To generate a neutron beam exhibiting a Maxwellian energy distribution with narrow emission angles for measuring the neutron capture reaction rates of the s-process nuclides,a monoenergetic 3.4 MeV proton beam produce...To generate a neutron beam exhibiting a Maxwellian energy distribution with narrow emission angles for measuring the neutron capture reaction rates of the s-process nuclides,a monoenergetic 3.4 MeV proton beam produced by the tandem-accelerator in the China Institute of Atomic Energy was utilized.The proton beam was first transmitted through a 60.5μm aluminum foil and then impinged on a natural LiF target to produce neutron beam via^(7)Li(p,n)7Be reaction.The quasi-Gaussian energy distribution of protons in the LiF target resulted in neutron energy spectra that agreed with a Maxwellian energy distribution at kT=(22±2)keV,which was achieved by integrating neutrons detected within an emission angle of 65.0°±2.6°using a ^(6)Li glass detector positioned at 65°relative to the proton beam direction.The narrow angular spread of the Maxwelliandistributed neutron beam enables direct measurement of neutron capture cross-sections for most s-process nuclides,overcoming previous experimental limitations associated with broad angular distributions.展开更多
With the increasing demand for controllable source logging,research on data-processing algorithms that meet accuracy requirements has become key to the development of controllable-source-logging tools.This study theor...With the increasing demand for controllable source logging,research on data-processing algorithms that meet accuracy requirements has become key to the development of controllable-source-logging tools.This study theoretically derives the relationship between the formation density and inelastic gamma count rate to investigate the data-processing methods for deuterium–tritium(D–T)source neutron-gamma density logging while drilling.Then,algorithms for the net inelastic gamma count-rate extraction and neutron transport correction are studied using Monte Carlo simulations.A new method for fast-neutron effect identification and additional correction is proposed to improve the density-calculation accuracy of gas-filled and heavy-mineral formations.Finally,the effectiveness and accuracy of the proposed data-processing methods are verified based on simulated and measured data.The results show that the density-calculation accuracy of water-bearing conventional formations in simulated data is±0.02 g/cm^(3).The accuracy of gas-filled and heavy-mineral formations after the additional fast-neutron effect correction is±0.025 g/cm^(3).For the measured data from the actual tool,the algorithms perform well in the density calculation.The density results obtained using the processing algorithms are consistent with the density data provided by NeoScope.Therefore,the D–T source neutron-gamma density-logging algorithms proposed in this study can obtain relatively accurate data-processing results for a variety of formations.This study provides technical support for engineering applications and the development of logging tools for controllable-source neutron-density logging.展开更多
This paper introduced a compact high flux polarized neutron beam generator scheme,which used air as the working medium and had low energy consumption.The neutron beam generator adopted a linear three compartment confi...This paper introduced a compact high flux polarized neutron beam generator scheme,which used air as the working medium and had low energy consumption.The neutron beam generator adopted a linear three compartment configuration,sequentially using nitrogen nucleus tandem near range accelerated polarization target spallation nuclear reaction technology,neutron multiplication technology,neutron beam polarization and near range acceleration technology,neutron focusing and shooting control technology.Through design and equivalent verification,it has been proven that the total length of the device does not exceed 5 m,the effective range can reach several hundred kilometers,the neutron flux at the muzzle is not less than 10^(25) n·cm^(-2)·s^(-1),which attenuates to 10^(10) n·cm^(-2)·s^(-1) at a distance of several 100 km,and this flux can effectively strike the target.It can be used as a defensive directed energy weapon with high energy density and has broad application prospects.展开更多
Elucidating the relationship between spin excitations and fermiology is essential for clarifying the pairing mechanism in iron-based superconductors(FeSCs).Here,we report inelastic neutron scattering results on the ho...Elucidating the relationship between spin excitations and fermiology is essential for clarifying the pairing mechanism in iron-based superconductors(FeSCs).Here,we report inelastic neutron scattering results on the hole overdoped Ba_(0.4)K_(0.6)Fe_(2)As_(2) near a Lifshitz transition,where the electron pocket at M point is nearly replaced by four hole pockets.In the normal state,the spin excitations is observed at incommensurate wave vectors with a chimney-like dispersion.By cooling down to the superconducting state,a neutron spin resonance mode emerges with a peak energy of Er=14-15 meV,weakly modulated along the L-direction.The incommensurability notably increases at low energies,giving rise to downward dispersions of the resonance mode.This behavior contrasts sharply with the upward dispersions of resonance observed in optimally doped Ba_(0.67)K_(0.33)Fe_(2)As_(2) contributed by the hole to electron scattering,but resembles those in KFe_(2)As_(2) and KCa_(2)Fe_(4)As_(4)F_(2) where the fermiology is dominated by hole pockets.These results highlight the critical role of electronic structure modifications near the Fermi level,especially in governing interband scattering under imperfect nesting conditions,which fundamentally shape the spin dynamics of FeSCs.展开更多
Prompt fission neutron uranium logging(PFNUL)is an advanced method for utilizing pulsed neutron bombardment of the ore layer and a fission reaction with uranium(^(235)U)to detect the transient neutrons produced by fis...Prompt fission neutron uranium logging(PFNUL)is an advanced method for utilizing pulsed neutron bombardment of the ore layer and a fission reaction with uranium(^(235)U)to detect the transient neutrons produced by fission and then directly measure and quantify uranium;however,the stability and lifetime performance of pulsed neutron sources are the key constraints to its rapid promotion.To address these problems,this study proposes a PFNUL technique for acquiring the time spectrum of dual-energy neutrons(epithermal and thermal neutrons)from the upper and lower detection structures and establishes a novel uranium quantification algorithm based on the ratio of epithermal and thermal neutron time windows(E/T)via a mathematical-physical modeling derivation.Through simulations on well-logging models with di erent uranium contents,the starting and stopping times of the time window(Δt)for uranium quantification in the dual-energy neutron time spectrum are determined to be 200 and 800μs,respectively.The minimum radius and height of the model wells are 60 and 120 cm,respectively,and the E/T values in the time window show an excellent linear relationship with the uranium content.The scale factor is K_(E/T)=1.92 and R^(2)=0.999,which verifies the validity of the E/T uranium quantification algorithm.In addition,experiments were carried out in the Nu series of uranium standard model wells,and the results showed that under di erent neutron source yields,the E/T-based uranium quantification method reduced the relative standard deviation of the scale factor of the uranium content from 33.41%to 1.09%,compared with a single epithermal neutron quantification method.These results prove that the E/T value uranium quantification method is una ected by the change in the neutron source yield,e ectively improves the accuracy and service life of the logging instrument,and has great scientific and popularization value.展开更多
