Re: Cross Post: Radioactivity in Watches?

[mgoldman@ucdavis.edu (Dr. Marvin Goldman)]

>Radsafers:
>
>I posted this from SAFETY in hopes that some interesting answers would
>surface for the questioner and for us.  I think we can help this gentleman.
>
>Kristin
>
>
>
>Date:    Mon, 24 Apr 1995 10:16:40 -0500
>From:    Rob MacCormick <ROB@HARV-EHS.MHS.HARVARD.EDU>
>Subject: Hot watch!
>
>Hello!
>     A colleague (who doesn't CURRENTLY subscribe) asked me to post the
>following with the hope of getting some feedback......A researcher
>discovered during a routine radiation survey that the face of his Seiko
>watch was producing a dose rate of 400cpm with a low energy NaI
>scintillation probe. No dose rate was detected at the back of the watch.
>
>     Because radium is no longer in use as a "luminant" (is this a
>word?), what isotope could be involved? Perhaps some kind soul who
>subscribes to RADSAFE could cross post this as I don't subscribe.....Any
>information would be most appreciated!
>
>     His email address is spaula@biosun.harvard.edu, I'll forward any
>responses posted to SAFETY.....Thanks in advance!
>
>Rob M
>
>Rob MacCormick
>Associate Industrial Hygienist
>Harvard University
>46 Oxford Street
>Cambridge, MA 02138-1995
>(617)-495-3055
>Fax:(617)-495-0593
>Rob@harv-ehs.mhs.harvard.edu
>rob_maccormick@harvard.edu
>
>************************************************************************
>Kristin Erickson, Radiation Safety Officer
>Office of Radiation, Chemical and Biological Safety
>C124 Research Complex-Eng.
>Michigan State University
>East Lansing, Michigan 48824
>Telephone: (517) 355-5008   Fax: (517)353-4871   Email: 10525kfb@msu.edu
>************************************************************************
Reply:
For many years after radium was banned from the watch-dial arena, tritium
was used.  However it tended to evaporate off the watch faces and I believe
that it is no longer in use.  It my be tritium, but I doubt that the
detector could see the weak beta through the crystal.  It could be a
promethium isotope, as I seem to remember that some other radionuclide was
used for a while.
M.Goldman