*"If there were no energy penalty to protons (or neutrons) leaving the nucleus, then the nucleus would fall apart. This doesn't happen."*
The nuclear force (or nucleon-nucleon interaction or residual strong force) is the force between two or more nucleons. It is responsible for binding of protons and neutrons into atomic nuclei. The energy released causes the masses of nuclei to be less than the total mass of the protons and neutrons which form them; this is the energy used in nuclear power and nuclear weapons. The force is powerfully attractive between nucleons at distances of about 1 femtometer (fm) between their centers, but rapidly decreases to insignificance at distances beyond about 2.5 fm. At very short distances less than 0.7 fm, it becomes repulsive, and is responsible for the physical size of nuclei, since the nucleons can come no closer than the force allows. The nucleus is held together by gluons that act in the form of virtual pions. The strong force counteracts the repulsive force between the protons in the nucleus. The binding energy exerted by the strong force contained inside the nucleus is an uncertain thing; it goes up and down at the whim of quantum mechanics; it varies with the uncertainty principle. This energy is comprised of two parts: a real energy and a virtual energy. It is this virtual energy that can vary widely and is not constrained by the laws of energy and momentum. When constrained inside the nucleus and when this nuclear energy is composed of these two parts get strong enough, it spills over the top of the coulomb barrier and forms a real particle outside the nucleus. This is quantum mechanical tunneling. The virtual part of this spillover energy only lasts for the briefest of instants and immediately goes away and only the real part remains to congeal into the newly radiated particle that has tunneled through the barrier. This process is called radioactive decay (AKA tunneling through the coulomb barrier). After this nuclear relaxation process, if the energy level inside the nucleus has been lowered enough so that it can never again surmount the coulomb barrier no matter how much virtual energy may appear, the element is said to be stable. Normally, If the proton appears a few femtometer beyond the nucleus, it is beyond the reach of the strong force. It is propelled away from the nucleus by the repulsive force of the other protons. When this repulsive force is neutralized by electron screening, the proton just drifts away at low energy until the electron screening is removed. At that time the proton is repelled from the nucleus. When there is no screening it takes a great deal of excitation energy to get through the coulomb barrier. The coulomb barrier is symmetric. It take as much energy to leave a nucleus as it take to get in. No the coulomb barrier means little amounts of energy is needed to leave the nucleus only if the proton is beyond the reach of the strong force. However, if the coulomb barrier is at full force and the nucleus is excited (aka unstable), that is, the nucleus just does not fit together in the right way, the proton will rattle around inside the nucleus until there is enough virtual energy to push it over through coulomb barrier. That is, the proton can only get over the coulomb barrier if by chance; the virtual energy gets strong enough to push the proton out of the nucleus. Cheers: Axil On Sat, Aug 11, 2012 at 8:37 PM, <[email protected]> wrote: > In reply to Axil Axil's message of Fri, 10 Aug 2012 20:34:44 -0400: > Hi, > [snip] > >(*C12* is C12 in an excited state - it has an additional 15.96 MeV that > it* > >* * > > > >*desperately wants to get rid of)* > > > >This is only true when the coulomb barrier is up at full strength. But > when > >the coulomb barrier is completely down, protons behave like neutrons. They > >can exit the nucleus with no energy penalty. > > > >I explain this in the thread “the bumpy road.” > > If there were no energy penalty to protons (or neutrons) leaving the > nucleus, > then the nucleus would fall apart. This doesn't happen. > > BTW the Coulomb barrier is partially a misnomer. It's a Coulomb barrier for > positively charged particles trying to enter the nucleus, but actually a > nuclear > binding force barrier for particles trying to leave the nucleus. > > Regards, > > Robin van Spaandonk > > http://rvanspaa.freehostia.com/project.html > >
