吸收限附近非对称反射条件下X射线的异常透射

研究了原子吸收限附近非对称布拉格条件下完整平板晶体的X射线异常透射．当衍射主要由原子散射因子的虚部引起时，在严格的布拉格角处，晶体内部驻波的波节位于衍射原子面上，从而导致异常透射的发生．透射波主要来源于晶体内部坡印廷矢量指向晶体下表面（入射面为上表面）的波场．该波场的有效吸收系数随非对称因子a的增大而减小，所以整个晶体的透射系数随a的增大而增大．当原子散射因子的实虚部对衍射的贡献之比一定时，晶体内坡印廷矢量偏离色散面实部法向的程度随反射的非对称程度的增大而增大． 关键词：

ANOMALOUS TRANSMISSION OF X-RAYS UNDER ASYMMETRICAL REFLECTION CONDITION NEAR THE ABSORPTION EDGE

Anomalous transmission of X-rays for plance-parallel perfect crystals under asymmetrical Bragg reflection condition near the atomic absorption edge is studied in detail. When diffraction is induced mainly by the imaginary part of atomic scattering factor, the nodes of the standing wave within the crystal lie on the atomic plane at the exact Bragg angle, which results in an anomalous transmission. The transmitted beam comes mainly from the wave-field with its Poynting vector Poynting toward the lower surface of the crystal (the entrance surface being the upper one). The effective absorption coefficient of this wave-field decreases with the asymmetrical factor a. Therefore, the transmitted coefficient of the whole crystal increases as a increases. For a given ratio between the contributions of the real and imaginary parts of atomic scattering factor to diffraction, the deviation of Poynting vector from the normal of the real part of the dispersion surface increases with the degree of asymmetrical reflection condition.