Geiger Readings for tritium watches

Davidt · Apr 6, 2022

Evening all.

Does anyone have any idea what late tritium (80’s/90’s) dials/hands register in a Geiger counter?

Ive recently bought a vintage Omega with incorrect hands. I assumed tritium as 1) who would replace the hands on a late 60’s Omega with old radium hands, and 2) the lume is quite a pale shade, not the yellow you usually associate with radium.

However, when placed next to my Geiger, the readings increase from background (c.0.05-0.12 uS/hr) to around 0.30uS/hr. This seems too low to be radium but somethings making the reading increase. With a half life of around 12 years, would new-ish tritium give these results?

Note-crystal was in place as was caseback. Counter was placed directly on top of crystal.

sxl2004 · Apr 6, 2022

Tritium does not register on a Geiger Counter.

sleepyastronaut · Apr 6, 2022

Foo2rama · Apr 6, 2022

It would be barely above background if you had something sensitive enough. I doubt you have something sensitive enough.

short half life.

Davidt · Apr 7, 2022

sxl2004
Tritium does not register on a Geiger Counter.

Ah, that rings a bell now. Because most counters measure gamma but tritium emits only alpha?

Could radium hands register as little as 0.30uS/hr?

Seaborg · Apr 7, 2022

Hello David,

First, tritium (3H) has a β- decay (18.59 keV), no α.
On the other hand, 226Ra (it's the only isotope you can get in watches as the others have a too short half-life) has an α decay (two actually: 4.6 and 4.7 MeV). The desintegration energy is two orders of magnitude higher than that of 3H β-. This makes it easier to measure as well as the half life is much longer (226Ra : 1600 years vs. 3H : 12 years). Associated to the α decay, 226Ra also emits a strong γ (186 keV), that's what we measure.

Second, what are the characteristics of your "Geiger Counter" ?
On the backside, I guess there is a small sticker describing the energy spectrum that can be detected by the apparatus. We need that.

Third, your measurements are super low, barely higher than the backgroundl level. So no worries.

I think you might measure some residual β- 3H decay, no radium for sure. In general, we say a material is no longer radioactive (strictly speaking have reached the environment background) after 10 periods (=10 half-lifes). So, tritium can still be measured with the appropriate device (needs 120 years to reach the background level). 226Ra will need 16000 years to reach that level....

Have a nice day.

R

Davidt · Apr 7, 2022

Hi @Seaborg, thanks for the detailed reply. Regardless as to whether it’s radium, at such low levels it doesn’t concern me. It more general interest as I can’t recall tritium watches registering any increase in this reader before. Then again, my newest tritium watches are from the late 60’s.

With a young family, if we were talking 30uS/hr I may think differently.

This is my counter.

“GQ GMC300Eplus Fulfill Digital Geiger Counter NULCEAR Radiation Detector Monitor Meter Dosimeter Beta Gamma X-ray”

Radiation detection: Beta, Gamma and X-Ray .

Sensitivity to Gamma Radiation: 0.1~1 MeV

Own Background: 0,2 Pulses/s

cvalue13 · Apr 7, 2022

Davidt
This is my counter.

Only morbidly curious as to why you have a home Geiger in the first place?

Wondering it I might “need” one but didn’t know it 😁

Seaborg · Apr 7, 2022

So your coutner can measure β, γ and X-rays.
The lower detection limit is 100 keV and the max is 1 MeV, so you're good for both the β of 3H and γ of 226Ra.

The dose rate (your reading on the counter, in μSv/h, but should be strictly speaking in μGy/h) depends on several parameters.
First, the distance. The longer the distance, the lower the dose rate (the atoms of atmosphere naturally "block" any radiation). The dose rate decreases in air as a function of 1/d², d being the distance.

Second, the "shielding". As you know, α are super dangerous (enormous energy) but can be stopped easily with a simple piece of paper. β are a little more penetrating and can be stopped by a thin metal foil, γ and X (that are photons with different wavelengths) go even deeper and depending on the wavelength, you will need serious shielding to stop them. Neutrons are even worse and I will not go into details here (no neutron radiations in watches).

Third, the quantity of radionucleides. The more radioactive material you have, the greater the dose rate (obviously).

So, if we go back to the watches, the β dose rate is dramatically decreasedecreased by the crystal. On the other hand, the γ dose rate is hardly affected.
With watches coming from the 60s, tritium is already almost gone (5 periods already) and also even more attenuated by the crystal. With more recent watches (let's say from the late 90s), the β measurements should be much higher (but still very low).

I hope this helps a little.

Cheers

fjf · Apr 7, 2022

I have experience with tritium measurement. Its beta radiation is so soft that you need what it is called an scintillation counter to be able to measure it. You must mix the sample containing 3H with scintillation liquid, and this emits light every time a beta particle hits it. You measure the light emitted. A few mm of air stop those electrons (beta radiation). A sheet of paper. Anything. There is no detector that can accurately measure it because of that. No worries. You have to ingest it to receive any radiation, and even then I doubt you could be seriously harmed.

Davidt · Apr 7, 2022

Thanks @Seaborg and @fjf.

