Determination of rare earths in plutonium by x-ray emission analysis

Abstract

A sensitive and accurate method for measuring trace rare earths in plutonium by X-ray emission analysis has been developed. Plutonium is separated from the rare earths by solvent extraction using tri-isooctylamine. The rare earths are then carrier-precipitated as fluorides and collected on a membrane filter in an "infinitely thin" layer. The rare earths on the filter are counted and ratioed to a terbium internal standard. This work has dealt with samarium, europium, gadolinium, dysprosium, and the elements that produce spectral interferences. However, the method is equally applicable to the other rare earths, assuming spectral interferences are avoided. Detection limits are on the order of 0.1 pg. The relative standard deviation for spike recoveries of the four rare earths at the 1-pg level is 8%.An important criterion for nuclear reactor fuel materials is the strict control of low levels of neutron-absorbing impurities such as boron, cadmium, and certain rare earthssamarium, europium, gadolinium, and dysprosium. As the Atlantic Richfield Hanford Company (ARHCO) has contracted to supply plutonium for the breeder reactor program, a method for determining low parts-per-million quantities of these rare earths in plutonium was needed. Because of a heavy development and sample load, X-ray emission spectrometry was the choice over emission spectroscopy, which is more commonly used for actinide matrices (1-7).The bulk of X-ray emission work for rare earths (8)(9)(10)(11)(12)(13)(14)(15)(16)(17) has been at greater than trace levels in samples such as ores and alloys. To be used effectively for trace analysis, three problems must be solved-separation from the plutonium (1) T.