A statistical analysis of the Kappa-type energy spectrum distribution of radiation belt electrons observed by Van Allen Probes

The energy spectrum of energetic electrons is a key factor representing the dynamic variations of Earth’s Van Allen radiation belts.Increased measurements have indicated that the commonly used Maxwellian and Kappa distributions are inadequate for capturing the realistic spectral distributions of radiation belt electrons.Here we adopt the Kappa-type(KT)distribution as the fitting function and perform a statistical analysis to investigate the radiation belt electron flux spectra observed by the Van Allen Probes.By calculating the optimal values of the key KT distribution parameters(i.e.,κandθ2)from the observed spectral shapes,we fit the radiation belt electron fluxes at different L-shells under different geomagnetic conditions.In this manner,we obtain typical values of the KT distribution parameters,which are statistically feasible for modeling the radiation belt electron flux profiles during either geomagnetically quiet or active periods.A comparison of the KT distribution model results with those using the Maxwellian or Kappa distribution reveals the advantage of the KT distribution for studying the overall properties of the radiation belt electron spectral distribution,which has important implications for deepening the current understanding of the radiation belt electron dynamics under evolving geomagnetic conditions.

Effect of surface modification on the radiation stability of diamond ohmic contacts

The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.

Effects of 1 MeV electron radiation on the AlGaN/GaN high electron mobility transistors

In this study, the effects of 1 MeV electron radiation on the D-mode GaN-based high electron mobility transistors(HEMTs) were investigated after different radiation doses. The changes in electrical properties of the device were obtained, and the related physical mechanisms were analyzed. It indicated that under the radiation dose of 5 × 10^(14) cm^(-2), the channel current cannot be completely pinched off even if the negative gate voltage was lower than the threshold voltage, and the gate leakage current increased significantly. The emission microscopy and scanning electron microscopy were used to determine the damage location. Besides, the radiation dose was adjusted ranging from 5 × 10^(12) to 1 × 10^(14) cm^(-2), and we noticed that the drain-source current increased and the threshold voltage presented slightly negative shift. By calculations, it suggested that the carrier density and electron mobility gradually increased. It provided a reference for the development of device radiation reinforcement technology.

On the loss mechanisms of radiation belt electron dropouts during the 12 September 2014 geomagnetic storm

Radiation belt electron dropouts indicate electron flux decay to the background level during geomagnetic storms,which is commonly attributed to the effects of wave-induced pitch angle scattering and magnetopause shadowing.To investigate the loss mechanisms of radiation belt electron dropouts triggered by a solar wind dynamic pressure pulse event on 12 September 2014,we comprehensively analyzed the particle and wave measurements from Van Allen Probes.The dropout event was divided into three periods:before the storm,the initial phase of the storm,and the main phase of the storm.The electron pitch angle distributions(PADs)and electron flux dropouts during the initial and main phases of this storm were investigated,and the evolution of the radial profile of electron phase space density(PSD)and the(μ,K)dependence of electron PSD dropouts(whereμ,K,and L^*are the three adiabatic invariants)were analyzed.The energy-independent decay of electrons at L>4.5 was accompanied by butterfly PADs,suggesting that the magnetopause shadowing process may be the major loss mechanism during the initial phase of the storm at L>4.5.The features of electron dropouts and 90°-peaked PADs were observed only for>1 MeV electrons at L<4,indicating that the wave-induced scattering effect may dominate the electron loss processes at the lower L-shell during the main phase of the storm.Evaluations of the(μ,K)dependence of electron PSD drops and calculations of the minimum electron resonant energies of H+-band electromagnetic ion cyclotron(EMIC)waves support the scenario that the observed PSD drop peaks around L^*=3.9 may be caused mainly by the scattering of EMIC waves,whereas the drop peaks around L^*=4.6 may result from a combination of EMIC wave scattering and outward radial diffusion.

High energy electron radiation effect on Ni/4H-SiC SBD and Ohmic contact

The Ni/4H-SiC Schottky barrier diodes （SBDs） and transfer length method （TLM） test patterns of Ni/4H-SiC Ohmic contacts were fabricated, and irradiated with i MeV electrons up to a dose of 3.43 × 10^14 e/cm^-2. After radiation, the forward currents of the SBDs at 2 V decreased by about 50%, and the reverse currents at -200 V increased by less than 30%. Schottky barrier height （ФB） of the Ni/4H-SiC SBD increased from 1.20 eV to 1.21 eV under 0 V irradiation bias, and decreased from 1.25 eV to 1.19 eV under -30 V irradiation bias. The degradation of ФB could be explained by the variation of interface states of Schottky contacts. The on-state resistance （Rs） and the reverse current increased with the dose, which can be ascribed to the radiation defects in bulk material. The specific contact resistance （ρc） of the Ni/SiC Ohmic contact increased from 5.11× 10^-5Ω· cm^2 to 2.97× 10^-4Ω· cm^2.

