Detecting short-term gravitational waves from post-merger hyper-massive neutron stars with a kilohertz detector

Gravitational waves emanating from binary neutron star inspirals,alongside electromagnetic transients resulting from the aftermath of the GW170817 merger,have been successfully detected.However,the intricate post-merger dynamics that bridge these two sets of observables remain enigmatic.This includes if,and when,the post-merger remnant star collapses to a black hole,and what are the necessary conditions to power a short gamma-ray burst,and other observed electromagnetic counterparts.Our focus is on the detection of gravitational wave(GW)emissions from hyper-massive neutron stars(NSs)formed through binary neutron star(BNS)mergers.Utilizing several kilohertz GW detectors,we simulate BNS mergers within the detection limits of LIGO-Virgo-KARGA O4.Our objective is to ascertain the fraction of simulated sources that may emit detectable post-merger GW signals.For kilohertz detectors equipped with a new cavity design,we estimate that approximately 1.1%-32%of sources would emit a detectable post-merger GW signal.This fraction is contingent on the mass converted into gravitational wave energy,ranging from 0.01M_(sun)to 0.1M_(sun).Furthermore,by evaluating other well-regarded proposed kilohertz GW detectors,we anticipate that the fraction can increase to as much as 2.1%-61%under optimal performance conditions.

Revise Thermal Winds of Remnant Neutron Stars in Gamma-Ray Bursts

It seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star(NS)merger event,GW170817/GRB 170817A/kilonova AT2017gfo,places irreconcilable constraints to models of the prompt emission of this gamma-ray burst(GRB).The observed time delay between the merger of the two NSs and the trigger of the GRB and the thermal tail of the prompt emission can hardly be reproduced by these models simultaneously.We argue that the merger remnant should be an NS(last for,at least,a large fraction of 1 s),and that the difficulty can be alleviated by the delayed formation of the accretion disk due to the absorption of high-energy neutrinos emitted by the NS and the delayed emergence of effective viscosity in the disk.Further,we extend the consideration of the effect of the energy deposition of neutrinos emitted from the NS.If the NS is the central object of a GRB with a distance and duration similar to that of GRB 170817A,thermal emission of the thermal bubble inflated by the NS after the termination of accretion may be detectable.If our scenario is verified,it would be of interest to investigate the cooling of nascent NSs.

Benchmark experiment on slab^(238)U with D-T neutrons for validation of evaluated nuclear data

A benchmark experiment on^(238)U slab samples was conducted using a deuterium-tritium neutron source at the China Institute of Atomic Energy.The leakage neutron spectra within energy levels of 0.8-16 MeV at 60°and 120°were measured using the time-of-flight method.The samples were prepared as rectangular slabs with a 30 cm square base and thicknesses of 3,6,and 9 cm.The leakage neutron spectra were also calculated using the MCNP-4C program based on the latest evaluated files of^(238)U evaluated neutron data from CENDL-3.2,ENDF/B-Ⅷ.0,JENDL-5.0,and JEFF-3.3.Based on the comparison,the deficiencies and improvements in^(238)U evaluated nuclear data were analyzed.The results showed the following.(1)The calculated results for CENDL-3.2 significantly overestimated the measurements in the energy interval of elastic scattering at 60°and 120°.(2)The calculated results of CENDL-3.2 overestimated the measurements in the energy interval of inelastic scattering at 120°.(3)The calculated results for CENDL-3.2 significantly overestimated the measurements in the 3-8.5 MeV energy interval at 60°and 120°.(4)The calculated results with JENDL-5.0 were generally consistent with the measurement results.

Free Energy of Anisotropic Strangeon Stars

Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate.Enormous energy is surely needed to understand various observations,such asγ-ray bursts,fast radio bursts and softγ-ray repeaters.In this paper,the elastic/gravitational free energy of solid strangeon stars is revisited for strangeon stars,with two anisotropic models to calculate in general relativity.It is found that huge free energy(>10^(46)erg)could be released via starquakes,given an extremely small anisotropy((p_(t)-p_(r))/p_(r)~10^(-4),with pt/pr the tangential/radial pressure),implying that pulsar-like stars could have great potential of free energy release without extremely strong magnetic fields in the solid strangeon star model.

