The equation of pseudo-Kossel curves

The geometry of the X-ray divergent beam technique in back reflection is examined. It is shown that the pseudo-Kossel lines obtained are not conics but equations of the fourth degree. The method of Lider & Rozhanskii is studied in detail and it is shown that the assumption that the lines are conics would lead to significant errors. An alternative method whereby all of the points on the lines could be utilized, and the unknown parameters found by a least-squares method, is suggested.