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采用中心能量为13.1 keV (最大能量小于30 keV)的轫致辐射光子碰撞Au靶, 在130°—170°的探测角度范围内以10°为间隔, 测量了碰撞产生的特征X射线Lι, Lα, Lβ和Lγ1的光谱. 根据实验测得的能谱结果, 综合考虑探测器的探测效率及靶材的吸收校准后, 计算了不同探测角度下特征X射线Lα与Lγ1及Lι与Lγ1的相对强度比; 而且, 还基于不同探测角度下X射线强度比值, 分析了特征X射线的角分布情况. 实验结果表明特征X射线Lα和Lι为各向异性发射. 此外, 计算了特征X射线Lι的各向异性参数为0.25, 并据此推断出L3支壳层的定向度A20为0.577 ± 0.081; 分析认为L3支壳层的定向度A20由该支壳层本身的物理特性决定, 但该支壳层的各向异性参数β会受到Coster-Kronig跃迁的影响而发生改变.The vacancy can be produced through impact ionization of target atom by energetic particles. It is of significant importance to study the vacancy state by the measurement of angular distribution of typical X-rays. At present, accurate ionization cross-section data of the atomic inner shell are urgently required in many areas. However, the precise measurement of ionization cross-section of the atomic inner shell is largely dependent on the fact that whether the characteristic radiation (e.g., X-ray) is isotropic.In this experiment, the characteristic Lι, Lα, Lβ and Lγ1 X-rays for Au target are measured by a silicon drift detector in an emission angle range from 130° to 170° in steps of 10°. A mini-X ray source is utilized to produce bremsstrahlung with the center energy of 13.1 keV.Considering detection efficiency of the detector and the absorption of the target, relative intensity ratios, I(Lα)/I(Lγ1) and I(Lι)/I(Lγ1), are obtained at different detection angles based on the experimental energy spectrum results. Moreover, the angular dependence of X-ray intensity ratio is investigated and it is found that the X-rays Lι and Lα exhibit anisotropic emission.According to the X-ray intensity ratio I(Lι)/I(Lγ1) and the P2(cosθ), and using the least square method, the anisotropic parameter β of characteristic X-ray Lι is derived to be 0.25. Due to the relation β = ακA20, the value of the alignment degree A20 for L3 sub-shell is determined to be 0.577 ± 0.08. Alignment degree A20 for L3 sub-shell is dependent on its intrinsic physical properties, while the anisotropy parameter β of typical X-rays can be affected by Coster-Kronig transition process.The behavior of the alignment for inner-shell vacancy states calls for more research results both in theory and in experiment. Therefore, it is quite relevant and meaningful to perform more experiments to further study the angular distribution of vacancy states by electrons, photons and ions impacting a target.
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Keywords:
- photoionization /
- characteristic X-rays /
- angular distribution /
- anisotropy parameter
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中国物理学会期刊
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