A multi-stop time-of-flight spectrometer for the measurement of positron annihilation-induced electrons in coincidence with the Doppler-shifted annihilation gamma photon

28 Jan 2020  ·  Chirayath V. A., Gladen R. W., McDonald A. D., Fairchild A. J., Joglekar P. V., Satyal S., Lim Z. H., Shead T. N., Chrysler M. D., Mukherjee S., Barnett B. M., Byrnes N. K., Koymen A. R., Greaves R. G., Weiss A. H. ·

Here we describe an advanced multi functional, variable-energy positron beam system capable of measuring the energies of multiple positron-induced electrons in coincidence with the Doppler-shifted gamma photon resulting from the annihilation of the correlated positron. The measurements were carried out using the unique characteristics of the digital time-of-flight spectrometer and the gamma spectrometer available with the advanced positron beam system... These measurements have resulted in (i) the first digital time of flight spectrum of positron annihilation-induced Auger electrons generated using coincident signals from a high-purity Ge detector and a micro-channel plate; (ii) a two-dimensional array of the energy of Doppler-broadened annihilation gamma and the time of flight of positron-annihilation induced Auger electrons or secondary electrons measured in coincidence with the annihilation gamma photon; and (iii) the time of flight spectra of multiple secondary electrons ejected from a bilayer graphene surface as a result of the impact and(or) annihilation of positrons. The novelty of the gamma electron coincidence spectroscopy has been demonstrated by extracting the Doppler-broadened spectrum of gamma photons emitted due to the annihilation of positrons exclusively with 1s electrons of carbon. The width of the extracted Doppler-broadened gamma spectrum has been found to be consistent with the expected broadening of the annihilation gamma spectrum due to the momentum of the 1s electrons in carbon. read more

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Instrumentation and Detectors Materials Science