Abstract
The relative yield of 3 gamma to 2 gamma annihilation was measured for a positron emitter, (22)Na, with the new scintillator detectors lanthanum chloride (LaCl(3):Ce) and lanthanum bromide (LaBr(3):Ce), which had been characterised for comparison with high-purity germanium (HPGe) and sodium iodide (NaI(Tl)) detectors. The information obtained from the ortho-positronium 3 gamma decay in positron emission tomography (PET) can be a measure of the oxygen content in biological tissues by determination of this relative yield. However, it requires high resolution spectroscopy and detection efficiency. Characterisation of the new generation of scintillator detectors determines whether they could replace conventional scintillators and semiconductors. A series of experiments was carried out with different samples in order to study the effect of ortho-positronium formation. The peak-to-peak and the peak-to-valley methods were compared in the measurement of the relative yield of 3 gamma to 2 gamma annihilation.