A focusing collimator for research in scanning.

Abstract

A description is given of the latest directional gamma detector developed at Oak Ridge National Laboratory. Gamma rays are detected by a 3-inch diameter by 2-inch thick NaI(Tl) crystal integrally mounted on a 3-inch phototube. The crystal is housed in a massive tungsten alloy shield, two inches thick at the sides and 3 inches thick at the front. The focusing element is a conical gold insert with 37 tapered hexagonal holes focused on a point 3 inches from its front face. Because of the use of tungsten and gold, the assembly is more expensive than lead collimating shields. However, it is believed that the increased expense may be justified by the unremarkably improved performance. In particular, the improved shielding of the new detector appears to have alleviated some of the problems in outlining the liver. (P.C.H.)