High energy electron radiation effect on Ni and Ti/4H-SiC Schottky barrier diodes at room temperature

This paper reports that Ni and Ti/4H-SiC Schottky barrier diodes （SBDs） were fabricated and irradiated with 1 MeV electrons up to a dose of 3.43 × 10^14 e/cm2. After radiation, the Schottky barrier height φB of the Ni/4H-SiC SBD increased from 1.20 eV to 1.21 eV, but decreased from 0.95 eV to 0.94 eV for the Ti/4H-SiC SBD. The degradation of φB could be explained by interface states of changed Schottky contacts. The on-state resistance Rs of both diodes increased with the dose, which can be ascribed to the radiation defects. The reverse current of the Ni/4H-SiC SBD slightly increased, but for the Ti/4H-SiC SBD it basically remained the same. At room temperature, φB of the diodes recovered completely after one week, and the RS partly recovered.

Selective linear etching of monolayer black phosphorus using electron beams

Point and line defects are of vital importance to the physical and chemical properties of certain two-dimensional(2D)materials.Although electron beams have been demonstrated to be capable of creating single-and multi-atom defects in 2D materials,the products are often random and difficult to predict without theoretical inputs.In this study,the thermal motion of atoms and electron incident angle were additionally considered to study the vacancy evolution in a black phosphorus(BP)monolayer by using an improved first-principles molecular dynamics method.The P atoms in monolayer BP tend to be struck away one by one under an electron beam within the displacement threshold energy range of 8.55-8.79 eV,which ultimately induces the formation of a zigzag-like chain vacancy.The chain vacancy is a thermodynamically metastable state and is difficult to obtain by conventional synthesis methods because the vacancy formation energy of 0.79 eV/edge atom is higher than the typical energy in monolayer BP.Covalent-like quasi-bonds and a charge density wave are formed along the chain vacancy,exhibiting rich electronic properties.This work proposes a theoretical protocol for simulating a complete elastic collision process of electron beams with 2D layers and will facilitate the establishment of detailed theoretical guidelines for experiments on 2D material etching using focused high-energy electron beams.

Nuclear geyser model of the origin of life:Driving force to promote the synthesis of building blocks of life

We propose the nuclear geyser model to elucidate an optimal site to bear the first life.Our model overcomes the difficulties that previously proposed models have encountered.Nuclear geyser is a geyser driven by a natural nuclear reactor,which was likely common in the Hadean Earth,because of a much higher abundance of 235U as nuclear fuel.The nuclear geyser supplies the following：（1）high-density ionizing radiation to promote chemical chain reactions that even tar can be used for intermediate material to restart chemical reactions,（2）a system to maintain the circulation of material and energy,which includes cyclic environmental conditions（warm/cool,dry/wet,etc.）to enable to produce complex organic compounds,（3）a lower temperature than 100℃ as not to break down macromolecular organic compounds,（4）a locally reductive environment depending on rock types exposed along the geyser wall,and（5）a container to confine and accumulate volatile chemicals.These five factors are the necessary conditions that the birth place of life must satisfy.Only the nuclear geyser can meet all five,in contrast to the previously proposed birth sites,such as tidal flat,submarine hydrothermal vent,and outer space.The nuclear reactor and associated geyser,which maintain the circulations of material and energy with its surrounding environment,are regarded as the nuclear geyser system that enables numerous kinds of chemical reactions to synthesize complex organic compounds,and where the most primitive metabolism could be generated.

