Positron annihilation lifetime spectroscopy using fast scintillators and digital electronics

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 943; p. 162507
• Main Authors: Fang, M., Bartholomew, N., Di Fulvio, A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 01.11.2019; Elsevier
• Subjects: CFD; Digitizer; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; Organic scintillator; Positron lifetime; Digitizer; CFD; Positron lifetime; Organic scintillator
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2019.162507

Positron Annihilation Lifetime Spectroscopy (PALS) is a non-destructive radiological technique widely used in material science studies. PALS typically relies on an analog coincidence measurement setup and allows the estimate of the positron lifetime in a material sample under investigation. The positron trapping at vacancies in the material results in an increased positron lifetime. In this work, we have developed and optimized a PALS experimental setup using organic scintillators, fast digitizers, and advanced pulse processing algorithms. We tested three pairs of different organic scintillators: EJ-309 liquid, EJ-276 newly developed plastic, and BC-418 plastic, and optimized the data processing parameters for each pair separately. Our high-throughput data analysis method is based on single-pulse interpolation and a constant fraction discrimination (CFD) algorithm. The setup based on the BC-418 detector achieved the best time resolution of 198.3±0.8 ps. We used such optimized setup to analyze two single-crystal quartz samples and found lifetimes of 161±4 ps, 343±12 ps and 1.34±0.05ns, in good agreement with the characteristic time constants of this material. The proposed experimental set up achieves a time resolution comparable to the minimum positron lifetime in quartz, which makes it possible to accurately characterize material vacancies by discriminating between the lifetimes of either the spin singlet or triplet states of positronium. The optimized data processing algorithms are relevant to all the applications where fast timing is important, such as nuclear medicine and radiation imaging.