Si(Au)探测器的快中子辐射损伤

在核实验中,半导体硅探测器常用来对带电粒子和中子进行探测。其能量响应和时间响应特性均十分良好,但是耐辐射性能却较差,尤其在伴有γ和中子本底的环境中,由于辐照引起探测器晶格损伤,导致半导体探测器性能退化,如探测器漏电流增大、能量分辨本领变差、能量亏损增加、时间响应增长等,严重影响探测器的使用和寿命。     

Radiation damage effects in tritium implanted Si(Li) detectors

Tritium implanted Si(Li) detectors suffer from the effects of radiation damage during the implantation. These effects are manifested as a pulse height defect and as a broadening of the response function, and thus cause problems in the determination of the tritium beta end-point energy and in the determination of the electron antineutrino mass from the shape of the spectrum near the end point. We use simple models of the trapping of charge carriers to illustrate some of these problems.     

Operando FT-IR study on basicity improvement of Ni(Mg,Al)O hydrotalcite-derived catalysts promoted by glow plasma discharge

CO₂ adsorption on the surface of hydrotalcite-derived mixed oxide catalysts was investigated under low pressure glow discharge plasma in operando conditions via FT-IR spectroscopy. Nickel catalysts were promoted with various transition metal species (Ce, Fe, La, Zr) to influence their physico-chemical properties. Fe and Zr species were successfully incorporated into hydrotalcite brucite layers. After calcination formed a single phase with Ni(Mg, Al)O mixed oxide, while La and Ce species formed separate phases. This had a consequence in the distribution of surface basic sites as well as in the affinity to CO produced upon CO₂ dissociation in plasma. Plasma treatment activated the surface of prepared materials and changed their properties via the generation of strong basic sites associated with low coordinated surface oxygen anions. Moreover, the CO₂ adsorption capacity of prepared materials increased after plasma treatment.     

Radiation damage in undoped CsI and CsI (Tl)

Radiation damage in undoped CsI and CsI(Tl) crystals using ⁶⁰ Co gamma radiation for doses up to ~4.2×10⁶ has been studied. Samples from various manufacturers were measured, ranging in size from 2.54-cm-long cylinders to a 30-cm-long block. Measurements were made on the change in optical transmission and scintillation light output as a function of dose. Although some samples showed a small change in transmission, a significant change in light output was observed for all samples. Recovery from damage was also studied as a function of time and exposure to UV light. A short-lived phosphorescence was observed in undoped CsI, similar to the phosphorescence seen in CsI(Tl)     

Low silicon U(Al,Si)3 stabilization by Zr addition

Previous knowledge states that (U,Zr)Al₃ and U(Al,Si)₃ phases with Zr and Si content higher than 6 at.% (7.7 wt%) and 4 at.% (1.4 wt%), respectively, does not partially transform to UAl₄ at 600 °C. In this work, four alloys within the quaternary system U-Al-Si-Zr were made with a fixed nominal 0.18 at.% (0.1 wt%) Si content in order to assess the synergetic effect of both Zr and Si alloying elements to the thermodynamic stability of the (U,Zr)(Al,Si)₃ phase. Heat treatments at 600 °C were undertaken and samples were analyzed by means of XRD, EPMA and EDS techniques. A remarkable conclusion is that addition of 0.3 at.% Si in the (U,Zr)(Al,Si)₃ phase reduces in 2.7 at.% the necessary Zr content to inhibit its transformation to U(Al,Si)₄.     

Synthesis of nanostructured multiphase Ti(C,N)/a-C films by a plasma focus device

Nanostructured multiphase Ti(C,N)/a-C films were deposited using a 3.3 kJ pulsed plasma focus device onto silicon (1 0 0) substrates at room temperature. The plasma focus device, fitted with solid titanium anode instead of usual hollow copper anode, was operated with nitrogen and Ar/CH₄ as the filling gas. Films were deposited with different number of shots, at 80 mm from top of the anode and at zero angular position with respect to anode axis. X-ray diffraction results show the diffraction peaks related to different compounds such as TiC₂, TiN, Ti₂CN, Ti and TiC_0.62 confirming the deposition of multiphase titanium carbo-nitride composite films on silicon. X-ray photoelectron spectroscopy confirms the formation of Ti–C, C–N, Ti–N, Ti–O and C–C bonds in the films. Scanning electron microscopy reveals that the nanostructure grains are agglomerates of smaller nanoparticles about 10–20 nm in size. Raman studies verify the formation of multiphase Ti(C,N) and also of amorphous graphite in the films. The maximum microhardness value of the composite film is 14.8 ± 1.3 GPa for 30 shots.     

