Radium - Geiger Counter Measurements

Great read. So is the take away that a Radex RD1706 would be a good model for vintage watches since it measures Gamma ( needed fir watches) as well as Beta. ( nice to have). Thanks

Or save 75 buck and buy the rd1503 gamma I don’t have that many watches with radium lume

**ADDENDUM - So I've looked into this a bit further. Turns out the detector I was using (ThermoFisher PRD) uses a NaI (sodium iodide) detector, which only detects gamma radiation. The purpose of PRDs (personal radiation detectors) is to detect radioactivity from outside that could harm a person, so gamma is the most relevant (is my understanding at least). So the readings I am getting with that are in fact entirely gamma. Other cheaper detectors that you can buy on Amazon are likely usually traditional geiger tubes. Radex for example uses an SBM-20 Russian military Geiger-Muller counter which detects beta and gamma radiation. Basically, if you're going to be measuring radiation, you need to know:

1. What type of detector you have and what type of radiation it detects
2. What type of radiation the radioactive lume emits

So this leads me to think that the drop off I'm seeing as I pull the detector away is still gamma radiation, but the radiation intensity drops off quickly with increasing distance. This principle is according to the Inverse Square law, whereby the intensity of radiation is inversely proportional to the square of the distance.
https://en.wikipedia.org/wiki/Inverse-square_law

It's also important to keep in mind that probably the most relevant area to measure in terms of our exposure is the caseback. Although the radiation is strong just above the crystal, this dissipates quickly with increasing distance. This means most of the time (unless you're holding your watch crystal up against your chest or body), the exposure from the watch face will be reduced by distance. The caseback on the other hand sits over your wrist, skin, bone marrow, etc. Radiation safety limits (e.g. like the ones I quote above) are likely values for TOTAL body exposure (e.g. 50 mSv/year for nuclear safety workers). There's no way to know for sure who much your total body receives with a source at the wrist, but I expect for most areas of the body it is minimal given your wrist is held away from your body most of the time, and the dial isn't always pointed towards your face/body.

Bottom line is, we just don't know whether this is safe or not. But, it is probably not that risky provided:
1. You don't own a huge collection of radium watches and sit on a regular basis in very close proximity to them (even within a few feet the radiation drops off significantly). In this scenario, radon gas is likely more dangerous and I have no idea as to the attributable risk to this (I'm just commenting on gamma radiation).
2. You don't play around with the lume or expose the dial itself. The more prominent danger with radium (or tritium) is ingestion, whereby the ingested radium is incorporated into bone and alpha radiation can now damage surrounding cells for the entirety of your life (since radium's half-life is longer than you'll be around). If you are opening the watch up and messing with the dial, or even just exposing the dial, that's a whole different ballgame and I recommend against this unless you know what you're doing.
3. If you were to wear your radium watch 24/7, 365 days a year, for 5 years (an unlikely scenario), then yes, you very well might receive a non-negligible exposure at the wrist. This exposure is probably most appropriately calculated using gamma readings from the caseback. I have no idea how much this translates to in terms of total body exposure, but it's probably quite a bit less. Whether this translates into an appreciable cancer risk, I don't know, but again, most sources I'm reading state that a cancer risk has not been able to be attributed to TOTAL body exposures of < 100 mSv. So lets say you take a watch emitting 1.0 uSv/hour at the caseback and you run the scenario above --> 4.32 mSv over 5 years at the wrist. To compare, a SINGLE abdominal CT scan exposes the stomach to 10 mSv.

To be clear, none of this is my professional opinion. I am interested in this as a hobby, and I have no professional experience with radiation detection. You can make your own determination whether this is a risk you want to take.