77TH ANNIVERSARY ADDRESS - Indian National Science Academy

Investigations of Absorption of X-rays near Laue DiffractionMaximaThe variation, if any, in the absorption of X-rays at and near the Lauediffraction maxima have been investigated in ‘thin’ diamond crystals. Thetotal transmitted intensity, which is sum of the normally diffracted, forwarddiffracted and the residual direct beams has been measured as a functionof the glancing angle q around the Laue diffraction maxima. A changein the total transmitted intensity is expected to show the change in theabsorption of X-rays. It is possible to quantitatively determine the value ofabsorption coefficient of the specimen from these experiments.Figure 25 shows a set of three curves obtained with a (111) naturaldiamond platelet, which was oriented for diffraction in the Laue geometry.3530Total Transmitted X-ray Intensityµ = 0.075 /mmX-ray Intensity, kc/s252015µ = 0.219 /mm ∆µ/µ = 65.58%at PeakResidual Beam +Forward Diffracted Beam105Diffracted Beam00 200 400 600 800 1000 1200Glancing Angle, arc secFig. 25: A set of three curves for a (111) natural diamond crystal. The top curve shows variation in thetotal transmitted intensity as a function of q; the middle curve shows changes in the intensityof the residual direct plus the forward diffracted beams and the lowest curve is the usualdiffraction curve. These have been recorded with Mo Ka 1radiation in symmetrical Lauegeometry and (+,-,+) configuration of the diffractometer28