar neutrinos with heavy water. The measurement of the NC rate relative to the CC rate provides a nearly model-independent method of observing neutrino oscillations. The NC interaction breaks up the deuteron producing a neutron and a proton. The interaction rate in the original design is measured by observing Čerenkov light from showers produced by neutron-capture γ rays from the capture of the NC neutrons by a selected additive to the heavy water. These signals overlap the CC and ES signals, so that the measurement of the NC rate requires the subtraction of two signals obtained at different times. This paper describes our investigation of an alternate detection method in which the thermalized neutrons are captured by (n, α) or (n, p) reactions on light nuclei. The resulting charged-particle products are uniquely detected by scintillators or proportional counters, completely separating this NC signal from the CC and ES Čerenkov signals, thus simplifying its measurement, improving its significance, and allowing observation of otherwise unobservable short-term NC fluctuations. Although background rates for the new techniques have not yet been determined, the experimental advantages justify further development work.
8
Mangan, M. A., C. L. Ruiz, G. W. Cooper, G. A. Chandler et D. J. Ampleford. « Inferring neutron yields using indium activation samples for small fractions of tritium added to deuterium fuel in inertial confinement fusion (ICF) experiments ». Review of Scientific Instruments 93, no 10 (1 octobre 2022) : 103514. http://dx.doi.org/10.1063/5.0101823.
Texte intégralRésumé :
In inertial confinement fusion experiments, the neutron yield is an important metric for thermonuclear fusion performance. Neutron activation diagnostics can be used to infer neutron yields. The material used for neutron activation diagnostic undergoes a threshold reaction so that only neutrons having energies above the threshold energy are observed. For thermonuclear experiments using deuterium (D) and tritium (T) fuel constituents, neutrons arising from D + D reactions (DD-neutrons) and neutrons resulting from D + T reactions (DT-neutrons) are of primary interest. Indium has two neutron activation reactions that can be used to infer yields of DD-neutrons and DT-neutrons. One threshold is high enough that only DT-neutrons can induce activation, the second reaction can be activated by both DD-neutrons and DT-neutrons. Thus, to obtain the DD-neutron yield, the contribution made by DT-neutrons to the total induced activity must be extracted. In DD-fuel experiments, DT-neutrons arise from secondary reactions, which are significantly lower in number than primary DD-neutrons, and their contribution to the inferred DD-neutron yield can be ignored. When the DD- and DT-neutron yields become comparable, such as when low tritium fractions are added to DD-fuel, the contribution of DT-neutrons must be extracted to obtain accurate yields. A general method is described for this correction to DD-neutron yields.
9
Shinoki, Masataka. « Measurement of cosmogenic neutron production in SK-Gd ». Journal of Physics : Conference Series 2156, no 1 (1 décembre 2021) : 012187. http://dx.doi.org/10.1088/1742-6596/2156/1/012187.
Texte intégralRésumé :
Abstract The Super-Kamiokande-Gd (SK-Gd) experiment has started after adding the gadolinium (Gd) into ultra-pure water in the SK detector. SK-Gd dramatically improves the sensitivity to supernova relic neutrino searches by tagging neutrons. Cosmic-ray muons penetrating into the SK detector induce hadronic showers. Such muon often break oxygen nuclei in water and produce unstable radioactive isotopes and neutrons, which are major background sources for supernova relic neutrino searches. On the other hand, the cosmogenic neutrons produced by muons can be used for the detector calibration source. Since cosmic-ray muons penetrate into the SK detector continuously with the rate of 2 event/s, the cosmogenic neutrons can be used to monitor the stability and uniformity of the Gd concentration in water. In this proceeding, we report the progress of cosmogenic neutron measurement in SK-Gd.
10
Biekert, A., C. Chang, L. Chaplinsky, C. W. Fink, W. D. Frey, M. Garcia-Sciveres, W. Guo et al. « A portable and monoenergetic 24 keV neutron source based on 124Sb-9Be photoneutrons and an iron filter ». Journal of Instrumentation 18, no 07 (1 juillet 2023) : P07018. http://dx.doi.org/10.1088/1748-0221/18/07/p07018.
Texte intégralRésumé :
Abstract A portable monoenergetic 24 keV neutron source based on the 124Sb-9Be photoneutron reaction and an iron filter has been constructed and characterized. The coincidence of the neutron energy from SbBe and the low interaction cross-section with iron (mean free path up to 29 cm) makes pure iron specially suited to shield against gamma rays from 124Sb decays while letting through the neutrons. To increase the 124Sb activity and thus the neutron flux, a >1 GBq 124Sb source was produced by irradiating a natural Sb metal pellet with a high flux of thermal neutrons in a nuclear reactor. The design of the source shielding structure makes for easy transportation and deployment. A hydrogen gas proportional counter is used to characterize the neutrons emitted by the source and a NaI detector is used for gamma background characterization. At the exit opening of the neutron beam, the characterization determined the neutron flux in the energy range 20–25 keV to be 6.00±0.30 neutrons per cm2 per second and the total gamma flux to be 245±8 gammas per cm2 per second (numbers scaled to 1 GBq activity of the 124Sb source). A liquid scintillator detector is demonstrated to be sensitive to neutrons with incident kinetic energies from 8 to 17 keV, so it can be paired with the source as a backing detector for neutron scattering calibration experiments. This photoneutron source provides a good tool for in-situ low energy nuclear recoil calibration for dark matter experiments and coherent elastic neutrino-nucleus scattering experiments.
11
Leinson, Lev B. « Hybrid cooling of the Cassiopeia A neutron star ». Monthly Notices of the Royal Astronomical Society 511, no 4 (22 février 2022) : 5843–48. http://dx.doi.org/10.1093/mnras/stac448.
Texte intégralRésumé :
ABSTRACT The observed rapid cooling of the neutron star Cassiopeia A is usually interpreted as being caused by transitions of neutrons and protons in the star’s core from the normal state to the superfluid and superconducting state. However, this so-called ‘minimal’ cooling paradigm faces the problem of numerically simulating the observed anomalously fast drop in the neutron star surface temperature using theoretical neutrino energy losses from superfluid neutrons. As a solution to this problem, I propose a somewhat more complex cooling model, in which, in addition to superfluid neutrons, direct Urca processes from a very small central part of the neutron star core are also involved. Numerical simulations of the cooling trajectory in this scenario show excellent agreement with observations of the Cassiopeia A neutron star. The proposed cooling scenario unambiguously relates the used equation of state and the mass of the neutron star. For a neutron star constructed according to BSk25 equation of state, the most appropriate are the mass $M=1.62\, {\rm M}_{\odot }$ and the radius R = 12.36 km. If BSk24 equation of state is used, then the most suitable solution is $M=1.60\, {\rm M}_{\odot }$ and R = 12.55 km.
