| 摘要 |
A computer controlled asymmetric texture-sensitive parafocussing X-ray powder diffractometer employs an incremental rotating specimen holder for azimuthal rotation through an angle DIAMETER . The specimen holder is rotatable through an angle alpha from a symmetric position in which the specimen surface normal makes an angle (90- theta ) DEG with both the source-to-specimen and detector-to-specimen directions. In order to maintain the Brentano focussing condition, the detector is supported on a slide which can be moved towards and away from the specimen by a stepper-motor drive. A ratio K of the detector-to-specimen distance R on the one hand and the X-ray source-to-specimen distance P on the other hand is constrained to a range c < K < f. The desired focussing condition is realized by computer control which maintains K = sin ( theta + alpha )/sin( theta - alpha ) and modifies the measured value of the intensity by multiplying it by 0.5 (K + 1) K<0.75>exp [ mu R(K - 1)], where mu is the linear absorption coefficient for air. |
