A double-source double-crystal X-ray spectrometer for high-sensitivity lattice-parameter difference measurements

A method of measuring the difference between the lattice parameter of a region of an unknown sample and that of a region of a standard reference crystal to a sensitivity of 1 part in 10⁹ is presented. Problems inherent in multiple-beam arrangements due to sample strains and non-uniformity have been overcome by the use of a new double-source arrangement in which the two X-ray beams sample the same spot on a crystal under study. Ways of identifying and preventing errors from significant mechanical and thermal effects arising in the sensitivity region explored are indicated.