Dr. Geiger helped found Physicians for Social Responsibility in 1961. The group argued that official predictions of the effects of nuclear war minimized the number of casualties and the extent of the destruction it would cause. At the group’s public meetings, Dr. Geiger’s job was “the bombing run” — offering a detailed account of what a one-megaton nuclear bomb would do to the city in which the meeting was being held.
He had a resonant voice and a crisp, forceful delivery. His presentations left audiences stunned, according to a colleague in the group, Dr. Ira Helfand.