12
Grenci, N., D. Cortes et M. Flaska. « Design of an epithermal neutron velocity selection system for the Penn State Breazeale Reactor ». Journal of Instrumentation 18, no 06 (1 juin 2023) : P06035. http://dx.doi.org/10.1088/1748-0221/18/06/p06035.
Texte intégralRésumé :
Abstract A series of mechanical neutron choppers to operate as a velocity selection system have been developed for the Pennsylvania State Breazeal Reactor (PSBR). This chopper system will provide pulsed epithermal neutrons in the energy range of 0.5–40 eV with 2% or better energy resolution, and with a transmission of 1E-6 or better. Four different chopper geometries have been evaluated for their utility as mechanical neutron choppers. Specifically, Fermi, ring, piston, and disc choppers have been evaluated to assess their potential neutronics performance and mechanical constructability. A series of high-speed disc choppers were selected for the final design, and optimization work was performed to maximize the neutron pulse intensity. It is estimated that the optimized system will produce an epithermal neutron intensity of approximately 96 n/s. This system can also be operated in a time of flight (TOF) configuration such that the neutrons arriving at the source have a white spectrum. This operation can be accomplished by leaving the second stage of choppers in the open position, or by removing it from the beam completely. Such unique source of epithermal neutrons produced by this chopper system will have applications in both prompt and delayed epithermal neutron activation analysis (ENAA), as well as in neutron resonance transmission analysis (NRTA).
13
Ghosh, Sayan, Abhijit Bandyopadhyay, Pijushpani Bhattacharjee, Sovan Chakraborty, Kamales Kar et Satyajit Saha. « Simulation of Nuclear Recoils due to Supernova Neutrino-induced Neutrons in Liquid Xenon Detectors ». Journal of Physics : Conference Series 2156, no 1 (1 décembre 2021) : 012135. http://dx.doi.org/10.1088/1742-6596/2156/1/012135.
Texte intégralRésumé :
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.
14
Kulikov, Gennady G., Anatoly N. Shmelev, Vladimir A. Apse et Evgeny G. Kulikov. « On a significant slowing-down of the kinetics of fast transient processes in a fast reactor ». Nuclear Energy and Technology 6, no 4 (20 novembre 2020) : 295–98. http://dx.doi.org/10.3897/nucet.6.60379.
Texte intégralRésumé :
The kinetics of nuclear reactors is determined by the average neutron lifetime. When the inserted reactivity is more than the effective delayed neutron fraction, the reactor kinetics becomes very rapid. It is possible to slow down the fast reactor kinetics by increasing the neutron lifetime. The authors consider the possibility of using the lead isotope, 208Pb, as a neutron reflector with specific properties in a lead-cooled fast reactor. To analyze the emerging effects in a reactor of this type, a point kinetics model was selected, which takes into account neutrons returning from the 208Pb reflector to the reactor core. Such specific properties of 208Pb as the high atomic weight and weak neutron absorption allow neutrons from the reactor core to penetrate deeply into the 208Pb reflector, slow down in it, and have a noticeable probability to return to the reactor core and affect the chain fission reaction. The neutrons coming back from the 208Pb reflector have a long ‘dead-time’, i.e., the sum of times when neutrons leave the reactor core, entering the 208Pb reflector, and then diffuse back into the reactor core. During the ‘dead-time’, these neutrons cannot affect the chain fission reaction. In terms of the delay time, the neutrons returning from the deep layers of the 208Pb reflector are close to the delayed neutrons. Moreover, the number of the neutrons coming back from the 208Pb reflector considerably exceeds the number of the delayed neutrons. As a result, the neutron lifetime formed by the prompt neutron lifetime and the ‘dead-time’ of the neutrons from the 208Pb reflector can be substantially increased. This will lead to a longer reactor acceleration period, which will mitigate the effects of prompt supercriticality. Thus, the use of 208Pb as a neutron reflector can significantly improve the fast reactor nuclear safety.
15
Zhou, Xue Mei, Gui Min Liu et Ya Fen Liu. « Study on Neutron Energy Spectrum in the TMSR ». Applied Mechanics and Materials 239-240 (décembre 2012) : 287–92. http://dx.doi.org/10.4028/www.scientific.net/amm.239-240.287.
Texte intégralRésumé :
Neutron energy spectrum has a high correlation with all kinds of nuclear processes in nuclear reactor. Neutron energy spectrums of the TMSR in some conditions were simulated using MCNP5.The distributions of thermal neutrons, epithermal and resonance neutrons, and fast neutrons in axial and radial were simulated, respectively. The simulation results indicate that thermal neutrons have a high ratio and control rods inserting the nuclear reactor have a serious effect on neutron distribution. The study of neutron energy spectrum is theoretical basis for measurement in the TMSR.
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Ho, Wynn C. G., Craig O. Heinke, Daniel J. Patnaude, Peter S. Shternin et Dmitry G. Yakovlev. « Hottest Superfluid and Superconductor in the Universe : Lessons from the Cooling of the Cassiopeia A Neutron Star ». Proceedings of the International Astronomical Union 7, S285 (septembre 2011) : 337–39. http://dx.doi.org/10.1017/s1743921312000981.
Texte intégralRésumé :
AbstractThe cooling rate of young neutron stars gives direct insight into their internal makeup. Using Chandra observations of the 330-year-old Cassiopeia A supernova remnant, we find that the temperature of the youngest-known neutron star in the Galaxy has declined by 4% over the last 10 years. The decline is explained naturally by superconductivity and superfluidity of the protons and neutrons in the stellar core. The protons became superconducting early in the life of the star and suppressed the early cooling rate; the neutron star thus remained hot before the (recent) onset of neutron superfluidity. Once the neutrons became superfluid, the Cooper pair-formation process produced a splash of neutrino emission which accelerated the cooling and resulted in the observed rapid temperature decline. This is the first time a young neutron star has been seen to cool in real time, and is the first direct evidence, from cooling observations, of superfluidity and superconductivity in the core of neutron stars.
