The discovery of radioactivity in the late 19th century elicited a lot of public interest, and by the 1920s speculation by scientists, science fiction authors, and politicians about the possibility of atomic bombs and explosives had become a pretty standard trope. There was an entire wave of radiation-related fads (like radium water, chocolate, and suppositories) that were supposed to give various invigorating health benefits, which was then followed by a crushing wave of radiophobia induced by things like the Radium Girls case (where women whose job it was to paint glow-in-the-dark radium dials on clocks were gravely injured by their exposure to it, which became an important piece of caselaw for occupational health in the workplace), the Eben Byers incident (in which a rich socialite consumed enough radium water to make his jaw fall off), and dark tales of X-ray technicians getting terrible scars from their intense exposures.

All of this was before the actual atomic bomb. The discovery of nuclear fission in 1939 got similar kinds of coverage, and it was actually pretty common throughout even the war despite attempts at press censorship.

All of which is to say there is a rich "pre-history" of nuclear hopes and fears, which became part of the framing and understanding of the atomic bomb as well. Most of the news stories about the atomic bomb right after Hiroshima, as an aside, were ghost written for the Army by William Laurence, a gee-whiz style New York Times reporter who had come to their attention by writing yet another story about the miracle of atomic energy in 1941.

For more on this, Spencer Weart's Nuclear Fear: A History of Images spends a lot of time on the pre-fission history of popular understanding of radiation and atomic energy.