Radium Painted Meters

UPDATED 7/14/2025

Like old wrist watches with “glow in the dark” hands and numerals, some meters of that era had radium paint on their needles and scales.  A Radium-containing compound was mixed with a phosphorescent material that emitted visible light without the need to “charge” the paint with an external light source. 

In this case, the Alpha particles (Helium nuclei) emitted by the decaying Radium 226 bombarded the phosphorescent material which converted the Alpha particles’ energy into visible light.  For a long time.  The phosphor material was typically Zinc Sulfide crystals.

The meter shown above has Radium paint on the needle and the 3 scale lines. This paint is usually a pale yellow to light brown color from the ones I have seen. This particular meter emits 0.5 mR/hr at the glass window, about 50 times the normally low background of 0.01 mR/h in this area.

My local background radiation level measurement of 0.01 mR/hr was made with a GQ Electronics GMC-800 Geiger counter “survey” meter. It cannot detect alpha radiation. Some sensitivity specifications:

Range of dose rate indications, μSv/h 0.00 to 2000
Range of exposure dose rate indications,mRem/h 0.00 to 200
Range of registered beta radiation energy 0.25 to 3.5 MeV
Range of gamma radiation energy, 0.1 to 1.25 MeV
Range of registered X-ray radiation energy 0.03 to 3.0 MeV

(By way of comparison, lantern mantles had Thorium in them. It included an unstable, naturally-occurring radioactive isotope 232Th as well.  Thorium oxide has a very high melting temperature and emits a very bright white light when heated by the burning lantern fuel.  When Coleman stopped selling the Thorium mantles, circa 1990, the replacement product apparently used Yttrium instead.  I had both types; the newer mantles put out about 60% of the light the Thorium mantles do.  The old – style Thorium mantles were routinely used by health-safety personnel as “check sources” to verify the proper basic operation of Geiger counters. They can typically measure up to about 0.10 mR/hr, about 10 times background at close range)

Above: The meter in my SCR-284 is relatively “hot” radioactivity-wise. More so than most of the other radios or meter that I have. Probably because there is a relatively large amount of radium-mix paint on the scale. 

Here is a measurement made with the GMC-800 Geiger counter at near-zero distance from the paint. It is about 80 times higher than my local background:

Radium 226 is primarily an Alpha and Gamma ray emitter and it stays “hot” for a long time (half life of 1600 years as it decays into Radon gas). It finally damaged the phosphor paint it was intended to excite in this meter. Very, very dim glow these days; the glow is gone but the Radium is still there. Like a radioactive home smoke detector, these things are not very dangerous if left intact. Don’t disassemble it…

These measurements are primarily from Gamma radiation – Alpha’s won’t penetrate the meter glass, nor will most Beta’s; sorry, no Neutrons. The GQ GMC-800 cannot detect alpha radiation.

My R-390A Receiver meters also had detectable levels of radiation:  The Carrier Level meter read 1.2 mR/hr, the Line meter read 0.4 mR/hr with an Eberline E120 Geiger counter at close range

My TBY meter (below) read 0.77 mR/hr, my GRC-9′s labeling each read just background.  Background radiation during these tests was 0.01 mR/hr. Probably no radium paint used on my GRC-9’s – your mileage may vary. They utilize the newer type of phosphorescent paint – you must “charge” it with a strong light source. There is no radioactive material in that type of paint.

Above:  The unusual panel meter on the TBY 2 Receiver-Transmitter.  A little radium paint on the “center” square and needle.  Aim here. It measures 0.77 mR/hr at extremely close range, about 77 times above local background.

The Transmitter and Receiver tuning dials look to me like radium paint but they show no detectable levels with the meter as close to them as I can get it. So the radiation seems to be solely from the meter dial and pointer. (The GM tube is directly underneath that black rectangle in this portable meter.)

Here is the DC voltmeter in my truck dashboard, again at close range. About 0.08 mR/hr. (0.08 mR/hr ~ 80 counts/minute with Gammas.

Here is a WWII era small boat compass. It’s pretty hot. That enclosed binnacle is probably full of Radon gas, a radioactive decay product of Radium. Don’t open it!

I remember that when I was a kid I looked at my fathers wristwatch hands under a low power microscope. In the dark, you could see the individual flashes of light emitted from the paint as an Alpha particle slammed into a phosphor crystal. Scintillating!

On a related note:  Military compasses and radiation.

The induction-damped Lensatic compass. In addition to general LandNav work, the Lensatic is especially good for taking Resection fixes (to locate your own position on a map relative to distant landmarks, a common task.) Or for identifying a distant “walk to” point along your intended route bearing.

Post WWII/Korean war era issued Lensatic types can use radioactive Tritium gas (AKA “3H”) which is a Beta radiation emitter. It interacts with phosphor powder lining tiny glass vials to be self luminous (self excited) at night. The current performance specification, MIL-PRF-10436N does not require a radioactive source although the wording is somewhat ambiguous to provide the prospective vendor some design latitude. It is optional (Reference 75). If radioactive material is present the compass will be marked accordingly.

The waiver of a radioactive exitation feature was probably related to the non-availability of Tritium from U.S. production reactors in the 1980’s. They were our only domestic source of that hydrogen isotope before a new reactor(s) was built later on.

However Tritium has a half-life of 12 years so older “surplus” compasses on the market can be quite dim from their original brightness when manufactured. Caveat emptor.

My go-to compass, above, (NSN 6605-01-196-6971, Oct 1986 manufacture date) is an example with simple phosphorescent markings, chargeable with a flashlight for night Ops. Apparently Tritium was not always a requirement of that MIL Spec/NSN definition, at least in 1986.

Radiation follows the inverse square law. If you double the distance from the source, the radiation flux is reduced by a factor of 4. Just like with explosives, and for the same reason, distance is your friend when dealing with sources. If you are VERY close, say by eating or inhaling the paint, you may have a serious health issue. Keep them sealed. Just be aware.