X-ray fluorescence measuring system employing balanced x-ray filters and circuit means to vary the effective relative transmission thereof

Claim 1

Apparatus for determining the quantity of a specific element in a plurality of samples which include said specific element as one component of a background mixture which includes other known elemental components which may also vary in amount from sample to sample, comprising, a source of radiation positioned to emit radiation onto said sample, said radiation having a quantum energy greater than the absorption edge of the specific element to be measured, first and second filters positioned to intercept radiation emitted from said sample in response to radiation from said source incident upon it, said first and second filters being formed of materials such that the absorption edge of said first filter is lower in energy than the characteristic X-rays from said specific element and the absorption edge of said second filter is higher in energy than the characteristic X-rays from said specific element, detector means for measuring the quantity of radiation transmitted through said first filter and the quantity of radiation transmitted through said second filter, said detector means including first and second detectors and wherein said first and second filters are positioned between said sample and said first and second detectors respectively, and means coupled to said detector means for taking the difference between a signal from said detector means proportional to the number of rays received by said detector means after transmission through said first filter during a period Tau and a signal from said detector means proportional to the number of rays received by said detector means after transmission through said second filter for a time F Tau where F differs from unity as indicative of the quantity of the specific element in said composition, the time F Tau being set such that variations in the composition of said mixture, other than variations in said specific element, effect a minimum contribution to said difference, and wherein said detector means includes first and second count rate meters connected to the outputs of said first and second detectors respectively, said count rate meters having substantially identical sensitivities, a portion of the output of said first count rate meter being connected to one input of a difference circuit within said difference taking means and a portion of the output of said second count rate meter being coupled to a second input of said difference circuit, the ratio of said portion of the output from said first count rate meter to said portion of the output of said second count rate meter being adjusted to be equal to the ratio between F Tau and Tau .