Calculating the electron temperature in the lightning channel by continuous spectrum

Based on the theory of plasma continuous radiation, the relationship between the emission intensity of bremsstrahlung and recombination radiation and the plasma electron temperature is obtained. During the development process of a return stroke of ground flash, the intensity of continuous radiation spectrum is separated on the basis of the spectrums with obviously different luminous intensity at two moments. The electron temperature of the lightning discharge channel is obtained through the curve fitting of the continuous spectrum intensity. It is found that electron temperature increases with the increase of wavelength and begins to reduce after the peak. The peak temperature of the two spectra is close to 25 000 K. To be compared with the result of discrete spectrum, the electron temperature is fitted by the O I line and N II line of the spectrum respectively. The comparison shows that the high temperature value is in good agreement with the temperature of the lightning core current channel obtained from the ion line information, and the low temperature at the high band closes to the calculation result of the atomic line, at a low band is lower than the calculation of the atomic line, which reflects the temperature of the luminous channel of the outer corona.

Effect of Electron Beam on the Structure and Crystallization Features of BaO-SrO-TiO_2-SiO_2 Glass

Glasses of BaO-SrO-TiO2-SiO2 after electronic radiation treatment of 50 - 1000 kgy were studied by means of IR spectra, DTA and visible light absorption method. The result shows that the glass structure is changed due to the formation of structure defect from oxygen vacancy and E’ color center, which resultsd in the crystallization process and new precursors, and decreasement of Tg temperature and crystallization peaks by 20 -50℃.

Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors(HEMTs)

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures,we set up a radiation damage model of AlGaN/GaN high electron mobility transistor （HEMT） to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results,consistent with the experimental results,indicate that thin AlGaN barrier layer,high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT;when the acceptor concentration induced is less than 10^14cm-3,the shifts in threshold voltage are not obvious;only when the acceptor concentration induced is higher than 10^16cm-3,will the shifts of threshold voltage remarkably increase;the increase of threshold voltage,resulting from radiation induced acceptor,mainly contributes to the degradation in drain saturation current of the current-voltage （Ⅰ-Ⅴ） characteristic,but has no effect on the transconductance in the saturation area.

Transport Properties of InAs-lnP Solid Solutions

Transport phenomena, namely electrical properties of n-type crystals of InAs and InP solid solutions were investigated in the temperature range 4.2-300 K before and after irradiation with fast neutrons and electrons. Maximum integral fluence of fast neutrons was 2× 1018 n.cm2. At the irradiation with 3 MeV electrons, the integrated electron fluence was 5 × 1017 e·cm2. We show that point type defects play an important role in the radiation processes. They are effective scattering centers of charge carriers in lnAs, InP and InPxASl.x solid solutions irradiated with 3 MeV energy electrons, especially for InAs-rich solid solutions. The charge carriers scattering mechanisms and accordingly the values of mobility are defined by disordered regions in samples irradiated with fast neutrons. The presence of minimum mobility value in composition dependence of mobility disappears after fast neutrons irradiation, which indicates that the contribution of ＂alloy＂ scattering is negligibly small in crystals irradiated with fast neutrons at both room and low temperatures.

The Instability of Terahertz Plasma Waves in Two Dimensional Gated and Ungated Quantum Electron Gas

The instability of terahertz（THz）plasma waves in two-dimensional（2D）quantum electron gas in a nanometer field effect transistor（FET）with asymmetrical boundary conditions has been investigated.We analyze THz plasma waves of two parts of the 2D quantum electron gas：gated and ungated regions.The results show that the radiation frequency and the increment（radiation power）in 2D ungated quantum electron gas are much higher than that in 2D gated quantum electron gas.The quantum effects always enhance the radiation power and enlarge the region of instability in both cases.This allows us to conclude that 2D quantum electron gas in the transistor channel is important for the emission and detection process and both gated and ungated parts take part in that process.

Medium-energy electron spectrometers on Macao Science Satellite-1

The Macao Science Satellite-1 is a two-satellite constellation specifically designed to study the geomagnetic field and particle radiation environment in low Earth orbit,particularly in the South Atlantic Anomaly region,with a low inclination orbit.Each of the two MSS-1 satellites carries a medium-energy electron spectrometer(MES).The MES sensor heads are based on pinhole imaging technology,which can simultaneously measure 50-600 keV electrons incident from nine directions with a field of view(FOV)of 180°×30°.The two MESs can realize the pitch angle coverage of medium energy electrons at most positions in the orbit.The MSS-1 A/B MESs can realize direct observation of precipitating electrons and electrons near their loss cones.It can help to study the electron generation mechanism in the inner radiation belt and quantify the precipitation of magnetospheric energetic electrons.Combined with the geomagnetic index,solar wind parameters,interplanetary magnetic field conditions,etc.,it can also help to build a dynamic evolution model of energetic electrons in the near-Earth space,to realize the early warning and prediction of space weather based on the observation data,which can provide safety for spacecraft and astronauts in the nearEarth space.

