The Plutonium Cohort: A Comparative Dosimetric and Ethical Analysis of the 18 Human Injection Experiments (1945-1947

Between April 1945 and July 1947, eighteen individuals in the United States were secretly injected with plutonium as part of the Manhattan Project's medical research program. While much has been written about individual cases, particularly Albert Stevens (CAL-1), a systematic comparative analysis of the entire cohort has been lacking. This paper fills that gap. It synthesizes historical, dosimetric, and ethical data from primary sources, including the ACHRE final report and the Rowland & Durbin (1975) dosimetry review. The analysis reveals that the cohort was highly heterogeneous in terms of age, injected activity (0.75 to 94.9 µg), isotopic composition, and survival time (17 days to 38 years). A key finding is that the highest known cumulative dose (64 Sv, CAL-1) resulted not from the highest injected activity, but from a unique combination of a rapidly decaying isotope (Pu-238) and long survival (20.7 years). The ethical analysis reveals a systematic pattern of deception that persisted for decades, including the explicit instruction to "never use the word plutonium in regard to these cases." This comparative approach provides a more nuanced understanding of the risks of internal alpha emitters and the historical failures that shaped modern research ethics.