Symmetrical positron annihilation lifetime spectrometer and single-sided measurements

Positron annihilation lifetime (PAL) spectroscopy is a useful tool in material defect studies. In this work, a symmetrical PAL spectrometer was developed based on a conventional system and 22Na radioactive source. Both detectors provide start and stop signals to double the counting rate without adding devices. Zero-channel position is calibrated automatically during the measurement to combine the two sub-spectra, which can be applied to larger systems with more detectors. The differences of zero-channel positions and time resolutions of two sub-spectra were simulated to confirm the feasibility of our work. Then we used polyimide film (Kapton film, the packaging material of 22Na source) as reference sample to collect PAL spectra with only one piece of tested sample (single-sided). The influences of high and unknown intensity of source components were simulated to check the importance of enough counts and accurate source correction. Symmetrical PAL spectrometer provides higher counting rate to meet the requirement of single-sided sample. Experimental results confirmed that our PAL spectrometer performs well for both double-sided and single-sided measurements.