The development of low-cost and highly efficient thermal neutron detection materials to substitute the rare and expensive^(3)He gas is important for applications requiring thermal neutron detection.Lithium-based glass...The development of low-cost and highly efficient thermal neutron detection materials to substitute the rare and expensive^(3)He gas is important for applications requiring thermal neutron detection.Lithium-based glass(Li glass)is a promising candidate due to its simple fabrication process and low cost.This paper reports the optical properties and scintillation performance of a new Ce^(3+)-doped Li glass,whose luminescence efficiency is significantly enhanced with a light yield of about 4770 ph/MeV,which is about 54%of that of BGO crystal,and the energy resolution is 14.5%for 662 keV gamma rays.The Ce^(3+)-doped Li glass shows a high light yield of about 7058 ph/neutron,which is about 1.18 times that of the reference GS20 glass.The Ce^(3+)-doped Li glass exhibits stronger gamma ray suppression capability compared to GS20 glass samples.Further optimizing the Ce^(3+)concentration and 6Li content is expected to achieve much superior neutron detection efficiency,positioning it as a promising alternative to^(3)He gas for efficient thermal neutron detection.展开更多
The application of a controllable neutron source for measuring formation porosity in the advancement of nuclear logging has garnered increased attention.The existing porosity algorithm,which is based on the thermal ne...The application of a controllable neutron source for measuring formation porosity in the advancement of nuclear logging has garnered increased attention.The existing porosity algorithm,which is based on the thermal neutron counting ratio,exhibits lower sensitivity in high-porosity regions.To enhance the sensitivity,the effects of elastic and inelastic scattering,which influence the slowing-down of fast neutrons,were theoretically analyzed,and a slowing-down model of fast neutrons was created.Based on this model,a density correction porosity algorithm was proposed based on the relationship between density,thermal neutron counting ratio,and porosity.Finally,the super multifunctional calculation program for nuclear design and safety evaluation(TopMC/SuperMC)was used to create a simulation model for porosity logging,and its applicability was examined.The results demonstrated that the relative error between the calculated and actual porosities was less than 1%,and the influence of deviation in the density measurement was less than 2%.Therefore,the proposed density correction algorithm based on the slowing-down model of fast neutrons can effectively improve the sensitivity in the high-porosity region.This study is expected to serve as a reference for the application of neutron porosity measurements with D–T neutron sources.展开更多
Beryllium(^(9)Be)serves as a crucial neutron multiplier and reflection material,being extensively employed in the nuclear industry.The evaluated nuclear data are utilized in the design of the nuclear devices.Following...Beryllium(^(9)Be)serves as a crucial neutron multiplier and reflection material,being extensively employed in the nuclear industry.The evaluated nuclear data are utilized in the design of the nuclear devices.Following the interaction between neutrons and^(9)Be,all neutrons generated stem from the^(9)Be(n,2n)^(8)Be reaction channel,except for the elastic scattering reaction channel.Nevertheless,the data of the outgoing neutron double differential cross section of the reaction channel provided by the latest internationally evaluated libraries still exhibit considerable discrepancies.A shielding integral experiment based on slab^(9)Be samples with measurements of neutron spectra leaked from different angles is an effective approach to verify the double differential cross-section data.Hence,in this study,a shielding integral experiment of^(9)Be samples of different thicknesses was conducted using a nanosecond pulsed deuterium-tritium neutron source established by the China Institute of Atomic Energy.The neutron time-of-flight spectra of three thicknesses(4.4 cm,8.8 cm,and 13.2 cm)and six angles(47°,58°,73°,107°,122°,and 133°)were measured by the neutron time-of-flight method,and 18 sets of experimental data were obtained.Additionally,the MCNP-4C program was used to obtain the simulated results of the leakage neutron spectra using the evaluated nuclear data of^(9)Be from the CENDL-3.2,ENDF/B-Ⅷ.0,JENDL-5,and JEFF-3.3 libraries.The simulated results of the leakage neutron spectra were compared with the experimental results,and the results showed that in the elastic scattering energy region,the simulated results from the CENDL-3.2,ENDF/B-Ⅷ.0,and JENDL-5 libraries were slightly higher at small angles and slightly lower at large angles.In the(n,2n)energy region,the simulated results from the CENDL-3.2 library were significantly different from the experimental results in terms of spectral shape,and the simulated results from the ENDF/B-Ⅷ.0 and the JENDL-5 libraries were in good agreement with the experimental results at small angles but low at large angles.The simulated results from the JEFF-3.3 library showed serious underestimation at all angles.展开更多
The neutron capture cross section for^(165)Ho was measured at the backstreaming white neutron beam line(Back-n)of the China Spallation Neutron Source(CSNS)using total energy detection systems,composed of a set of four...The neutron capture cross section for^(165)Ho was measured at the backstreaming white neutron beam line(Back-n)of the China Spallation Neutron Source(CSNS)using total energy detection systems,composed of a set of four C_(6)D_(6)scintillator detectors coupled with pulse height weighting techniques.The resonance parameters were extracted using the multilevel multichannel R-matrix code SAMMY to fit the measured capture yields of the^(165)Ho(n,γ)reaction in the neutron energy range below100 eV.Subsequently,the resonance region’s capture cross sections were reconstructed based on the obtained parameters.Furthermore,the unresolved resonance average cross section of the^(165)Ho(n,γ)reaction was determined relative to that of the standard sample^(197)Au within the neutron energy range of 2 keV to 1 MeV.The experimental data were compared with the recommended nuclear data from the ENDF/B-VIII.0 library,as well as with results of calculations performed using the TALYS-1.9 code.The comparison revealed agreement between the measured^(165)Ho(n,γ)cross sections and these data.The present results are crucial for evaluating the^(165)Ho neutron capture cross section and thus enhance the quality of evaluated nuclear data libraries.They provide valuable guidance for nuclear theoretical models and nuclear astrophysical studies.展开更多
