Why Don't all Neutrons Decay Into Protons?

If Neutrons decay into Protons and Protons do not decay then why is it that we still have Neutrons. Shouldn't they all have decayed to Protons by now?
- Melvin Weber (age 69)
Reserve, Louisiana USA

Hello Melvin,

That's a good question.  The neutrons that decay are floating around by themselves without any interactions.  Their average lifetime is a bit shy of 15 minutes.   The reaction is  neutron --> proton + electron + anti-neutrino of the electron type plus a tad of kinetic energy.   A free proton can't decay into a neutron + positron + neutron because of energy conservation.  

Now, inside a nucleus if you try to cram too many protons inside, the Coulomb energy starts growing.  Eventually it becomes energetically advantageous for the extra proton to get rid of the excess charge by turning into a neutron and ejecting the positron out of the nucleus.   You might want to check out this nice Wiki-article for more information: 

 

LeeH

 

(published on 12/18/2013)