Breadth of the Compton Modified Line with the Double Crystal Spectrometer

Three experimenters using the double crystal spectrometer have recently reported very much narrower structure for the Compton modified line than the structure observed photographically by DuMond and Kirkpatrick with the multicrystal spectrograph whose resolution was entirely adequate to reveal such a narrow structure. We have repeated the experiment using a double crystal spectrometer similar to theirs. The results obtained are in satisfactory agreement with the previous observations of Compton line breadth by DuMond and Kirkpatrick with the multicrystal spectrograph and in disagreement with the experimenters who used double crystal spectrometers. The conclusions drawn are: (1) The Compton modified line due to Mo $K\alpha$ radiation scattered by graphite at angles of 165° ± 10° and examined with the double crystal spectrometer has a breadth of from 21 to 22 XU at half-maximum height; (2) Under the above conditions there is no appreciable separation of the $K\alpha$ doublet in the shifted position; (3) No fine structure exists in the scattered spectrum of intensity greater than one-fifth the modified line intensity; (4) The ratio of modified to unmodified line intensity is estimated at (7.3:1); (5) There appears to be no essential difference between the results obtained with the single crystal, multicrystal and double crystal spectrometers in the study of this problem.