卢旺达Gatumba地区花岗伟晶岩的地质、地球化学特征及其成因研究综述

Gatumba花岗伟晶岩矿区位于卢旺达西部,在约150 km2的范围内出露130多条大型伟晶岩脉,它是卢旺达目前最重要的稀有金属矿产地。该地区的花岗伟晶岩具有完整的区域分带,从内到外(以Gitarama岩基为中心)依次为:黑云母伟晶岩、二云母伟晶岩、白云母伟晶岩及矿化伟晶岩,其中矿化伟晶岩属于LCT(Lithium-Caesium-Tantalum)型伟晶岩。从区域上看,这些花岗伟晶岩与强过铝质的G4花岗岩(Generation 4th,时代约为986±10 Ma)在时空上密切相关,其形成时代约为950~980 Ma,普遍认为G4花岗岩是Gatumba地区花岗伟晶岩的母岩。不同分带伟晶岩中的单矿物(如:黑云母、钾长石、电气石)化学成分分析的结果显示,从靠近岩体的贫矿伟晶岩到远端的矿化伟晶岩呈现出一种岩浆连续分离结晶演化的趋势。此外,利用瑞利分离结晶模型进行岩浆演化过程模拟的结果表明(以G4花岗岩为起始点),从黑云母伟晶岩到矿化伟晶岩演化程度越来越高,它们分别代表G4花岗岩母岩浆发生0~69%(F=0~69)、69%~92%(F=69~92)、92%~98%(F=92~98)及98%(F≥98)分离结晶作用的产物。综合现有认识可知,花岗岩结晶分异成因模式是Gatumba地区花岗伟晶岩出现不同区域分带的最合理解释。

K-Shell Ionization of Molybdenum and Iron by Electron Bombardment

K-ionization cross sections of Mo and Fe by electron impact were measured by detecting characteristic x-ray emitted by thin solid Him targets of known mass thickness with a Si(Li)detector.Rejection correction of a substrate was done by bipartition model of electron transport.The experrmenta.1 results are compared with theoretical calculation and empirical formula calculation.

L-Shell Ionization Study of Tungsten by Electron Impact

L-shell partial production cross sections of L_(α)-,L_(β)-,L_(γ)-rays by electron impact were measured by observing the counts of x-rays from an impacted thin tungsten target.The total production cross sections and mean ionization cross sections were deduced from the measured results.The electron beam energy range was found to be 11-36 keV.The influence of electrons reflected by the backing on ionization cross sections has been corrected.The experimental results agree well with the theoretical predictions.

Activation Cross Section Measurement for the ^(165)Ho(n,γ)^(166)Ho^(m) Reaction

The cross sections for the 165Ho（n.γ）166Ho? reaction have been measured rel-ative to the 197Au（n.γ）198Au reaction at neutron energies of 203,676 and 974 keV usingthe activation technique in combination With high resolution HPGe detector gamma rayspectroscopy Experimental data were given for the first time.