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Abe, K., Y. Haga, Y. Hayato, K. Hiraide, K. Ieki, M. Ikeda, S. Imaizumi et al. « Neutron tagging following atmospheric neutrino events in a water Cherenkov detector ». Journal of Instrumentation 17, no 10 (1 octobre 2022) : P10029. http://dx.doi.org/10.1088/1748-0221/17/10/p10029.
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Abstract We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218±9 μs.
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Ozawa, Naohiro. « The Emergence of Weak Interaction ». Hyperscience International Journals 2, no 3 (septembre 2022) : 108–14. http://dx.doi.org/10.55672/hij2022pp108-114.
Texte intégralRésumé :
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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Bedenko, Sergey V., Vladimir V. Knyshev, Mariya Ye Kuznetsova, Igor O. Lutsik et Igor V. Shamanin. « Peculiarities of the radiation formation in dispersed microencapsulated nuclear fuel ». Nuclear Energy and Technology 5, no 1 (20 mars 2019) : 23–29. http://dx.doi.org/10.3897/nucet.5.33978.
Texte intégralRésumé :
A computational study has been performed for various options of the thorium reactor core loading. Neutronic studies of fuel have been conducted, its isotopic composition has been calculated, and the alpha emitters and the sources of neutron and photon radiation in the microencapsulated nuclear fuel have been analyzed. The studies had the purpose of developing the methodology used to estimate the radiation characteristics of nuclear fuel with a complex inner structure. Emphasis is placed on calculating the quantitative and spectral composition of the neutrons formed as the result of (a, n) reactions on small- and average-mass nuclei. The ratio of the quantity of the neutrons resulting from the (a, n) reactions to the quantity of the neutrons formed as the result of spontaneous fission has been calculated for fuel with heterogeneous and homogeneous arrangements of fissionable and structural elements. The developed tools will make it possible to estimate the neutron radiation dose, to revise the traditional fresh and spent fuel handling procedures, and to estimate, using the Rossi alpha method, the neutron multiplication factor in deeply subcritical systems. The neutron yield and spectrum were calculated using an analytical model and verified codes such as WIMS-D5B, ORIGEN-APP, SOURCES-4C and SRIM-2013.
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Usoskin, I. G., G. A. Kovaltsov, H. Kananen et P. Tanskanen. « The World Neutron Monitor Network as a tool for the study of solar neutrons ». Annales Geophysicae 15, no 4 (30 avril 1997) : 375–86. http://dx.doi.org/10.1007/s00585-997-0375-9.
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Abstract. The use of the World Neutron Monitor Network to detect high-energy solar neutrons is discussed in detail. It is shown that the existing network can be used for the routine detection of intense sporadic solar-neutron events whenever they occur. A technique is suggested involving the weighted summation of responses of separate monitors to solar neutrons. It is demonstrated that the use of this method improves the significance of solar-neutron event detection. Different results of the simulation of the neutron-monitor sensitivity to solar neutrons have been tested with respect to their application for practical use. It is shown that the total number of neutrons with energy above 300 MeV injected from the Sun during a solar flare can be estimated directly from the time-integrated neutron-monitor response to solar neutrons without any model assumptions. The estimation technique has been developed.
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Šagátová, Andrea, Marko Fülöp, Andrej Novák, Branislav Vrban, Jakub Lüley, Štefan Čerba, Ivan Benkovský et Bohumír Zaťko. « Conversion of fast neutrons for neutron radiography with TPX2 detector ». Nukleonika 69, no 2 (1 juin 2024) : 135–40. http://dx.doi.org/10.2478/nuka-2024-0020.
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Abstract The Timepix2-based hybrid-pixel detector with a 500 μm thick silicon sensor was employed for fast-neutrons registration to be applied in neutron radiography of metallic printed circuit heat exchanger (PCHE). Two energies of neutrons were experimentally tested. The detection of 3.55 MeV neutrons from the deuteron–deuteron (DD) reaction was compared to 15.7 MeV neutrons from the deuteron–tritium (DT) neutron generator. In order to distinguish the signal induced by the registered neutrons from the accelerator background, filtration of the recorded particle spectral tracks was applied. The benefit of applying hydrogen-based converter layer for 3.55 MeV neutrons was observable. On the other hand, in the case of 15.7 MeV neutrons, the direct registration by interaction with the sensor Si significantly dominates the conversion.
22
Mahdavi, Mohammad, et Maryam Shahbahrami. « Multiplication of Fast Neutrons Source Flux by Using Deuterium-Helium-3 Plasma ». ISRN High Energy Physics 2013 (30 mai 2013) : 1–4. http://dx.doi.org/10.1155/2013/689739.
Texte intégralRésumé :
The production of fast neutrons source is examined by using a thermal neutron flux inside plasma. In order to reach a favorable yield of fast neutrons flux, the parameters such as energy loss rate, reaction probability, and neutron absorption length are calculated. The nuclear conversion efficiency, , of thermal neutron to fast neutrons is obtained to be by calculating the physical parameters for the plasma designed.
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Mumpower, Matthew R., Tsung-Shung H. Lee, Nicole Lloyd-Ronning, Brandon L. Barker, Axel Gross, Samuel Cupp et Jonah M. Miller. « Let There Be Neutrons ! Hadronic Photoproduction from a Large Flux of High-energy Photons ». Astrophysical Journal 982, no 2 (20 mars 2025) : 81. https://doi.org/10.3847/1538-4357/adb1e3.
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Abstract We propose that neutrons may be generated in high-energy, high-flux photon environments via photo-induced reactions on pre-existing baryons. These photohadronic interactions are expected to occur in astrophysical jets and surrounding material. Historically, these reactions have been attributed to the production of high-energy cosmic rays and neutrinos. We estimate the photoproduction off of protons in the context of gamma-ray bursts, where it is expected there will be sufficient baryonic material that may be encompassing or entrained in the jet. We show that typical stellar baryonic material, even material completely devoid of neutrons, can become inundated with neutrons in situ via hadronic photoproduction. Consequently, this mechanism provides a means for collapsars and other astrophysical sites containing substantial flux of high-energy photons to be favorable for neutron-capture nucleosynthesis.
