The influence of radiation on Ps formation in PE studied by coincidence Doppler-broadening spectroscopy

The high-resolution Doppler-broadening spectroscopy of positron-annihilation gamma rays emitted during an experiment on positron annihilation lifetime spectroscopy (PALS) has been applied to study the radiation and oxygen effects on positronium (Ps) formation in polyethylene (PE). Using two Ge detectors, the DB spectra were obtained by measuring the coincidences of two photons. While the Ps formation rate decreased with elapsed time during the PALS experiment, the increase of annihilation on oxygen-containing groups was monitored by coincidence Doppler-broadening spectroscopy (CDBS). This suggested that the decrease in Ps formation was associated with the carbonyl groups (–CO) formed by radiation emitted from the positron sources.