Calibration and interpretation of Mössbauer isomer shift of the 81-keV transition in133Cs

Abstract

Radioactive 133 Xe was implanted into five host materials ͑Al, V, Cr, Rh, Mo͒ by means of an isotope separator. Internal conversion electron spectra of the 81-keV transition in 133 Cs were measured with an iron-free magnetic spectrometer and Mössbauer spectra were recorded independently. From the correlation between the weighted-mean Mössbauer isomer shifts and the intensity ratios of (Oϩ P)-shell to N 1 -shell conversion electrons, the change of the nuclear charge radius of the 81-keV transition in 133 Cs was deduced to be ⌬R/Rϭϩ(1.5Ϯ0.5)ϫ10 Ϫ4 for a uniform charge distribution of Rϭ1.2ϫA 1/3 fm or, equivalently, ⌬͗r 2 ͘ ϭϩ(6.6Ϯ2.4)ϫ10 Ϫ3 fm 2 . This calibration makes it possible to reasonably interpret the extremely high isomer shifts observed in some refractory metals implanted with 133 Xe, where we take into consideration an increase in s-electron density originated from a decrease in the shielding effect on the s electrons by a removal of the 5 p electron from the Cs impurity atom, which is attributed to the broadening of the valence band with compression and the resulting increase in overlap between the host and the impurity valence bands.