Experimental comparison of the relative yield of 3γ/2γ positron annihilation using semiconductor and scintillation detectors

Abstract

The yield of three photon positron annihilation is measured using semiconductor and scintillation detectors in a comparison for applications in positron emission tomography, particularly in the exploitation of three photon positron annihilation imaging where good energy resolution and good efficiency are required. In this experimental study four detectors, High-purity Germanium (HPGe), Sodium Iodide (NaI(Tl)), Lanthanum Chloride (LaCl₃:10%Ce³⁺) and Lanthanum Bromide (LaBr₃:5%Ce³⁺) were used. The peak-to-peak method was used with a ²²Na source to determine these yields. Aluminium was employed as a reference material as its high electron density reduces positronium formation and lifetimes. Teflon was also used in order to enhance the formation of ortho-positronium, since quenching is low, leading to increased three photon positron annihilation. The relative 3γ/2γ yields obtained were (3.04±0.11)·10⁻², (2.17±0.11)·10⁻², (3.26±0.10)·10⁻² and (2.03±0.11)·10⁻² for LaBr₃:Ce, LaCl₃:Ce, NaI(Tl) and HPGe detectors, respectively. Among these detectors LaBr₃:Ce proved to be the detector of choice for three photon imaging applications as it has both good energy resolution and efficiency.