Experimental bremsstrahlung yields for MeV proton bombardment of beryllium and carbon

Experimental bremsstrahlung yields for 2, 3 and 4 MeV protons on thin beryllium and carbon targets have been measured. The yields have been corrected for detector efficiency, self-absorption in the target and fitted to 9th order polynomials over the X-ray energy range 1-10 keV for easy comparison with theoretical calculations.     

Cross-sectional investigation of radiation damage of 2 MeV proton-irradiated silicon carbide

Cross-sectional investigation is an important method to study ion irradiation effects in the depth direction. In this study, 2 Me V H~+was implanted in 6 H-SiC single crystals to investigate the effects of light ion irradiation on SiC. Raman spectroscopy and scanning electronic microscopy(SEM) were carried out on crosssectional samples to reveal the in-depth damage states and dopant behavior. The most damaged region is a little shallower than that predicted by the SRIM procedure,owing to the uncertainty in SRIM simulations. Layered structures representing zones of varying damage after2 MeV H ion irradiation are clearly observed. Two bands are observed in SEM images, of which on band corresponds to the damage peak, while the other band at the end of the H ion-affected area is probably a result of H diffusion propelled by a hydrogen-rich layer during irradiation.A charge accumulation effect related with conductivity on the sample surfaces during SEM tests is observed in theH-implanted area. A model is proposed to explain these phenomena.     

Ion beam induced luminescence of polyethylene terephthalate foils under MeV H and He ion bombardment

The evolution of the ion beam induced luminescence (IBIL) of the polyethylene terephthalate (PET) foils was studied under the irradiation of H and He ions of MeV energy. The optical and chemical changes of the samples were also examined by photo-stimulated luminescence and optical absorption measurements after the irradiation. A prominent broad emission peak of IBIL appeared at around 380 nm, and its intensity monotonically decreased during the ion irradiation. The decay curves of the emission intensity were quantitatively explained as a function of the electronic energy deposition of the incident H and He ions. On the contrary, to the decrease of the main emission peak, a growth of new peaks was observed in the wavelengths between 500 and 600 nm.     

Absorption and outgassing of helium during He+ ion bombardment of niobium

Conclusions The capute and outgassin of helium during bombardment by He⁺ ions of energy up to 15 KeV of a niobium target witha temperature of 290–1800°K have been studdied. It has been shown that as the temperature during irradation, T_b, is increased the coefficient of gaseous emission, , increases, while the number of injected atoms, N₀, and the capture coefficient decrease. For temperature greater than 1500°K practically 100% of the bombarding atoms are released to the vacuum. As the dose is increased, and N₀ increase and falls. An increase in to unity indicates saturation of saturation of theniobium by helium. The irradiation dose at which this saturation sets in and its level decrease with the temperature T_b.As a result of an analysis of the outgassing spectra, it has been shown thatthe release of helium occurs in three stages, each of which is due to one of the following causes: diffusion of individual atoms dissolved in the lattice; relase of helium from gas bubbles located in the volume of the metal; release of gas due to bursting of the shells of surface blisters. The last process has a basic role in outgassing at large irradiation doses.Translated from Atomnaya Énergiya, Vol. 38, No. 3, pp. 152–155, March, 1975.     

1.55 MeV 3He离子辐照单晶Si引起的损伤效应研究

室温下使用1.55 MeV、5×1013-5×1016/cm2注量的3He离子注入单晶Si,采用透射电子显微镜(TEM)观测分析了高温退火后单晶Si中由注入引起的损伤形貌,同时使用核反应分析(NRA)技术研究了3He气体原子的热解吸.结果显示,低注量3He离子注入在Si中产生的缺陷主要为一些小尺寸的位错或位错环;在中等照射剂量,退火导致了气泡和气泡团簇的形成并伴随着高密度的位错环从这些气泡团簇中发射出来;而对于较高的照射剂量,3He离子注入加上随后的高温退火则在离子射程附近产生了一个具有确定边界的空腔带.结合NRA结果对实验现象进行了分析.     

