You are here:

Physics/Old Compass Card - Radium?


I read your post regarding radium watch dials and have a related question.  
I recently purchased an old boat compass which I was planning to take apart and refill with fluid.  My search of the Internet revealed that since it is a fairly old compass, it probably had a radium dial and that I should not attempt to take it apart for fear of releasing radium.
I have not taken the compass apart, but it is dry.  I was wondering if the original fluid leaking out would have contaminated the outside of the compass and the copper container that houses it? Am I in danger from just handling this?
I notice some flaking of the numbers on the compass and assume this may be the radium paint flaking off.  As long as I don't take the compass apart is the radiation being contained in the compass?  The compass is constructed of glass, brass and some sort of plastic bowl that contained the liquid.
So basically I'm wondering if this thing is a ticking time bomb even if I don't take it apart.  
Also I started wire brushing some bronze fittings on the outside of the compass. Is it possible that the bronze corrosion contained radiation and have I just spread it further by my wire brushing?
Meanwhile I'm trying to track down a Geiger counter to see if this thing is emitting anything. So another question, if it is not emitting anything on the outside, is it safe to take apart or is radiation being contained in the compass unit even without compass fluid?
The other question I have, is when these old things were in use did they emit radiation or was it all contained in the compass fluids?
Thanks for anything you can offer.  I'm not sure whether to keep this thing or pitch it . . . and if I pitch it, what's a safe way for disposal?

Danger is the key word here...there's a difference between detectable radioactive material and dangerous exposure levels.  It is in fact likely that wherever that fluid leaked out to has a detectable level of contamination, radium has a long half-life.  The outside probably doesn't have much material, but you can always clean it with paper towels and dispose of the cloths.  Even if you scan it with a Geiger counter and it reads pretty hot the alpha radiation is only dangerous if the material itself is physically ingested.  The secondary gamma rays (if you're detecting it more than a few inches from the surface and it's still really hot) are the only reason to worry about here.

When radium decays, it emits radon, so keep it in an area that's ventilated to the outside just in case.  That gave me an idea, you can stick it on a counter top under a bowl.  Most hardware stores sell radon detection kits which are simple to use.  If radon is collecting in the bowl (the enclosed space will vastly enhance the collection process, so it's still not necessarily dangerous), *then* spend your money on a Geiger counter or borrow one.  But make sure you know someone who knows what the readings mean.  Better still, stick it in some tupperware and take it to the nearest decent-sized university and see if their physics department has a Geiger counter that they're willing to wave at it for a few seconds (that's all the time it would take to know "danger" vs "detectable" levels).  They'll probably know what to do with that, their radiation safety officer will have disposal procedures if it's truly not safe.

Question:  does it still glow in the dark?


All Answers

Answers by Expert:

Ask Experts


Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

©2017 All rights reserved.