Lead(Pb)plays a significant role in the nuclear industry and is extensively used in radiation shielding,radiation protection,neutron moderation,radiation measurements,and various other critical functions.Consequently,...Lead(Pb)plays a significant role in the nuclear industry and is extensively used in radiation shielding,radiation protection,neutron moderation,radiation measurements,and various other critical functions.Consequently,the measurement and evaluation of Pb nuclear data are highly regarded in nuclear scientific research,emphasizing its crucial role in the field.Using the time-of-flight(ToF)method,the neutron leakage spectra from three^(nat)Pb samples were measured at 60°and 120°based on the neutronics integral experimental facility at the China Institute of Atomic Energy(CIAE).The^(nat)Pb sample sizes were30 cm×30 cm×5 cm,30 cm×30 cm×10 cm,and 30 cm×30 cm×15 cm.Neutron sources were generated by the Cockcroft-Walton accelerator,producing approximately 14.5 MeV and 3.5 MeV neutrons through the T(d,n)^(4)He and D(d,n)^(3)He reactions,respectively.Leakage neutron spectra were also calculated by employing the Monte Carlo code of MCNP-4C,and the nuclear data of Pb isotopes from four libraries:CENDL-3.2,JEFF-3.3,JENDL-5,and ENDF/B-Ⅷ.0 were used individually.By comparing the simulation and experimental results,improvements and deficiencies in the evaluated nuclear data of the Pb isotopes were analyzed.Most of the calculated results were consistent with the experimental results;however,a few areas did not fit well.In the(n,el)energy range,the simulated results from CENDL-3.2 were significantly overestimated;in the(n,inl)D and the(n,inl)C energy regions,the results from CENDL-3.2 and ENDF/B-Ⅷ.0 were significantly overestimated at 120°,and the results from JENDL-5 and JEFF-3.3 are underestimated at 60°in the(n,inl)D energy region.The calculated spectra were analyzed by comparing them with the experimental spectra in terms of the neutron spectrum shape and C/E values.The results indicate that the theoretical simulations,using different data libraries,overestimated or underestimated the measured values in certain energy ranges.Secondary neutron energies and angular distributions in the data files have been presented to explain these discrepancies.展开更多
The Van Allen radiation belts are doughnut-shaped zones surrounding Earth, filled with highly energetic charged particles whose sources or loss mechanisms have been investigated for decades. As for the inner belt, cos...The Van Allen radiation belts are doughnut-shaped zones surrounding Earth, filled with highly energetic charged particles whose sources or loss mechanisms have been investigated for decades. As for the inner belt, cosmic ray albedo neutron decay(CRAND),radial diffusion, and local acceleration have been considered principal sources of electrons, whereas protons are predominantly from CRAND and solar protons. In this article, lightning-induced neutrons from Earth's upper atmosphere are suggested as a possible source of protons and electrons in the inner radiation belt. These terrestrial neutrons can contribute to the inner belt population by undergoing nuclear decay. Several approaches are proposed and discussed to evaluate the potential contribution of lightning-induced neutrons to the inner belt, including magnitude estimation, Monte Carlo simulations, and in situ observations. This article discusses some avenues of further study to determine the contribution of lightning-induced neutrons to the inner radiation belt.展开更多
A time-of-flight Highly Granular Neutron Detector(HGND)with a multilayer longitudinal structure of interleaved absorber and scintillator plates,high transverse granularity,and time resolution of approximately 150 ps i...A time-of-flight Highly Granular Neutron Detector(HGND)with a multilayer longitudinal structure of interleaved absorber and scintillator plates,high transverse granularity,and time resolution of approximately 150 ps is currently under development.The detector is designed to identify neutrons produced in nucleus-nucleus collisions and measure neutron kinetic energies of 0.3-4 GeV by the time-of-flight method in the BM@N experiment at the NICA accelerator complex at JINR.To validate the concept of full-scale HGND,a compact HGND prototype was first designed and built,and its performance was studied in the BM@N experiment.The acceptance of the HGND prototype and the detection efficiency of forward neutrons emitted in hadronic fragmentation and electromagnetic dissociation(EMD)of 3.8A GeV124Xe projectiles interacting with a CsI target were calculated by means of the DCM-QGSM-SMM and RELDIS models,respectively.The energy distributions of the forward spectator neutrons and neutrons from the EMD were measured and compared with the simulations.The developed methods will be used to calibrate the full-scale HGND and study its efficiency.展开更多
^(147,149)Sm are slow neutron capture(s-process)nuclides in nuclear astrophysics,whose(n,γ)cross sections are important input parameters in nucleosynthesis network calculations in the samarium(Sm)region.In addition,^...^(147,149)Sm are slow neutron capture(s-process)nuclides in nuclear astrophysics,whose(n,γ)cross sections are important input parameters in nucleosynthesis network calculations in the samarium(Sm)region.In addition,^(149)Sm is a fission product of ^(235)U with a 1%yield,and its neutron resonance parameters play a critical role in reactor neutronics.According to the available nuclear evaluation databases,a significant disagreement has been observed in the resonance peaks of the ^(147,149)Sm(n,γ)crosssectional data within the energy range of 20-300 eV.In this study,tutron capture cross section of a natural samarium target was measured at the back-streaming white neutron beamline of the China Spallation Neutron Source.The neutron capture yield was obtained,and the neutron resonance parameters for ^(147)Sm at 107.0,139.4,241.7,and 257.3 eV and ^(149)Sm at 23.2,24.6,26.1,28.0,51.5,75.2,90.9,125.3,and 248.4 eV were extracted using the SAMMY code based on R-matrix theory.For the parameters Γ_(n) and Γ_(γ) in these energies of ^(147,149)Sm,the percentages consistent with the results of the CENDL-3.2,ENDF/B-Ⅷ.0,JEFF-3.3,JENDL-4.0,and BROND-3.1 database are 27%,65%,65%,42%,and 58%,respectively.However,27% of the results were inconsistent with those of the major libraries.This work enriches experimental data of the ^(147,149)Sm neutron capture resonance and helps clarify the differences between different evaluation databases at the above energies.展开更多
The neutron total cross-section spectrometer(NTOX)applied on the Back-n beamline at the China Spallation Neutron Source(CSNS)is based on a multicell fission chamber and utilizes ^(235,238)U for neutron detection.To re...The neutron total cross-section spectrometer(NTOX)applied on the Back-n beamline at the China Spallation Neutron Source(CSNS)is based on a multicell fission chamber and utilizes ^(235,238)U for neutron detection.To reduce the experimental uncertainty in the resonance energy region of ^(235,238)U and improve the neutron detection efficiency,a fast scintillator-based neutron total cross-section(FAST)spectrometer was designed.A prototype based on a large-area square ^(6)Li-enriched Cs_(2)LiLaBr_(6)(CLLB)scintillator was constructed and beam-tested.The size of the CLLB scintillator was 50.8 mm×50.8 mm×6 mm,and its side was coupled to an array of 1×8 S14160 MPPC to avoid the irradiation from the high-intensity neutrons and rays.The beam test was performed using a broad-energy pulsed neutron and the time-of-flight(TOF)technique on the Back-n beamline.The results demonstrate that the prototype exhibits good neutron/ γ discrimination capability under strong flash irradiation.The prototype was applied to measure the neutron total cross-section of ^(nat)Pb and the result was compared with that obtained using the NTOX.The two results were consistent in the energy region of 0.3 eV to 1 keV,and the prototype showed a higher detection efficiency and did not exhibit fission resonance effect.This type of spectrometer can be used as a complement to the NTOX in the low-energy range and provides a technical reference and framework for developing the FAST spectrometer on the Back-n beamline.展开更多
