DIFFERENTIAL FLUORESCENCE MONITOR FOR ELEMENTS OF ADJACENT ATOMIC NUMBER BUT GROSSLY DIFFERENT CONCENTRATIONS

A TECHNIQUE IS PROPOSED WHEREBY ENERGY-DISPERSIVE X-RAY FLUORESCENCE ANALYSIS CAN BE MADE TO ACCURATELY MEASURE SMALL CONCENTRATIONS ( 1%) OF AN ELEMENT IN A SAMPLE WHOSE COMPOSITION IS DOMINATED (>90%) BY AN ELEMENT OF SIMILAR BUT LARGER ATOMIC NUMBER (Z). SUCH MEASUREMENT IS NOW PRECLUDED BY THE OVERWHELMING FLUORESCENCE SIGNAL FROM THE DOMINANT ELEMENT. THE PROPOSED TECHNIQUE WOULD EMPLOY A PRIMARY PHOTON SOURCE, A SECONDARY FLUORESCER, ONE OR MORE FILTERS, AND DIFFERENTIAL ANALYSIS OF THE OBSERVED SPECTRA. THE KEY FEATURES OF THE TECHNIQUE ARE (1) REDUCTION OF THE FLUORESCENCE FROM THE INTERFERING ELEMENT BY APPROPRIATELY SHIFTING THE INCIDENT ENERGY BELOW THE EXCITATION OF THE DOMINANT (K) X RAYS AND (2) INCORPORATION OF SECONDARY EFFECTS BY USE OF A DIFFERENCING SCHEME. AS ANINITIAL DEMONSTRATION OF THE TECHNIQUE, WE WILL ATTEMPT TO SHOW THAT IT IS POSSIBLE TO DETECT MANAGANESE (Z=25) AT THE 1% LEVEL IN CARBON STEEL HAVING 98% IRON (Z=26). EXPERIMENTAL VERIFICATION OF THE TECHNIQUE WILL BE UNDERTAKEN.