Deposition of titanium nitride on Si(1 0 0) wafers using plasma focus

Titanium nitride thin films were deposited on Si(1 0 0) substrates by using a low energy (2.3 KJ) Mather-type plasma focus device. The composition of the deposited films was characterized by X-ray diffraction (XRD). The crystallite size has strong dependence on the numbers of focus shots. The crystallinity of TiN thin films is found to increase with increasing the number of focus shots. The effect of different number of focus shots on micro structural changes of thin films was characterized by Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM). SEM results showed net-like structure for film deposited for 15 numbers of shots, which are elongated grains of Si₃N₄ in amorphous form embedded into TiN crystals. The average surface roughness was calculated from AFM images of the thin films. These results indicated that the average surface roughness increased for films deposited with increased number of focus shots. The least crystallite size and roughness are observed for film deposited with 25 focus shots.     

Radiation Damage to Amine Extractants, (II)

Radiation damage to 5 v/0 alkyl amine/kerosene modified with lauryl alcohol was studied for changes brought thereby in their behavior in Th and Pa extraction by scrubbing with 3N nitric acid, and stripping with 0.01 N nitric acid at 25°C.

Eight amines were used; Tri-n-octyl amine, N-cyclohexyl dilauryl amine, N-benzyl dilauryl amine, N-cyclohexyl lauryl amine, Dilauryl amine, Amberlite LA-1, Amberlite LA-2 and Primene JM-T. These solvents were used virgin as well as irradiated by ⁶⁰Co γ-ray to various doses up to 10⁸R. No marked changes in extraction-scrubbing-stripping behavior were observed in all the amines tested, except N-cyclohexyl lauryl amine and Dilauryl amine, which tended to form either third phase or emulsion.     

Production of defects in molybdenum by a deuterium glow discharge plasma

Conclusions Cathode bombardment of monocrystalline molybdenum surfaces oriented perpendicular to the [111] direction in a deuterium glow discharge plasma at a burning voltage of 500 V with a discharge current density of 4.5 mA/cm² and a temperature of 800°C leads to formation in the surface layer of edge and nearly edge loops with Burgers vectors b=a/2 111 lying in the {111} and {321} planes and the Burgers vectors b=a 100 lying in the {100}, {115}, and {117} planes. All loops with diameters >100 Å were injection loops. It is proposed that the smaller defects that can be seen in an electron microscope are also aggregates of interstitial atoms. The formation of dislocation loops with Burgers vectorsb=a 100 has been explained in terms of the large compressive stresses which arise in the surface layer of the foil during bombardment. The production of a large number of highly mobile interstitial atoms in the surface layer of a single crystal by the deuterium plasma and their subsequent diffusion to sinks probably play a dominant role in radiation-enhanced self- and heterogeneous diffusion.Translated from Atomnaya Énergiya, Vol. 48, No. 3, pp. 157–161, March, 1980.     

Synthesis of nanostructured multiphase (Ti,Al)N/a-Si3N4 thin films using dense plasma focus device

A 2.3 kJ pulsed plasma focus device was used to prepare thin films of nc-(Ti,Al)N/a-Si₃N₄ at room temperature. The plasma focus device, fitted with copper anode encapsulated with Ti_0.5Al_0.5 anode, was operated with nitrogen as the filling gas. Films were deposited with various number of focus shots, at 90 mm from top of the anode and at zero angular position with respect to anode axis. XRD patterns show the growth of polycrystalline (Ti,Al)N thin films with orientations in the (1 1 1), (2 0 0), (2 2 0) and (3 1 1) crystallographic planes. Behavior of lattice constant, grain size and film roughness of deposited film as a function of variation in number of focus shots is discussed. SEM micrographs of film deposited with 15 number of focus shots exhibit well-developed net like structure of nc-(Ti,Al)N/a-Si₃N₄ and possibly nc-(Ti,Al)N/a-Si₃N₄/a-AlN or nc-TiN/a-Si₃N₄/a-AlN. Surface Roughness ranging 64 nm to 89 nm was also observed.     

Radiation damage induced by 5 keV Si ion implantation in strained-Si/Si0.8Ge0.2

The damage distributions induced by ultra low energy ion implantation (5 keV Si⁺) in both strained-Si/Si_0.8Ge_0.2 and normal Si are measured using high-resolution RBS/channeling with a depth resolution better than 1 nm. Ion implantation was performed at room temperature over the fluence range from 2 × 10¹³ to 1 × 10¹⁵ ions/cm². Our HRBS results show that the radiation damage induced in the strained Si is slightly larger than that in the normal Si at fluences from 1 × 10¹⁴ to 4 × 10¹⁴ ions/cm² while the amorphous width is almost the same in both strained and normal Si.     