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Ma, Baolong, Yujiro Ikeda, Yoshie Otake, Makoto Teshigawara, Yasuo Wakabayashi, Masahide Harada, Motoki Ooi, Takao Hashiguchi, Yutaka Yamagata et Shin Takeda. « Slab geometry type cold neutron moderator development based on neutronic study for Riken Accelerator-driven compact Neutron Source (RANS) ». EPJ Web of Conferences 231 (2020) : 04004. http://dx.doi.org/10.1051/epjconf/202023104004.
Texte intégralRésumé :
Cold neutrons with energy less than several meV are good probes for material research, and they have been available on large neutron facilities, whereas it is not commonly available on compact accelerator-driven neutron source. RIKEN Accelerator-driven Neutron Source (RANS) is a pulsed neutron facility which provides thermal neutrons and high energy neutrons at several MeV. We started a project to implement a cold neutron moderator for RANS to broaden cold neutrons applications. A cold neutron moderator system with a mesitylene moderator at 20K and a polyethylene pre-moderator at room temperature in the slab geometry was designed for RANS. So far, the thickness of the pre-moderator and mesitylene have been optimized to get the highest cold neutron flux by using a Monte Carlo simulation code, PHITS. Graphite reflector dimensions were also proven to have significant effect to increase the cold neutron intensity.
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Kotila, Jenni. « Rare weak decays and neutrino mass ». Journal of Physics : Conference Series 2453, no 1 (1 mars 2023) : 012012. http://dx.doi.org/10.1088/1742-6596/2453/1/012012.
Texte intégralRésumé :
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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Chen, Zekun, Konstantin Kouzakov, Yu-Feng Li, Vadim Shakhov, Konstantin Stankevich et Alexander Studenikin. « Collective neutrino oscillations in moving and polarized matter ». Journal of Physics : Conference Series 2156, no 1 (1 décembre 2021) : 012180. http://dx.doi.org/10.1088/1742-6596/2156/1/012180.
Texte intégralRésumé :
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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Khalimonchuk, V. A. « Mid-Weighed Kinetic Parameters for Use in the Two-Group Diffusion Model of Reactor Dynamics with Fuel Based on a Mixture of Fission Isotopes ». Nuclear and Radiation Safety, no 1(81) (12 mars 2019) : 58–61. http://dx.doi.org/10.32918/nrs.2019.1(81).10.
Texte intégralRésumé :
In the model of reactor kinetics based on the description of neutron transport in the two-group diffusion approximation, the number of equations describing the change in the concentration of delayed neutron precursors depends not only on the number of groups of delayed neutrons, but also on the number of fissile isotopes present in nuclear fuel. Since each isotope is characterized by six groups of delayed neutrons, the total number of differential equations describing concentrations of delayed neutron precursors is equal to the product of the number of fissile isotopes (M) and the number of groups of delayed neutrons for each isotope (i = 6). This is true provided that the decay constant of the concentrations of delayed neutron precursors that were formed from the division by fast or thermal neutrons can be taken in the same way. In fact, there is a difference, though small, in these values for the two energy groups. Therefore, the number of the corresponding equations is twice as high. In this paper, a mathematical expression is obtained for the weighted average decay constant of delayed neutron predecessors from fission by fast and thermal neutrons in a multiplying medium with several fissile isotopes. This, together with the conventional procedure of weighing the fraction of delayed neutrons from fission by fast or thermal neutrons in a similar multiplying medium, allows the two-group diffusion model of the reactor kinetics to be limited to only six equations for the concentrations of delayed neutron precursors and thus the kinetic model of the reactor to be simplified.
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Roberts, Joyce A. « The Manuel Lujan Jr. Neutron Scattering Center ». MRS Bulletin 22, no 9 (septembre 1997) : 42–46. http://dx.doi.org/10.1557/s0883769400033996.
Texte intégralRésumé :
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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Broussard, L. J., K. M. Bailey, W. B. Bailey, J. L. Barrow, K. Berry, A. Blose, C. Crawford et al. « New search for mirror neutron regeneration ». EPJ Web of Conferences 219 (2019) : 07002. http://dx.doi.org/10.1051/epjconf/201921907002.
Texte intégralRésumé :
The possibility of relatively fast neutron oscillations into a mirror neutron state is not excluded experimentally when a mirror magnetic field is considered. Direct searches for the disappearance of neutrons into mirror neutrons in a controlled magnetic field have previously been performed using ultracold neutrons, with some anomalous results reported. We describe a technique using cold neutrons to perform a disappearance and regeneration search, which would allow us to unambiguously identify a possible oscillation signal. An experiment using the existing General Purpose-Small Angle Neutron Scattering instrument at the High Flux Isotope Reactor at Oak Ridge National Laboratory will have the sensitivity to fully explore the parameter space of prior ultracold neutron searches and confirm or refute previous claims of observation. This instrument can also conclusively test the validity of recently suggested oscillation-based explanations for the neutron lifetime anomaly.
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Andrianova, Olga N., Evgeniya S. Teplukhina, Gennady M. Zherdev, Zhanna V. Borovskaya et Andrey P. Zhirnov. « Precision neutronic calculations of experiments on the neutron transmission through the reflector layers at the BFS critical facilities for expanding the verification database to justify lead cooled fast reactor designs ». Nuclear Energy and Technology 6, no 4 (20 novembre 2020) : 269–74. http://dx.doi.org/10.3897/nucet.6.60303.
Texte intégralRésumé :
The paper presents the results of the efforts concerned with expanding the verification database and estimating the calculation uncertainty of the power density in the steel reflector of lead cooled fast reactor designs based on experiments performed in different years at the BFS critical assemblies by analyzing and revising earlier calculation and experimental studies on the transmission of neutrons through the steel reflector layers. The discussion includes experiments at the BFS-66 critical assembly to model neutron and photon fluxes in the reactor core shielding compositions, as well as experiments at the BFS-64 and BFS-80-2 critical assemblies to model the transmission of neutrons and gamma quanta through the reflector layers of various materials. The information provided in earlier materials with the descriptions of the above experiments has been analyzed and expanded through respective data required to prepare precision calculation models for Monte-Carlo neutronic codes. Precision neutronic models have been developed based on actualized and updated data with a detailed description of the BFS heterogeneous structure and experimental devices, and test calculations have been carried out to confirm their efficiency. The calculations of key neutronic characteristics measured at the BFS-66, -64 and -80-2 assemblies were performed using codes based on the Monte Carlo method (MCU-BR, MCNP, MMK-RF, MMK-ROKOKO) with BNAB-RF and MDBBR50 neutron data and the ROSFOND evaluated neutron data library. The developed precision calculation neutronic models of the experiments discussed can be used to justify lead cooled fast reactor designs, to verify neutronic codes and neutron data, and to evaluate the associated uncertainties.