Position-sensitive neutron detectors play an important role in neutron scattering studies. Detectors based on ~6LiF/ZnS(Ag) scintillator and wave-shifting fiber have the advantages of high neutron detection efficiency...Position-sensitive neutron detectors play an important role in neutron scattering studies. Detectors based on ~6LiF/ZnS(Ag) scintillator and wave-shifting fiber have the advantages of high neutron detection efficiency, high position resolution,and large-area splicing, and can well meet the requirement of large area neutron detection for neutron diffractometers. An engineering detector prototype based on a ~6LiF/ZnS(Ag) scintillation screen and SiPM array readout was fabricated for the General Purpose Powder Diffractometer of China Spallation Neutron Source(CSNS). The detector has an active area of 196 mm × 444 mm, with a pixel size of 4 mm × 4 mm. The key performances of the detector prototype were tested at the BL20 neutron beam line of CSNS. The test results show that the neutron detection efficiency of the detector was 32% and 42% at wavelengths of 1.4 ? and 2.8 ?, respectively. An interpolated neutron detection efficiency of 40.2% at a wavelength of 2 ? was obtained. The tested neutron efficiency non-uniformity of the detector was 10.2%, which is less than one-half that of the current general purpose powder diffractometer scintillator neutron detectors at CSNS. This work achieves, for the first time, an efficiency uniformity of < 11% in large-area mosaic neutron detectors, alongside significant advancements in electromagnetic interference immunity and cost-effectiveness.展开更多
The prompt fission neutron spectrum(PFNS)is a key nuclear data quantity that is of particular interest and plays a crucial role in understanding and modeling fission processes.An array comprising 48 liquid scintillati...The prompt fission neutron spectrum(PFNS)is a key nuclear data quantity that is of particular interest and plays a crucial role in understanding and modeling fission processes.An array comprising 48 liquid scintillation detectors and a parallelplate avalanche counter(PPAC)was developed at the China Institute of Atomic Energy(CIAE)to measure the PFNS of actinide nuclei.Efficiency and energy calibrations were performed for all the liquid scintillators,and their efficiencies were consistently found to be better than 5%.The time resolutions of the PPAC and liquid scintillators were measured to be 1.08 ns and 1.16 ns using~(252)Cf and~(207)Bi sources,respectively.The pulse shape discrimination of the liquid scintillator was utilized to identify neutron andγsignals on an event-by-event basis,and the figure of merit was deduced as 1.12 at a 200 ke Vee threshold.The contribution to the PFNS from multiple scattered neutrons was evaluated via Geant4 simulations,and those originating from the environment were found to be comparable to the crosstalk between the detectors.The neutron efficiency of the entire detection array was calibrated using a~(252)Cf spontaneous fission source and was demonstrated to be consistent with the Geant4 simulation results,which verified the reliability of the detection array.展开更多
We present a theoretical model for detecting axions from neutron stars in a QCD phase of quark matter. The axions would be produced from a quark-antiquark pair uu¯or dd¯, in loop(s) involving gluons. The chi...We present a theoretical model for detecting axions from neutron stars in a QCD phase of quark matter. The axions would be produced from a quark-antiquark pair uu¯or dd¯, in loop(s) involving gluons. The chiral anomaly of QCD and the spontaneously broken symmetry are invoked to explain the non-conservation of the axion current. From the coupling form factors, the axion emissivities ϵacan be derived, from which fluxes can be determined. We predict a photon flux, which may be detectable by Fermi LAT, and limits on the QCD mass ma. In this model, axions decay to gamma rays in a 2-photon vertex. We may determine the expected fluxes from the theoretical emissivity. The sensitivity curve from the Fermi Large Area Telescope (Fermi LAT) would allow axion mass constraints for neutron stars as low as ma≤10−14eV 95% C.L. Axions could thus be detectable in gamma rays for neutron stars as distant as 100 kpc. A signal from LIGO GWS 170817 could be placed from the NS-NS merger, which gives an upper limit of ma≤10−10eV.展开更多
Neutron imaging techniques were investigated at Peking University based on a 4.5 MV Van de Graaff accelerator.The thermal neutron radiography,fast neutron radiography and fast neutron resonance radiography were tested...Neutron imaging techniques were investigated at Peking University based on a 4.5 MV Van de Graaff accelerator.The thermal neutron radiography,fast neutron radiography and fast neutron resonance radiography were tested.The low neutron flux limits the image quality.A new radio frequency quadrupole (RFQ) accelerator based on neutron source with a yield of 1 012 n/s is being set up.展开更多
The current work addresses the challenge of elucidating the performance of fluoroelastomers within the HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)based polymer-bonded explosives(PBXs).To simulate the confine...The current work addresses the challenge of elucidating the performance of fluoroelastomers within the HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)based polymer-bonded explosives(PBXs).To simulate the confined interface in PBXs,bilayer films of F2314/HMX and F2311/HMX were designed.Neutron reflectivity(NR),nanoindentation,and X-ray reflectivity(XRR)were employed to examine the layer thickness,interface characteristics,diffusion behavior,and surface morphology of the bilayers.NR measurements revealed interface thicknesses of 45Å and 98Å for F2314/HMX and F2311/HMX,respectively,indicating deeper penetration of F2311 into the HMX matrix.NR also suggested a denser polymer network with a higher scattering length density(SLD)near the HMX interface for both fluoroelastomers,while the bound layer of F2311 was notably thicker.Nanoindentation cross-checks and confirms the presence of a bound layer,highlighting the differences in stiffness and diffusion ability between the two polymers.The consistency between the NR and nanoindentation results suggests that F2311 demonstrates better flexibility and elasticity,whereas F2314 is stiffer and more plastic.Accordingly,the structures and performances of different fluoroelastomers at the HMX interface are discussed,which can provide valuable insights into the selection of binders for PBX formulations tailored to specific applications.展开更多
A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger...A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger ejecta,which are sensitive to the equation of state(EoS)of the neutron star.We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact of various EoS on the r-process nucleosynthesis and the kilonova emission.Our results show that both the abundance patterns of merger ejecta and kilonova light curves are strongly dependent on the neutron star EoSs.Given the mass of two neutron stars,the merger with a softer EoS tends to generate a larger amount of ejected material,and may lead to a brighter kilonova peak luminosity.The relationship between the neutron star EoS and the peak luminosity provides a probe for constraining the properties of EoS in multi-messenger observations of neutron star mergers.展开更多
基金National Natural Science Foundation of China(12125509,11961141003,12275361,U2267205,12175152,12175121)National Key Research and Development Project(2022YFA1602301)Continuous-support Basic Scientific Research Project。
文摘To generate a neutron beam exhibiting a Maxwellian energy distribution with narrow emission angles for measuring the neutron capture reaction rates of the s-process nuclides,a monoenergetic 3.4 MeV proton beam produced by the tandem-accelerator in the China Institute of Atomic Energy was utilized.The proton beam was first transmitted through a 60.5μm aluminum foil and then impinged on a natural LiF target to produce neutron beam via^(7)Li(p,n)7Be reaction.The quasi-Gaussian energy distribution of protons in the LiF target resulted in neutron energy spectra that agreed with a Maxwellian energy distribution at kT=(22±2)keV,which was achieved by integrating neutrons detected within an emission angle of 65.0°±2.6°using a ^(6)Li glass detector positioned at 65°relative to the proton beam direction.The narrow angular spread of the Maxwelliandistributed neutron beam enables direct measurement of neutron capture cross-sections for most s-process nuclides,overcoming previous experimental limitations associated with broad angular distributions.