The Completeness of Accreting Neutron Star Binary Candidates from the Chinese Space Station Telescope

A neutron star(NS)has many extreme physical conditions,and one may obtain some important information about an NS via accreting neutron star binary(ANSB)systems.The upcoming Chinese Space Station Telescope(CSST)provides an opportunity to search for a large sample of ANSB candidates.Our goal is to check the completeness of the potential ANSB samples from CSST data.In this paper,we generate some ANSBs and normal binaries under the CSST photometric system by binary evolution and binary population synthesis method and use a machine learning method to train a classification model.Although the Precision(94.56%)of our machine learning model is as high as before study,the Recall is only about 63.29%.The Precision/Recall is mainly determined by the mass transfer rate between the NSs and their companions.In addition,we also find that the completeness of ANSB samples from CSST photometric data by the machine learning method also depends on the companion mass and the age of the system.ANSB candidates with a low initial mass companion star(0.1 M_(⊙)to 1 M_(⊙))have a relatively high Precision(94.94%)and high Recall(86.32%),whereas ANSB candidates with a higher initial mass companion star(1.1 M_(⊙)to 3 M_(⊙))have similar Precision(93.88%)and quite low Recall(42.67%).Our results indicate that although the machine learning method may obtain a relatively pure sample of ANSBs,a completeness correction is necessary for one to obtain a complete sample.

Probing the Internal Physics of Neutron Stars through the Observed Braking Indices and Magnetic Tilt Angles of Several Young Pulsars

The braking indices of pulsars may contain important information about the internal physics of neutron stars(NSs),such as neutron superfluidity and internal magnetic fields.As a subsequent paper of Cheng et al.,we perform the same analysis as that done in the previous paper to other young pulsars with a steady braking index,n.Combining the timing data of these pulsars with the theory of magnetic field decay,and using their measured magnetic tilt angles,we can set constraints on the number of precession cycles,ξ,which represents the interactions between superfluid neutrons and other particles in the NS interior.For the pulsars considered in this paper,the results show thatξis within the range of a few×10~3 to a few×10~6.Interestingly,for the Crab and Vela pulsars,the constraints onξobtained with our method are generally consistent with that derived from modeling of the glitch rise behaviors of the two pulsars.Furthermore,we find that the internal magnetic fields of pulsar with n<3 may be dominated by the toroidal components.Our results may not only help to understand the interactions between the superfluid neutrons and other particles in the interior of NSs but also be important for the study of continuous gravitational waves from pulsars.

FPGA-based position reconstruction method for neutron beam flux spatial distribution measurement in BNCT

A new measurement method for the spatial distribution of neutron beam flux in boron neutron capture therapy(BNCT)is being developed based on the two-dimensional Micromegas detector.To address the issue of long processing times in traditional offline position reconstruction methods,this paper proposes a field programmable gate array based online position reconstruction method utilizing the micro-time projection chamber principle.This method encapsulates key technical aspects:a self-adaptive serial link technique built upon the dynamical adjustment of the delay chain length,fast sorting,a coordinate-matching technique based on the mapping between signal timestamps and random access memory(RAM)addresses,and a precise start point-merging technique utilizing a circular combined RAM.The performance test of the selfadaptive serial link shows that the bit error rate of the link is better than 10-12 at a confidence level of 99%,ensuring reliable data transmission.The experiment utilizing the readout electronics and Micromegas detector shows a spatial resolution of approximately 1.4 mm,surpassing the current method’s resolution level of 5 mm.The beam experiment confirms that the readout electronics system can obtain the flux spatial distribution of neutron beams online,thus validating the feasibility of the position reconstruction method.The online position reconstruction method avoids traditional methods,such as bubble sorting and traversal searching,simplifies the design of the logic firmware,and reduces the time complexity from O(n2)to O(n).This study contributes to the advancement in measuring neutron beam flux for BNCT.