The readings were taken with the counter literally laid in the watch crystal. With the counter on the table, the reading was 0.05 - 0.15 uS/hr. With the counter on the crystal the reading was 0.18-0.30uS/hr.

I repeated this several times and the results were consistent. From this is it possible to suggest whether radium in the incorrect hands was the likely source of this increase, or could it be residual emissions from tritium decay, or another unknown source.

I don’t have concerns around the safety of the hands, I won’t be eating them regardless! It’s general curiosity as I like to use a counter to determine radium/tritium and it would be useful to know if newer tritium can penetrate crystals and result in minor increases.

thanks again

Davidt · Apr 7, 2022

cvalue13
Only morbidly curious as to why you have a home Geiger in the first place?

Wondering it I might “need” one but didn’t know it 😁

Purely for helping to identify radium in watch dials to help with determining originality.

I also occasionally check my bananas!

cvalue13 · Apr 7, 2022

Davidt
I also occasionally check my bananas!

on a quick google search for your model, I was surprised the results were apparently so produce safety oriented?

should I be fearing my produce more?

Davidt · Apr 7, 2022

cvalue13
on a quick google search for your model, I was surprised the results were apparently so produce safety oriented?

should I be fearing my produce more?

I think we’re ok unless there’s an attack of the killer tomatoes!

watchyouwant · Apr 7, 2022

cvalue13
Only morbidly curious as to why you have a home Geiger in the first place?

Wondering it I might “need” one but didn’t know it 😁

I have the same Geiger. If you deal in vintage Rolex Sub's, late 1950's to early 60's , this is one necessary tool to evaluate originality. Good to take to Auctions viewings ..

Dogmann · Apr 7, 2022

@watchyouwant

Do you also wear a full Hazmat suit whilst using it at Auction Viewings? as that conjures an interesting image in my mind? and the look of those around you would of course be priceless.

Marc

watchyouwant · Apr 7, 2022

Dogmann
@watchyouwant

Do you also wear a full Hazmat suit whilst using it at Auction Viewings? as that conjures an interesting image in my mind? and the look of those around you would of course be priceless.

Marc

Don`t worry, Marc. All serious Dealers have a Geiger with them..... Hazmat suits are something for the unexperienced Dealers. We all glow a bit in the dark ..... Different, hardened Generation. Especially the ones, who deal in Military watches from the 40`s.

fjf · Apr 7, 2022

If your counter reads something, all I can say is that I doubt it is tritium. It's half-life is about 12 years, and the radiation is too soft.

Davidt
Thanks @Seaborg and @fjf.

The readings were taken with the counter literally laid in the watch crystal. With the counter on the table, the reading was 0.05 - 0.15 uS/hr. With the counter on the crystal the reading was 0.18-0.30uS/hr.

I repeated this several times and the results were consistent. From this is it possible to suggest whether radium in the incorrect hands was the likely source of this increase, or could it be residual emissions from tritium decay, or another unknown source.

I don’t have concerns around the safety of the hands, I won’t be eating them regardless! It’s general curiosity as I like to use a counter to determine radium/tritium and it would be useful to know if newer tritium can penetrate crystals and result in minor increases.

thanks again

Rudi99 · Apr 8, 2022

Seaborg
First, tritium (3H) has a β- decay (18.59 keV), no α.
On the other hand, 226Ra (it's the only isotope you can get in watches as the others have a too short half-life) has an α decay (two actually: 4.6 and 4.7 MeV). The desintegration energy is two orders of magnitude higher than that of 3H β-. This makes it easier to measure as well as the half life is much longer (226Ra : 1600 years vs. 3H : 12 years). Associated to the α decay, 226Ra also emits a strong γ (186 keV), that's what we measure.

Second, what are the characteristics of your "Geiger Counter" ?
On the backside, I guess there is a small sticker describing the energy spectrum that can be detected by the apparatus. We need that.

Third, your measurements are super low, barely higher than the backgroundl level. So no worries.

I think you might measure some residual β- 3H decay, no radium for sure. In general, we say a material is no longer radioactive (strictly speaking have reached the environment background) after 10 periods (=10 half-lifes). So, tritium can still be measured with the appropriate device (needs 120 years to reach the background level). 226Ra will need 16000 years to reach that level....

I guess we are all happy to have a nuclear scientist among the forum members...! 👍

padders · Apr 8, 2022

fjf
If your counter reads something, all I can say is that I doubt it is tritium. It's half-life is about 12 years, and the radiation is too soft.

I disagree. Read back for the reason why from the Prof, no tritium is yet old enough to be fully at background yet, well maybe the 1960s stuff wouldn't give much of a return but stuff from the 1990s has only undergone 2 half lives so is still at a quarter the potency when new.

Geiger Readings for tritium watches

Davidt

sxl2004

sleepyastronaut

Foo2rama

Davidt

Seaborg

Davidt

cvalue13

Seaborg

fjf

Davidt

Davidt

cvalue13

Davidt

watchyouwant

Dogmann

watchyouwant

fjf

Rudi99

padders

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