Radiation construction and excellent performances of Ag NPs/TiO_(2)/PEG/PVP multifunctional aerogel:Adsorption-photocatalytic degradation,photosensitive antibacterial and cytotoxicity

A cutting-edge method known as photocatalytic antibacterial technology can effectively eliminate drug-resistant bacterial strains and boast a wide-ranging antimicrobial capability.In the study,a novel Ag NPs/TiO_(2)/PEG/PVP(ATPP)aerogel photocatalyst was synthesized by an electron beam in-situ radiation method using polyethylene glycol(PEG),polyvinylpyrrolidone(PVP),AgNO_(3),and TiO_(2)as raw materials.ATPP was characterized by X-ray diffraction spectroscopy(XRD),X-ray photoelectron spectroscopy(XPS)and solid ultraviolet diffuse reflectance spectroscopy(UV-Vis DRS).The results demonstrated that silver ions were reduced to silver nanoparticles by electron beam radiation method.At the same time,the doping of silver nanoparticles(Ag NPs)enhanced visible-light adsorption.The degradation rate of methylene blue(MB)on 5%(in mass)ATPP could reach 81%under visible light for 180 min.Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)were used as model bacteria to explore the antimi-crobial properties of ATPP by zone of the inhibition method,plate counting method and live/dead bacterial staining.Cyclic antibacterial experiments showed that the antibacterial effect of ATPP was sustainable.Meanwhile,MTT assay and Hoechst33342/PI double staining were used to prove that the composite had good biocompatibility.The aerogel photocatalytic material has the potential to decrease microbial presence in both medical and environmental settings,making it a valuable tool for such applications.

Effect of seed electron injection on chorus-driven acceleration of radiation belt electrons

Using the hybrid finite difference method, we solve the Fokker-Planck equation to study the effect of seed electron injection on acceleration of radiation belt electrons driven by chorus waves. Numerical results show that in the absence of injection chorus waves can accelerate electrons at large pitch angles （ae〉60°）, producing enhancements in the phase space density （PSD） of （1-2 MeV ） electrons by a factor of 100-1000 within 1-2 days. In the presence of injection, chorus waves yield increase in PSD of electrons by accelerating the injected seed electrons. Meanwhile, the PSD evolution increases as the pitch angle in- creases but decreases as electron energy increases. Moreover, the PSD evolution can extend to higher energies with a time scale of 1-2 days for 1-2 MeV energies. When the injection increases by a factor of 10 higher than the initial value and re- mains for about two days, maximum values of PSD for 1 or 2 MeV increase to 6 or 3 times respectively higher than those without injection in two days. The current results suggest that the injected seed electrons play an important role in the evolu- tion of the radiation belt electrons.

Investigation of electrons inside the satellite by the Geant4 simulation

The measurement of the electron radiation inside the satellite is important for engineering and space environment researches.The particle radiation detectors (PRD) on board CBERS-1 and CBERS-2 made great contribution to understanding of the space environment.Then,what is the radiation relationship between inside and outside the satellite? The Monte Carlo simula-tion with Geant4 was implemented to study the problem.The boundaries of the energy bins of 0.5 and 2 MeV were precisely corresponding to outside energies of 0.99 and 2.52 MeV,respectively.Besides the changes of the energy bins,the fluxes inside were smaller than those of the corresponding bins outside.The spectrum inside the satellite was harder than that outside.An indicator was that the flux ratio of the high energy bin to the low energy bin increased more than 20% from outside to inside.The geometric factor (GF) relates to the incident energy of electrons.By using the AE-8 model to derive the incident spec-trum,the GFs of the low and high energy bins were 1.15 and 0.70 cm2 sr,respectively.GF of the low energy bin was larger than that of the high energy bin.But they were both smaller than the previous results.It was due to the scattering,straggle and shielding effects.

