低温下活性炭吸附分离Kr和Xe

研究了低温下活性炭吸附分离Kr和Xe的方法。Kr和Xe混合气在-78 ℃活性炭吸附柱上进行富集,根据Kr、Xe在活性炭柱上脱附条件的差异实现了Kr和Xe的分离。结果表明,Kr和Xe的回收率均大于90%,Kr样品中Xe的去污系数达10⁴以上,Xe样品中Kr的去污系数达10³以上。     

碳分子筛上氪、氙的动态吸附及脱附性能

为筛选快速分离Kr/Xe的材料,研究了不同碳分子筛（CMS）对氙（Xe）和氪（Kr）的动态吸附性能与脱附性能,探讨了压力、气体流量、温度等因素对Kr、Xe的动态吸附系数与脱附率的影响。结果表明,碳分子筛Aladdin TDX-01对Xe的吸附容量最大,其次为光复TDX-01,低温时,Aladdin TDX-01对Kr的动态吸附系数大于光复TDX-01。Aladdin TDX-01碳分子筛对Kr和Xe的吸附能力均随压力升高而增强,随着原料气流量增加而减少,动态吸附系数随着温度升高而降低;采用N2吹扫对Kr、Xe进行脱附,随着N₂流量增大、温度升高,Kr、Xe的脱附时间缩短。Aladdin TDX-01碳分子筛在25 ℃、100 kPa条件下对Xe的动态穿透吸附系数为1 283 mL/g,在-50 ℃、100 kPa条件下对Kr的动态穿透吸附系数为474 mL/g。     

Production of Multiply-Charged Ions of Ne, Ar, Kr and Xe by the Electron-Bonbarded Hot Cathode IoN Source of IPCR

Production of multiply-charged ions of Ne, Ar, Kr and Xe has been studied by use of an electron-bombarded hot cathode type ion source of the IPCR 160cm cyclotron, which is similar to Morozov's source. These multiply-charged ions were accelerated by a 3rd harmonics acceleration mode in the cyclotron and detected with a beam probe fixed at the radius of 55cm. Observed multiply-charged ions are Ne2+, Ne3+, Ne4+, Ne5+, Ar3+, Ar4+ Ar5+, Ar6+, Ar7+, Ar8+, Kr6+, Kr7+, Kr8+, Kr9+, Xe9+, Xe10+ and Xe11+. Relative abundance of each charge state of four elements were measured. In case of Kr and Xe , the intensity of observed multiply-charged ions decreased to 1/3 or 1/4 when the charge number is increased by one. Intensities of Ar4+, Ar6+, Ar8+, Kr6+ and Kr8+ were measured as a function of the operation conditions of the ion source, such as arc voltage, arc power and gas flow rate. It was found that a smaller gas flow and a higher arc power brought about a higher yield in all the measured ions. Obtained current intensities of ion source output are 40?A Ar8+, 600?A Kr6+, 40?A Kr9+, 150?A Xe9+ and 10?A Xe11+ respectively.     

Color center creation in LiF crystals irradiated with Xe, Kr and N ions: Dependence on fluence and beam current density

Single LiF crystals were irradiated with Xe (195 MeV), Kr (117 MeV), and N (18 MeV) ions. Using absorption spectroscopy, color center creation was analyzed as a function of the ion energy loss, fluence, and flux. The concentration of single F centers and F₂ centers versus fluence and flux exhibits a nonlinear evolution with saturation at higher fluences. For LiF irradiated with N ions at high fluence, the concentration of F centers is proportional to the cube root of the flux indicating the strong interaction of primary hole centers. Macroscopic hillocks were observed in all irradiated LiF crystals by atomic force microscopy.     

Swift heavy ion induced magnetic phase transition of Fe–Rh alloy

We report the effects of swift heavy ion irradiation on structure and magnetic properties of Fe–50at.%Rh alloys. The alloys are irradiated with 120–200 MeV heavy ions (Ni, Kr or Xe) at room temperature. Before and after the irradiations, the magnetization and the lattice parameter are measured by using superconducting quantum interference device (SQUID) and X-ray diffractometer (XRD), respectively. The lattice parameter at room temperature increases by about 0.3% and antiferromagnetic–ferromagnetic transition temperature decreases below 5 K by the irradiations. Effects of electronic excitation due to swift heavy ions on the change in magnetic properties and lattice structure are discussed.     

