INTERACTION DELOCALIZATION IN CHARACTERISTIC X-RAY-EMISSION FROM LIGHT-ELEMENTS

Recently the first observation of a channelling effect in oxygen K-she ll X-ray emission was reported in this journal by Qian et al. [Ultrami croscopy 41 (1992) 147], who pointed out that this would allow oxygen to be used as a reference site in atom location by channelling enhance d microanalysis (ALCHEMI) applied to oxides. Experimental results for characteristic X-ray emission in spinel are reported which confirm the ir results. Calculations of ionization cross sections and the effectiv e ionization potential for each of the constituent atoms of the spinel MgAl2O4 have been carried out from first principles. This allows a qu antitative theoretical insight into the channelling effect for the lig ht elements Al, Mg and O which incorporates delocalization of the ioni zation interaction.