基金supported by the Natural Science Foundation of Shandong(ZR2022MD019)Technology Development Project of China Oilfield Services Limited(G2317A-0414T077)+3 种基金Science and Technology Project of China National O shore Oil Corporation(CNOOC-KJ GJHXJSGG YF 2022-01)Open Fund Project of CNPC Logging(CNLC2022-9C06)Fundamental Research Foundation for Central Universities(22CX01001A-2)China National Petroleum Corporation Scientific Research and Technology Development Project(2021DJ3801)。
文摘With the increasing demand for controllable source logging,research on data-processing algorithms that meet accuracy requirements has become key to the development of controllable-source-logging tools.This study theoretically derives the relationship between the formation density and inelastic gamma count rate to investigate the data-processing methods for deuterium–tritium(D–T)source neutron-gamma density logging while drilling.Then,algorithms for the net inelastic gamma count-rate extraction and neutron transport correction are studied using Monte Carlo simulations.A new method for fast-neutron effect identification and additional correction is proposed to improve the density-calculation accuracy of gas-filled and heavy-mineral formations.Finally,the effectiveness and accuracy of the proposed data-processing methods are verified based on simulated and measured data.The results show that the density-calculation accuracy of water-bearing conventional formations in simulated data is±0.02 g/cm^(3).The accuracy of gas-filled and heavy-mineral formations after the additional fast-neutron effect correction is±0.025 g/cm^(3).For the measured data from the actual tool,the algorithms perform well in the density calculation.The density results obtained using the processing algorithms are consistent with the density data provided by NeoScope.Therefore,the D–T source neutron-gamma density-logging algorithms proposed in this study can obtain relatively accurate data-processing results for a variety of formations.This study provides technical support for engineering applications and the development of logging tools for controllable-source neutron-density logging.
基金sponsored by National Natural Science Foundation of China (Grant No. 12405215)
文摘This paper introduced a compact high flux polarized neutron beam generator scheme,which used air as the working medium and had low energy consumption.The neutron beam generator adopted a linear three compartment configuration,sequentially using nitrogen nucleus tandem near range accelerated polarization target spallation nuclear reaction technology,neutron multiplication technology,neutron beam polarization and near range acceleration technology,neutron focusing and shooting control technology.Through design and equivalent verification,it has been proven that the total length of the device does not exceed 5 m,the effective range can reach several hundred kilometers,the neutron flux at the muzzle is not less than 10^(25) n·cm^(-2)·s^(-1),which attenuates to 10^(10) n·cm^(-2)·s^(-1) at a distance of several 100 km,and this flux can effectively strike the target.It can be used as a defensive directed energy weapon with high energy density and has broad application prospects.
基金supported by the National Key Research and Development Program of China(Grant Nos.2023YFA1406100,2018YFA0704200,2022YFA1403400 and 2021YFA1400400)the National Natural Science Foundation of China(Grant Nos.11822411 and 12274444)+2 种基金the Strategic Priority Research Program(B)of the CAS(Grant Nos.XDB25000000 and XDB33000000)K.C.Wong Education Foundation(GJTD-2020-01)AP by HBNI-RRCAT and MPCST under the FTYS program。
文摘Elucidating the relationship between spin excitations and fermiology is essential for clarifying the pairing mechanism in iron-based superconductors(FeSCs).Here,we report inelastic neutron scattering results on the hole overdoped Ba_(0.4)K_(0.6)Fe_(2)As_(2) near a Lifshitz transition,where the electron pocket at M point is nearly replaced by four hole pockets.In the normal state,the spin excitations is observed at incommensurate wave vectors with a chimney-like dispersion.By cooling down to the superconducting state,a neutron spin resonance mode emerges with a peak energy of Er=14-15 meV,weakly modulated along the L-direction.The incommensurability notably increases at low energies,giving rise to downward dispersions of the resonance mode.This behavior contrasts sharply with the upward dispersions of resonance observed in optimally doped Ba_(0.67)K_(0.33)Fe_(2)As_(2) contributed by the hole to electron scattering,but resembles those in KFe_(2)As_(2) and KCa_(2)Fe_(4)As_(4)F_(2) where the fermiology is dominated by hole pockets.These results highlight the critical role of electronic structure modifications near the Fermi level,especially in governing interband scattering under imperfect nesting conditions,which fundamentally shape the spin dynamics of FeSCs.
基金supported by the National Natural Science Foundation of China(No.42374226)Jiangxi Provincial Natural Science Foundation(Nos.20232BAB201043,gpyc20240073,and 20232BCJ23006)+2 种基金Nuclear Energy Development Project(20201192-01)Fundamental Science on Radioactive Geology and Exploration Technology Laboratory(2022RGET20)National Key Laboratory of Uranium Resource Exploration-Mining and Nuclear Remote Sensing(ECUT)(2024QZ-TD-09)。
文摘Prompt fission neutron uranium logging(PFNUL)is an advanced method for utilizing pulsed neutron bombardment of the ore layer and a fission reaction with uranium(^(235)U)to detect the transient neutrons produced by fission and then directly measure and quantify uranium;however,the stability and lifetime performance of pulsed neutron sources are the key constraints to its rapid promotion.To address these problems,this study proposes a PFNUL technique for acquiring the time spectrum of dual-energy neutrons(epithermal and thermal neutrons)from the upper and lower detection structures and establishes a novel uranium quantification algorithm based on the ratio of epithermal and thermal neutron time windows(E/T)via a mathematical-physical modeling derivation.Through simulations on well-logging models with di erent uranium contents,the starting and stopping times of the time window(Δt)for uranium quantification in the dual-energy neutron time spectrum are determined to be 200 and 800μs,respectively.The minimum radius and height of the model wells are 60 and 120 cm,respectively,and the E/T values in the time window show an excellent linear relationship with the uranium content.The scale factor is K_(E/T)=1.92 and R^(2)=0.999,which verifies the validity of the E/T uranium quantification algorithm.In addition,experiments were carried out in the Nu series of uranium standard model wells,and the results showed that under di erent neutron source yields,the E/T-based uranium quantification method reduced the relative standard deviation of the scale factor of the uranium content from 33.41%to 1.09%,compared with a single epithermal neutron quantification method.These results prove that the E/T value uranium quantification method is una ected by the change in the neutron source yield,e ectively improves the accuracy and service life of the logging instrument,and has great scientific and popularization value.