用制备色谱法分离氪氙

叙述了通过改变填充5A分子筛色谱柱的载气流速和色谱柱温度,改变氪、氙的保留时间,实现氪、氙分离。分离后,在低温下分别用活性炭收集。结果表明,延长氪、氙色谱柱保留时间的间隔,可提高氪、氙的去污系数;在–80oC低温下,活性炭能很好地收集氪和氙,回收率>95%。     

In situ and postradiation analysis of mechanical stress in Al2O3:Cr induced by swift heavy-ion irradiation

Optical spectroscopy and TEM techniques have been applied to study the radiation damage and correlated mechanical stresses in Al₂O₃ and Al₂O₃:Cr single crystals induced by (1-3) MeV/amu Kr, Xe and Bi ion irradiation. Mechanical stresses were evaluated in situ using a piezospectroscopic effect through the shift of the respective lines in ionoluminescence spectra. It was found that dose dependence of the stress level for Xe and Bi ions, when ionization energy loss exceeds the threshold of damage formation via electronic excitations, exhibits several alternate stages showing the build-up and relaxation of stresses. The beginning of relaxation stages is observed at fluences associated with beginning of individual ion track regions overlapping. The residual stress profiles through the ion irradiated layers were deduced from depth-resolved photostimulated spectra using laser confocal scanning microscopy set-up. It was determined that stresses are compressive in basal plane and tensile in perpendicular direction in all samples irradiated with high energy ions.     

钍基液态燃料熔盐实验堆氙毒分析

熔盐堆作为第四代核能系统堆型之一,液态燃料形态的特点使其可以实现在线处理和在线添料。为了提高中子经济性可以利用在线处理的氦鼓泡法,将氦气通入反应堆一回路,去除堆芯内的裂变气体(如Xe、Kr)。基于钍基熔盐液态堆(Thorium Molten Salt Reactor-Liquid Fuel1,TMSR-LF1)概念设计,结合熔盐实验堆(Molten Salt Reactor Experiment,MSRE)氙毒模型,分析了鼓泡法去除氙毒中~(135)Xe扩散规律和去除效率对氙毒的影响,并给出了对应的初始有效增殖因子的变化规律。分析结果表明,虽然存在~(135)Xe会大量向石墨扩散的可能性,但是鼓泡法仍然可以有效去除TMSR-LF1堆芯内的~(135)Xe,减小堆芯毒性,提高反应性。     

复杂混合气体组分在低温活性炭表面的吸附特性

为实现大体积气体中微量放射性气体Kr、Xe同位素的测量,须将混合气体进行浓集并将目标气体吸附于10 mL左右的活性炭源盒中。本实验对混合气体中各组分在活性炭分离柱上的吸附性能进行研究,建立了通过去除其他杂质气体、浓集大体积气体制备放射性Kr和Xe活度源的方法。根据反应堆流出气体和核爆可能生成的气体组分,配制了模拟气体,使用活化的4A分子筛对其中的水和CO₂进行模拟去除,获得了流程中去除水和CO₂的实验条件;选择5个低温点(273、264、255、246、238 K),在低温活性炭柱上对H₂、CO、CH₄、Kr和Xe的吸附特性进行研究,测定了各气体在不同温度下的吸附穿透曲线。结果表明,室温下4A分子筛对水和CO₂有较好的吸附效果。低温下,H₂、CO不易在活性炭表面吸附;CH₄、Kr吸附性质相似;Xe吸附能力较强。低温下难以去除的CH₄可在高温下氧化去除。因此,可根据混合气体中各组分性质的不同实现杂质气体的去除和目标气体Kr、Xe的回收测量。     

