Weak extra peak in rocking curves of X-ray reflexion for incident beams obtained by successive asymmetric reflexions

A numerical calculation is made on the intensity distribution of the beam obtained from the X-ray collimator system of monolithic silicon crystal, in which double 422 asymmetric Bragg-case diffractions of Cu Kα1 take place successively. It is concluded that a weak subsidiary peak found in the rocking curve obtained with a double-crystal diffractometer of parallel setting using a collimator of the above type is caused by the relative angular shift of the range of total reflexion for each crystal component due to the refraction effect.