Measurement of uranium isotopes in human tissue samples by TIMS

Although efforts have been devoted to developing improved instrumentation and sample preparation, accurate measurement of uranium isotopes in environmental and biological samples presents an analytical challenge. This is especially true when mass spectrometric techniques are used to detect minor isotopes such as 234U and 236U. This note reports the measurement of 234U, 235U, 236U and 238U by thermal ionization mass spectrometry in 20 human tissue samples from the United States Transuranium and Uranium Registries Case 1028. This Registrant was occupationally exposed to highly enriched and processed uraniumvia inhalation, clearly confirmed by the isotopic ratios (234U/238U, 235U/238U, and 236U/238U) obtained in this work. The tissues were selected to give a best estimate of the total amount of uranium deposited in the body and to calculate the resulting internal radiation dose. For all of the tissue samples, 234U is the dominant dose contributor, while contributions from other isotopes are much less significant.