Six-Meter Radius Bent-Crystal Spectrograph for Nuclear Gamma Rays

Abstract

A six-meter radius bent-crystal spectrograph for the precision measurement of nuclear gamma-ray wavelengths has been designed, constructed, and placed into operation at the Massachusetts Institute of Technology. This instrument is particularly well suited for directly measuring neutron capture gamma rays produced by samples placed in the through port of the MIT research reactor. The spectrograph is designed to measure wavelengths of gamma rays in the energy region from 0.1 to 4.0 Mev with an estimated precision that varies from about 0.01% at 0.1 Mev to 0.3% at 4 Mev. Photographic methods are used to record the gamma-ray lines on the focal circle. A bent crystal is used to diffract and focus the gamma rays. Line width and efficiency data have been obtained for the (310), (003), and (006) planes of quartz. The efficiency of the instrument is quite low. In order to record a line at 2.0 Mev an exposure time of about 6000 curie hours is required.