a reprise on Radium and Tritium dials ( confirming Tritium from Radium dials)

[Horologist]

Although this topic has been repeatedly discussed on just about every horology forum, there is still some confusion about differentiating Tritium from Radium dials.

My interest is mainly on the early 1960's Tritium dials which weren't labelled with "T" during that early transition from the use of Radium to Tritium. I believe they exist as I recall reading a post on this topic on some very old post (not sure of forum).

My understanding is that the best non invasive observations is by use of a Geiger counter compared to relying on a UV light.( I still have old Tritium dialed watches which glow brightly in the dark for lengthy periods)

Tritium mainly emits Beta particles which are faintly picked up by a Geiger counter to my knowledge.

As Radium 226 mostly emits alpha and gamma particles, the Geiger counter will not pick up presence of alpha particles as;

they are firstly, heavy and blocked even by a piece of paper and secondly most Geiger counters I have known do not have the feature to detect them.
My understanding is that any detected radiation pointing to the presence of Radium, would be from the accompanying gamma rays which would be picked up by the Geiger counter (not detected in Tritium).

Hypothetically, if one were to measure the Geiger counter readings of a 1962 Seamaster 135.003 which would most likely be Radium and compare it to the readings of the same model with a Tritium labelled dial with expectations of showing different radiation readings, would it be fair to assume that comparing those two readings to another unlabeled 135.003 Tritium dial , should have closer readings to the T labelled model???

Although a Geiger counter would not confirm an unlabeled dial to be Radium from the absence of detecting alpha particles, one would expect that it would at least rule out the dial to be Radium if the readings are closer to the known labeled Tritium dial??? .

I am aware that most, especially those new to this can be confused as to what is a true control to distinguishing radium versus Tritium, which I thought of resurfacing the topic again.

Edited: Mon. 10:50am

 

[Dan S]

A tritium dial won’t give you a Geiger reading significantly above background.

 

[speedb]

Dan S

A tritium dial won’t give you a Geiger reading significantly above background.

This - the half-life of tritium is 12.3 years so after ~60 years it would have gone through almost five half lives - just over 3% of original radioactive material remaining will not measure higher than background, especially for a weak beta emitter.

 

[Horologist]

Dan S

A tritium dial won’t give you a Geiger reading significantly above background.

It would be interesting to see what the Geiger readings would have been when the "dial was new" before it's half life period.

I suppose the Geiger readings on those new Ball brand watches that still use Tritium would be of some indication?

 

[SOG53]

Have you tried UV flashlight? Radium lume lights up but glow is immediately gone when turn off light Tritium lights up and fades more slowly over 10-30 seconds after removing light.
And UV flashlight much cheaper than Geiger counter.

 

[Horologist]

SOG53

Have you tried UV flashlight? Radium lume lights up but glow is immediately gone when turn off light Tritium lights up and fades more slowly over 10-30 seconds after removing light.
And UV flashlight much cheaper than Geiger counter.

Yes, I have used the UV flashlight and you raise an interesting point. .

I have a plated generic vintage watch ( labelled "Jewellex" housing a manual Lanco movement) which was gifted new in 1965 as an infant arrival gift which was never serviced when it stopped working ( therefore never tampered with). The dial has a "T" on bottom surrounded by a circle ( denoting Tritium lume). When I shine a UV light on it, the glow on the hands go on for more than 30 seconds in the dark. ( dial has no llume dots). I also had a Longines conquest from 1967 with "T" next to Swiss made and glow goes out almost after a few seconds but not as long as the watch above.

I have a non date Rolex perpetual from 1962/1963 which I suspect to have radium hour dots and lumed hands, considering there is no "T" designation next to "Swiss". When I shine a UV light on it, the glow disappears after only a few seconds in the dark. So is it radium or Tritium? how long is too long or too short? It is like asking how long is a piece of string for me. .

What I have noticed is that a lot of this depends on the amount of radium used in the mix (as my understanding from other cited sources is that the Suppliers of dials and hands (Universo) offered not only different lume substances but also different lume intensities).

(image taken from https://www.watchprosite.com/rolex/...-radioactivity-on-a-dial-/732.978163.6840528/)