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Tingsuwatit, A., A. Maity, S. J. Grenadier, J. Li, J. Y. Lin et H. X. Jiang. « Boron nitride neutron detector with the ability for detecting both thermal and fast neutrons ». Applied Physics Letters 120, no 23 (6 juin 2022) : 232103. http://dx.doi.org/10.1063/5.0093591.
Texte intégralRésumé :
The detection of fast neutrons is regarded technically challenging because the interaction probability of fast neutron with matter is extremely low. Based on our recent development of hexagonal boron nitride (BN) semiconductor thermal neutron detectors with a record high efficiency of 59%, we report here the feasibility studies of BN detectors for detecting fast neutrons. A BN detector with a detection area of 2.1 cm2 was fabricated from a 90 μm thick BN epilayer. In the presence of a bare Cf-252 source emitting fast neutrons ranging from 1 to 9 MeV, the detection efficiency was estimated to be about 0.1%. The measured mean free path of fast neutron in BN is about 7.6 cm. Together with the capability of BN for thermal neutron detection, the present results indicate that by incorporating BN with a large thickness, BN neutron detectors are expected to possess the unique capability of directly detecting thermal to fast neutrons as well as outstanding features resulting from the ultrawide bandgap of BN. The identification of a single material that is sensitive to both thermal and fast neutrons is valuable for the development of novel neutron detection technologies.
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Kulikov, G. G., A. N. Shmelev et V. A. Apse. « Improving Nuclear Safety of Fast Reactors by Slowing Down Fission Chain Reaction ». International Journal of Nuclear Energy 2014 (16 octobre 2014) : 1–18. http://dx.doi.org/10.1155/2014/373726.
Texte intégralRésumé :
Light materials with small atomic mass (light or heavy water, graphite, and so on) are usually used as a neutron reflector and moderator. The present paper proposes using a new, heavy element as neutron moderator and reflector, namely, “radiogenic lead” with dominant content of isotope 208Pb. Radiogenic lead is a stable natural lead. This isotope is characterized by extremely low micro cross-section of radiative neutron capture (~0.23 mb) for thermal neutrons, which is smaller than graphite and deuterium cross-sections. The reflector-converter for a fast reactor core is the structure capable of transforming some part of prompt neutrons leaked from the core into the reflected neutrons with properties similar to those of delayed neutrons, that is, sufficiently large contribution to reactivity at the level of effective fraction of delayed neutrons and relatively long lifetime, comparable with lifetimes of radionuclides-emitters of delayed neutrons. It is evaluated that the use of radiogenic lead makes it possible to slow down the chain fission reaction on prompt neutrons in the fast reactor. This can improve the fast reactor safety and reduce some requirements to the technologies used to fabricate fuel for the fast reactor.
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Kasilov, Valentin, Sergey Gokov, Sergiy Kalenik, Sergey Kochetov, Leonid Saliy, Vitaliy Tsyats'ko, Evgen Tsyats'ko et Oleg Shopen. « Concept of Neutron Source Creation for Nuclear Medicine on the Basis of Linear Electron Accelerator ». 4, no 4 (10 décembre 2021) : 160–63. http://dx.doi.org/10.26565/2312-4334-2021-4-21.
Texte intégralRésumé :
We review the current status of the development of sources of epithermal neutrons sources based on reactors and accelerators for boron neutron capture therapy (BNCT), a promising method of malignant tumor treatment. The scheme is proposed of the source prototype for the production of thermal and epithermal neutrons using the delayed neutrons generated with help of linear electron accelerator at the target containing the fissile material. The results of an experiment are presented in which the half-life curves of radioactive nuclei formed during fission and emitting delayed neutrons are measured. It is shown that an activated target containing fissile material is a compact small-sized source of delayed neutrons. It can be delivered to the shaper, where, using a moderator, an absorber, and a collimator, neutrons of thermal or epithermal energies are formed over a certain period of time, after which this target is sent to the activator, and another target comes in its place. Thus, a pulsed neutron flux is formed. Such a neutron beam can be used in nuclear medicine, in particular, in neutron capture therapy in the treatment of cancer. An important task in the implementation of neutron capture therapy, when irradiating patients, is to control both the intensity and the energy spectrum of the neutron flux. To solve this problem, an earlier developed activation-type neutron ball spectrometer can be used, which will allow optimization of various parameters of the shaper, collimator and filters in order to obtain the most powerful neutron fluxes.
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Hälg, Roger Antoine, et Uwe Schneider. « Neutron dose and its measurement in proton therapy—current State of Knowledge ». British Journal of Radiology 93, no 1107 (mars 2020) : 20190412. http://dx.doi.org/10.1259/bjr.20190412.
Texte intégralRésumé :
Proton therapy has shown dosimetric advantages over conventional radiation therapy using photons. Although the integral dose for patients treated with proton therapy is low, concerns were raised about late effects like secondary cancer caused by dose depositions far away from the treated area. This is especially true for neutrons and therefore the stray dose contribution from neutrons in proton therapy is still being investigated. The higher biological effectiveness of neutrons compared to photons is the main cause of these concerns. The gold-standard in neutron dosimetry is measurements, but performing neutron measurements is challenging. Different approaches have been taken to overcome these difficulties, for instance with newly developed neutron detectors. Monte Carlo simulations is another common technique to assess the dose from secondary neutrons. Measurements and simulations are used to develop analytical models for fast neutron dose estimations. This article tries to summarize the developments in the different aspects of neutron dose in proton therapy since 2017. In general, low neutron doses have been reported, especially in active proton therapy. Although the published biological effectiveness of neutrons relative to photons regarding cancer induction is higher, it is unlikely that the neutron dose has a large impact on the second cancer risk of proton therapy patients.
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Kelly, Keegan J., Matthew Devlin, Jaime A. Gomez, John M. O’Donnell, Terry N. Taddeucci, Robert C. Haight, Hye Young Lee et al. « Measurements of the Prompt Fission Neutron Spectrum at LANSCE : The Chi-Nu Experiment ». EPJ Web of Conferences 193 (2018) : 03003. http://dx.doi.org/10.1051/epjconf/201819303003.