基金supported by the National Key R&D Program of China(Grant No.2023YFF0721700)the National Natural Science Foundation of China(Grant No.12475312).
文摘The development of low-cost and highly efficient thermal neutron detection materials to substitute the rare and expensive^(3)He gas is important for applications requiring thermal neutron detection.Lithium-based glass(Li glass)is a promising candidate due to its simple fabrication process and low cost.This paper reports the optical properties and scintillation performance of a new Ce^(3+)-doped Li glass,whose luminescence efficiency is significantly enhanced with a light yield of about 4770 ph/MeV,which is about 54%of that of BGO crystal,and the energy resolution is 14.5%for 662 keV gamma rays.The Ce^(3+)-doped Li glass shows a high light yield of about 7058 ph/neutron,which is about 1.18 times that of the reference GS20 glass.The Ce^(3+)-doped Li glass exhibits stronger gamma ray suppression capability compared to GS20 glass samples.Further optimizing the Ce^(3+)concentration and 6Li content is expected to achieve much superior neutron detection efficiency,positioning it as a promising alternative to^(3)He gas for efficient thermal neutron detection.
基金supported by the Anhui Provincial Major Science and Technology Project(No.201903c08020003)the Taishan industrial Experts Program。
文摘The application of a controllable neutron source for measuring formation porosity in the advancement of nuclear logging has garnered increased attention.The existing porosity algorithm,which is based on the thermal neutron counting ratio,exhibits lower sensitivity in high-porosity regions.To enhance the sensitivity,the effects of elastic and inelastic scattering,which influence the slowing-down of fast neutrons,were theoretically analyzed,and a slowing-down model of fast neutrons was created.Based on this model,a density correction porosity algorithm was proposed based on the relationship between density,thermal neutron counting ratio,and porosity.Finally,the super multifunctional calculation program for nuclear design and safety evaluation(TopMC/SuperMC)was used to create a simulation model for porosity logging,and its applicability was examined.The results demonstrated that the relative error between the calculated and actual porosities was less than 1%,and the influence of deviation in the density measurement was less than 2%.Therefore,the proposed density correction algorithm based on the slowing-down model of fast neutrons can effectively improve the sensitivity in the high-porosity region.This study is expected to serve as a reference for the application of neutron porosity measurements with D–T neutron sources.
基金supported by the National Natural Science Foundation of China(Nos.11775311,U2167203,U2067205 and 12075105)Research and development project of China National Nuclear Corporation(FD010241222552)+2 种基金Continuous-Support Basic Scientific Research Project(BJ010261223282)Major Science and Technology Projects of Gansu Province(22ZD6GB020)Fundamental Research Funds for the Central Universities(lzujbky-2024-jdzx10)。
文摘Beryllium(^(9)Be)serves as a crucial neutron multiplier and reflection material,being extensively employed in the nuclear industry.The evaluated nuclear data are utilized in the design of the nuclear devices.Following the interaction between neutrons and^(9)Be,all neutrons generated stem from the^(9)Be(n,2n)^(8)Be reaction channel,except for the elastic scattering reaction channel.Nevertheless,the data of the outgoing neutron double differential cross section of the reaction channel provided by the latest internationally evaluated libraries still exhibit considerable discrepancies.A shielding integral experiment based on slab^(9)Be samples with measurements of neutron spectra leaked from different angles is an effective approach to verify the double differential cross-section data.Hence,in this study,a shielding integral experiment of^(9)Be samples of different thicknesses was conducted using a nanosecond pulsed deuterium-tritium neutron source established by the China Institute of Atomic Energy.The neutron time-of-flight spectra of three thicknesses(4.4 cm,8.8 cm,and 13.2 cm)and six angles(47°,58°,73°,107°,122°,and 133°)were measured by the neutron time-of-flight method,and 18 sets of experimental data were obtained.Additionally,the MCNP-4C program was used to obtain the simulated results of the leakage neutron spectra using the evaluated nuclear data of^(9)Be from the CENDL-3.2,ENDF/B-Ⅷ.0,JENDL-5,and JEFF-3.3 libraries.The simulated results of the leakage neutron spectra were compared with the experimental results,and the results showed that in the elastic scattering energy region,the simulated results from the CENDL-3.2,ENDF/B-Ⅷ.0,and JENDL-5 libraries were slightly higher at small angles and slightly lower at large angles.In the(n,2n)energy region,the simulated results from the CENDL-3.2 library were significantly different from the experimental results in terms of spectral shape,and the simulated results from the ENDF/B-Ⅷ.0 and the JENDL-5 libraries were in good agreement with the experimental results at small angles but low at large angles.The simulated results from the JEFF-3.3 library showed serious underestimation at all angles.
基金supported by the National Natural Science Foundation of China(Nos.12465024,12365018,U2032146)Inner Mongolia National Science Foundation(Nos.2024ZD23,2024FX30,2023MS01005)+1 种基金Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region(NMGIRT2217)Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region(NJYT23109)。
文摘The neutron capture cross section for^(165)Ho was measured at the backstreaming white neutron beam line(Back-n)of the China Spallation Neutron Source(CSNS)using total energy detection systems,composed of a set of four C_(6)D_(6)scintillator detectors coupled with pulse height weighting techniques.The resonance parameters were extracted using the multilevel multichannel R-matrix code SAMMY to fit the measured capture yields of the^(165)Ho(n,γ)reaction in the neutron energy range below100 eV.Subsequently,the resonance region’s capture cross sections were reconstructed based on the obtained parameters.Furthermore,the unresolved resonance average cross section of the^(165)Ho(n,γ)reaction was determined relative to that of the standard sample^(197)Au within the neutron energy range of 2 keV to 1 MeV.The experimental data were compared with the recommended nuclear data from the ENDF/B-VIII.0 library,as well as with results of calculations performed using the TALYS-1.9 code.The comparison revealed agreement between the measured^(165)Ho(n,γ)cross sections and these data.The present results are crucial for evaluating the^(165)Ho neutron capture cross section and thus enhance the quality of evaluated nuclear data libraries.They provide valuable guidance for nuclear theoretical models and nuclear astrophysical studies.
