Radium Clock

Uses. — Radium compounds find a limited use in such instruments as the spinthariscope, Fig. 6, and Strutt s radium clock. The latter is an electroscope so arranged that the leaves are alternately charged by radium and discharged by grounding. It is a curious contrivance which transforms the radiating energy of radium into motion which approaches perpetual. (SeeFig. 7.)... 

Other uses are to produce phosphorescence and fluorescence in organic compounds and for scintillation screens on instruments used to detect radiation. Radium salts were used in the past to paint the dials of luminous clock faces that glow in the dark. 

At one time, women painted clock and watch dials with luminous radium paint that was a mixture of radium salts and zinc sulfide. They would place the small brushes between their lips and tongue to make the bristles more pointed, in order to paint fine lines with the radium paint. Over the years, they developed cancers that resulted in badly eaten-away and disfigured lips and jaws. Once the danger was known, luminous radium paint was banned for this use. Today, promethium (Pm-147), with a half-life of 2.4 years, is used for this purpose. 

Until the 1960s, radium was a component of the luminous paints used for watch and clock dials, instrument panels in airplanes, military instruments, and compasses (Blaufox 1988). 

A second radionuclide to which humans are likely to be exposed is radium, Ra. Occupational exposure to radium is known to have caused cancers in humans, most tragically in the cases of a number of young women who were exposed to radium because of their employment in painting luminescent radium-containing paint on the dials of watches, clocks, and instruments.9 These workers would touch their tongues with the very fine brushes used for the radioactive paint in order to point the brushes. Many eventually developed bone cancer and died from this malady. 

Radium was once used in paint that was applied on the hands and numbers of clocks and watches. The visible radiation it emitted made it possible to read the numbers in the dark. But the radiation proved very harmitil to the people who applied the radium paint to the ratches and clocks. 

After the war-time demand had ceased, other applications of the paint were made and quickly became popular. Now, in addition to watch and clock dials, luminous paint is used to mark street signs, door plates, push buttons, or almost anything that may need to be located in the dark. The amount of radium used in this manner has been enough to cause serious concern in regard to the future supply, but the largest use of radium at present is in treating cancer. 

Before radiums dangerous radioactive properties were understood, it was used to make paints for watches and clocks that could be seen in the dark. Currently, radium is used in medical facilities like hospitals and other treatment centers to produce a radioactive gas called radon, which is used to treat cancer patients. 

Workers at Radium Dial in Ottawa, Illinois, are shown in this undated photo. The town today still grapples with the tragedy of the workers who suffered as a result of hand-painting clock-face dials using radium-laced paint in the 1920s and the subsequent cleanup process after the company s buildings were demolished years later. (AP Photo/Ottawa Daily Times)... 

Naturally occurring radionuclides such as radium isotopes and radon-222 have gained popularity as tracers of SGD due to their enrichment in ground-water relative to other sources and their built-in radioactive clocks . The enrichment of these tracers is owed to the fact that the water-sediment ratio in aquifers is usually quite small and that aquifer sediments (and sediments in general) are enriched in many U and Th series isotopes while many of these isotopes are particle reactive and remain bound to the sediments, some like Ra can easily partition into the aqueous phase. Radon-222 (tia = 3.82 days) is the daughter product of Ra (G/2= 1600 years) and a noble gas therefore, it is even more enriched in groundwater than radium. 

Growth and decay of Ra after isolation of radium from 4n series at secular equilibrium. The top curve gives the decay of Ra after the first isolation relative to the secular rate. The growth curve shows the time dependence of Ra that comes from Ra (via Ac and Th). The middle decay curve shows Ra that decays (with the clock restarted) after thorium is removed when growth and decay are equal (about 22 days from t = 0). The bottom decay curve shows decay following a third purification (about 10 days after the second]... 

Radium was also utilized in self-luminous paints for watch, clock and instrument dials and for emission in automatic control systems. Safer radioisotopes for technical properties, such as cobalt-60 and cesium-137, can nowadays be tailored in nuclear reactors and have entirely replaced radium. This has released us from the need for radium, which is a great advantage, as radium is so difficult to handle from an environmental point of view. It forms gaseous radon, affecting its surroundings. And the problem remains for a long time, as the most usual radidum isotope, Ra, has a half-life of 1600 years. Nowadays the use of radium has ceased. The annual amount manufactured is only round 100 g. 

---