Survey of elemental specificity in positron annihilation peak shapes

Abstract

Recently the detailed interpretation of positron-annihilation ␥-ray peak shapes has proven to be of interest with respect to their chemical specificity. In this contribution, we show highly resolved spectra for a number of different elements. To this purpose, annihilation spectra with strongly reduced background intensities were recorded in the two detector geometry, using a variable-energy positron beam. Division of the subsequently normalized spectra by a standard spectrum ͑in our case the spectrum of pure silicon͒ yields quotient spectra, which display features characteristic of the sample material. First we ascertain that the specific spectrum of an element is conserved in different chemical compounds, demonstrated here by identical oxygen spectra obtained from both SiO 2 /Si and MgO/Mg. Second, we show highly resolved spectra for a number of different elements ͑Fe . . . Zn, Ag, Ir . . . Au͒. We show that the characteristic features in these spectra vary in a systematic fashion with the atomic number of the element and can be tentatively identified with particular orbitals. Finally, for 26 different elements we compare the maximum intensity in the quotient spectra with the relative atomic density in the corresponding element. To our knowledge, this is the most comprehensive survey of such data made to date.

Characterization of densified fully stabilized nanometric zirconia by positron annihilation spectroscopy

“…Figure 1͑b͒ shows a distinct peak at a momentum value of ϳ2 a.u., which is consistent with prior PAS observations on oxides. The peak is known to be characteristic of annihilations with oxygen in the lattice 29 ͑as opposed to the metal on the lattice͒. It is worth emphasizing that in this high-momentum regions annihilations are with core electrons and therefore not caused by open volume.…”

Doppler-broadening measurements of positron annihilation with high-momentum electrons in pure elements

“…Until now, measurements and calculation [9,12,24] of positron-core-electron momentum were done on some pure elements but the picture is far from being complete. Discrepancies exist between different sets of measured and calculated data [9,24].…”

“…Recently the promising problem of analyzing the positron annihilation with core electrons has been attacked both experimentally and theoretically [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The chemical selectivity of the positron probe can be used to detect impurity atoms associated to open volume defects.…”

Systematic Measurements of Doppler-Coincidence Spectra for Positron Annihilation in Pure Metals and Semiconductors

“…Al ready i n the pi oneer work [20] num ero us tri al s of Ùtti ng pro cedures i n order to describ e the shap e of the ra ti o curves were presented. Myl er and Sim pson [20] used three overl appi ng G aussian curves for appro xi mati ng the Si-based ra ti o curves for el ements f rom Z = 2 7 to 30.…”

“…Myl er and Sim pson [20] used three overl appi ng G aussian curves for appro xi mati ng the Si-based ra ti o curves for el ements f rom Z = 2 7 to 30. We show such a tri al for present da ta for ato m s fro m Z = 2 2 to 30 i n Fi g. 12; for space reasons onl y m ost signi Ùcant Ùgures are shown.…”