As I said, it was a major plot point in a cheesy 1957 B-movie. I doubt anyone would argue that
The Giant Claw was on the cutting edge of conceptual innovation, so the idea was probably familiar to the general public even then. And it showed up in at least three places that I know of in 1966-7 mass media --
Star Trek, the
Batman feature, and the
Lost in Space episode "The Anti-Matter Man." That indicates that the concept had already suffused popular culture fairly widely.
After all, unlike the dark ages of superstition and ignorance we currently live in, Americans back then were actually interested in science. The post-WWII era was a time of great optimism about scientific and technological progress, and breakthroughs like the detection of antiprotons and antineutrons in 1955-6 were covered in the news and followed with interest. Indeed, I checked the
New York Times archives, and the discovery of the "negative proton" in October 1955 was reported
on the front page of the
Times, with two followup articles over the next two months. It was most likely covered on TV and radio news as well.