Researchers from the University of Northampton and Kingston University have discovered that the glow-in-the-dark wristwatches that were popular in the first half of the 20th century – and widely given out to British and American servicemen – emit an extremely carcinogenic radioactive gas at concentrations up to 12 times higher than the maximum safe level.
The startling revelation about radium dial watches came from an analysis of 30 specimens by Dr Robin Crockett and professor Gavin Gillmore as part of an international report about radon exposure.
“These results show that the radon emitted from individual watches can potentially pose a serious cancer risk,” Dr Crockett said in a statement, alluding to the established link between radon and lung cancer. “This is of concern because in addition to military watches being particularly prized by collectors, many individual radium-dial watches are kept as mementos by ex-servicemen and their descendants.”
Radon is a colorless and odorless gas continually present in the environment due to the decay of naturally occurring uranium and thorium ore into radium, which in turn – with a half-life of 1,600 years – undergoes alpha decay into radon, producing ionizing radiation in the process. Because such ores are more abundant in certain regions and get transported during industrial processes, public health organizations recommend that homes and buildings should have their radon levels periodically tested.
Using radiation detectors, Crockett and Gillmore determined that the radon emitted by the entire collection of watches produced approximately 13,400 becquerels per meter cubed (Bq/m3) of radiation when placed in a space of similar size as a storage room or small bedroom. Public Health England recommends that indoor spaces should aim for no more than 100 Bq/m3.
The three watches that were in the worst physical condition, and thus had the least shielding around the radium paint, emitted between 200 and 1,200 Bq/m3 each.