Microstructures and micromechanical behaviors of high -entropy alloys investigated by synchrotron X-ray and neutron diffraction techniques: A review

High-entropy alloys(HEAs)possess outstanding features such as corrosion resistance,irradiation resistance,and good mechan-ical properties.A few HEAs have found applications in the fields of aerospace and defense.Extensive studies on the deformation mech-anisms of HEAs can guide microstructure control and toughness design,which is vital for understanding and studying state-of-the-art structural materials.Synchrotron X-ray and neutron diffraction are necessary techniques for materials science research,especially for in situ coupling of physical/chemical fields and for resolving macro/microcrystallographic information on materials.Recently,several re-searchers have applied synchrotron X-ray and neutron diffraction methods to study the deformation mechanisms,phase transformations,stress behaviors,and in situ processes of HEAs,such as variable-temperature,high-pressure,and hydrogenation processes.In this review,the principles and development of synchrotron X-ray and neutron diffraction are presented,and their applications in the deformation mechanisms of HEAs are discussed.The factors that influence the deformation mechanisms of HEAs are also outlined.This review fo-cuses on the microstructures and micromechanical behaviors during tension/compression or creep/fatigue deformation and the application of synchrotron X-ray and neutron diffraction methods to the characterization of dislocations,stacking faults,twins,phases,and intergrain/interphase stress changes.Perspectives on future developments of synchrotron X-ray and neutron diffraction and on research directions on the deformation mechanisms of novel metals are discussed.

High-resolution neutronics model for ^(238)Pu production in high-flux reactors

We proposed and compared three methods(filter burnup,single energy burnup,and burnup extremum analysis)to build a high-resolution neutronics model for 238Pu production in high-flux reactors.The filter burnup and single energy burnup methods have no theoretical approximation and can achieve a spectrum resolution of up to~1 eV,thereby constructing the importance curve and yield curve of the full energy range.The burnup extreme analysis method combines the importance and yield curves to consider the influence of irradiation time on production efficiency,thereby constructing extreme curves.The three curves,which quantify the transmutation rate of the nuclei in each energy region,are of physical significance because they have similar distributions.A high-resolution neutronics model for ^(238)Pu production was established based on these three curves,and its universality and feasibility were proven.The neutronics model can guide the neutron spectrum optimization and improve the yield of ^(238)Pu by up to 18.81%.The neutronics model revealed the law of nuclei transmutation in all energy regions with high spectrum resolution,thus providing theoretical support for high-flux reactor design and irradiation production of ^(238)Pu.

The EOSs and the Blatant Discrepancy in Modelling Massive Neutron Stars: Origin and a Possible Solution Method

Exploring the state of ultra-cold supranuclear dense matter that makes up the cores of massive neutron stars is one of the greatest unresolved problems in modern physics. In this letter, we show that when the interiors of pulsars are made of compressible and dissipative normal matter, the commonly used solution procedures combined with the known EOSs yield widely scattered solutions and poorly determined radii. A remarkable agreement emerges, however, if pulsars harbour cores that are made of incompressible entropy-free superfluids (SuSu-matter) embedded in flat spacetimes. Such supranuclear dense matter should condensate to form false vacua as predicated by non-perterbative QCD vacuum. The solutions here are found to be physically consistent and mathematically elegant, irrespective of the object’s mass. Based thereon, we conclude that the true masses of massive NSs may differ significantly from those revealed by direct observation.

Probing into the Possible Range of the U Bosonic Coupling Constants in Neutron Stars Containing Hyperons

