He's using a pancake mica detector. He's also detecting alpha and gamma. That would account for his very high readings. I'm sure if he used a typical sodium iodide detector, the reading would be much lower from just gamma radiation.

The total measurement will be higher if you're measuring alpha and gamma, but biologically, the alpha radiation isn't as "dangerous". It usually doesn't penetrate skin.

@Leica does your detector also detect alpha radiation? Maybe that's why your reading is extremely high.

 

You can't compare measurements of alpha + gamma to that of just gamma.

 

I've also always wondered whether you can correlate the size of lume plots to the actual amount of radium. Lume is lume, and radium was mixed in with phosphor. So just because there's a lot of lume, doesn't necessarily mean there's more radium. It probably does. But not necessarily. I wonder if anyone has access to the amounts of radium added to watches at production compared to the size of the lume.

Interestingly, if you go back to my original post, my Tissots have much higher gamma radiation readings compared to my LeCoultre, despite the LeCoultre having much larger lume plots.

 

from my understanding, does it needs to be very close (without barrier) to measure alpha ? could it be that the low end geiger meter arent picking every particles?

 

I’m not sure what you mean? If you’re measuring just above the crystal you would be picking up some alpha. But yes, you do need to be very close to measure alpha. A few centimètres of air would attenuate much of the alpha radiation, is my understanding at least.

What I’m saying is that if your detector detects both alpha and gamma, that would explain your unusually high readings compared to most of us using detectors that only detect gamma.

 

mine is tube sensor.

so i did two additional tests
1) with a 4cm stainless steel sheet , it reads 1.9-2.3 range
2) 6inches away from the watch it reads 13.5uSv/hr

I found an old clock from thrifty with lots lume paint on it but it reads 15.7uSv/hr directly from the crystal

 

so alpha will penetrate the crystal? sorry i am bit confused

 

I just looked up your Geiger counter. It’s a pancake detector that detects alpha and gamma. Yes a certain fraction of alpha will penetrate the crystal. It will be attenuated but will not be gone altogether.

That’s why you’re getting such a high reading. Just like the guy in the video you posted. You’re measuring both alpha and gamma.

The combined reading from alpha and gamma emissions will always be higher than if you just measured gamma alone. If you want to know the amount of gamma emissions from your watch, you’ll need to borrow/buy a separate detector that only measures gamma (such as a sodium iodide detector).


Hope that helps.

 

thank you!

i will try it on another counter.

i guess measuring 6inches away from the watch is closer to gamma accuracy? i assumed alpha does not travel that far . it reads 13.5uSv/hr

 

Well you can’t guarantee your measuring no alpha at all at that distance, but probably much less.

If anything the experiment you did with the steel probably attenuated all the alpha. You were probably measuring mostly gamma at that point, although a fraction of the gamma would have been attenuated by steel as well.

The most reliable way is to compare your readings with that of another detector that only reads gamma.

 

does that mean alpha could be dangerous as well, if it were able to penetrate crystal and travel at a distance?

i found a good reference at my local university site.

http://riskmanagement.sites.olt.ubc.ca/files/2015/09/Radiation-Reference-Manual-2011-1.pdf#page=47



anyways, i will order a radex counter from amazon .

 

My understanding is that alpha radiation is considered relatively harmless from an external source, since it is blocked by our epidermis (skin). If you ingest/inhale an alpha emitter however, alpha particles have a very high energy and are dangerous if internalized (e.g. radon gas), or the story of the radium girls licking their radium paint brushes. But the alpha emissions from a watch worn on the wrist would be considered fairly harmless.

 

"Alpha radiation: Alpha particles consist of two protons and two neutrons, and since they have no electrons, carry a positive charge. Due to their size and charge, alpha particles are barely able to penetrate skin and can be stopped completely by a sheet of paper. "

unless there is a leak , wouldn't it not able to penetrate a watch crystal ?


I saw these two Radex counter on amazon , seems like both are GM tube.

 

Too many variables to make any confident generalities, I would say. I have a LeCoultre that measures very high.

 

Generally I think when you read that alpha particles are attenuated/blocked by a sheet of paper, they're referring more to the fact that in general, alpha particles don't penetrate very far through things or through the air. That doesn't mean no alpha particles at all make it through a sheet of paper. Same applies to a watch crystal. Most of the alpha is blocked, but you probably still do detect a significant amount since it's not all blocked by the crystal.

I don't think anyone out there has ever done a dedicated study looking at what percentage of alpha emissions emitted by radium indices is actually blocked by the crystal and what percentage makes it through.

 

would alluminum foil block the alpha particles?

 

I tested a 1958 red sub , it is even hotter than mine at 187uSv/hr , 65k CPM . now I just need to find a gamma only counter.

 

Anybody have one of these watches serviced? How much extra cost is charged on.

 

The watchmaker I use charges nothing extra. I doubt he even checks or cares whether the piece has Radium. For a guy who works on stuff like this every day, he's surprisingly nonchalant about it.

 

For anyone looking for a good summary of the risks and precautions to take, I found this was actually a good resource:

http://nuclearsafety.gc.ca/eng/resources/radiation/could-your-collectible-item-contain-radium.cfm