Migration of Sodium in Feldspar by Electron Beam - An Experimental Study

Abstract Quantitative analysis of Na in minerals like feldspar in an Electron Probe Micro Analyser (EPMA) confronts two problems - the first one arising at the time of data acquisiton of Xrays of Na (say Kα) and the second one during conversion of measured xray intensity ratios into true concentration while using certain correction procedure The fall in the count rate of Na xray signals as a function of time under stationary electron beam in EPMA is quite well known. This was attributed to volatilization of Na during electron bombardment. Another explanation for this phenomenon has been that Na+ ions made mobile in the crystal lattice of feldspar by the electron beam, move away from the point of its impact. This results in the fall in the count rate of Na with a corresponding increase in me count rate of matrix element like Si, Al.