基金supported by the National Natural Science Foundation of China(Nos.11775311 and U2067205)the Stable Support Basic Research Program Grant(BJ010261223282)the Research and Development Project of China National Nuclear Corporation。
文摘Lead(Pb)plays a significant role in the nuclear industry and is extensively used in radiation shielding,radiation protection,neutron moderation,radiation measurements,and various other critical functions.Consequently,the measurement and evaluation of Pb nuclear data are highly regarded in nuclear scientific research,emphasizing its crucial role in the field.Using the time-of-flight(ToF)method,the neutron leakage spectra from three^(nat)Pb samples were measured at 60°and 120°based on the neutronics integral experimental facility at the China Institute of Atomic Energy(CIAE).The^(nat)Pb sample sizes were30 cm×30 cm×5 cm,30 cm×30 cm×10 cm,and 30 cm×30 cm×15 cm.Neutron sources were generated by the Cockcroft-Walton accelerator,producing approximately 14.5 MeV and 3.5 MeV neutrons through the T(d,n)^(4)He and D(d,n)^(3)He reactions,respectively.Leakage neutron spectra were also calculated by employing the Monte Carlo code of MCNP-4C,and the nuclear data of Pb isotopes from four libraries:CENDL-3.2,JEFF-3.3,JENDL-5,and ENDF/B-Ⅷ.0 were used individually.By comparing the simulation and experimental results,improvements and deficiencies in the evaluated nuclear data of the Pb isotopes were analyzed.Most of the calculated results were consistent with the experimental results;however,a few areas did not fit well.In the(n,el)energy range,the simulated results from CENDL-3.2 were significantly overestimated;in the(n,inl)D and the(n,inl)C energy regions,the results from CENDL-3.2 and ENDF/B-Ⅷ.0 were significantly overestimated at 120°,and the results from JENDL-5 and JEFF-3.3 are underestimated at 60°in the(n,inl)D energy region.The calculated spectra were analyzed by comparing them with the experimental spectra in terms of the neutron spectrum shape and C/E values.The results indicate that the theoretical simulations,using different data libraries,overestimated or underestimated the measured values in certain energy ranges.Secondary neutron energies and angular distributions in the data files have been presented to explain these discrepancies.
基金supported by the National Natural Science Foundation of China (No. 42225405 and No. 42350710200)。
文摘The Van Allen radiation belts are doughnut-shaped zones surrounding Earth, filled with highly energetic charged particles whose sources or loss mechanisms have been investigated for decades. As for the inner belt, cosmic ray albedo neutron decay(CRAND),radial diffusion, and local acceleration have been considered principal sources of electrons, whereas protons are predominantly from CRAND and solar protons. In this article, lightning-induced neutrons from Earth's upper atmosphere are suggested as a possible source of protons and electrons in the inner radiation belt. These terrestrial neutrons can contribute to the inner belt population by undergoing nuclear decay. Several approaches are proposed and discussed to evaluate the potential contribution of lightning-induced neutrons to the inner belt, including magnitude estimation, Monte Carlo simulations, and in situ observations. This article discusses some avenues of further study to determine the contribution of lightning-induced neutrons to the inner radiation belt.
基金supported by the Institute for Nuclear Research of the Russian Academy of Sciences。
文摘A time-of-flight Highly Granular Neutron Detector(HGND)with a multilayer longitudinal structure of interleaved absorber and scintillator plates,high transverse granularity,and time resolution of approximately 150 ps is currently under development.The detector is designed to identify neutrons produced in nucleus-nucleus collisions and measure neutron kinetic energies of 0.3-4 GeV by the time-of-flight method in the BM@N experiment at the NICA accelerator complex at JINR.To validate the concept of full-scale HGND,a compact HGND prototype was first designed and built,and its performance was studied in the BM@N experiment.The acceptance of the HGND prototype and the detection efficiency of forward neutrons emitted in hadronic fragmentation and electromagnetic dissociation(EMD)of 3.8A GeV124Xe projectiles interacting with a CsI target were calculated by means of the DCM-QGSM-SMM and RELDIS models,respectively.The energy distributions of the forward spectator neutrons and neutrons from the EMD were measured and compared with the simulations.The developed methods will be used to calibrate the full-scale HGND and study its efficiency.
基金supported by the Natural Science Foundation of Hunan Province,China(No.2025JJ60020)the National Key Research and Development Program(No.2022YFA1603300)+1 种基金National Natural Science Foundation of China(Nos.12275338 and 12388102)China Institute of Atomic Energy(No.CIAE-FWGKJT-23-0820).
文摘^(147,149)Sm are slow neutron capture(s-process)nuclides in nuclear astrophysics,whose(n,γ)cross sections are important input parameters in nucleosynthesis network calculations in the samarium(Sm)region.In addition,^(149)Sm is a fission product of ^(235)U with a 1%yield,and its neutron resonance parameters play a critical role in reactor neutronics.According to the available nuclear evaluation databases,a significant disagreement has been observed in the resonance peaks of the ^(147,149)Sm(n,γ)crosssectional data within the energy range of 20-300 eV.In this study,tutron capture cross section of a natural samarium target was measured at the back-streaming white neutron beamline of the China Spallation Neutron Source.The neutron capture yield was obtained,and the neutron resonance parameters for ^(147)Sm at 107.0,139.4,241.7,and 257.3 eV and ^(149)Sm at 23.2,24.6,26.1,28.0,51.5,75.2,90.9,125.3,and 248.4 eV were extracted using the SAMMY code based on R-matrix theory.For the parameters Γ_(n) and Γ_(γ) in these energies of ^(147,149)Sm,the percentages consistent with the results of the CENDL-3.2,ENDF/B-Ⅷ.0,JEFF-3.3,JENDL-4.0,and BROND-3.1 database are 27%,65%,65%,42%,and 58%,respectively.However,27% of the results were inconsistent with those of the major libraries.This work enriches experimental data of the ^(147,149)Sm neutron capture resonance and helps clarify the differences between different evaluation databases at the above energies.
基金supported by the National Natural Science Foundation of China(No.12375296)the Key Laboratory of Nuclear Data Foundation(No.JCKY2022201C153)+1 种基金the Science and Technology Innovation Program of Hunan Province(No.2024RC3205)the Natural Science Foundation of Hunan Province,China(No.2024JJ2044).
