Radioluminescence

[Pigeon]

Radioluminescence is the phenomenon by which luminescence is produced in a material by the bombardment of ionizing radiation such as beta particles.

Tritium illumination

Tritium is used as a source of beta particles in a large variety of applications where electricity is not available for illumination. For example, gun sights and emergency exit signs.

Radium dials

A 1950s radium clock, exposed to ultraviolet light to increase luminescence

Historically a mixture of radium and copper-doped zinc sulfide was used to paint instrument dials giving a greenish glow. Phosphors containing copper doped zinc sulfide (ZnS:Cu), yielding blue-green light and copper and magnesium doped zinc sulfide (ZnS:Cu,Mg), yielding yellow-orange light are also used. Radium based luminescent paint is no longer used due to the radiation hazard posed to those manufacturing the dials. These phosphors are not suitable for use in layers thicker than 25 mg/cm², as the self-absorption of the light then becomes a problem. Furthermore, zinc sulfide undergoes degradation of its crystal lattice structure, leading to gradual loss of brightness significantly faster than the depletion of radium.

ZnS:Ag coated spinthariscope screens were used by Ernest Rutherford in his experiments discovering atomic nucleus.

Mechanism

Radioluminescence occurs when an incoming radiation particle collides with an atom or molecule, exciting an orbital electron to a higher energy level. The electron then returns to its ground energy level by emitting the extra energy as a photon of light.

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[Pigeon]

Undark was a trade name for luminous paint made with a mixture of radioactive radium and zinc sulfide, as produced by the U.S. Radium Corporation between 1917 and 1938.

It was used primarily in watch dials. The people working in the industry who applied the radioactive paint became known as the Radium Girls, because many of them became ill and some died from exposure to the radiation emitted by the radium contained within the product. The product was the direct cause of Radium jaw in the dial painters.

Undark was also available as a kit for general consumer use and marketed as glow-in-the-dark paint.

The Radium Girls were female factory workers who contracted radiation poisoning from painting watch dials with glow-in-the-dark paint at the United States Radium factory in Orange, New Jersey around 1917.

The women, who had been told the paint was harmless, ingested deadly amounts of radium by licking their paintbrushes to sharpen them; some also painted their fingernails and teeth with the glowing substance.
Radiation exposure

The U.S. Radium Corporation hired some 70 women to perform various tasks including the handling of radium, while the owners and the scientists familiar with the effects of radium carefully avoided any exposure to it themselves; chemists at the plant used lead screens, masks and tongs. US Radium had even distributed literature to the medical community describing the “injurious effects” of radium. The owners and scientists at US Radium, familiar with the real hazards of radioactivity, naturally took extensive precautions to protect themselves.

An estimated 4,000 workers were hired by corporations in the U.S. and Canada to paint watch faces with radium. They mixed glue, water and radium powder, and then used camel hair brushes to apply the glowing paint onto dials. The then-current rate of pay, for painting 250 dials a day, was about a penny and a half per dial ($0.27 per dial in today's terms). The brushes would lose shape after a few strokes, so the U.S. Radium supervisors encouraged their workers to point the brushes with their lips, or use their tongues to keep them sharp. For fun, the Radium Girls painted their nails, teeth and faces with the deadly paint produced at the factory. Many of the workers became sick. It is unknown how many died from exposure to radiation. The American factory sites became Superfund cleanup sites.

Five of the women challenged their employer in a case that established the right of individual workers who contract occupational diseases to sue their employers

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