The micro-determination of uranium and thorium

Abstract

Methods are described for the analysis of the uranium and thorium contents of iron and stone meteorites. These elements are present in concentrations of about 10(^-s)gram per gram, and normally the quantity of meteorite available was limited (10 - 50 gram). Using the fluorimetric method for the microdetermination of uranium, 2 x 10(^-3)gram Uranium could be determined with an accuracy of 10%. Thorium estimates were accomplished by ɤ - particle scintillation counting of Thorium C in radioactive equilibrium with the thorium series; the counter had an extremely low background (about 0.9 counts oer hour). The Thorium C could be regenerated from the higher members of the thorium disintegration series and it could therefore be determined with an accuracy of 25%. A method was developed for the isolation of the uranium from meteorites using a retrograde solvent extraction technique involving nitric acid and diethyl other. Other chemical procedures evolved, permitted the analysis of both the uranium and thorium in single samples of meteorite. The techniques employed included solvent extractions, co-precipitations and a chromatographic separation of submierogram quantities of uranium and thorium was also accomplished by precipitating the latter element, with a sireonium carrier, using an organic precipitant. Methods for the removal of traces of uranium and thorium from reagents are also described. The determinations were correlated with the helium content of the meteorites to calculate their pre bable ages. The absolute amount of meteoritic helium, together with its isotopic analysis, enabled probable amounts of helium produced independently by cosmic rays and the naturally-occurring radio-elements to be estimated. Results suggest a probable age for eight meteorites of about 75 x 106 years, while six others appear to have solidified less than one million years ago.