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
Department of Physics, University of Texas at Arlington, Arlington, Texas 76019, USA.
First Point Scientific Inc., Agoura Hills, California 91301, USA.
Rev Sci Instrum. 2020 Mar 1;91(3):033903. doi: 10.1063/1.5140789.
In this study, 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/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.
在本研究中，我们描述了一种先进的多功能可变能量正电子束系统，该系统能够测量多个“正电子诱导”电子的能量，同时测量与相关正电子湮灭产生的多普勒频移伽马光子。测量是利用先进正电子束系统配备的数字飞行时间光谱仪和伽马光谱仪的独特特性进行的。这些测量结果包括：(i) 首次利用高纯锗探测器和微通道板的符合信号生成的正电子湮灭诱导俄歇电子的数字飞行时间谱；(ii) 与湮灭伽马光子符合测量的多普勒展宽湮灭伽马能量和正电子湮灭诱导俄歇电子/二次电子飞行时间的二维阵列；(iii) 正电子撞击和/或湮灭双层石墨烯表面时从其表面射出的多个二次电子的飞行时间谱。通过专门提取由正电子与碳的1s电子湮灭发射的伽马光子的多普勒展宽谱，证明了伽马 - 电子符合光谱学的新颖性。已发现提取的多普勒展宽伽马谱的宽度与由于碳中1s电子的动量导致的湮灭伽马谱的预期展宽一致。
