Ar16+ 离子与Au和Mo靶相互作用产生的X射线截面随入射角度的变化

本实验工作是在兰州重离子加速器国家实验室ECR离子源完成。实验采用能量为336keV的低能高电荷态Ar16+离子轰击Au、Mo金属靶，入射离子与靶表面之间的夹角分别是20°，25°，……，80°，入射角与出射角之和为90°。测量了不同角度下Mo的Lα、Lβ，Au的Mα和Ar的Kα特征X射线谱，对实验谱进行了高斯拟合，计算了不同入射角下的各条X射线的产额和产生截面，并将靶原子发射出的X射线截面与ECPSSR和带结合能修正的BEA理论计算的结果进行了比较。发现当入射角较小时，Ar16+与金属靶相互作用时所产生出的各条特征X射线截面随入射角的增加而增加，当入射角达到40°左右后X射线截面基本上保持不变。与ECPSSR计算值相比，本实验中Au的X射线截面比较接近，实验值比ECPSSR计算值小不到一个量级；而Mo的X射线截面实验值比ECPSSR计算值大3-4个量级，但产额与带结合能修正的BEA计算值很接近

97MeV~(16)O + ~(51)V反应中α粒子发射机制研究

利用近物所1.7米回旋加速器加速出的97MeV的~(16)O束流轰击~(51)V靶，九组不同的望远镜系统用于对~(16)O + ~(51)V反应中击射α粒子进行单举测量及α粒子与类弹产物符合测量。所有的探测器组号通过电子学线路和近物原的MODAS 1数据获取系统以事件方式记录在磁带上，实现了42参数同时获取。与此同时，利用所提供的束流，完成了CsI(Tl)晶体phoswich探测器的调试工作，得到了好的结果。在VAX/11-780计算机上用PAX数据分析程序对实验数据进行离线分析，得到了α粒子单举能谱、角分布，E-O平面内d~2σ/dEαΩ等高图和速度平面内d_2σ/PCdEdΩ截面等高图；得到了复合核蒸发和直接α粒子发射的截面值。同时也得到了α粒子——类弹产物符合的α粒子能谱和前方向击射α粒子与类弹产物符合的两维能量联图。为了对直接机制中予平衡发射α粒子的贡献有一估计，用激子模型对~(16)O + ~(51)V反应系统进行了理论计算，得到了复合核蒸发及予平衡发射α粒子产额占总产额中所占的比份。实验结果和理论分析表明：除复合核蒸发和予平衡发射的贡献外，还有其它反应机制的存在。通过二体和三体运动学对所得到的符合实际数据进行分析，证明了类弹、类靶跟随发射和弹核破裂(break-up)机制的存在。综合所有的实际结果，我们认为：~(16)O + ~(51)V反应系统中α粒子主要采源于复合核的蒸发和予平衡发射机制，除此而外还应包括类弹、类靶发射和弹核破裂等反应机制的贡献

策勒绿洲4种杨树的生理生态学特性的研究——P-V曲线和持水力的研究

通过对策勒绿洲的 4种杨树 (新疆杨、箭杆杨、胡杨和灰胡杨 )的P -V曲线和持水力的测定分析 ,得出了初步结论 :人工栽培种新疆杨和箭杆杨的抗旱性能低于乡土树种胡杨和灰胡杨

Pt based anode catalysts for direct ethanol fuel cells

In the present work several Pt-based anode catalysts supported on carbon XC-72R were prepared with a novel method and characterized by means of XRD, TEM and XPS analysis. It was found that all these catalysts are consisted of uniform nanosized particles with sharp distribution and Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. Cyclic voltammetry (CV) measurements and single direct ethanol fuel cell (DEFC) tests jointly showed that the presence of Sn, Ru and W enhances the activity of Pt towards ethanol electro-oxidation in the following order: Pt1Sn1/C > Pt1Ru1/C > Pt1W1/C > Pt1Pd1/C > Pt/C. Moreover, Pt1Ru1/C further modified by W and Mo showed improved ethanol electro-oxidation activity, but its DEFC performance was found to be inferior to that measured for Pt1Sn1/C. Under this respect, several PtSn/C catalysts with different Pt/Sn atomic ratio were also identically prepared and characterized and their direct ethanol fuel cell performances were evaluated. It was found that the single direct ethanol fuel cell having Pt1Sn1/C or Pt3Sn2/C or Pt2Sn1/C as anode catalyst showed better performances than those with Pt3Sn1/C or Pt4Sn1/C. It was also found that the latter two cells exhibited higher performances than the single cell using Pt1Ru1/C, which is exclusively used in PEMFC as anode catalyst for both methanol electro-oxidation and CO-tolerance. This distinct difference in DEFC performance between the catalysts examined here would be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and additives. It is thought that an amount of -OHads, an amount of surface Pt active sites and the conductivity effect of PtSn/C catalysts would determine the activity of PtSn/C with different Pt/Sn ratios. At lower temperature values or at low current density regions where the electro-oxidation of ethanol is considered not so fast and its chemisorption is not the rate-determining step, the Pt3Sn2/C seems to be more suitable for the direct ethanol fuel cell. At 75 degreesC, the single ethanol fuel cell with Pt3Sn2/C as anode catalyst showed a comparable performance to that with Pt2Sn1/C, but at higher temperature of 90 degreesC, the latter presented much better performance. It is thought from a practical point of view that Pt2Sn1/C, supplying sufficient -OHads and having adequate active Pt sites and acceptable ohmic effect, could be the appropriate anode catalyst for DEFC. (C) 2003 Elsevier B.V. All rights reserved.

On the reactivity of Mo species for methane partial oxidation on Mo/HMCM-22 catalysts

By characterizing fresh and used Mo/HMCM-22 catalysts with ICP-AES, XRD, NH3-TPD technique, UV - Vis DRS and UV Raman spectroscopy, the reactivity of Mo species for methane partial oxidation into formaldehyde were directly studied with a new point of view. By comparing the fresh and used catalysts, it was found that the tetrahedral Mo species bonding chemically to the support surface were practically unchanged after the reaction, while the polymolybdate octahedral Mo species, which had a rather weak interaction with the MCM-22 zeolite, leached out during the reaction, especially when the Mo loading was high. Correspondingly, it was found from the time-on-stream reaction data that the HCHO yield remained unchanged, while COx decreased with the reaction time during the reaction. By combining the characterization results and the reaction data, it can be drawn that the isolated tetrahedral molybdenum oxo-species (T-d) is responsible for HCHO formation, while the octahedral polyoxomolybdate species (O-h) will lead to the total oxidation of methane.