文摘The neutron total cross-section spectrometer(NTOX)applied on the Back-n beamline at the China Spallation Neutron Source(CSNS)is based on a multicell fission chamber and utilizes ^(235,238)U for neutron detection.To reduce the experimental uncertainty in the resonance energy region of ^(235,238)U and improve the neutron detection efficiency,a fast scintillator-based neutron total cross-section(FAST)spectrometer was designed.A prototype based on a large-area square ^(6)Li-enriched Cs_(2)LiLaBr_(6)(CLLB)scintillator was constructed and beam-tested.The size of the CLLB scintillator was 50.8 mm×50.8 mm×6 mm,and its side was coupled to an array of 1×8 S14160 MPPC to avoid the irradiation from the high-intensity neutrons and rays.The beam test was performed using a broad-energy pulsed neutron and the time-of-flight(TOF)technique on the Back-n beamline.The results demonstrate that the prototype exhibits good neutron/ γ discrimination capability under strong flash irradiation.The prototype was applied to measure the neutron total cross-section of ^(nat)Pb and the result was compared with that obtained using the NTOX.The two results were consistent in the energy region of 0.3 eV to 1 keV,and the prototype showed a higher detection efficiency and did not exhibit fission resonance effect.This type of spectrometer can be used as a complement to the NTOX in the low-energy range and provides a technical reference and framework for developing the FAST spectrometer on the Back-n beamline.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12275181)Guangdong Basic and Applied Basic Research Foundation (Grant No. 2022B1515120071)+1 种基金Promotion Project of Scientific Research Capability of Key Construction Disciplines in Guangdong Province (Grant No. 2022ZDJS118)Natural Science Foundation of Top Talent SZTU (Grant No. GDRC202205)。
文摘Position-sensitive neutron detectors play an important role in neutron scattering studies. Detectors based on ~6LiF/ZnS(Ag) scintillator and wave-shifting fiber have the advantages of high neutron detection efficiency, high position resolution,and large-area splicing, and can well meet the requirement of large area neutron detection for neutron diffractometers. An engineering detector prototype based on a ~6LiF/ZnS(Ag) scintillation screen and SiPM array readout was fabricated for the General Purpose Powder Diffractometer of China Spallation Neutron Source(CSNS). The detector has an active area of 196 mm × 444 mm, with a pixel size of 4 mm × 4 mm. The key performances of the detector prototype were tested at the BL20 neutron beam line of CSNS. The test results show that the neutron detection efficiency of the detector was 32% and 42% at wavelengths of 1.4 ? and 2.8 ?, respectively. An interpolated neutron detection efficiency of 40.2% at a wavelength of 2 ? was obtained. The tested neutron efficiency non-uniformity of the detector was 10.2%, which is less than one-half that of the current general purpose powder diffractometer scintillator neutron detectors at CSNS. This work achieves, for the first time, an efficiency uniformity of < 11% in large-area mosaic neutron detectors, alongside significant advancements in electromagnetic interference immunity and cost-effectiveness.
基金supported by Continuous-Support Basic Scientific Research Project(No.BJ010261223282)the National Natural Science Foundation of China(Nos.U2167201,11975318)+2 种基金the State Key Laboratory of Nuclear Physics and TechnologyPeking University(No.NPT2023KFY01)the Research and Development Project of China National Nuclear Corporation。
文摘The prompt fission neutron spectrum(PFNS)is a key nuclear data quantity that is of particular interest and plays a crucial role in understanding and modeling fission processes.An array comprising 48 liquid scintillation detectors and a parallelplate avalanche counter(PPAC)was developed at the China Institute of Atomic Energy(CIAE)to measure the PFNS of actinide nuclei.Efficiency and energy calibrations were performed for all the liquid scintillators,and their efficiencies were consistently found to be better than 5%.The time resolutions of the PPAC and liquid scintillators were measured to be 1.08 ns and 1.16 ns using~(252)Cf and~(207)Bi sources,respectively.The pulse shape discrimination of the liquid scintillator was utilized to identify neutron andγsignals on an event-by-event basis,and the figure of merit was deduced as 1.12 at a 200 ke Vee threshold.The contribution to the PFNS from multiple scattered neutrons was evaluated via Geant4 simulations,and those originating from the environment were found to be comparable to the crosstalk between the detectors.The neutron efficiency of the entire detection array was calibrated using a~(252)Cf spontaneous fission source and was demonstrated to be consistent with the Geant4 simulation results,which verified the reliability of the detection array.
文摘We present a theoretical model for detecting axions from neutron stars in a QCD phase of quark matter. The axions would be produced from a quark-antiquark pair uu¯or dd¯, in loop(s) involving gluons. The chiral anomaly of QCD and the spontaneously broken symmetry are invoked to explain the non-conservation of the axion current. From the coupling form factors, the axion emissivities ϵacan be derived, from which fluxes can be determined. We predict a photon flux, which may be detectable by Fermi LAT, and limits on the QCD mass ma. In this model, axions decay to gamma rays in a 2-photon vertex. We may determine the expected fluxes from the theoretical emissivity. The sensitivity curve from the Fermi Large Area Telescope (Fermi LAT) would allow axion mass constraints for neutron stars as low as ma≤10−14eV 95% C.L. Axions could thus be detectable in gamma rays for neutron stars as distant as 100 kpc. A signal from LIGO GWS 170817 could be placed from the NS-NS merger, which gives an upper limit of ma≤10−10eV.
基金supported by National Natural Science Foundation of China(No.10735020No.10575006)
文摘Neutron imaging techniques were investigated at Peking University based on a 4.5 MV Van de Graaff accelerator.The thermal neutron radiography,fast neutron radiography and fast neutron resonance radiography were tested.The low neutron flux limits the image quality.A new radio frequency quadrupole (RFQ) accelerator based on neutron source with a yield of 1 012 n/s is being set up.
基金supported in part by the National Natural Science Foundation of China(Nos.12335018,12105264,and 12275248)NSAF Joint Fund Project(Nos.U2230107,U1730244,U2130207)+1 种基金Innovation and Development Fund of China Academy of Engineering Physics(No.CXKS20240052)Central Guidance for Local Science and Technology Development Fund Project(No.2023ZYDF075).
文摘The current work addresses the challenge of elucidating the performance of fluoroelastomers within the HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)based polymer-bonded explosives(PBXs).To simulate the confined interface in PBXs,bilayer films of F2314/HMX and F2311/HMX were designed.Neutron reflectivity(NR),nanoindentation,and X-ray reflectivity(XRR)were employed to examine the layer thickness,interface characteristics,diffusion behavior,and surface morphology of the bilayers.NR measurements revealed interface thicknesses of 45Å and 98Å for F2314/HMX and F2311/HMX,respectively,indicating deeper penetration of F2311 into the HMX matrix.NR also suggested a denser polymer network with a higher scattering length density(SLD)near the HMX interface for both fluoroelastomers,while the bound layer of F2311 was notably thicker.Nanoindentation cross-checks and confirms the presence of a bound layer,highlighting the differences in stiffness and diffusion ability between the two polymers.The consistency between the NR and nanoindentation results suggests that F2311 demonstrates better flexibility and elasticity,whereas F2314 is stiffer and more plastic.Accordingly,the structures and performances of different fluoroelastomers at the HMX interface are discussed,which can provide valuable insights into the selection of binders for PBX formulations tailored to specific applications.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12403043,12347172,and 12133003)M.H.C.also acknowledges support from the China Postdoctoral Science Foundation(grant Nos.GZB20230029 and 2024M750057)supported by the Guangxi Talent Program(Highland of Innovation Talents).
文摘A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger ejecta,which are sensitive to the equation of state(EoS)of the neutron star.We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact of various EoS on the r-process nucleosynthesis and the kilonova emission.Our results show that both the abundance patterns of merger ejecta and kilonova light curves are strongly dependent on the neutron star EoSs.Given the mass of two neutron stars,the merger with a softer EoS tends to generate a larger amount of ejected material,and may lead to a brighter kilonova peak luminosity.The relationship between the neutron star EoS and the peak luminosity provides a probe for constraining the properties of EoS in multi-messenger observations of neutron star mergers.
