Radiation emissions from glow-in-the-dark toys

[ChumpusRex]

A while ago I bought some novelty keyrings which contained tritium powered lamps.

The marketing information mentioned that the beta particles would be contained by the acrylic shell of the keyring. A not unreasonable claim given the low energy of the tritium beta emission, and lack of associated gamma.

The keyring itself consists of a thin tritium filled glass rod about 25 mm long, and 1-2 mm in diameter. This is embedded in an acrylic cylinder about 8 mm in diameter.

Out of curiosity, I tested one of these keyrings with a GM counter and was somewhat surprised to find it recorded about 100 c/s above background. Presumably this is due to bremsstrahlung generation in the acrylic.

I'm wondering whether this sort of activity is typical of such a device. I was under them impression that the acrylic was a poor generator of bremsstrahlung, so didn't really readily detectable emissions. Perhaps I'm kicking myself for keeping them in my trouser pockets for 2 years, without even considering the emission of X-rays.

I've no idea what sort of activity is in the lamp - but some sources have suggested about 50 MBq

 

[rcgldr]

I miss the good old days, when clock dials used radium and radioactive sensitive paint.

 

[Danger]

Yeah. When I was a wee lad, my dad used to let me wear his Timex in bed for the glow from the radium. (Of course, that might have some bearing on why I'm now Danger rather than 'Danny Nice'. )

 

[Gokul43201]

Jeff, Danger: radium was not what made watch hands glow in the dark; it's what made the glow last longer. The emission from traces of radium was absorbed by a traditional phosphor pigment (probably ZnS or similar) which then re-emitted over time. The pigment alone (without the repeated excitation) wouldn't glow for more than an hour or two.

 

[Danger]

I was aware of that, Gokul, but the matter in question was that radium was an acceptable part of wearable technology in the 50's and 60's. Regardless of whether or not the noticeable glow was sustained by it, it was still sitting there on our wrists. Personally, I dont' care. I thrive on things that are supposed to kill you. Radium's a kitty compared to some of the things that have tried to plant me.