Quantitative determination of the electron beam radiation dose for SARS-CoV-2 inactivation to decontaminate frozen food packaging

The spread of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) from cold-chain foods to frontline workers poses a serious public health threat during the current global pandemic. There is an urgent need to design concise approaches for effective virus inactivation under different physicochemical conditions to reduce the risk of contagion through viral contaminated surfaces of cold-chain foods. By employing a time course of electron beam exposure to a high titer of SARS-CoV-2 at cold-chain temperatures, a radiation dose of 2 kGy was demonstrated to reduce the viral titer from 10^(4.5)to 0 median tissue culture infectious dose(TCID_(50))/mL. Next,using human coronavirus OC43(HCoV-OC43) as a suitable SARS-CoV-2 surrogate, 3 kGy of high-energy electron radiation was defined as the inactivation dose for a titer reduction of more than 4 log units on tested packaging materials. Furthermore, quantitative reverse transcription PCR(RT-qPCR) was used to test three viral genes,namely, E, N, and ORF1ab. There was a strong correlation between TCID50and RT-qPCR for SARS-CoV-2detection. However, RT-qPCR could not differentiate between the infectivity of the radiation-inactivated and nonirradiated control viruses. As the defined radiation dose for effective viral inactivation fell far below the upper safe dose limit for food processing, our results provide a basis for designing radiation-based approaches for the decontamination of SARS-CoV-2 in frozen food products. We further demonstrate that cell-based virus assays are essential to evaluate the SARS-CoV-2 inactivation efficiency for the decontaminating strategies.

Test particle simulation on the ion and electron zebra stripes and their time evolution in inner radiation belt

During February 15–16, 2014, the energetic electron spectrogram for four successive inner radiation belt crossing show clearly the electron zebra structures and their time evolution which last for about 17 h. Unfortunately, the time of flight(TOF) in RBSPICE measurement is turned off below 3 RE, and the ion measurement is contaminated by electrons. Thus in this study we studied the differences between the ion and electron zebra stripe structures and their time evolution using simple theory and test particle simulation, combining the electron measurement from RBSIPICE onboard Van Allen Probes. Theoretical analysis predicts that the ion zebra stripe structures should lie at a higher energy range than the corresponding electron zebra stripe structures due to that the directions of gradient B drift and corotation E×B drift are the same for electrons while opposite for ions. Test particle simulation with the dipole magnetic field and Volland-Stern electric field model have shown that the ion and electron zebra stripe structures could be produced by the convection electric field penetrating into the inner magnetosphere in this event, with their time evolution determined by total drift velocity that are different for ions and electrons. The predicted differences between the ion and electron zebra stripe structures are partially verified through observation. The ion zebra stripe structures could have potential influence to the ring current.

Heijiangdan Ointment(黑绛丹膏)Relieves Oxidative Stress from Radiation Dermatitis Induced by ^(60)Co γ-Ray in Mice

Objective：To investigate the effects of Heijiangdan Ointment（黑绛丹膏,HJD） on oxidative stress in （60）Co γ-ray radiation-induced dermatitis in mice.Methods：Female Wistar mice with grade 4 radiation dermatitis induced by ^（60）Co γ-rays were randomly divided into four groups（n=12 per group）;the HJD-treated,recombinant human epidermal growth factor（rhEGF）-treated,Trolox-treated,and untreated groups,along with a negative control group.On the 11 th and 21 st days after treatment,6 mice in each group were chosen for evaluation.The levels of superoxide dismutase（SOD）,malondialdehyde（MDA）,and lactate dehydrogenase（LDH） were detected using spectrophotometric methods.The fibroblast mitochondria were observed by transmission electron microscopy（TEM）.The expressions of fibroblast growth factor 2（FGF-2） and transforming growth factor β1（TGF-β1） were analyzed by western blot.Results：Compared with the untreated group,the levels of SOD,MDA and LDH,on the 11 th and 21 st days after treatment showed significant difference（P〈0.05）.TEM analysis indicated that fibroblast mitochondria in the untreated group exhibited swelling and the cristae appeared fractured,while in the HJD group,the swelling of mitochondria was limited and the rough endoplasmic reticulum appeared more relaxed.The expressions of FGF-2 and TGF-β1 increased in the untreated group compared with the negative control group（P〈0.05）.After treatment,the expression of FGF-2,rhEGF and Trolox in the HJD group were significantly increased compared with the untreated group（P〈0.05）,or compared with the negative control group（P〈0.05）.The expression of TGF-β1 showed significant difference between untreated and negative control groups（P〈0.05）.HJD and Trolox increased the level of TGF-β1 and the difference was marked as compared with the untreated and negative control groups（P〈0.05）.Conclusion：HJD relieves oxidative stress-induced injury,increases the antioxidant activity,mitigates the fibroblast mitochondrial damage,up-regulates the expression of growth factor,and promotes mitochondrial repair in mice.