Texte intégralRésumé :
The goal of the Chi-Nu experiment at the Los Alamos Neutron Science Center is to measure the prompt fission neutron spectra from major actinides using a double time-of-flight method with a pulsed, white incoming neutron source. Fission events are detected with a parallel-plate avalanche counter and outgoing neutrons are detected with either a 6Li-glass or liquid scintillator detector array for low- or high-energy neutrons, respectively. A detector response matrix for the interaction of neutrons with the experimental environment for neutrons measured with the Chi-Nu 6Li-glass detector array has been calculated to obtain a full understanding of the measured Chi-Nu data and also to allow for nearly instantaneous production of simulated Chi-Nu data spectra. Prompt fission neutron spectra corresponding to 19 incoming neutron energy ranges from 0.7-20 MeV have been extracted using the ratio-of-ratios method with Chi-Nu 6Li-glass data on the neutron-induced fission of 235U.
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Namakonov, V., S. Andreyev, D. Gabbasov, A. Moseyeva et D. Sergina. « MEASUREMENT OF 14 MEV NEUTRONS TRANSMISSION THROUGH LITHIUM HYDRIDE LAYERS WITH TIME-OF-FLIGHT METHOD ». PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. SERIES : NUCLEAR AND REACTOR CONSTANTS 2020, no 4 (26 décembre 2020) : 33–39. http://dx.doi.org/10.55176/2414-1038-2020-4-33-39.
Texte intégralRésumé :
The results of experiments on transmission of 14 MeV neutrons through lithium hydride layers of thickness up to 25 cm are presented in the article. The measurements were performed with time-of-flight method on a pulse channel of neutron generator NG-12I. The operating mode of the neutron generator is pulse-periodic. Neutrons passing through the layers of Li hydrides were registered by detector based on a 70×70 mm stilbene crystal scintillator. NIM standard modules were used as measuring equipment. The neutron yield from the generator target was estimated by neutron monitor with a fluorine plastic activation detector. Activity of radiation-exposed neutron activation detectors was measured using a gamma spectrometer with high purity germanium detector (HPGe). The averaged 14 MeV neutrons flux from the target was ∼2⋅108 n/s. The measurement results were used to obtain instrumental neutron spectra for samples of various thicknesses and to estimate coefficients of 14 MeV neutrons passing through the layers of Li hydrides. The obtained results can be used for validation of neutron-physical calculations and for improvement of neutron constants libraries.
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Mozafari Vanani, M. J., Y. Kasesaz, M. Hosseinipanah et A. Akhound. « Collimated neutron beam design for TRR thermal column ». Journal of Instrumentation 16, no 12 (1 décembre 2021) : P12023. http://dx.doi.org/10.1088/1748-0221/16/12/p12023.
Texte intégralRésumé :
Abstract Tehran Research Reactor (TRR) is the main neutron source in Iran which can be used for different applications of neutrons such as neutron radiography and neutron therapy. TRR has a thermal column which can provide high intensity flux of thermal neutrons for users. The aim of this study is to design a neutron collimator for TRR thermal column to produce parallel neutron beam with suitable intensity of thermal neutrons. To achieve this goal, Monte Carlo code of MCNX has been used to evaluate different configurations, geometries and materials of neutron collimator. The results show that the final selected configuration can provide a uniform thermal neutron beam with a flux of 1.21E+13 (cm-2·s-1) which is suitable for many different neutron applications.
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GOLDBERG, HAIM. « TEV ANTINEUTRINOS FROM CYGNUS OB2 ». International Journal of Modern Physics A 20, no 06 (10 mars 2005) : 1132–39. http://dx.doi.org/10.1142/s0217751x05024006.
Texte intégralRésumé :
High energy cosmic ray experiments have identified an excess from the region of the Galactic Plane in a limited energy range around 1018 eV ( EeV ). This is very suggestive of neutrons as candidate primaries, because the directional signal requires relatively-stable neutral primaries, and time-dilated neutrons can reach Earth from typical Galactic distances when the neutron energy exceeds an EeV . We here point out that if the Galactic messengers are neutrons, then those with energies below an EeV will decay in flight, providing a flux of cosmic antineutrinos above a TeV which is observable at a kilometer-scale neutrino observatory. The expected event rate per year above 1 TeV in a detector such as IceCube, for example, is 20 antineutrino showers (all flavors) and a 1° directional signal of [Formula: see text] events. A measurement of this flux can serve to identify the first extraterrestrial point source of TeV antineutrinos.
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Morris, Elizabeth M., et J. David Cooper. « Density measurements in ice boreholes using neutron scattering ». Journal of Glaciology 49, no 167 (2003) : 599–604. http://dx.doi.org/10.3189/172756503781830403.
Texte intégralRésumé :
AbstractThis paper describes the use of a neutron probe to measure detailed stratigraphy in ice and snow. The Wallingford neutron probe, developed for measurement of soil moisture, consists of an annular radioactive source of fast neutrons around the centre of a cylindrical detector for slow (thermal) neutrons. In snow and ice, the fast neutrons lose energy by scattering from hydrogen atoms, and the number of slow neutrons arriving at the detector (the count rate) is related to the density of the medium. Calibration equations for count rate as a function of snow density and borehole diameter have been derived. Snow-density profiles from boreholes obtained using the probe show that, despite the smoothing produced by the neutron-scattering process, annual variations in density can be resolved. The potential contribution of the neutron probe to improvements in mass-balance monitoring is discussed.
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Kulikov, Gennady G., Anatoly N. Shmelev, Vladimir A. Apse et Evgeny G. Kulikov. « Safety features of fast reactor with heavy atomic weight weakly neutron absorbing reflector ». Nuclear Energy and Technology 6, no 1 (11 mars 2020) : 15–21. http://dx.doi.org/10.3897/nucet.6.50867.
