In the last 10-15 years there has been a significant effort toward development and studies of new, more efficient and faster materials for detection of ionizing radiation. A growing demand for better scintillator crystals for detection of 511 keV gamma rays has been due mostly to recent advances in modern imaging systems employing positron emitting radionuclides for medical diagnostics in neurology, oncology and cardiology. While older imaging systems were almost exclusively based on BGO and NaI:Tl crystals the new systems, e.g. ECAT Accel, developed by Siemens/CTI, are based on recently discovered and developed LSO (Lu2SiO5:Ce, Ce-activated lutetium oxyorthosilicate) crystals. Interestingly, despite very good properties of LSO, there still is a strong drive toward development of new scintillator crystals that would show even better performance and characteristics.
In this presentation we shall review research conducted in the 90ties by a group led by Alex Lempicki in Boston, USA and then continued by a group in Torun, Poland. In particular we shall present spectroscopic and scintillator characterization of BaF2:Ce, YAP (YAlO3:Ce, cerium activated yttrium aluminate perovskite), and two relatively new complex oxide materials, namely LSO and LuAP (LuAlO3, lutetium aluminate perovskite) activated with Ce. We shall present and discuss results of measurements of scintillation light yields, scintillation time profiles, VUV spectroscopy and low temperature thermoluminescence performed on these crystals. We shall demonstrate that all these experiments can be consistently interpreted in the frame of a scintillation model that assumes radiative recombination of electron-hole pairs via Ce ions as a prime scintillation mechanism.