During the first half of the present century, Radium, a naturally occurring radioactive element, was mixed with phosphors and applied in the manner of a pigment to produce self-luminous paints. Such paints were widely used where a degree of visibility in low light or dark conditions was required. While the development was initially spurred by military applications, the technique was adapted to many other uses, even to the point of being used on the faces of wrist watches and clocks marketed to the general public. Unfortunately, cancers began to appear among workers who applied the Radium activated self-luminous paints and it was soon determined that Radium was the cause. Though painting techniques were improved to the point where unacceptable risks could be avoided, growing concerns about radiation and radioactive materials eventually resulted in a halt to the production of new devices using Radium activated self-luminous paints. Concurrently other less dangerous radioisotopes were also found to be effective in activating such paints, the most recent to enjoy fairly wide use being Tritium.
One of the tasks routinely carried out today in aviation instrument shops is to refurbish used instruments. From time to time this might involve scraping off and repainting dial faces or indicator needles and pointers. Concerns were raised that these might have been originally painted with Radium activated self-luminous paints and that the workers and shop might have become contaminated with radioactive dust.
RHSC carried out measurements to establish whether or not there was any significant contamination of the instrument shops and provided recommendations to preclude even minute levels of contamination or the spread of tiny quantities of Radium or other similarly used radioisotopes.
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