Texte intégralRésumé :
The purpose of the present study is the justification of the possibility of improving fast reactor safety by surrounding reactor cores with reflectors made of material with special neutron physics properties. Such properties of 208Pb lead isotope as heavy atomic weight, small neutron absorption cross section, and high inelastic scattering threshold result in certain peculiarities in neutron kinetics of the fast reactor equipped with 208Pb reflector, which can significantly enhance reactor safety. The reflector will also make possible generation of additional delayed neutrons characterized by the “dead” time. This will improve the resistibility of the fission chain reaction to stepwise reactivity excursions and exclude prompt supercriticality. Let us note that generation of additional delayed neutrons can be shaped by reactor designers. The relevance of the study amounts to the fact that generation of additional delayed neutrons in the reflector will make it possible mitigating the consequences of a reactivity accident even if the introduced reactivity exceeds the effective fraction of delayed neutrons. At the same time, the role of the fraction of delayed neutrons as the maximum permissible reactivity for reactor safety is depreciated. Scientific originality of the study pertains to the fact that the problem of yield of additional neutrons with properties close to normal delayed neutrons, has not been posed before. The authors suggest a new method for enhancing safety of fast reactors by increasing the fraction of delayed neutrons due to the time delay of prompt neutrons during their transfer in the reflector. In order to benefit from the expected advantages, the following combination is acceptable: lead enriched by 208Pb is used as a neutron reflector while natural lead or other material (sodium, etc.) is used as a coolant in the reactor core.
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Potashev, S., Y. Burmistrov, A. Drachev, S. Karaevsky, E. Konobeevski, A. Kasparov, I. Meshkov et al. « A Possibility of Detecting Fast Neutrons in a 10B Solid-gas Detector ». KnE Energy 3, no 1 (9 avril 2018) : 115. http://dx.doi.org/10.18502/ken.v3i1.1732.
Texte intégralRésumé :
The possibility of detecting thermal and fast neutrons in 10B solid-gas detector is considered. The simulation of the neutron detection process shows a significant difference in the detector signals caused by neutrons of different energies. An experimental verification of the detector’s operation was performed using W-Be photoneutron source with different ratio of fast and thermal neutrons incident on the detector. The measured amplitude spectra of the signals for different neutron energies were compared with the simulation results. The qualitative agreement between experimental and calculated data indicates the possibility of using this detector for recording thermal and fast neutrons.
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Fragopoulou, M., V. Konstantakos, M. Zamani, S. Siskos, T. Laopoulos et G. Sarrabayrouse. « High sensitive depleted MOSFET-based neutron dosimetry ». HNPS Proceedings 18 (23 novembre 2019) : 145. http://dx.doi.org/10.12681/hnps.2562.
Texte intégralRésumé :
A new dosemeter based on a depleted Metal-Oxide-Semiconductor field effect transistor, sensitive to both neutrons and gamma radiation was manufactured at LAAS-CNRS Laboratory, Toulouse France. In order to be used for neutron dosimetry a thin film of lithium fluoride was deposited on the surface of the gate of the device. The characteristics of the dosemeter such as its response to neutron dose were investigated. The response in thermal neutrons was found to be high. In fast neutrons the response was lower than that of thermal neutrons but higher than the one presented in literature.
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Gutiérrez, Miguel, Manuel Masip et Sergio Muñoz. « The Solar Disk at High Energies ». Astrophysical Journal 941, no 1 (1 décembre 2022) : 86. http://dx.doi.org/10.3847/1538-4357/aca020.
Texte intégralRésumé :
Abstract High energy cosmic rays illuminate the Sun and produce an image that could be observed in up to five different channels: a cosmic-ray shadow (whose energy dependence has been studied by HAWC); a gamma-ray flux (observed at E ≤ 200 GeV by Fermi-LAT); a muon shadow (detected by ANTARES and IceCube); a neutron flux (undetected, as there are no hadronic calorimeters in space); a flux of high energy neutrinos. Since these signals are correlated, the ones already observed can be used to reduce the uncertainty in the still undetected ones. Here we define a simple setup that uses the Fermi-LAT and HAWC observations to imply very definite fluxes of neutrons and neutrinos from the solar disk. In particular, we provide a fit of the neutrino flux at 10 GeV–10 TeV that includes its dependence on the zenith angle and on the period of the solar cycle. This flux represents a neutrino floor in indirect dark matter searches. We show that in some benchmark models the current bounds on the dark matter–nucleon cross section push the solar signal below this neutrino floor.
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Delapalme, A. « Use of Extinction Corrections in Neutron Diffraction Experiments ». Australian Journal of Physics 41, no 3 (1988) : 383. http://dx.doi.org/10.1071/ph880383.
Texte intégralRésumé :
The study of extinction by neutrons reveals many features of the extinction problem: theory and practical cases, polarised and unpolarised neutron cases. Special attention is given to the usual extinction corrections for neutron diffraction experiments, showing the relative importance of structure factor, wavelength, Lorentz factor, mosaic and the path of neutrons through the crystal. Two problems are reviewed: (a) how to detect the presence of extinction in both cases of a single crystal experiment with polarised and unpolarised neutrons; and (b) after experimental evidence for extinction in a neutron diffraction experiment, how to follow a reliable way to correct the neutron diffraction data in both cases of polarised and unpolarised neutron experiments. Some examples are given.
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Rasche, Daniel, Markus Köhli, Martin Schrön, Theresa Blume et Andreas Güntner. « Towards disentangling heterogeneous soil moisture patterns in cosmic-ray neutron sensor footprints ». Hydrology and Earth System Sciences 25, no 12 (22 décembre 2021) : 6547–66. http://dx.doi.org/10.5194/hess-25-6547-2021.
Texte intégralRésumé :
Abstract. Cosmic-ray neutron sensing (CRNS) allows for non-invasive soil moisture estimations at the field scale. The derivation of soil moisture generally relies on secondary cosmic-ray neutrons in the epithermal to fast energy ranges. Most approaches and processing techniques for observed neutron intensities are based on the assumption of homogeneous site conditions or of soil moisture patterns with correlation lengths shorter than the measurement footprint of the neutron detector. However, in view of the non-linear relationship between neutron intensities and soil moisture, it is questionable whether these assumptions are applicable. In this study, we investigated how a non-uniform soil moisture distribution within the footprint impacts the CRNS soil moisture estimation and how the combined use of epithermal and thermal neutrons can be advantageous in this case. Thermal neutrons have lower energies and a substantially smaller measurement footprint around the sensor than epithermal neutrons. Analyses using the URANOS (Ultra RApid Neutron-Only Simulation) Monte Carlo simulations to investigate the measurement footprint dynamics at a study site in northeastern Germany revealed that the thermal footprint mainly covers mineral soils in the near-field to the sensor while the epithermal footprint also covers large areas with organic soils. We found that either combining the observed thermal and epithermal neutron intensities by a rescaling method developed in this study or adjusting all parameters of the transfer function leads to an improved calibration against the reference soil moisture measurements in the near-field compared to the standard approach and using epithermal neutrons alone. We also found that the relationship between thermal and epithermal neutrons provided an indicator for footprint heterogeneity. We, therefore, suggest that the combined use of thermal and epithermal neutrons offers the potential of a spatial disaggregation of the measurement footprint in terms of near- and far-field soil moisture dynamics.
