Mössbauer studies withI131andI125sources implanted in iron

Abstract

Using implanted sources of ${\mathrm{I}}^{131}$ and ${\mathrm{I}}^{125}$ in iron, the hyperfine (hf) fields and recoilless fractions of the daughter nuclei, ${\mathrm{Xe}}^{131}$ and ${\mathrm{Te}}^{125}$, respectively, have been investigated by means of the Mössbauer effect of their first-excited-state $\gamma$ transitions. In both cases, the Mössbauer spectra consist of different components, indicating that the implanted atoms occupy a number of inequivalent sites. We performed measurements at different temperatures to deduce recoilless fractions for the observed components and the relative occupations of the different sites. The data for both cases have been fitted with a model that assumes three different hf spectral components, identified as having high ($h$), intermediate ($i$) and low ($l$) hf fields. For Fe ${\mathrm{Xe}}^{131}$, values $B_{\mathrm{hf}}^{\mathrm{}\left(h\right)\mathrm{}}=1.55\mathrm{}\pm 0.10$ MG, $B_{\mathrm{hf}}^{\mathrm{}\left(i\right)\mathrm{}}=1.16\mathrm{}\pm 0.15$MG, and $B_{\mathrm{hf}}^{\mathrm{}\left(l\right)\mathrm{}}=190\mathrm{}\pm 60$MG were found; for Fe ${\mathrm{Te}}^{125}$: $B_{\mathrm{hf}}^{\mathrm{}\left(h\right)\mathrm{}}=681\mathrm{}\pm 4$kG, $B_{\mathrm{hf}}^{\mathrm{}\left(i\right)\mathrm{}}=540\mathrm{}\pm 15$kG, and $B_{\mathrm{hf}}^{\mathrm{}\left(l\right)\mathrm{}}=190\mathrm{}\pm 60$kG. In agreement with channeling results, the $h$ component is ascribed to Xe or Te atoms in substitutional sites. A calculation of hf fields for various defect clusters makes it probable that the $i$ component corresponds to impurity atoms associated with one vacancy in a nearest-neighbor position. The $l$ component is not sharply defined; it is assumed to correspond to several different vacancy clusters, consisting of an impurity atom associated with two or more vacancies.