Yes, Hiroshima and Nagasaki are obvious comparisons with the amount of instantaneous radiation affecting thousands of individuals. My initial thoughts went to

Yes, Hiroshima and Nagasaki are obvious comparisons with the amount of instantaneous radiation affecting thousands of individuals. My initial thoughts went to Marie Curie (small amounts over time), and Harry Daghlian and Louis Slotin, or other Los Alamos engineers involved in criticality accidents. Plus, other clean-up workers working in disasters like Chernobyl whose deaths from radiation caused illnesses most likely went unpublished. So at best, that puts him in 10th place with a very loose interpretation, or otherwise significantly behind, and maybe in the top 10 of living individuals. The phrase "in history" is poor writing, however.