RESUMO
This study re-examines the risk to health from radium ((226)Ra) dial watches. 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)). 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. 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 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)). 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. This assumes exposure from the back of the watch which is generally around 60-67% of that from the front. The maximum skin dose from a wristwatch was 14 mSv, with 4.2 mSv effective dose in vest pocket. Radium ((226)Ra) decays to the radioactive gas radon ((222)Rn), and atmospheric radon concentration measurements taken around a pocket watch in a small sealed glass sphere recorded 18,728 B qm(-3). All watches were placed in a room with a RAD7 real-time radon detector. Radon concentration average was 259±9 Bq m(-3) over 16 h, compared to background average over 24h of 1.02 Bq m(-3). 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. Estimates of the activity of (226)Ra 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. The risk from old watches containing radium appears to have been largely forgotten today. This paper indicates a health risk, particular to collectors, but with knowledge and appropriate precautions the potential risks can be reduced.
