The original recording features an insistent Minimoog bass line (playing eighth notes), with chords played on the distinctive "choir" disc of the Vako Orchestron. Morse code signals spelling out "R-A-D-I-O-A-C-T-I-V-I-T-Y" are also present, near the beginning of the track and again near the end. The second time it is followed by "I-S I-N T-H-E A-I-R F-O-R Y-O-U A-N-D M-E".
The song was re-recorded as a radically different version for The Mix album in 1991 and was issued as a single in an edited form with remixes by François Kevorkian and William Orbit. While the original does not offer a value judgement on the safety of radioactivity, the 1991 version drops all references to radio and incorporates additional lyrics with a pointed anti-nuclear theme, remaking the central lyrical hook as "stop radioactivity" and also referring to "contaminated population" and mentioning by name Chernobyl, Harrisburg (Three Mile Island), Sellafield and Hiroshima.
"Radioactivity" has remained a regular part of Kraftwerk's live sets over the years. On its original performances in 1976, the band tried out an experimental light-beam operated "percussion cage", where Wolfgang Flür attempted to trigger electronic drum sounds by interrupting light beams using arm gestures. This system was environmentally unstable and frequently failed.
The band performed the Mix version at the "Stop Sellafield" concert in 1992. The song was performed during Kraftwerk's set at Coachella to commemorate the anniversary of the Chernobyl incident on April 26 (the date of the band's performance). Live versions of "Radioactivity" feature on both English and German versions of the band's 2005 live album Minimum-Maximum.
In 2012, Kraftwerk performed the new remix of "Radioactivity" during No Nukes 2012, held in Japan. To commemorate the Fukushima Daiichi nuclear disaster, Hütter sang alternate lyrics to the song in Japanese. The new lyrics were translated into Japanese language by Ryuichi Sakamoto, and make direct reference to Fukushima. This version of the song also has notable lyric changes such as "Chernobyl, Harrisburg, Sellafield, Fukushima". This altered version of the song is also the version Kraftwerk performs live to this day, albeit with the second chorus switching back to the English or German lyrics sung on the Mix version, depending on where they perform. This version also appears on the band's 2017 live album 3-D The Catalogue.