In reply to Harry Veeder's message of Mon, 18 Mar 2013 21:40:15 -0400: Hi, [snip] >On Mon, Mar 18, 2013 at 5:10 PM, <[email protected]> wrote: >> In reply to Eric Walker's message of Sun, 17 Mar 2013 22:56:07 -0700: >> Hi, >> [snip] >>>On Sun, Mar 17, 2013 at 2:50 PM, <[email protected]> wrote: >>> >>> >>>> BTW there is no potential barrier here. The proton and the electron carry >>>> opposite charges, so they are attracted to one another, rather than >>>> repelled. >>>> >>> >>>I take it that when physicists refer to a "potential barrier," they mean >>>specifically an electrostatic potential barrier, and not simply an energy >>>threshold that must be overcome? >>> >>>Eric >> >> A barrier usually implies an impediment that gets in the way of a reaction >> that >> would otherwise release energy. However the formation of a neutron from a >> proton >> and an electron does not release energy, it consumes it. >> >> Regards, >> >> Robin van Spaandonk >> >> http://rvanspaa.freehostia.com/project.html >> > >Some sort of "barrier" is necessary to stymie the mutual attraction of >electrons and protons otherwise matter would quickly consist of >nothing but neutrons. Isn't this barrier supplied by the weak force?
The weak force doesn't actually present a barrier. It presents a chance that something will occur. Electrons and protons don't normally combine into neutrons because their combined mass is inadequate. It's 782 keV short of the mass of a free neutron. However, they could combine to form a reduced mass neutron as part of the nucleus of a heavier atom. This does in fact happen with some isotopes. It's called "electron capture" (EC). In this case, even though the mass of the proton is also reduced, the net result (an isotope of the previous element in the periodic table), is sufficiently more stable than the initial isotope to more than make up for the difference. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
