Ortho-para-positronium quenching by transition-metal ions in glass

Abstract

Positron lifetimes have been studied in CaO.P2O5 glasses doped with various transition-metal ions (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Ce). Present measurements show that all the transition-metal ions, except cerium, decrease I2 while the change in tau 2 is within experimental error. This is suggested to be due to 'spin-conversion' by which part of the o-Ps, by reacting with the transition-metal ion impurities in glass, are converted into p-Ps; the extent of conversion depends on the nature and the concentration of the impurity ions. Of all the transition-metal ions studied, vanadium(IV) is most effective and cerium(III) and cerium(IV) are least effective in quenching o-Ps; these have been explained as due to the unique nature of the vanadyl (VO2+) group and the shielded 4d electron of cerium respectively.