Abstract
The extraction of material positron lifetime components from positron annihilation lifetime spectroscopy measurements, performed using conventional unmoderated radionuclide positron sources, requires accurate knowledge of both the spectrometer instrument timing resolution function (IRF) and annihilation events extrinsic to the material, the source correction terms. Here we report the results from study of spectrometer performance made using two reference samples, high purity polycrystalline aluminium, and stainless steel supplied by the National Metrology Institute of Japan (NMIJ RM 5607-a). Both prepared with directly deposited 22NaCl positron sources. The IRFs obtained by fitting spectra from both reference samples were monitored with time to evaluate spectrometer stability and to compare methods of IRF determination. Using the aluminium IRFs the analysis of spectra from the NMIJ stainless steel reference samples yielded a single lifetime component with value 106.9(9) ps.
Highlights
Positron annihilation lifetime spectroscopy (PALS) enables the detection, and often identification, of open-volume defects in materials, varying in size from monovacancies to large vacancy cluster [1,2,3]
The spectrometer instrument timing resolution function (IRF) shape parameter values obtained from 34 Al-DD spectra measured over a period of 153 days are given in table 1, the standard deviations are shown
The resulting IRF was used for a series POSITRONFIT runs with three unconstrained lifetime components and a fixed source correction comprising a lifetime of 390 ps with an intensity that was incremented in 0.1 % steps over an appropriate range, which for Al-DD was typically between 1.5–2.5 %
Summary
Positron annihilation lifetime spectroscopy (PALS) enables the detection, and often identification, of open-volume defects in materials, varying in size from monovacancies to large vacancy cluster [1,2,3]. We report the results from study of spectrometer performance made using two reference samples, high purity polycrystalline aluminium, and stainless steel supplied by the National Metrology Institute of Japan (NMIJ RM 5607-a). Using the aluminium IRFs the analysis of spectra from the NMIJ stainless steel reference samples yielded a single lifetime component with value 106.9(9) ps.
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