Towards both larger and smaller Scintispheres®

High-resolution scintillation spectrometers based on the use of large-volume spherical CsI(Tl) spectrometers viewed by conventional 1 cm² PIN diodes, have been shown to have excellent performance characteristics. In particular, their unique geometry, the small area of contact between the diode and the crystal´s surface and the high reflectivity of the packing material, combine to provide a detector in which there is a very small variance in the signal generated by energy deposits in different regions of the crystal. In view of the unique spectral-resolution achieved using the first prototype Scintispheres (S100-PIN and S300-PIN) to be manufactured, it was natural to explore the boundaries within which this technology might be useful. This paper presents the results of a series of modelling exercises and experimental investigations aimed at finding the range of detector volumes that can usefully be constructed based on the use of PIN photodiodes. For a given amplifier performance, the predicted spectral-resolution of a range of Scintisphere^® volumes have been estimated as a function of energy. This study was made both for the CsI(Tl) material used in the original devices and for other materials which may be important when the speed of operation and stopping power are important design parameters. These studies also considered the performance limits that might be achievable in small volume Scintispheres. This paper also presents the results obtained when our deconvolution algorithm is applied to a wide range of standard scintillation spectrometers. These demonstrate the high spectral-resolution and sensitivity that can be achieved using this technique.