| 摘要 |
An interactive computer controlled asymmetric texture-sensitive parafocussing X-ray powder diffractometer employs an incremental rotating specimen device which permits azimuthal rotation (through the angle phi of the disc-shaped specimen about its surface normal. The rotating specimen device, rotatable about the principal diffractometer axis, can be offset an angle alpha from the symmetric position in which the specimen surface normal makes the angle (90- theta ) DEG with both the source-to-specimen and detector-to-specimen directions. In order to maintain the Brentano focussing condition, the photon-counting detector is supported on a slide which is translated towards or away from the specimen by a stepper-motor drive lead screw. K, the ratio of the detector-to-specimen and x-ray source-to-specimen distances is constrained to the specified range c<K<f, where c is the smallest and f the largest ratio achieved. The focussing condition is realized by computer control which maintains K=sin ( theta + alpha )/sin ( theta - alpha ) and modifies the measured intensity by multiplying its value by 0.5(K+1)K0.75exp[ mu R(K-1)] where R is the source-to-specimen distance, and mu , the linear absorption coefficient for air.
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