We saw what Frank did with his BGO crystals (he made a monster directional detector). I had a different plan, more suited to my pastime of collecting radioactive rocks: I wanted to take advantage of the high density and energy absorption cross-section of the material by making very small yet sensitive handheld detectors for field use. Unlike NaI, BGO is tolerant of mechanical and thermal stresses, making it particularly adaptable to field instruments.
Shown below are the parts of a ~1x1" square BGO detector, having eight of the little PET scanner crystals coupled with silicone gel to a 1x1" square dual-anode PMT from the same PET scanner. The dynode resistors and caps are soldered directly to the pins of the PMT. The dynode resistance is 10M, with 44M between the cathode and Dynode 1. The dual anodes and dual Dynode 7 electrodes are in parallel. The whole thing fits into a padded 1 1/2" copper pipe with end caps.
Mel Stairs and I have played with these little units in hunting thorium minerals in New Mexico.
-Carl
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2006-05-01 17:58 "micro" BGO detector 
(Carl Willis) [Latest: 2006-05-02 14:40]