Selectable wavelength X-ray source, spectrometer and assay method

An X-ray fluorescence analysis spectrometer comprising:

• an X-ray source having means for producing any selected one of a plurality of different specific predetermined X-ray spectra, said X-ray source having means for producing an accelerated charged particle beam and having at least one first primary target positioned to intercept said charged particle beam to produce primary X-rays in response to bombardment thereby and having a first plurality of spacedapart secondary targets each of different composition and means for directing said primary X-rays to any selected one of said secondary targets to produce secondary X-rays thereat which have different X-ray spectra at different ones of said secondary targets,
• means for supporting a substance to be analyzed in position to receive said X-rays produced by said selected ones of said secondary targets,
• an X-ray detector disposed for detecting characteristic fluorescent X-rays emitted from said substance in response to said irradiation thereof, and
• a self-cycling system coupled to said detector and to said X-ray source and having means for controlling said X-ray source to initially irradiate said substance with a polychromatic X-ray spectrum and means coupled to said detector for analyzing the wavelength spectrum of characteristic X-ray fluorescence from said substance in response to said polychromatic irradiation thereof to indentify wavelengths characteristic of specific elements, said self-cycling system further having logic circuit means controlling said X-ray source to sequentially irradiate said substance with a plurality of specific X-ray spectra each selected to cause strong X-ray fluorescence from a particular separate one of said specific elements, and further having means for registering a value having a magnitude proportional to the amount of characteristic fluorescent X-rays of each of said elements which are detected during said irradiation of said substance by said specific X-ray spectra.