1.5 MeV He+离子注入SI-GaAs制备太赫兹光电导天线

用1.5MeV He+离子注入半绝缘砷化镓晶体(SI-GaAs),以其为基体制成光电导天线。太赫兹时域光谱测量显示,以离子注入晶体为基体的光电导天线,其时域信号强度是未注入晶体的3倍,略强于以LT-GaAs晶体为基体的光电导天线,但拥有比LT-GaAs晶体为基体的光电导天线略宽的频谱宽度和相当的信噪比。实验结果表明,用1.5MeV He+室温注入SI-GaAs制备太赫兹光电导天线的最佳注量约为1×1016ions·cm-2。     

Experimental results of the erosion of molybdenum due to blistering by He+ bombardment

We report some preliminary measurement of the erosion rate of plasma dumps when bombarded with 100 keV He⁺ ions at high power density ( 1 MW/m²). The expected erosion rates, based on measurements of He blistering that were made at lower power density ( 0.3 MW/m²), indicate a potentially serious problem for fusion reactors. Our tests use a reactorlike power density and produce He blisters at a rate that is slower than predicted by 2 to 4 orders of magnitude, depending on the temperature of the molybdenum target.     

Energy Dependence of MeV He+ Ion-Induced Re-Emission of Hydrogen Isotopes Implanted into Graphite

The energy dependence of MeV He⁺ ion-induced re-emission of hydrogen isotopes (H and D) implanted into graphite has been measured by means of the elastic recoil detection (ERD) technique in order to clarify the collision process for the ion-induced detrapping. The experimental re-emission profiles have been analyzed by solving the mass balance equations, in which the ion-induced detrapping cross section σ _d and the rate constants of the retrapping Σ ^T and local molecular recombination K between an activated hydrogen atom and a trapped one are taken into account. The values of σ _d and K/Σ _T have been determined from the best-fit analytical solution to the experimental re-emission profiles. It has been found that the average values of σ _d and K/Σ _T for H are twice as large as those for D, which is the so-called isotope effect.

It has been shown that the experimental values of σ _d and their energy dependence agree well with the theoretical ones, which are calculated using the power-law approximations for Thomas-Fermi potential, on the assumption that the ion-induced detrapping of hydrogen isotopes takes place due to elastic displacement collisions with energetic carbon recoils produced by incident MeV He⁺ ions.     

Analysis of the anisotropy,stoichiometry and polytypes in pyrolytic carbon and silicon carbide coatings

Silicon carbide (SiC) and pyrolytic carbon (PyC) coatings in tristructural isotropic (TRISO) coated fuel particles were characterised by a combination of 2-modulator generalised ellipsometry microscopy (2-MGEM), Raman spectroscopy and transmission electron microscopy. We compared the values of anisotropy obtained from 2-MGEM and Raman spectroscopy to investigate the effect of sampling area and microstructure. No linear correlation in anisotropy was found between these two techniques despite both sampling areas of 2–5 μm. The largest deviations were observed for highly anisotropic samples with optical anisotropy factors (OPTAFs) above 1.1. For medium and low anisotropy samples (OPTAF < 1.1) the relationship is close to linear. The limited use of only the average value of diattenuation does not give an accurate representation of the characteristics of the coatings as significant areas can exist with considerably higher diattenuations that could increase the probability of failure under neutron irradiation. We also observe a change in the diattenuation of SiC due to the presence of stacking faults as confirmed by Raman spectroscopy. Raman spectroscopy was also used to perform semiquantitative analysis of the Si and carbon excess in SiC in four TRISO particles.     

用锥形玻璃毛细管聚焦获取MeV能量He~+微米离子束

用锥形玻璃毛细管聚焦离子束方法获取微米离子束成本低、使用方便,我们制备了出口口径35-110μm不等的多种锥形玻璃毛细管,并用其在2×1.7 MV串列加速器上获得了出射束流密度比入射束流密度大的MeV能量He~+微离子束。用金硅面垒探测器(SBD)测量在毛细管与入射束夹角不同条件下出射的微米束的能谱,并对锥形玻璃毛细管聚束的机制做初步定性讨论。     

Cesium migration in silicon carbide

Pyrolytic silicon carbide has been exposed to cesium vapor at elevated temperatures and the distribution of the metal has been examined by ion analysis. A strong influence of microstructural defects on the cesium migration has been observed. Silicon carbide samples of different microstructure have been investigated. Striations in the structure caused an enhanced diffusion of the cesium into the silicon carbide.     

