|Fig. 1: Radium factory workers painting watch dials. (Source: Wikimedia Commons.)|
Radium is a radioactive and highly reactive alkaline earth metal discovered by Marie and Pierre Curie in 1898. In its pure form, it is a silvery white metal. Radium is part of the decay chains of uranium and thorium, and is found naturally in uranite and other ores of uranium and thorium. Radium was originally produced in Austria as a byproduct of uranium and silver mining. As demand for uranium grew, other countries quickly began seeking uranium mines. Large deposits of uranite—and consequently, radium supplies—were discovered in the United States, Canada, Congo, Kazakhstan, and the Czech Republic.
Radium has few practical uses in industry, and consequently radium production is mostly a byproduct of uranium refinement. One particular application of radium is in radioluminescent paint. Pierre and Marie Curie first noticed that radium would glow by itself, but it was Henri Becquerel who discovered that radium glows when in the presence of other compounds. Specifically, Becquerel discovered that emitted alpha and beta particles are able to excite crystalline materials to emit photons. This discovery was soon exploited by William Hammer to create radioluminescent paint. 
Radioluminescent paint combines a radioactive salt with zinc sulfide crystals or similar crystalline compound. The radium-based paint can be applied in a number of ways, including manually with a paintbrush, mechanically via machine press, or by dusting radium salt particles onto free paint. Radioluminescent paint first came into industrial use in 1917 when the Radium Luminous Material Corporation - later known as the United States Radium Corporation - developed a paint known as Undark, which used zinc sulfide crystals and radium salt and was the first radioluminescent paint. In 1917, the Radium Luminous Material Corporation began producing luminous watch faces and clock dials using Undark in Essex County, New Jersey.  Factory workers wore no protective gear, and were instructed to lick the tip of their paintbrushes to create a fine point.  While they were assured that the paint was non-toxic, this claim proved to be tragically wrong.
Production of luminous watch faces continued for several years. By 1923, at least five women had died from radium poisoning.  In 1925, the Essex County medical examiner confirmed that the cause of death of several factory workers had been radiation poisoning brought on by the ingestion of radium salts.  In 1926, the factory workers brought a class-action lawsuit against the Radium Luminous Material Corporation, and in 1927 their main factory in New Jersey was forced to close under the burden of legal costs. The predominantly female factory workers became known as the Radium Girls, since they were one of the first cases of widespread radiation poisoning in the Atomic Age.
Production of luminous clock faces and watch dials continued for several years after the original Radium Girls. By the 1940s, factory workers had begun wearing protective gear while handling radioluminescent paint. During this time, radium's toxicity was firmly established in the medical community; in particular, radium was linked to bone cancer, mandibular necrosis, and anemia. As the negative health effects of radium became more apparent, radium fell out of vogue as the base for radioluminescent paint, and other elements with lower activity such as strontium, promethium, and tritium began to replace radium, until the 1960s when industrial use of radium had been all but ceased. The greatest legacy of the Radium Girls was the establishment of worker safety standards in environments with ionizing radiation. Indeed, the lessons learned from the Radium Girls helped shape the safety standards used during the Manhattan project.  The case of the Radium Girls was one of the many growing pains during the dawn of the atomic age. While their deaths were indeed tragic, it was because of their experiences that we began to establish safety standards for handling radioactivity, which has ultimately proven invaluable to nuclear weapons and nuclear energy manufacturing during the century since the first Undark watches were manufactured.
© Timothy Anderson. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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