Digital methods for the coincident measurement of the energies of positron-induced electrons and Doppler-shifted annihilation gamma quanta

Here we describe the methods employed for the analysis of digitized data produced by electron time-of-flight and gamma spectrometers that are part of the recently completed advanced positron beam system at the University of Texas at Arlington. The digitization of the data acquisition methods enabled the coincident measurement of the energies of the positron-induced electrons and the Doppler shifted annihilation gamma. Additionally, the digitization of data acquisition methods has led to the development of a multi-stop time-of-flight spectrometer. The digital analysis methods employed in the extraction of timing and energy information from the detector traces have resulted in (i) a digital time-of-flight spectrum of positron-induced secondary electrons utilizing signals from a micro-channel plate (MCP) electron detector and a high-purity germanium gamma detector (HPGe); (ii) a two-dimensional spectrum representing the correlation between the energy of the annihilation gamma and the times-of-flight of positron-induced secondary electrons; and (iii) the first spectra of positron-induced multiple secondary electrons. The digital analysis methods, when applied to positron annihilation-induced Auger electron spectroscopy (PAES), will be capable of providing the energy and momentum of the electron with which the positron annihilates. This information will allow the determination of the contribution of individual atomic orbital levels to the total Doppler broadening spectrum, and may contribute to the understanding of the interaction of positrons with novel two-dimensional materials. The digital multi-stop time-of-flight spectrometer is expected to aid in the quest to unravel the complex decay pathways associated with the Auger decay of annihilation-induced core holes.