1. Oct 8, 2008

### Bixby

If a rate meter backs into a number of 2 million disintegrations per minute, is this a lot of a little?

I am curious about a comparison - like it is the same amount of radiation coming from a smoke detector. Or - run for your life, that is pure plutonium you are dealing with. :)

Thanks.

2. Oct 10, 2008

### Minte

When determining what is a lot, think, "what does the meter go up to?" Think about the scale of it.

(One Becquerel (Bq) is 60 DPM, by the way.)

Really, it matters how big the sample is. If you've got a massive DPM count, then either the sample is huge or you're dealing with an unstable isotope with a short half-life.

One mole of a substance is 6.022*10^23 atoms, and its mass is its atomic weight in grams. A mol of Radon-222 would weigh 222g, and has a half-life of 3.82 days. You can do the conversions and calculations if you want, but that's not a terribly high DPM count. Radon-222 has an -activity- of 154,000 Curie/g, however, and that's a good amount for the DPM.

What really matters for deadliness is what -type- of emission it is (and the activity). If the DPM is a gazillion, but it's only emitting low-energy alpha particles, hide behind a piece of glass or something and you'll be fine. However, if you've got beta or gamma (or any other kind of emission, generally), it'll take some lead to block it. Get a count in Rads, Rems, Sieverts, Curies, Grays, or some other unit like that. :)

(I took so long composing this post that I'm sure I made a mistake somewhere. Spot it and win a prize. ^^" )