[R-390] R390A meters

[Charles Steinmetz]

Roger wrote:

>   The recent posts about replacing the meters on R390A has me wondering. I have a 67 EAC that appears to have the original meters. They are black face with white scale and needle and they do glow in the dark. I read previously that those meters are safe as long as you don't disassemble them. Is there new info that contradicts that thinking?

 From your description, yes, you have radioactive meters.

The active ingredient in the radioluminescent paint is Radium 226. 
Ra226 is primarily an alpha radiation source, and alpha particles are 
easily blocked -- a few cm of air, a sheet of paper, and human skin are 
all effective shields, as are the glass and metal case of the meter.

However:

The decay of Ra226 also produces beta radiation, incidental gamma 
radiation, and Radon gas (you can see the radioactive series here: 
<https://www.ld-didactic.de/software/524221en/Content/Appendix/Ra226Series.htm>) 
  The beta, and particularly the gamma, radiation penetrate much more 
than the alpha radiation.  Also, radon gas can leak out of the meter. 
So, there is *some* radiation risk.

How much risk is the "some"?  With low levels of radiation such as 
these, and the widely varying exposure factors among the user base, that 
is a question each user must answer for him/herself.  Someone who spends 
14 hours a day glued to a 390/A at very close range has a very different 
risk profile than someone who only goes into the shack once or twice a 
week for a few hours, not all of which is spent at very close range to a 
390/A.  Also, the accumulation of Radon in the shack depends on how well 
sealed the room is.

My dad was the Radiation Safety Officer at a research hospital that did 
extensive work with radionuclides (including his own work), so I was 
reasonably well schooled in the subject before I was allowed into his 
lab.  My personal view is that if one does not open the meter, the risk 
is very to extremely low -- in the "probably better advised not to sleep 
with it pressed against your genitals" class.  But people will assess 
the risk differently, anywhere from the very cavalier "There is no real 
risk at all" to the ultraconservative "The risk is unacceptable if the 
additional exposure accounts for more than 0.1% of the background 
radiation."

Also, the user's age is a factor.  Anyone who is age 50 or older is very 
unlikely to have reduced mortality from any exposure to radiation short 
of an acute radiation event.

Note that millions of people have used radium baths over the centuries, 
and they are still popular spa destinations to this day: 
<https://listverse.com/2015/07/10/10-places-around-the-world-where-you-can-take-a-radium-bath/>

If you are really concerned, get a dosimeter and measure the exposure in 
your actual situation.

Best regards,

Charles