Observations on implanted xenon-133 sources

Abstract

Mössbauer spectra of the 81 keV line of 133 Cs excited in the decay of 133 Xe implanted in iron are presented for a large range of xenon concentrations. The spectra indicate that there are two main locations for the Xe atoms: high field sites, with | H | = 273±10 kOe and an isomer shift δ H ≃ - 1.1 mm/s and low (or zero) field sites, with | H | < 25 kOe and δ 0 = - 0·2 to - 0·4 mm/s. For doses below about 2 x 10 14 Xe atoms/cm 2 (implanted at 50 keV) the intensity ratio of the Mössbauer spectra of Cs nuclei at high and low field sites varies irregularly between 0·1 and 0·3, while at a high dose (~ 10 15 at./cm 2 ) and also after annealing foils with a low dose this ratio becomes large. The considerable spread of the isomer shifts at low field sites may arise from non-equivalence of these sites, at which the Xe atoms are supposed to have formed clusters. The remarkably large isomer shift for the high field sites, for which the Xe atoms are believed to be substitutionally implanted, could be caused by promotion of about two 5 p electrons to the conduction band. Spectra are also presented for 133 Xe sources implanted in vanadium and chromium. The source in vanadium again gives evidence of the existence of two different sites, presumably a cluster site and a substitutional site. The source in chromium shows one broad line with large isomer shift.