[time-nuts] Atomic Clocks: It is important that they keep good time, Part 1

[Warren Kumari]

On Fri, Jan 4, 2019 at 6:59 PM Steve Allen <sla at ucolick.org> wrote:

> On Fri 2019-01-04T17:05:21-0500 paul swed hath writ:
> > Ed agree with your coment that a 30 or greater year old led may be
> dimming.
>
> Not nearly as much as an entirely different clock illumination:
> radium watch dial paint

I remember my mom's wind-up travel clock glowing brightly.  50 years
> later there is nothing.



I used to have a Rolex submariner with a tritium paint based dial -- I
really loved the watch, but the tritium had sufficiently decayed that it
would no longer fluoresce - this didn't affect the utility, but made me
sad.... It was made in ~1989 and marked SWISS T < 25 for "less than 25
milliCurie" (apparently much less, they started out at ~5 milliCurie). In
~2016, the tritium would have decayed to ~1 milliCurie. Tritium paint is
(apparently) no longer legal in the USA, but when I was in Hong Kong I
found someone who had "new" paint, and willing to repaint the face --
unfortunately I didn't have time on that trip to have it done, and when I
went back a few months later the shop had closed down...

There is a (apparently) a group of watch dial enthusiasts who get a
specific brand of tritium based exit sign which has tritium paint embedded
in the plastic (most tritium exit signs are the small gas capsules
instead), grind them up and then extract the paint from the ground plastic
using solvents. I briefly toyed with this idea before deciding this was bad
mojo and sold the watch...


> I brought it into the lab just to check that
> it is still radioactive (wouldn't want to have lost that radium
> somewhere).  It's the zinc sulfide crystals, the radiation damages
> them and they stop producing light.
>

Hmmmm. I wonder if that is actually what happens with the tritium paint -
the dial I had would *just* have a visible glow if I had it in a perfectly
dark room and let my eyes adjust for a while. If the tritium level had
decayed from 5 milliCurie to 1 milliCurie I would have guessed that the
glow should just have been 1/5th of original. The dial would still
fluoresce nicely under UV, so I'm not sure what that means...

W


> --
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-- 
I don't think the execution is relevant when it was obviously a bad idea in
the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair of
pants.
   ---maf