On the Theory and Use of Ross Filters

Abstract

Resolving power, preferred thickness and balance errors of Ross filters for x-ray monochromatization are discussed. It is theoretically impossible to balance two filters of elementary composition because of scattering, L limits and K jump, even if the absorption coefficients of the two filters vary similarly with wave-length between the limits, which is not known to be the case. It suffices, however, to obtain good balance for wave-lengths near the pass band since others longer and shorter may be relatively reduced by pre-filtration through a filter whose composition is the same as that of the high atomic number member of the balanced pair. The K jump balance error may be completely removed by adding a slightly absorbing filter of low atomic number to one member of the pair. By employing a specially designed ionization chamber Ross filters may be used simultaneously instead of alternately and a considerable gain in speed and accuracy achieved.