larry@kitty.UUCP (Larry Lippman) (10/25/86)
In article <1724@iuvax.UUCP>, reid@gold.bacs.indiana.edu writes: > I bought a British-made "Betalight Torch" tritium lamp at a hamfest. > ... > It has a 22-mm-diameter light-emitting area. The light intensity > is roughly equivalent to that of the lightbulb inside an elec- > tronic wristwatch. > > It's a neat gadget but how dangerous is it? The low-energy (18.6 > KeV) beta particles cannot penetrate the glass tube, however, > soft X-rays are emitted as they are absorbed. A physicist friend > measured 40 counts per second of 12-KeV X-rays coming from the > device, using a detector which completely enveloped it. While I don't work with radiation measurement on a regular basis, I'll take a stab at giving you an answer. Tritium, being a radioactive isotope of hydrogen, is a beta emitter. The inherent beta energy of tritium (0.0186 MeV, as you pointed out) is quite small. It takes at least 0.070 MeV of beta energy to penetrate the skin. X-rays are produced by an effect called "bremsstrahlung" (don't ask; it's a German word, but that's the proper term), which occurs when a high velocity charged particle (usually electron, but also beta particle) strikes a target and is slowed down. In this case, the target is the glass tube. Since I don't know the thickness and total surface area of the glass tube, I can't accurately calculate the activity and quantity of tritium contained therein. However, I can make a few assumptions: 1. In general, less than 1% of all beta radiation is converted to x-rays by means of bremsstrahlung. I will assume that the glass is not THAT thick so that all x-rays emitted will pass through and be measured by your physicist friend's detector. 2. I will assume the tritium source is emanating (40)(100)= 4,000 cps of beta radiation. Activity is measured in Curies (Becquerels, for you SI fans). (4,000)/(3.7*10**10)= 0.11 uCi. That ain't much. Say, even 10 times that figure (I doubt it's more than that) - or about 1.1 uCi. That still ain't much, and is less radioactivity than the americium in a home smoke detector. 3. Assuming, worst case, that you have 1.1 uCi of tritium, and you were somehow able to ingest it all (you can't get any worse than this!), the "CRC Handbook of Radioactive Nuclides" says that you will receive a total body dose of (1.1)(0.00013)= 0.00014 rems. The NRC says that the natural background radiation dose for the U.S. is something like 0.1 rem/year. So, in comparison, your tritium lamp shouldn't pose much hazard - even if I were incorrect by two orders of magnitude! Tritium has a half-life of about 12.6 years, and I would guess that for this lamp to be sold as "surplus", its age is probably approaching that half-life period. I have two points of caution: (1) Just because it appears that the quantity of tritium contained in the lamp is miniscule, doesn't mean you should do something DUMB with it - like break open the tube, allow children to play with it, or keep it in your pants pocket :-); and (2) my calculations are all based upon the disintegration rate which your physicist friend claims to have measured, so if his measurement is wrong, then so are my calculations! ==> Larry Lippman @ Recognition Research Corp., Clarence, New York ==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo|utzoo}!/ ==> FAX: 716/741-9635 {G1,G2,G3} "Have you hugged your cat today?"