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

Gladen, R. W.; Chirayath, V. A.; Fairchild, A. J.; Köymen, A. R.; Weiss, A. H.

doi:10.1016/j.nima.2019.162887

Cited by 6 publications

(7 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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.…”

Section: Resultsmentioning

confidence: 99%

“…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].…”

Section: Methodsmentioning

confidence: 99%

“…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.…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2020

Self Cite

View full text Add to dashboard Cite

This work is dedicated to Prof. Peter S. Pershan on his 85th birthday. His many pioneering contributions to physics research have provided an inspiring model.We present initial results that demonstrate the ability of Doppler broadening spectroscopy (DBS) to extract elemental information from the topmost atomic layer of a sample surface. Doppler broadening spectra from graphene grown on a polycrystalline Cu substrate was compared to the Doppler broadened spectra obtained after the partial removal of the bilayer graphene from the Cu surface. The Doppler broadening of the annihilation photopeak showed a clear difference between the as-inserted and the partially sputtered sample. We posit that this difference was due to the contribution of the gamma photons originating from the annihilation of positrons with the substrate (Cu) electrons to the total Doppler broadened spectrum. The Doppler broadened spectrum of the partially sputtered sample was well fit with a line shape produced by combining the Doppler broadened gamma spectrum of the as-inserted sample with the theoretically calculated annihilation gamma photo peak from bulk Cu. The fraction of the calculated Doppler broadened spectrum from bulk Cu in the fit spectrum is consistent with the increase in intensity of the Cu M2,3VV Auger peak observed in the positron annihilation induced Auger electron spectra (PAES) of the partially sputtered sample. This suggests that analysis of the high momentum region of the gamma photopeak due to photons emitted following the annihilation of surface trapped positrons can provide a quantitative estimate of the elemental composition of the top surface. Our results provide evidence for the feasibility of using DBS as a new spectroscopic technique for the elemental characterization of the topmost atomic layer of surfaces.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…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.…”

Section: Experimental Apparatusmentioning

confidence: 99%

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

et al. 2020

Self Cite

View full text Add to dashboard Cite

We present preliminary results that were collected using a new positron beam system at the University of Texas at Arlington. The beam allows for the coincident measurement of the energy of positron annihilation gamma photon and time-coincident positron-induced electrons. This system enables the parallel collection of a 2dimensional array of coincident pairs of gamma and electron energies over the full energy range of relevance. Here, we present gamma spectra constructed from the correlation of secondary electrons with the delayed annihilation of positronium, and the observation of pick-off annihilations that results from this analysis. These measurements will play an important role in determining the contributions due to pick-off annihilations to the Doppler-broadened gamma spectra from the internal or external exposed surfaces of materials. Subtracting the background properly is crucial for the measurement of the Doppler broadened spectrum of annihilation gamma photons originating from the annihilation of positrons with electrons of specific electronic core levels.

show abstract

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Gladen

Chirayath

Fairchild

et al. 2020

Nuclear Instruments and Methods in Physics Research Section A:

Self Cite

View full text Add to dashboard Cite

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

Cited by 6 publications

References 32 publications

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

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

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

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

Contact Info

Product

Resources

About