The range of the U bosonic coupling constants in neutron star matter is a very interesting but still unsolved problem which has multifaceted influences in nuclear physics,particle physics,astrophysics and cosmology.The combination of the theoretical numerical simulation and the recent observations provides a very good opportunity to solve this problem.In the present work,the range of the U bosonic coupling constants is inferred based on the three relations of the mass–radius,mass-frequency and mass-tidal deformability in neutron stars containing hyperons using the GM1,TM1 and NL3 parameter sets under the two flavor symmetries of SU(6)and SU(3)in the framework of the relativistic mean field theory.Combined with observations from PSRs J1614-2230,J0348+0432,J2215-5135,J0952-0607,J0740+6620,J0030-0451,J1748-2446ad,XTE J1739-285,GW170817 and GW190814 events,our numerical results show that the U bosonic coupling constants may tend to be within the range from 0 to 20 GeV^(-2)in neutron star containing hyperons.Moreover,the numerical results of the three relations obtained by the SU(3)symmetry are better in accordance with observation data than those obtained by the SU(6)symmetry.The results will help us to improve the strict constraints of the equation of state for neutron stars containing hyperons.

Simulation Study on Constraining Gravitational Wave Propagation Speed by Gravitational Wave and Gamma-ray Burst Joint Observation on Binary Neutron Star Mergers

Theories of modified gravity suggest that the propagation speed of gravitational waves(GW)v_gmay deviate from the speed of light c.A constraint can be placed on the difference between c and v_gwith a simple method that uses the arrival time delay between GW and electromagnetic wave simultaneously emitted from a burst event.We simulated the joint observation of GW and short gamma-ray burst signals from binary neutron star merger events in different observation campaigns,involving advanced LIGO(aLIGO)in design sensitivity and Einstein Telescope(ET)joint-detected with Fermi/GBM.As a result,the relative precision of constraint on v_gcan reach~10~(-17)(aLIGO)and~10^(-18)(ET),which are one and two orders of magnitude better than that from GW170817,respectively.We continue to obtain the bound of graviton mass m_g≤7.1(3.2)×10~(-20)eV with aLIGO(ET).Applying the Standard-Model Extension test framework,the constraint on v_gallows us to study the Lorentz violation in the nondispersive,nonbirefringent limit of the gravitational sector.We obtain the constraints of the dimensionless isotropic coefficients S_(00)^(4)at mass dimension d=4,which are-1×10^(-15)<S_(00)^(4)<9×10^(-17)for aLIGO and-4×10^(-16)<s_(00)^(4<8<10^(-18))for ET.

Cross section determination of^(27)Al(n,2n)^(26)Al reaction induced by 14-MeV neutrons uniting with D-T neutron activation and AMS techniques

Aluminum is the primary structural material in nuclear engineering,and its cross section induced by 14-MeV neutrons is of great significance.To address the issue of insufficient accuracy for the^(27)Al(n,2n)^(26)Al reaction cross section,the activation method and accelerator mass spectrometry(AMS)technique were used to determine the^(27)Al(n,2n)^(26)Al cross section,which could be used as a D-T plasma ion temperature monitor in fusion reactors.At the China Academy of Engineering Physics,neutron activation was performed using a K-400 neutron generator produced by the T(d,n)4He reaction.The^(26)Al∕^(27)Al isotope ratios were measured using the newly installed GYIG 1 MV AMS at the Institute of Geochemistry,Chinese Academy of Sciences.The neutron flux was monitored by measuring the activity of 92mNb produced by the 93Nb(n,2n)92mNb reaction.The measured results were compared with available data in the experimental nuclear reaction database,and the measured values showed a reasonable degree of consistency with partially available literature data.The newly acquired cross-sectional data at 12 neutron energy points through systematic measurements clarified the divergence,which has two different growth trends from the existing experimental values.The obtained results are also compared with the corresponding evaluated database,and the newly calculated excitation functions with TALYS−1.95 and EMPIRE−3.2 codes,the agreement with CENDL−3.2,TENDL-2021 and EMPIRE−3.2 results are generally acceptable.A substantial improvement in the knowledge of the^(27)Al(n,2n)^(26)Al reaction excitation function was obtained in the present work,which will lay the foundation for the diagnosis of the fusion ion temperature,testing of the nuclear physics model,evaluation of nuclear data,etc.

