I recently purchased a tritium keychain, composed of a small glass vial of tritium gas partially enclosed in a stainless steel fob. Here are the Amazon links so you can see a specific example:
The glass vial is 12mm long and 2mm diameter. Here's a picture of what they look like for future-proofing against link rot:
The seller claims (in slightly broken English) that this product is perfectly safe:
Because the beta decay of tritium will only emit electronic high-speed mobile, do not penetrate the human body, there is no harm to human body. The half-life is 12.3 years, electrons produce beta decay of tritium is very weak, a piece of paper can be blocked, so the tritium gas in the lamp is closed extremely safe, even if the glass tube rupture, the release of tritium gas, and the use of people to complete inhalation, but also far less than people in the normal life of the day is the amount of radiation. Tritium gas emission technology has been applied in many civil fields.
I'm aware from my own research that inhaling or ingesting the contents of the vial won't kill me, but won't be a good thing. However, my question is about the radiation emitted from the vial inside the fob, assuming it does not break.
The seller claims that the beta particles cannot penetrate the human body. However, doing a little basic reading into beta particles led me to this:
Beta particles are able to penetrate living matter to a certain extent and can change the molecular structure of molecules exposed to this type of radiation. In many cases, such changes can be considered to be damaging with results possibly as severe as cancer or death. If the struck molecule is DNA, it can cause spontaneous mutation.
Additionally, I found some forum posts online saying that the vial itself is safe, but when encased in stainless steel it emits Bremsstrahlung radiation in the form of X-Rays. That seems to be supported by this Physics SE answer about detecting X-Rays from similar tritium keychains.
All of this leads to the question: how do the beta radiation and Bremsstrahlung radiation emitted by the tritium gas compare to other common sources of background radiation I receive? How do those levels compare to the standard safety guidelines for radiation doses?
Best Answer
The beta electrons have a maximum energy of 18.6 keV and all of them are absorbed by the glass or plastic. But there is some Bremsstrahlung x-ray intensity. I measured the spectrum in 2015 with an Amptek silicon energy-dispersive detector, see below. The intensity was low - it took several days to collect these data. The maximum of the continuum is consistent with the maximum beta energy. There are also characteristic peaks of zinc $K_\alpha$. I attribute those to x-ray fluorescence from a zinc-oxide phosphor.
The spectrum is similar in energy to what one would receive from old-fashioned cathode-ray tv-screens with a similar energy of the electron beam. But the visible light from these key chains is many orders of magnitude weaker than that of a CRT screen. The "current" of beta electrons is only $3.7\cdot10^5 \times 1.6 \cdot 10^{-19} = 0.06$ picoampere, which is much less than the typical electron beam current of a CRT display, about a milliampere. (But CRT screens often have heavy (lead etc) glass on the front.)