Position reconstruction of heavy-ion interactions in plastic scintillator detectors

Active stoppers in the field of low-energy nuclear spectroscopy are detector systems wherein both radioactive ions and their decay products are measured. Information regarding the time and the position of the interactions is needed in order to correlate the daughter radiation with its parent such that physical properties of the decaying system can be obtained. Whereas silicon-based technologies (e.g. segmented double-sided silicon strip detectors) are well established for this use, they exhibit a limited timing resolution that prohibit fast-timing measurements of nuclear states fed by β or α decay. The use of detector systems based on organic plastic scintillator material coupled with silicon photomultipiers as active stoppers offers the attractive possibility of providing excellent timing properties for some experimental cases where short-lived excited nuclear states are fed by particle radiation. In this work, we investigate the position resolution for heavy-ion interactions of the ' β Plast' plastic scintillator detectors developed for use in DESPEC (DEcay SPECtroscopy) experiments at the GSI/FAIR facility. We present a novel method of extracting interaction positions employing k-nearest neighbour, non-generalising search methods using a highly-segmented double-sided silicon strip detector to provide reference samples. A KD-Tree search method with a Euclidean metric yields resolutions of σ X = 1.43(5) mm and σ Y = 1.27(2) mm in the X and Y directions, respectively.