Spectroscopic Observations of Ten Galactic Wolf-Rayet Stars at Bosscha Observatory:Determination of Stellar Parameters and Mass-loss Rates

We present optical spectra of 10 Galactic Wolf-Rayet(WR)stars that consist of five WN and five WC stars.The optical observation was conducted using a low-resolution spectrograph NEO-R1000(λ/Δλ~1000)at GAO-ITB RTS(27.94 cm,F/10.0),Bosscha Observatory,Lembang.We implemented stellar atmosphere Postdam Wolf-Rayet(PoWR)grid modeling to derive stellar parameters.The normalized optical spectrum can be used to find the best model from the available PoWR grid,then we could derive stellar temperature and transformation radius.To derive luminosity,stellar radius and color excess,we conducted a Spectral Energy Distribution(SED)analysis with additional data on the near-ultraviolet spectrum from the International Ultraviolet Explorer(IUE)database,and UBV and 2MASS JHK broadband filter data.Additional analysis to derive asymptotic terminal wind velocity was conducted from the P-Cygni profile analysis of the high-resolution IUE ultraviolet spectrum.With previously derived parameters,we could determine the mass loss rate of the WR stars.Furthermore,we compared our results with previous work that used PoWR code and the differences are not more than 20%.We conclude that the PoWR spectral grid is sufficient to derive WR stellar parameters quickly and could provide more accurate initial parameter input to the PoWR program code.

Study of the response of 10B-doped MCP to wide-energy range neutrons from eV to MeV

Neutron-sensitive microchannel plates(nMCPs)have applications in neutron detection,including energy spectrum measurements,neutron-induced cross sections,and neutron imaging.10B-doped MCPs(B-MCPs)have attracted significant attention owing to their potential for exhibiting a high neutron detection efficiency over a large neutron energy range.Good spatial and temporal resolutions are useful for neutron energy-resolved imaging.However,their practical applications still face many technical challenges.In this study,a B-MCP with 10 mol%10B was tested for its response to wide-energy neutrons from eV to MeV at the Back-n white neutron source at the China Spallation Neutron Source.The neutron detection efficiency was calibrated at 1 eV,which is approximately 300 times that of an ordinary MCP and indicates the success of 10 B doping.The factors that caused the reduction in the detection efficiency were simulated and discussed.The neutron energy spectrum obtained using B-MCP was compared with that obtained by other measurement methods,and showed very good consistency for neutron energies below tens of keV.The response is more complicated at higher neutron energy,at which point the elastic and nonelastic reactions of all nuclides of B-MCP gradually become dominant.This is beneficial for the detection of neutrons,as it compensates for the detection efficiency of B-MCP for high-energy neutrons.

Performance optimization of the neutron-sensitive image intensifier used in neutron imaging

As a non-destructive testing technology,neutron imaging plays an important role in various fields,including material science,nuclear engineering,and fundamental science.An imaging detector with a neutron-sensitive image intensifier has been developed and demonstrated to achieve good spatial resolution and timing resolution.However,the influence of the working voltage on the performance of the neutron-sensitive imaging intensifier has not been studied.To optimize the performance of the neutron-sensitive image intensifier at different voltages,experiments have been performed at the China Spallation Neutron Source(CSNS)neutron beamline.The change in the light yield and imaging quality with different voltages has been acquired.It is shown that the image quality benefits from the high gain of the microchannel plate(MCP)and the high accelerating electric field between the MCP and the screen.Increasing the accelerating electric field is more effective than increasing the gain of MCPs for the improvement of the imaging quality.Increasing the total gain of the MCP stack can be realized more effectively by improving the gain of the standard MCP than that of the n MCP.These results offer a development direction for image intensifiers in the future.