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Agafonova, Natalia, Walter Fulgione, Alexey Malgin, Konstantin Manukovskiy, Olga Ryazhskaya, Stanley Yen et Andrey Yudin. « Possible explanation of the neutrino signal from SN1987A detected with the LSD ». EPJ Web of Conferences 191 (2018) : 03004. http://dx.doi.org/10.1051/epjconf/201819103004.
Texte intégralRésumé :
On February 23 1987 in 2:52 UT the neutrino telescope LSD under Mont Blanc detected neutrino signal, which could not be explained within the framework of the standard collapse model. We show that the LSD signal could be a consequence of the detection of gamma-quanta emitted from neutron-capture reactions on by iron nuclei contained in the composition of the experimental setup. Neutrons are produced in neutrino-nuclei reactions in the surrounding granite rock and steel structures of the detector.
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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 et O. A. Shopen. « Thermal and Epithermal Neutron Generation for Nuclear Medicine Using Electron Linear Accelerator ». East European Journal of Physics 3, no 3 (14 décembre 2016) : 64–72. http://dx.doi.org/10.26565/2312-4334-2016-3-05.
Texte intégralRésumé :
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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Liu, Yang, Zhen Ni Xing et Guo Zheng Zhu. « Low-Flux Neutron Radiation Detection Technology with High Sensitivity ». Applied Mechanics and Materials 668-669 (octobre 2014) : 924–27. http://dx.doi.org/10.4028/www.scientific.net/amm.668-669.924.
Texte intégralRésumé :
Boron-containing plastic scintillator detectors have a high detection efficiency for low-intensity thermal neutrons and fast neutrons which is currently the preferred types of neutron detector. This article is based on Monte Carlo method, studied boron-containing plastic scintillator for neutron detection performance, and analysis the energy deposition flux characteristics and detection efficiency when low intensity fission neutron incident to the boron plastic scintillator. We obtain the low-flux neutron detector performance in a variety of neutron source energy, boron-containing plastic scintillator diameter and length. Results showed that, when the boron-containing plastic scintillator lengths increase, the energy deposition flux will increase. When the length and diameter is constant, increasing source strength can increase the energy deposition flux brought by the recoil proton to a certain extent. When the source intensity over after thermal neutrons, due to the decrease of the cross section, the energy deposition fluxes brought by the react of neutrons and will decrease. The results provide help for low intensity fission neutron radiation detection technology with high sensitivity.
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Wang, Li-Min, Bing-Huang Duan, Xian-Guo Xu, Hao Li, Zhi-Jun Chen, Kun-Jie Yang et Shuo Zhang. « Simulation of neutron irradiation damage in lead lanthanum zirconate titanate by Monte Carlo method ». Acta Physica Sinica 71, no 7 (2022) : 076101. http://dx.doi.org/10.7498/aps.71.20212041.
Texte intégralRésumé :
Lead lanthanum zirconate titanate (PLZT) has a broad application prospect for energy storage devices with high energy density, since it possesses excellent dielectric and energy storage properties. To investigate the irradiation damage to the PLZT induced by neutrons with different energy, the primary energetic recoil spectra of each kind of element are first extracted from the transportation simulations of neutrons with energy ranging from 1 to 14 MeV, respectively. Then, the displacement damages (including vacancies and interstitial atoms) induced by each type of recoil with different energy are simulated based on the binary collision approximation method. Finally the number of defects in PLZT produced by neutrons with an energy range from 1 to 14 MeV is calculated based on the recoil energy spectra and the defect number produced by the recoils. The results show that the number of defects produced in the PLZT material with a thickness of 3 cm is approximately independent of the neutron energy for the fast neutrons with energy in a range from 1 to 14 MeV, even though the primary recoil energy spectra from neutrons with different energy are completely different. The average number of defects produced in 3-cm-thick PLZT is about 460 ± 120 vacancies/neutrons. For neutrons with energy ranging from 1 to 14 MeV, the produced defect concentration in PLZT decreases slightly with the depth increasing within a thickness of 3 cm. The difference in defect concentration in this 3 cm is in a range of 50%. This decrease is caused mainly by the fact that some of neutrons are back-scattered during transport. The average defect concentration produced by neutron irradiation in the PLZT with a thickness of 3 cm is slightly(～20%) higher than that in the PLZT with a thickness of 1 mm. The reason for the higher defect concentration in a thicker (3 cm) PLZT can be attributed to the following facts: (i) the (n, 2n) reactions between neutron and material can make the number of neutrons increase during transport; (ii) the scattering can make the path of neutron longer; (iii) the inelastic scattering can lead to a smallnumber of moderated neutrons, which have a slightly larger interaction cross section with materials. This indicates the damage produced in thick PLZT is quite complicated and closely related to the process of neutron transport. This work presents a method of calculating the displacement damage of neutrons in materials, and the simulation results can provide guidance for studying the neutron irradiation effects of PLZT-based electronic devices.
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Obeid, M. H., A. Ismail, A. Bitar et R. Shweikani. « ESTIMATION OF SCATTERED NEUTRONS CONTRIBUTION IN A NEUTRON CALIBRATION BUNKER USING A MONTE CARLO SIMULATION ». Radiation Protection Dosimetry 198, no 1-2 (janvier 2022) : 37–43. http://dx.doi.org/10.1093/rpd/ncab184.
Texte intégralRésumé :
Abstract The contribution of scattered neutrons is inevitable in neutron calibration facilities. This contribution complicates the measurements of neutron radiation, therefore, it should be estimated to correct the response of neutron probe instruments. In the present work, Monte Carlo simulation was performed for a neutron calibration bunker using the MCNP-4C code. This simulation aimed to calculate the contribution ratio of scattered neutrons to the neutron field. To simulate the neutron field, 241Am-Be neutron source defined in the ISO 8529-1 was used. The results of the simulation reported in this work were found to be consistent with those found experimentally in previous work. Additionally, the distribution of both the ambient dose equivalent rate and the contribution ratio of scattered neutrons in the bunker were mapped using this simulation.