Improvement of light coupling in BGO detector module by optimization of the crystal shape

A detector shape optimization study was carried out for the high-resolution 4×4 array BGO-PMT (bismuth-germanate-photomultiplier-tube) coupling scheme to be used in the spherical positron emission tomograph. To improve the light collection efficiency in the BGO detector array, the authors used bullet-nose-shaped BGO crystal at both the front- and the back-side of the detector, the latter being coupled to the PMT´s photocathode. It was hypothesized that the smooth, round front-side bullet-nose shape, by eliminating the sharp corners of the crystal, would improve the light collection efficiency and that the bullet-nose shape at the back-side of crystal, coupled to the PMT, would provide optimal coupling between the crystal and the PMT by the focusing property of the bullet-nose shape. Computer simulations and experimental studies were carried out, confirming these suppositions