From key@physics.utoronto.ca Wed Mar 12 18:53:53 2008 Date: Wed, 12 Mar 2008 18:53:47 -0400 From: Tony Key To: huong le , key@physics.utoronto.ca Subject: Re: question about beta decay! Great question, Huong.  Indeed a free proton cannot spontaneously decay into the neutron since, as you point out, there is not enough energy - the decay products, neutron, positron, neutrino, have more mass than the proton.  However, inside a nucleus, the extra energy can be provided from the binding energy of the nucleus.  This won't happen unless it is energetically favourable.  I did mention this in class - explaining that if the "free" proton did decay, all Hydrogen nuclei would not exist, but it was a throwaway line.  You are thinking about things in the right way. TonyK huong le wrote: Hello, Prof! I have a problem understanding beta decay. As far as I know, beta decays happen only when nuclear mass of the parent is greater than nuclear mass of the daugter plus the beta particle. However, in the process of beta plus decay, a proton is converted into a neutron and a positron (right???),if so, i have a conflict here because the mass of neutron is bigger than the mass of proton; consequently the mass of the daugter is bigger than the mass of the parent(???). I am confused. Please help. Looking forward to your reply! Have a good day. Huong Le ____________________________________________________________________________ Ask a question on any topic and get answers from real people. Go to Yahoo! Answers.