THE 1ST DETECTION OF NATURALLY-OCCURRING U-236 WITH ACCELERATOR MASS-SPECTROMETRY

The IsoTrace heavy element AMS system has been successfully used to de tect naturally-occurring U-236(U-236/U-238 = (5.6 +/- 1.5) x 10(-10)) in samples of uranium ore from Cigar Lake, Saskatchewan, Canada. This level of U-236 agrees with that previously claimed for samples of a pr ocessed uranium ore (D.J. Rokop, D.N. Metta and C.M. Stevens, Int. J. Mass Spectrom. Ion Phys. 8 (1972) 259 [1]), and is consistent with the amount of Pu-239 found in pitchblende (W.A. Myers and M. Lindner, J. Inorg. Nucl. Chem. 33 (1971) 3233 [2]). This experiment illustrates th e general capability of a small tandem-based AMS system for analyzing actinides, in particular U-236. It can be shown that the isotope-ratio detection limit of this system, is at present 5 x 10(-8) for detectin g a less abundant actinide isotope one mass unit above, and 5 x 10(-10 ) one mass unit below, a major isotope.