Beyond Tomorrow was the first adult science fiction series on radio - maybe. Some sources say three episodes aired on CBS in April 1950, but other sources say the programs were recorded and scheduled, but never aired.
The series was hosted by John W. Campbell Jr, perhaps the most influential person in the development of science fiction from the late 1930s through the 1960s. Campbell was the editor of Astounding Science Fiction magazine (which later became Analog) all those years, and he directed his authors with a strong hand. He insisted on specific themes for his magazine, and he directed authors to change endings if he didn't like what they had written.
This episode, a western-science fiction story called Incident at Switchpath, was written by Theodore Sturgeon. The magazine version was named The Sky is Full of Ships, but they changed the title for radio because they were afraid the words "ships" might be heard as something else.
From April 11, 1950, here is Beyond Tomorrow and Incident at Switchpath.