Method and apparatus for measuring the concentration of an element in a mixture by an X-ray absorption analysis technique

Claim 1

A PROCESS FOR MEASURING THE CONCENTRATION OF A REQUIRED ELEMENT IN A MIXTURE BY AN X-RAY ABSORPTION ANALYSIS TECHNIQUE COMPRISING THE STEPS OF SELECTIVELY DIRECTING X-RAYS HAVING A CONTINUOUS SPECTRUM ONTO A FIRST ONE OF TWO SELECTED TARGETS, WHEREOF SAID FIRST ONE OF SAID TARGETS HAS CHARACTERISTIC FLUORESCENT X-RAYS OF ENERGY JUST BELOW AN ABSORPTION EDGE OF THE SAID REQUIRED ELEMENT, AND THE SECOND OF SAID TARGETS HAS CHARACTERISTIC FLUORESCENT XRAYS OF ENERGY JUST ABOVE THE SAID ABSORPTION EDGE OF THE REQUIRED ELEMENT, THEREBY TO EXCITE SAID FLUORESCENT XRAYS OF THE FIRST TARGET, PASSING SUCH FLUORESCENT X-RAYS THROUGH THE SAID MIXTURE, THROUGH ONE FILTER OF A PAIR OF DIFFERENTIAL FILTERS, OF WHICH ONE FILTER IS SELECTED TO HAVE AN ABSORPTION EDGE SLIGHTLY BELOW THE ENERGY OF THE FLUORESCENT X-RAYS OF THE FIRST TARGET AND THE OTHER FILTER IS SELECTED TO HAVE AN ABSORPTION EDGE SLIGHTLY ABOVE THE ENERGY OF THE FLUORESCENT X-RAYS OF THE FIRST TARGET, THE PAIR OF FILTERS HAVING ESSENTIALLY THE SAME ABSORPTION CHARACTERISTICS OUTSIDE THE ENERGY BAND BETWEEN THE ABSORPTION EDGES OF THE FILTERS, MEASURING THE INTENSITY OF THE FILTERED X-RAYS, PASSING THE FLUORESCENT X-RAYS FROM THE FIRST TARGET THROUGH THE SAID MIXTURE AND THROUGH THE OTHER FILTER OF THE SAID PAIR OF DIFFERENTIAL FILTERS, MEASURING THE INTENSITY OF THE FILTERED X-RAYS, DETERMINING THE DIFFERENCE BETWEEN THE TWO MEASURED INTENSITIES, REPEATING THE WHOLE OF SUCH PROCESS USING THE SECOND OF SAID TARGETS AND A DIFFERENT PAIR OF DIFFERENTIAL FILTERS TO OBTAIN A SECOND DIFFERENCE BETWEEN TWO MEASURED INTENSITIES, DETERMINING THE RATIO OF SAID DIFFERENCES AND COMPARING SUCH RATIO WITH A SUITABLE CALIBRATION CURVE TO DETERMINE THE CONCENTRATION OF THE SAID REQUIRED ELEMENT.