后处理厂释放气体中稳定惰性气体同位素在核保障监督中的应用研究

用Origen2．1计算模式对压水堆元件中Kr,Xe相关同位素与燃耗的关系进行了计算,并估算了后处理厂烟囱释放气体中Kr,Xe各稳定同位素的来源,丰度和原子浓度.^82Kr,^129Xe可用作环境样品中惰性气体同位素的天然本底;裂片^83Kr／^86Kr．^84Kr／^86Kr、^131Xe／^134Xe和^132Xe／^134Xe的丰度比值,可用于指示乏燃料燃耗,进而估算正在被分离的钚同位素组成,并有可能对后处理厂实行保障监督。     

Electrical conductivity increase of Al-doped ZnO films induced by high-energy-heavy ions

We have investigated the effects on electrical properties of Al-doped ZnO (AZO) semiconductor films induced by 90 MeV Ni, 100 MeV Xe and 200 MeV Xe ions. The AZO films with c-axis orientation on SiO₂-glass substrate were prepared by using a RF-sputter-deposition method at 400 °C. We find that the conductivity increases by two order of magnitude under high-energy-heavy ion irradiation, as has already been observed for 100 keV Ne ion irradiation. We also find that the efficiency of the conductivity enhancement, which is defined as the conductivity increment per a unit of ion fluence, scales super-linearly with the electronic stopping power (S_e). The carrier density and mobility for unirradiated and irradiated AZO films are presented.     

MeV He+ bombardment of silicon carbide and carbon

Samples of carbon, graphite, and silicon carbide have been bombarded with 0.6 and 3.5 MeV He⁺ to doses ranging from 0.03 C/cm² to 1.5 C/cm² (ion currents ranged from 10 μA/cm² to 100 μA/cm²). All samples experience surface uplifting. At 0.6 MeV, blisters form on near-theoretical density silicon carbide whereas on permeable graphite the surface appears to expand outward by separating along the existing pore and crack structure. These surface features are not observed for bombardment at 3.5 MeV. For larger doses, large effective sputtering coefficients for silicon carbide result from flaking off of successive layers. Smaller erosion rates are observed for a pyrolytic carbon with intermediate porosity, and no net erosion has been observed for the permeable graphite. Surface porosity is thought to play an important role in determining the effects of the ion bombardment.     

Structural changes in anatase TiO2 thin films irradiated with high-energy heavy ions

In order to investigate possible structural changes due to high-density electronic excitation, anatase TiO₂ thin film specimens were irradiated with 230 MeV ¹³⁶Xe¹⁵⁺ ions and 200 MeV ¹⁹⁷Au¹³⁺ ions. X-ray diffraction (XRD) patterns were measured before and after irradiation. The intensity of the XRD peak assigned to the (0 0 4) planes of anatase TiO₂ decreases in an exponential manner as a function of ion-fluence. This result can be explained by the formation of the cylindrical damaged regions (i.e. ion tracks) with diameters of 9.6 and 16.3 nm for 230 MeV Xe and for 200 MeV Au ion irradiations, respectively. The difference in the track diameter between Xe ion irradiation and Au ion irradiation can be attributed to the difference in the electronic stopping power (and to the ion-velocity effect, if any). For 200 MeV Au ion irradiation, splitting of the (0 0 4) peak is observed. The original (0 0 4) TiO₂ peak remains in the same position, but the new peak shifts to higher angles as fluence increases.     

Dislocation mobility study of heavy ion induced track damage in LiF crystals

The track damage created in LiF crystals by swift U, Xe and Kr ions with a specific energy of 11.1 MeV/u was studied using dislocation mobility measurements, track etching, SEM, AFM and optical microscopy. The results demonstrate high sensitivity of dislocation mobility to track core damage. The relationship between the energy loss of ions, dislocation mobility and track structure is discussed.     

SIMS analysis of an UO2 fuel irradiated at low temperature to 65 MWd/kgHM

The results of a wide-ranging post-irradiation study of a PWR nuclear fuel by secondary ion mass spectrometry are presented. The average cross-section burn-up and the radial burn-up profile were determined from the radial distributions of one or more of the stable isotopes of fission product Nd. The fission gas Kr was analysed in-situ in a nuclear fuel for the first time and an investigation of the total fission gas content of the high burn-up structure using depth profiling was performed. It was confirmed that Kr is together with Xe in the pores of the high burn-up structure, and that almost all the fission gas lost from the fuel matrix is contained in the pores. In addition to Xe and Kr, the volatile fission products Te, Cs, I and Rb were also detected in the pores. The radial distributions of the minor actinides in the fuel are also reported. It was found that ²³⁷Np, unlike the isotopes of Pu, Am, and Cm, does not increase in concentration at the fuel rim.     

