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

Elemental Characterization of the Topmost Atomic Layer of Surface Using Doppler Broadening Spectroscopy

“…The "bulk"-like spectrum was collected by biasing the sample to −20 kV with respect to the field-free tube, whereas the Doppler broadening spectrum from the asinserted and partially sputtered sample surfaces was measured with the settings described above for PAES measurements. Particularly, the Doppler broadening spectra representing as-inserted and partially sputtered surfaces were collected simultaneously with the PAES spectrum, though not in true coincidence [8]. The voltage pulse from the HPGe detector used for the construction of gamma energy histogram using the analog electronics also served as the start signal for the time-offlight measurement using digital data acquisition techniques.…”

“…The advanced positron beam, including the data acquisition system used for the present experiment, has been described elsewhere [8,9] and only a brief description will be given here. A monoenergetic beam of low energy positrons are produced by a 22 Na source housed inside of a source holder with a parabolic face onto which a thin film of solidified Ne is grown [10].…”

“…The time difference between the signal from the HPGe detector and the MCP is used to produce a histogram of the measured flight times of the electrons, whereas the amplitude of the HPGe detector pulse is used to produce a histogram of the gamma energy. The time-of-flight spectra shown in the manuscript has been constructed using digital data acquisition and analysis techniques [8], whereas the gamma spectrum has been constructed using conventional analog electronics. The HPGe pulse used for the construction of the gamma energy histogram by analog electronics also served as the trigger for the digital data acquisition, making the two spectra representative of the same surface features.…”

Estimation of Ortho-Positronium Pick-Off Contributions to the Coincident Measurement of the Energy Spectra of Positron-Induced Electrons and Annihilation Gamma Quanta

“…Timing with the HPGe detector was enabled by an implementation of the extrapolated leading edge timing algorithm in the analysis software (a detailed description of which is provided in Ref. [6]), resulting in a timing (101) We measure this ∆t as the time difference between the detection of an HPGe detector pulse and a micro-channel plate (MCP) electron detector pulse via custom software that additionally constructs a two-dimensional array representing the coincident measurement of the electron ToF and the annihilation gamma energy [6]. Figure 2a is an electron ToF spectrum resulting from the application of the aforementioned settings.…”

Efficient machine learning approach for optimizing the timing resolution of a high purity germanium detector

“…Recently, our group has shown [32,33], that timing using an HPGe detector with ~ 20 ns resolution-when employing a conventional digital ELET algorithm-can lead to a novel annihilation γ-ecoincidence technique that can provide unique surface electronic and chemical structure information. The γ-ecoincidence technique, first demonstrated by Eshed et al, and Kim et al, [34,35] combines Positron annihilation induced Auger Electron Spectroscopy (PAES) [36] with the measurement of the Doppler broadening of the annihilation γ.…”