Heats of formation of (U,Mo)Al3 and U(Al,Si)3

The heats of formation of (U,Mo)Al₃ intermetallic compounds were obtained by measuring the reaction heats of U-Mo/Al dispersion samples by differential scanning calorimetry. Based on literature data for the reaction heats of U₃Si/Al and U₃Si₂/Al dispersion samples, the heats of formation of U(Al,Si)₃ as a function of the Si content were calculated. The heat of formation of (U,Mo)Al₃ becomes less negative as the Mo content increases. Conversely, the heat of formation of U(Al,Si)₃ becomes more negative with increasing Si content.     

Response of TlCl(I,Be) Crystals to Energetic Ionizing Radiation

Studies of scintillation TlCl(I,Be) crystals have been conducted using 8-GeV negative pions and 50- to 130-MeV positrons. Pulse shapes and resolutions of these crystals have been measured. Pulses from TlCl(I,Be) are observed to have a fast rise time (?2 nsec) and a complicated decay scheme consisting of at least three separate components. Attempts were also made to observe the Cerenkov radiation from these crystals due to highly relativistic particles. The resolution of the pulse height spectrum for a 2.9-cm diameter by 3.8-cm length TlCl(I,Be) scintillator was measured for 8-GeV negative pions. For comparison, the resolution of the same size CsI(Tl) scintillator was measured using the same experimental configuration. The resolution of CsI(Tl) is only slightly greater than theoretical prediction. The resolution of TlCl(I,Be) is greater, being limited by photon statistics even for 35 MeV of deposited energy. The resolution of a 7.6-cm diameter by 7.6-cm length TlCl(I,Be) crystal used as a Total Absorption Shower Counter for 50-130 MeV positrons has also been measured. This resolution is in reasonable agreement with previously reported data.     

A computational study of bond-breaking process of Cu–Si bond during ion sputtering of a Cu/Si(1 1 1) surface, based on molecular orbital theory

A theoretical approach based on molecular orbital theory has been provided. By applying this theory to a bond-breaking process, the ionization probability of Cu adsobates sputtered from a “5×5”-Cu/Si(1 1 1) surface has been studied. Three important aspects have been confirmed: (1) importance of a long range electrostatic potential such as the image potential, (2) importance of the coulomb repulsive potential between the Cu 4s spin-up and spin-down electron, and finally (3) acceleration and deceleration effects depending on charge state, which is a result of the interplay of the molecular bonding interaction and the long range electrostatic interaction. The measurements of ionization probability will provide us more information of the adiabatic potential curves of the reactants from the surfaces.     

Radiation Dosage Due to Neutrons Produced in a Vehicle by Protons in the Trapped Radiation Belt

The rate of production of neutrons by geomagnetically trapped protons incident on a vehicle was measured by a neutron counting system carried into the trapped radiation belt by a pod flow piggy back on an Atlas rocket on December 19, 1961. The flux of neutrons produced by radiation belt protons incident on the pod was determined to be at least 700 neutrons/(cm2 sec); the actual value depends somewhat on the energy spectrum of the neutrons. This flux was estimated to be equivalent to a dose rate in tissue of 0.10 rems/hr. On the basis of proton flux measurements made in the radiation belt by Freden and White, a calculation was made of the tissue dosage which would have been received in the same environment directly from protons. These calculations were made by obtaining a numerical integration of the dE/dx times RBE times flux product over the entire energy spectrum. The total dose calculated amounted to 2.78 rems/ hr. Further calculations were made to estimate the dose rates which would have been received by tissue in the same environment but with varying amounts of shielding around the vehicle. The proton dose is, of course, reduced by the shield but the neutron dose actually increases as the shielding thickness is increased. It is seen that the neutron dose equals the proton dose at .3 rems/hr. when aluminum shielding of 2.6" surrounds the vehicle and it exceeds the proton dose with thicker shielding.     

制备高分辨率Si(Li)X射线探测器的进展

Si(Li)半导体探测器对低能X射线具有能量分辨率好、探测效率高、输出脉冲正比于入射光子能量等特点,故已日益引起人们的兴趣。为使Si(Li)探测器有更高的能量分辨率,制造者正努力研究工作在低温的探测器和前置放大器。一般的Si探测器都有一个耗尽层范围,这个耗尽层是对射线灵敏的部分,它的厚度ω可表示为ω=0.3(ρν)~(1/2),这里ρ是使用的P型材料的电阻率,ν,是加到探测器上的反向偏压,由前式可知,用10000Ω/cm的材料,加200V偏压,也只能得到0.4mm厚的耗尽层,这种厚度对测量X射线显然是太薄了,即使是