Defect evolution in MeV ion-implanted silicon

Lightly doped silicon samples of both n- and p-type have been implanted with low doses of H, B and Si ions using energies between 1 and 6 MeV. The resulting electrically active point defects were characterized by deep level transient spectroscopy (DLTS) and several of these defects involve oxygen and/or carbon, two major impurities in as-grown crystalline silicon. Both interstitial- and vacancy-type defects are observed; in particular, interstitial carbon is found to migrate at room temperature with a diffusion constant of 1 × 10⁻¹⁵ cm² s⁻¹ and is effectively trapped by interstitial oxygen atoms. The concentration of implantation-induced defects increases linearly with dose but the defect production decreases at high enough dose rates. This dose rate effect depends on the ion mass and is qualitatively predicted by computer simulations of the defect reaction kinetics.     

Measuring the generation lifetime profile modified by MeV H+ ion implantation in silicon

A silicon wedge mask with thickness varying from approximately 5 μm to a few hundred μm has been used for converting the depth distribution of defect concentration induced by 4 MeV H⁺ ion implantation in silicon to a lateral scale on the surface, i.e. the distance from the edge of the wedge mask. Thus, using proper devices fabricated on bulk Si prior to ion implantation, depth profiles of the generation lifetime of minority charge carriers and of the different defect densities can be measured by the transient capacitance method and by Deep Level Transient Spectroscopy (DLTS), respectively. The distribution of lifetime follows well that of the implantation induced vacancies calculated by the TRIM code in the applied dose range (from 1 × 10¹⁰ to 3 × 10¹¹ H⁺/cm²). The correlation between implantation dose and lifetime decrease is also discussed.     

Epitaxial silicon carbide for X-ray detection

We present the first experimental results of X-ray detection and spectroscopy by means of Schottky junctions on epitaxial silicon carbide (SiC). The devices have a junction area of 3 mm² on an n-type 4H-SiC layer 30 μm thick with a dopant concentration of 1.8×10 cm at 300 K, the reverse current density of the best device varies between 2 pA/cm² and 18 pA/cm² as the mean electric field is increased from 40 kV/cm up to 170 kV/cm. The devices have been tested with X and γ rays from ²⁴¹Am; the best measured energy resolution is 2.7 keV FWHM at room temperature     

Irradiation damage in reaction-bonded silicon carbide

Reaction-bonded SiC loses nearly 50% of its fracture strength when exposed to neutron irradiation. Young's modulus also decreases rapidly. The damage occurs soon after exposure and levels out with continuing exposure up to $\text{3 × 10}{}^{21}\text{n/cm}{}^2$. Both α- and β-SiC undergo a nearly Isotropic expansion that saturates with increasing irradiation. Silicon undergoes a very small expansion and mechanical property degradation. The strength reduction in SiC is explained in terms of differential lattice expansions between SiC and Si which result in misfit strains and subsequent crack growth and critical flaw size extension.     

Thermal conductivity mapping of pyrolytic carbon and silicon carbide coatings on simulated fuel particles by time-domain thermoreflectance

Thermal conductivity of pyrolytic carbon and silicon carbide coatings on spherical particles has been mapped using time-domain thermoreflectance. The thermal conductivities measured for pyrolytic carbon ranged between 3.4 and 13.5 W/m K. The effect of porosity, pore-size distribution, anisotropy, in-plane disorder and domain sizes is discussed. A thermal conductivity of 168 W/m K was obtained for SiC. Mapping of the thermal conductivity of coated fuel particles provides useful data for modeling fuel performance during the operation of nuclear reactors.