The mechanisms of in-pile fission gas release from UO2

In-pile release mechanisms of fission gas from UO₂ at low temperatures were studied. The release of ¹³³Xe, ¹³⁵Xe, ¹³⁸Xe, ^85mKr, ⁸⁸Kr and ⁸⁷Kr from a sintered UO₂ pellet was measured at temperatures ranging from 250 to 930°C using a graphite specimen holder. The release from the holder, in which a fraction of fission gas was recoil-implanted, was subtracted to obtain the net release from the UO₂ pellet. Knock-out release from the UO₂ was measured directly, and it was found that it was not the main release mechanism, at least not for short-lived nuclides. A ‘pseudo-recoil’ release model is proposed to explain the low temperature release under irradiation. In the model, some of the defects produced by fission fragments act as short-lived carriers for fission gas.     

MeV能量Si~+引起二次离子发射的研究

利用北京大学2×1.7 MV串列加速器终端的飞行时间(TOF)谱仪,分别用1.5、2.0和3.0MeV三种能量的初级束Si+轰击样品来研究其二次离子发射现象,使用的样品包括石墨、碳纳米管等。结果表明,采用合理的降噪方法后得到了高信噪比和高时间分辨率的二次离子质谱,实现了全质量范围无遗漏记谱。利用H-C12峰刻度之后,计算得出二次离子各成分的最可能构成及产额,碳纳米管样品表面氢质量含量为8.15%。同时,发现MeV能区二次离子产额与Si+阻止本领之间的关系并非简单的正相关。     

Heavy Ion Source with Pulsed Magnetic Field

A compact P.I.G. ion source with pulsed field and end extraction is described. The source produces multiply ionized N, C, Ne, A, Kr and Xe. Pulsed currents of C3+, N3+, Ne3+, A3+, Kr3+ , Xe6+ between a few tens of ?A and a few hundreds of ?A have been obtained. Small size and power consumption make it compatible with a Van de Graaff terminal where space and power are at a premium.     

Behaviors of fine (IG-110) and ultra-fine (HPG-510) grain graphite irradiated by 7 MeV Xe26+ ions

Developing a molten salt reactor needs molten salt-impermeable nuclear graphite. Ultra-fine grain graphite is a good choice as it is better in permeability than fine grain graphite. In this paper, ultra-fine grain graphite(HPG-510) and fine grain graphite(IG-110) samples are irradiated at room temperature by 7 MeV Xe ions to doses of 1 × 10~(14)-5 × 10~(15) ions/cm~2. Scanning electron microscopy, transmission electron microscopy(TEM), Raman spectroscopy and nano-indentation are used to study the radiation-induced changes. After irradiation of different doses, all the HPG-510 samples show less surface fragment than the IG-110 samples. The TEM and Raman spectra,and the hardness and modulus characterized by nano-indentation, also indicate that HPG-510 is more resistant to irradiation.     

Cross-sections and transport properties of F ions in Ar, Kr and Xe

The aim of the current work is to determine with relatively high accuracy the elastic momentum-transfer cross-sections of F⁻ ions in collisions with noble gases Ar, Kr and Xe. We have applied a simple form of momentum-transfer theory (MTT) based on elastic collisions as the first step in order to develop negative fluorine ion/Ar, Kr, Xe elastic momentum-transfer cross-sections based on the available data for reduced mobilities at 300 K as a function of E/N. In our procedure MTT is used only as the initial step to make adjustments and thus save a lot of computation time. However, our final results have been all obtained by exact Monte Carlo (MC) technique that has been well tested and documented. The unfolded cross-sections were validated or further improved by assuring a good agreement between our MC calculated transport data and the available experimental results for reduced mobility and longitudinal diffusion in the range from 1 Td to 500 Td. We have also calculated the net rates of elastic scattering and detachment.