The Simpsons has taught me a lot, like Homer’s words of wisdom, “You tried your best and you failed miserably. The lesson is, never try.” The Simpsons also taught me that radioactive substances possess an eerie green glow. In the iconic opening sequence, Homer accidentally flicks a phosphorescent green rod of plutonium down his back before leaving the nuclear power plant. While cartoons are probably not the most reliable source of scientific information, the question still remains: do radioactive elements actually glow green? Technically, the answer is no. But as we’ll discover soon, radioactivity still indirectly generates pretty luminescent colours!
First, what even is this mysterious radioactivity? A radioactive element is unstable, so it shoots out particles and high-energy radiation as it undergoes “radioactive decay.” The emitted particles, called alpha and beta particles, can be stopped by a few centimetres of air or a thin aluminium sheet respectively. However the radiation, called gamma radiation, can penetrate our skin and damage our cells and requires a thick sheet of lead to stop it! Sustained exposure to radioactivity can therefore cause all sorts of nastiness like cancer and radiation sickness. But we can’t directly sense these harmful rays and particles; they’re completely invisible to us. This is partially why radioactive substances are dangerous; you can receive a damaging dose of radiation without even realising it.
The “glowing green” myth arose thanks to the popularity of radium watch dials throughout the first half of the 20th century. In these dials, radium, a radioactive element, is mixed with a paint containing a chemical called phosphor. Alpha particles emitted by radium as it decays hit the phosphor, causing it to emanate a greenish light. This provides a battery-free source of illumination, but safety considerations have since significantly diminished the use of “radioluminescent” paint. Rightly so, as demonstrated by the “Radium Girls” who were employed to paint the dials. They would keep the tip of their paintbrush fine by licking it, and some even painted their nails and teeth. In doing so they ingested radium and suffered horrific health problems.
So the radioactive element doesn’t directly produce the characteristic glow we’ve come to know and love. Instead it’s all about teamwork between the element and its phosphorescent or fluorescent friends. But some radioactive elements can even make air glow. For example, actinium emits particles that smash into oxygen, causing the oxygen to radiate faint blue light. Similarly, a blue glow is observed in nuclear reactors due to high-speed ejected particles interacting with the air – a phenomenon called Cherenkov radiation.
All in all, it’s probably not the best idea to learn your science from TV shows like The Simpsons. I’d also recommend that you don’t emulate Homer’s nonchalance when it comes to radioactive substances – you don’t want to end up like the Radium Girls!
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