# Radiation emitted from K-40?

1. Jun 4, 2010

### ampzor

How would I be able to calculate the amount of microcuries of radiation emitted from 3 grams of K-40? I think I have a way of figuring it out but it is pretty lengthy and I am sure that I am over thinking this a bit too much.

2. Jun 4, 2010

### Bob S

The half life of K-40 is 1.277 x 109 years = 4.03 x 1016 seconds. The half life is Ln(2) = 0.693 x the 1/e lifetime. So the 1/e lifetime is about 5.81 x 1016 seconds.

3 grams of K-40 contains (3/40) x 6.02 x 1023 = 4.51 x 1022 atoms.

There are about 4.51 x 1022/5.81 x 1016 = 7.76 x 105 dps (decays per second) in 3 grams of K-40..

1 Curie = 3.7 x 1010 dps.

Bob S

3. Jun 5, 2010

### minerva

The specific radioactivity per unit mass for a particular radionuclide, measured in Ci/g or Bq/g for example, is more commonly known as the "specific activity". Whilst you can calculate it from first principles if you know the half-life, as elucidated above, usually you just look up the specific activity of whatever radionuclide you're working with in literature tables.

4. Jun 6, 2010

### ampzor

Thank you Bob S.

5. Jun 11, 2010

### techocharles

does any one know if the http://iphonecarmount.org" [Broken] gives out radiation?

Last edited by a moderator: May 4, 2017
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