The Apparent Shape of X-ray Lines and Absorption Limits

Abstract

Effect of instrumental factors on the observed intensity distribution of x-ray lines and at absorption limits.—(1) Slit width. In the case of two slits of equal width, sharp lines reflected from a perfect crystal should give an isosceles triangle distribution. If the two slit widths are unequal, the triangle is truncated; this may shift the relative position of the lines of a partly resolved doublet. (2) Slit height widens the isosceles triangles slightly, making the long-wave-length side less steep. (3) Non-uniform energy distribution over the focal spot produces corresponding lack of symmetry. An actual distribution curve obtained with very narrow slits showed two unequal maxima near the edges of the spot. The same three factors affect the apparent sharpness of the absorption limit. In particular, the finite slit width results in the rounding off of a sharp discontinuity into a skew-symmetrical S curve consisting of parts of two parabolas whose axes are vertical and separated a distance equal to the angular slit width.