Until well in the 60ties, luminous paints containing Radium ( Ra -226) or Promethium (Pm. So as the tell-tale glow continues to fade, how will you prevent your ancient watch dial or whatever from deteriorating and contaminating your great, great grandchildren’s home, or ending up in a landfill and in the local water supply?Įven without the phosphor, pure radium emits enough alpha particles to excite nitrogen in the air, causing it to glow. The luminous paints are stimulated to glow by a radioactive substance.
The radiation emitted is completely harmless as long as you don’t ingest or inhale the radium-in which case it becomes a serious cancer risk. The isotope of radium used has a half life of 1200 years, but the chemical phosphor that makes it glow has broken down from the constant radiation-so if you have luminescent antiques that barely glow, you might want to have them tested with a Geiger counter and take appropriate precautions.
#Radium luminous paint full
Glow-in-the-dark items that recharge to full brightness after brief exposure to sunlight or a fluorescent light only to dim again over a couple of hours are photoluminescent, and contain no radiation.Īn aside on aging radium: By now, most radium paint manufactured early in the 20th century has lost most of its glow, but it’s still radioactive. In most consumer products, though, radioluminescence has been replaced by photoluminescence, phosphors that emit light of one frequency after absorbing photons of a difference frequency.
Today, in applications where it is warranted (like spacecraft instrument dials and certain types of sensors, for example), the radiation source is tritium (radioactive hydrogen) or an isotope of promethium, either of which has a vastly shorter half life than radium. The half-life of radium is approximately 1,600 years. The time required for the intensity to decrease by one-half is referred to as the half-life. The intensity of radiation from radioactive materials decreases over time. Radium is produced by the radioactive decay of uranium. The use of radioluminescent paint was mostly phased out by the mid-1960s. Radium is a radioactive substance found in nature.
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