Crockett, Robin G M

Gillmore, Gavin K

University of Northampton's Research Explorer

Modelling radon emissions from radium-dial watches

NECTAR

Radon Emissions from Radium-Dial Watches.!Gavin K Gillmore(1) and Robin G M Crockett (2) !1. School of Geography, Geology and the Environment, Kingston University, KT1 2EE, UK.!2. School of Science and Technology, University of Northampton, NN2 6JD, UK.!Introduction – Context!Preliminary research during the latter half of 2011 has indicated that significant and potentially hazardous radon concentrations can arise from radium-dial watches stored in the built environment. Radium (226Ra) decays via alpha-particle emission to radon (222Rn); in addition, mesothorium (228Ra) and radiothorium (228Th) were also used in such watches and decay to thoron (220Rn).!!!Observation of such levels is largely unreported in the literature and our preliminary conclusion is that whilst collectors might be aware of the radiation hazard that arises directly from the radioactive material content of such watches, they are probably not aware of the large radon (and thoron) hazard that can arise, particularly if the watches are kept in a poorly ventilated room in a private house.!Main Experiment!In the main experiments conducted to date, a set of radium-dial watches representative of a small private collection, was placed in a controlled access room, of volume 67 m3, that is continuously ventilated to the external environment. A ventilated room was chosen to minimise any health hazard that might arise from the radon emanations.!The radon concentration was monitored using a RAD7 placed adjacent to the set of watches. Two three-week records from May-July 2011 are shown in Figure 3.!The normal radon concentration at the maximum ventilation rate was ca. 10 Bq m–3. This rose to ca. 190-230 Bq m–3 following the placement of the watches in the room, again at maximum ventilation. When the ventilation rate decreased to a ‘standby’ setting, the radon concentration increased rapidly to ca. 2-3 kBq m–3, then decreased rapidly to the lower concentration when the ventilation rate returned to maximum.!! !References!1. !Boerner, A.J., Buchholz, M.A., 2007.  Radium Timepiece Dose Modelling. Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, USA. DE-AC05-06 OR23100 for the US Nuclear Regulatory Commission.!2. !Baker, A.C., Toque, C., 2005.  A review of the potential for radium from luminising activities to migrate in the environment.  Journal of Radiological Protection, 25, 127-140.!Table 1. !Watch Data.!Analysis!The three resuls...!1. !Extrapolation of the Newmart wrist watch sealed-container experiment results indicates that the zero-ventilation equilibrium concentration in the 67 m3  room arising from the whole set of watches is on the order of 5 kBq m–3.!2. !Calculation of the radon activity in the 67 m3 room based on the total inferred radium content (see Table 1) indicates that the zero-ventilation equilibrium concentration is on the order of 6 kBq m–3.!3. !Monte-Carlo simulation using parameters derived from  the actual radon concentration monitored in the 67 m3 room indicates that the zero-ventilation equilibrium concentration could exceed 10 kBq m–3, possibly 25-30 kBq m–3,in the effective sub-volume ‘seen’ by the RAD7.!All three figures are greatly in excess of the UK Action Levels; 200 Bq m-3 domestic, 400 Bq m-3 workplace.!!!Conclusions!The research has confirmed that there is also a risk to collectors from radon gas emitted from radium-dial watches. Routine radon concentrations of ca. 200 Bq m-3, i.e. the UK Domestic Action Level, peaking to over 3 kBq m-3, were recorded in this study: such levels represent a significant potential health hazard. Those peak levels accord with the estimated equilibrium concentration of ca. 5 kBq m-3 and 6 kBq m-3 derived from single-watch measurements and the inferred radium content respectively.!Also, it should be noted that the room volume of approximately 67 m-3 is likely