SMALL-GAP WIDTH MEASUREMENT WITH A FINITE X-RAY SOURCE

Theoretical work was carried out in order to assess the feasibility of measuring small gap widths by using X-rays. The work was done using o ptical geometry, and the effect of the various geometrical parameters (source dimension, geometrical enlargement, gap width, and film positi on relative to the no-umbra point) on the apparent gap size was invest igated. The influence of some other parameters (eg full reflectance of the beam from the gap edges or misalignment of the source and the gap axis) is also discussed. The results, which are presented graphically and analytically, enable the user to plan a measurement in an optimal way and help in analysing the results correctly.