OVERVIEW AND DOSIMETRY OF THE HANFORD AMERICIUM ACCIDENT CASE

Postmortem examinations of selected tissues from an individual who rec eived a massive internal exposure to Am-241 and succumbed to pre-exist ing cardiovascular disease 11 y later are summarized. Significant find ings include acellularity of the marrow, marked peritrabecular fibrosi s, and a lack of bone surface remodeling, confirmed by bone-surface al pha-spectrometry; tissue concentrations of Am-241 that indicate bone a nd liver as the primary deposition sites, in general agreement with th e new ICRP model, but not with the older models; a distribution of Am- 241 in soft tissues in general agreement with that observed in animals ; and the absence of any other gross or microscopic pathological findi ngs attributable to the exposure. Cumulative absorbed doses to the bon e, bone surface, liver, and lung were 18, 520, 8, and 1.6 Gy, respecti vely. The probability of not observing a fatal cancer based on BEIR-IV risk factors for these absorbed doses was 12%.