PRECIOUS METALS ASSAY BY MEANS OF MICROBEAM XRF TECHNOLOGY

There have been increasing demands for a means whereby the transactors and dealers in jewelry can accurately and efficiently appraise the pr ecious metal contents on the premises. These values of such articles c annot be obtained accurately or nondestructively by conventional metho ds, such as specific gravity measurement, touchstone method, fire assa y method, atomic absorption spectrometry and the like. A new method of microbeam X-ray fluorescence analysis (Microbeam XRF) has been develo ped to analyze the type and quantity of precious metal elements. In th is method a beam of X-ray generated from a low powered X-ray tube is c ollimated by a collimator with a diameter of 0.1-5 mm. An object to be analyzed is positioned by moving a three-dimensional sample stage til l the sample can be observed clearly with optical microscope. The X-ra y beam will coincide with the viewing point on the surface of the samp le. The X-rays produced are detected in a high efficient proportional detector. Its spectrum, whose scattering background is lower than that with the broad beam method, is recorded and analyzed by a multichanne l analyzer. The intensities of selected peaks corresponding to target elements are then determined and the relative compositions of the elem ents are also calculated by a fundamental parametric method. Two sets of standards (No. SYS-01) were measured by the instrument. It showed t hat the precision of gold measurement was 0.1% and the correlative coe fficient between the measurement results and the given values of the s tandards was better than 99.998%. A piece of gold necklace was also ch ecked step by step. The microbeam XRF is a reliable and accurate metho d for precious metals jewelry assay.