Assembly Instructions

The collet assembly consists of several expanding rings, one set of solid tapered and the other a spring collet. They are placed on top of each other, alternating between the two kinds, with a spring collet on the top facing the scintillator and the collet nut. As the collet nut is screwed in, it presses against the assembly and the spring collets slide inward against the tapered solid ones, thus clamping against the light guide. Care should be taken, when placing these two different kind of collets inside each other, so as not to align the gaps in the plastic and create light leaks. The collets are not continuous rings, otherwise they would not be compressible, and the gaps can allow light all the way into the PMT if they are aligned. The collet nut is placed first around the light guide and the successive layers of the moulded collets are then placed around the light guide; one should make sure that enough free length of exposed light guide remains to enter the housing to slightly compress the PMT and base assembly, as in the case of the 2" base. Once the slight compression of the spring loaded PMT-socket assembly is verified, the set of collet rings is moved to enter the housing and rest firmly against the snap/stop ring inside the front tubular housing. Then the collet ring is screwed in using the special tool until the light guide is firmly bedded in the housing and cannot be moved in or out. The remaining procedure is the same as that of the 2" base. Due to the two diameter shape of the 5" PMT and its mu-metal shield, insertion of the PMT pins into the socket is a blind operation. It has to be done by feel and experience; the pins can only go in a specific PMT-socket geometry and it needs experience to learn when the correct alignment has been achieved. Let someone who has experience do it, bending of the socket pins at the base of the PMT results in destroyed PMTs, and they are expensive. WARNING: The plastic insulator sleeve inside the front tubular aluminum housing should be in place BEFORE the mu-metal shield/PMT assembly is inserted. Failure to assure the proper location of the insulating plastic sleeve may result in electrical shock.