to be considerably larger than the volume of a typical private collector’s storage space, implying higher concentrations would have been observed in such circumstances. There are considerable numbers of such watches that remain in circulation and these are readily collectible and are easily obtained through (online) auction sites such as eBay.!!Sealed-Container Experiments!There were three sealed-container experiments.!In the first experiment, the Helvetia UK Military pocket watch (see Table 1) was placed in a sealed container (volume 7 L). A CR39 detector was placed in the container with watch. The detector was removed after two days and the etch revealed that it had been overwhelmed by α-particle strikes: the detector surface was saturated with irresolvable overlapping α-particle tracks, as shown in Figure 1. Similar results were obtained for other watches.!The second experiment was as the first experiment, for the same Helvetia pocket watch, but using a Sarad Doseman instead of the CR39 detector. The Doseman recorded an average radon concentration of 18.7 kBq m-3 over a 48 hour period.!In the third experiment, the less-active Newmark wrist watch (see Table 1) was placed in the same container with a CR39 detector and a RAD7 connected in a closed loop continuously monitoring the radon concentration. The CR39 detector was removed after 72 hours and the container resealed for a further 120 hours. The exponential increase of the radon concentration, with the step at 72 hours, is shown in Figure 2.!Watch Manufacture Details Inferred Radium  Make / Brand Notes Date Origin µCi kBq  Buren Grandprix / Bravingtons UK Military G.S.T.P. 1930s Swiss 1.000 37.000 P Buren Grandprix / Bravingtons UK Military G.S.T.P. 1930s Swiss 0.688 25.438 P Cyma  1940s Swiss 0.563 20.813 P Damas UK Military G.S.T.P. 1940s Swiss 0.313 11.563 P Helevetia UK Military G.S.T.P. 1930s Swiss 0.938 34.688 P Ingersoll Cadet US “Dollar” Watch 1940s USA 0.250 9.250 P Ingersoll Radiolite US “Dollar” Watch 1930s USA 0.313 11.563 P Ingersoll Waterbury US “Dollar” Watch 1950s USA 0.375 13.875 P Ingersoll Triumph  1950s UK 0.281 10.406 P Ingraham Biltmore Radium US “Dollar” Watch 1950s USA 0.281 10.406 P Ingraham Rex Radium US “Dollar” Watch 1950s USA 0.063 2.313 P Moeris UK Military G.S.T.P. 1940s Swiss 1.063 39.313 P Unsigned Military  1930s-40s Swiss 0.750 27.750 P Waltham UK Navy post 1941 USA 0.438 16.188 P Westclox Pocket Ben  1950s USA 0.188 6.938 P Pocket Compass  1914-1918 Unkn’n 1.000 37.000 P Arta Liga Watch Factory 1949 Swiss 0.044 1.619 W Avalon Imp’d Swiss Movement 1960s USA 0.063 2.313 W Bulova (dial only) US Military 1951 USA 0.313 11.563 W Bulova (dial only) US Military 1951 USA 0.188 6.938 W Buren Eldis  1940s Swiss 0.044 1.619 W Buren  1950s Swiss 0.125 4.625 W Elgin  1960s Swiss 0.031 1.156 W Hamilton (dial only)  1920s USA 0.031 1.156 W Helvetia  1950s Swiss 0.094 3.469 W Ingersoll Triumph Anglo-Celtic Watch Co. 1950s UK 0.125 4.625 W Ingersoll Wrist  1920s USA 0.013 0.463 W Ingraham St Regis Radium  1950s USA 0.094 3.469 W Moeris UK Military A.T.P. 1940s Swiss 0.875 32.375 W Newmark  1950s UK 0.063 2.313 W Newmark  1950s UK 0.188 6.938 W Normandie  1940s Swiss 0.125 4.625 W Rodania  1950s Swiss 0.094 3.469 W Vertext  1940s-50s Unkn’n 0.031 1.156 W 20 wristwatch hands  1930s-50s UK 0.063 2.313 W Key:  G.S.T.P. General Service Timepiece/Temporary Pattern  /  General Service Tradde Pattern  A.T.P. Army Time Piece  P Pocket watch  W Wrist watch !Fig 1. !Overlapping α-particle tracks (x15).!!Helvetia UK Military Pocket Watch!Fig 2. !Radon Exponential Increase.!!Newmark Wrist Watch!Fig 3. !Radon Concentration in Room, May-July 2001.!

http://nectar.northampton.ac.uk/11645/1/Crockett_Robin_2012_EGU_Radon_emissions_from_radium_dial_watches.pdf

Modelling radon emissions from radium-dial watches

Abstract

Similar works

Full text

Available Versions

University of Northampton's Research Explorer

NECTAR

University of Northampton's Research Explorer