Design and implementation of the monochromator shielding for the cold neutron spectrometers XINGZHI and BOYA

An innovative monochromator shielding is designed and implemented for the cold neutron spectrometers XINGZHI and BOYA operated by Renmin University of China at China Advanced Research Reactor.Via Monte Carlo simulations and careful mechanical designs,a shielding configuration has been successfully developed to satisfy safety requirements of below 3μSv/h dose rate at its exterior,meanwhile fulfilling space,floor load and nonmagnetic requirements.Composite materials are utilized to form the sandwich-type shielding walls:the inner layer of boron carbide rubber,the middle layer of steel-encased lead and the outer layer of borated polyethylene.Special-shaped liftable shielding blocks are incorporated to facilitate a continuous adjustment of the neutron energy while preventing radiation leakage.Our work has demonstrated that by utilizing composite shielding materials,along with the sandwich structure and liftable shielding blocks,a compact and lightweight shielding solution can be achieved.This enables the realization of advanced neutron scattering instruments that provide expanded space of measurement,larger energy and momentum coverage,and higher flux on the sample.This shielding represents the first of its kind in neutron scattering instruments in China.Following its successful operation,it has been subsequently employed by other neutron instruments across the country.

Rotating Massive Strangeon Stars and X-Ray Plateau of Short GRBs

Strangeon stars,which are proposed to describe the nature of pulsar-like compact stars,have passed various observational tests.The maximum mass of a non-rotating strangeon star could be high,which implies that the remnants of binary strangeon star mergers could even be long-lived massive strangeon stars.We study rigidly rotating strangeon stars in the slowly rotating approximation,using the Lennard-Jones model for the equation of state.Rotation can significantly increase the maximum mass of strangeon stars with unchanged baryon numbers,enlarging the mass-range of long-lived strangeon stars.During spin-down after merger,the decrease of radius of the remnant will lead to the release of gravitational energy.Taking into account the efficiency of converting the gravitational energy luminosity to the observed X-ray luminosity,we find that the gravitational energy could provide an alternative energy source for the plateau emission of X-ray afterglow.The fitting results of X-ray plateau emission of some short gamma-ray bursts suggest that the magnetic dipole field strength of the remnants can be much smaller than that of expected when the plateau emission is powered only by spin-down luminosity of magnetars.

10B-doped MCP detector developed for neutron resonance imaging at Back-n white neutron source

Neutron resonance imaging(NRI)has recently emerged as an appealing technique for neutron radiography.Its complexity surpasses that of conventional transmission imaging,as it requires a high demand for both a neutron source and detector.Consequently,the progression of NRI technology has been sluggish since its inception in the 1980s,particularly considering the limited studies analyzing the neutron energy range above keV.The white neutron source(Back-n)at the China Spallation Neutron Source(CSNS)provides favorable beam conditions for the development of the NRI technique over a wide neutron energy range from eV to MeV.Neutron-sensitive microchannel plates(MCP)have emerged as a cutting-edge tool in the field of neutron detection owing to their high temporal and spatial resolutions,high detection efficiency,and low noise.In this study,we report the development of a 10B-doped MCP detector,along with its associated electronics,data processing system,and NRI experiments at the Back-n.Individual heavy elements such as gold,silver,tungsten,and indium can be easily identified in the transmission images by their characteristic resonance peaks in the 1–100 eV energy range;the more difficult medium-weight elements such as iron,copper,and aluminum with resonance peaks in the 1–100 keV energy range can also be identified.In particular,results in the neutron energy range of dozens of keV(Aluminum)are reported here for the first time.

An Asymmetric Galactic Stellar Disk Traced by OB-type Stars from LAMOST DR7

Using 9943 OB-type stars from LAMOST DR7 in the solar neighborhood,we fit the vertical stellar density profile with the model including a single exponential distribution at different positions(R,Φ).The distributions of the scale heights and scale length show that the young disk traced by the OB-type stars is not axisymmetric.The scale length decreases versus the azimuthal angleΦ,i.e.,from.■kpc withΦ=-3°to■kpc withΦ=9°.Meanwhile we find signal of non-symmetry in the distribution of the scale height of the north and south of the disk plane.The scale height in the north side shows signal of flaring of the disk,while that of the south disk stays almost constant around h_(s)=130 pc.The distribution of the displaceeent of the disk plane Z_(0)also shows variance versus the azimuthal angleΦ,which displays significant differences with the warp model constrained by the Cepheid stars.We also test different values for the position of the Sun,and the distance between the Sun and the Galactic center affects the scale heights and the displacement of the disk significantly,but that does not change our conclusion that the disk is not axisymmetric.