Ruggedized photomultiplier tube and optical coupling in armored detector

Abstract

A photomultiplier tube and a method and apparatus for molding an optical coupler thereto are described. An optical coupler molding fixture includes a frame and a frame base. A photomultiplier tube is positioned within the frame between a spring and a shim. The optical coupler is formed with a mold which is positioned against the shim. A cavity is created radially interior to the shim between the photomultiplier tube and the mold. The optical coupler is molded to a faceplate of the photomultiplier tube with the fixture oriented so that its longitudinal axis L is parallel to the ground. A clamping structure presses the mold against the shim and provides the optical coupler material a non-leak space in which to cure. The optical coupler material is injected into the mold through a fill hole, and may be injected at ambient temperature. Curing time may range from one week at ambient temperatures to four hours at 65° C. The mold can be machined to create any form desired for the optical coupler. The shim can be sized and configured to allow for adjustment in the thickness of the optical coupler. The optical coupler may be as thin as less than 0.015 inches in thickness. If, for example, a thicker optical coupler is desired, the shim may be made thicker. The edge of the photomultiplier tube housing which abuts the shim is checked for its perpendicularity to the longitudinal axis L. Without perpendicularity, proper alignment of the photomultiplier tube is less likely.