![]() Workers also began to paint their fingernails with the glowing material. The luminous material was painted on with a brush that was kept sharp by pointing the bristles with the tongue. The tech was cutting-edge at the time, and with the need for legible watch dials for soldiers during WWI, workers could take pride in helping the war effort. It was a glamorous gig that required artistry and skill. In the 1910s and ’20s, a working-class woman could make a decent living painting luminous material onto watch dials. There's some interesting science behind it, different methods of illuminating a dial - and some surprising history. But watchnerds are especially into their watch "lume." That's the term they use for the luminescent material that keeps their watches legible in the dark, and it's all but essential to any sport watch. This paper indicates a health risk, particular to collectors, but with knowledge and appropriate precautions the potential risks can be reduced.You don't need to be a watchnerd for a glow-in-the-dark watch dial to elicit a childlike sense of delight. The risk from old watches containing radium appears to have been largely forgotten today. Estimates of the activity of 226Ra in the watches ranged from 0.063 to 1.063 μCi (2.31 to 39.31 kBq) for pocket watches and from 0.013 to 0.875 μCi (0.46 to 32.38 kBq) for wrist watches. Over 6 weeks highs of the order of 2000 Bq m − 3 were routinely recorded when the heating/ventilation system in the room was operating at reduced rates, peaking at over 3000 Bq m − 3 on several occasions. Radon concentration average was 259 ± 9 Bq m − 3 over 16 h, compared to background average over 24 h of 1.02 Bq m − 3. All watches were placed in a room with a RAD7 real-time radon detector. ![]() Radium ( 226Ra) decays to the radioactive gas radon ( 222Rn), and atmospheric radon concentration measurements taken around a pocket watch in a small sealed glass sphere recorded 18,728 Bq m − 3. The maximum skin dose from a wristwatch was 14 mSv, with 4.2 mSv effective dose in vest pocket. This assumes exposure from the back of the watch which is generally around 60–67% of that from the front. For this condition we estimated maximum skin dose for our pocket watches as 16 mSv per year, with effective doses of 5.1 mSv and 1.169 mSv when worn in vest and trouser pockets respectively. A phantom experiment using a TLD suggested an effective dose equivalent of 2.2 mSv/y from a 1 μCi (37 kBq) radium dial worn for 16 h/day throughout the year (dose rate 0.375 μSv h − 1). Eighteen wristwatches have also been assessed, but their dose rates are generally much lower (the arithmetic mean being 3.0 μSv h − 1), although the highest ambient dose equivalent rate noted was 20 μSv h − 1. A pocket compass gave rise to a similar ambient dose equivalent rate, of 20 μSv h − 1, to the pocket watches, with its cover open. Ambient dose equivalent rates have been measured for fifteen pocket watches giving results of up to 30 μSv h − 1 at a distance of 2 cm taken with a series 1000 mini-rad from the front face (arithmetic mean ambient dose equivalent for pocket watches being 13.2 μSv h − 1). This study re-examines the risk to health from radium ( 226Ra) dial watches.
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