New Rugged High-Temperature Photomultipliers

A new photomultiplier has been designed which, up to temperatures of 150°C, is suitable for scintillation counting of the natural radioactivity of sediments traversed by an oil well. It uses a special head-on photocathode which is a compromise of stability, sensitivity and noise. The tube envelope is made of a succession of parallel Kovar and glass rings fused together. Venetian-blind dynodes of the Lallemand type are welded to the inner side of the Kovar rings and bleeder resistors to the outer side. This structure combines excellent mechanical properties (ruggedness, freedom from microphonics) with the very high electrical insulation needed, even at elevated temperatures. Taking advantage of the great versatility of the multiplier structure, several other types of tubes were built with conventional photocathodes (S-11 and S-17) and 14 and 18 stages. They are intended for applications requiring good performance associated with ruggedness.