We have been instrumental in working with our supplier of detectors, Rexon Components, Inc., to improve the design of the pre amp/high voltage base used on our BGO (Bismuth Germanate) detectors. Rexon uses high quality 8 stage PMTs (photo multipliers) to get good resolution at high count rates with BGO at high gamma energies (up to 8 MeV or more). An eight stage PMT instead of the more traditional 10 stage PMT is used, because such high gain saturates the PMT at such high gamma energy.

Our extensive experience with BGO detectors revealed that they often suffered from saturation and non-linearity above 3 MeV. Without neutron sources, the highest energy that can be used to test detectors is 2.614 MeV, from the natural radioactivity of ²³²Th. But natural sources of ²³²Th are very weak. The highest energy obtainable from small NRC license exempt sources is about 1.4 MeV. Higher energy gamma-rays can be produced from various fast, thermal, and activation reactions using neutrons. But, unfortunately, possession of any neutron source requires (in the U. S.) a radioactive materials license.

The current market for scintillation detectors does not justify for most detector manufacturers (Rexon Compnents, Inc. included) the administrative and financial burdens of obtaining a radioactive materials license in order to test detectors at high energy. Therefore Rexon had no ability to test or even know about the saturation and non-linearity problems above 3 MeV. Our experience with various BGO detectors made by Rexon and access to neutron sources allowed us to discover this problem and make extensive tests for Rexon to determine the cause. Namely, it is the use of the 10 stage divider base that resulted in too high a voltage drop in the last stage of the PMT. With this knowledge, Rexon developed an 8 stage voltage divider that was developed specifically for their detectors. A prototype of this new base was tested at the Applied Physics Institute and yielded fantastic results. The non-linearity was eliminated and the saturation now occurred at count rates that were up to 10 times higher than before.

This is an example where our unique experience with and access to various radioactive sources, detectors, electronics, and so forth can be applied to problems in industry that would be very difficult or impossible to solve without this unique experience. These eight stage bases are now commercially available at Rexon Components, Inc.

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