Meseaworthy

Radioactive decay article question

I noticed that you have done a great number of contributions on this article.

However, I am not particularly confident that this line is true.

"In an example of this, a carbon-14 atom (the "parent") emits radiation (a beta particle, antineutrino, and a gamma ray) and transforms to a nitrogen-14 atom (the "daughter"). "

Carbon has a lower atomic mass than nitrogen. How is it possible that after the radioactive decay nitrogen is resultant from an element which is lower on the periodic table? — Preceding unsigned comment added by Meseaworthy (talk • contribs) 17:47, 13 December 2010 (UTC)

Atomic masses are averages. The atomic mass for "carbon" reflects mostly carbon-12, since only 1% is C-13, and not enough C-14 exists to affect the mass at all. If you look at just the mass for the nuclides we're talking about, C-14 and N-14, you'll find that C-14 DOES have a larger mass. The C-14 isotope mass is 14.003241989 u (see the isotopes of carbon article). That's not larger than than the nitrogen average weight 14.0067 u but it IS larger than the N-14 isotope weight, which is 14.0030740048 (see isotopes of nitrogen). If you subtract 14.0030740048 (N-14) from 14.003241989 (C-14) you get a mass difference of + 0.000168 u. Multiply that by the conversion factor of 931.494 MeV/u and get the decay energy of C-14, which is 0.1564 Mev, or 156.49 KeV. If you look at the carbon-14 page you see it's 156.476 KeV. If I'd been more careful with my significant digits, I've had hit it exactly. SBHarris 20:08, 13 December 2010 (UTC)