On Fri, Jul 25, 2014 at 8:00 AM, Bob Higgins <rj.bob.higg...@gmail.com> wrote:
The strong force is like fly paper - it is so short range (fraction of a > nucleon diameter), you have to essentially "touch" before sticking. So you > end up with 3 possibilities of this close approach: ... > I used to think of scattering this way too -- sort of like billiard balls colliding. More recently my understanding of scattering has changed, although it may still be less adequate than the model you propose. When you have a particle such as a neutron incident upon a nucleus, there is a chance that tunneling will occur. The waveform of the neutron might squeeze through the potential barrier of the nucleus and tunnel inside it; in the case of a neutron, the potential barrier is very low. If the neutron tunnels through the potential barrier, you'll now have a new nucleus in an excited state, with an additional neutron. Although nucleons are often thought of as being rigid, a composite nucleus is more like a drop of water -- vibrating with all kinds of modes and splashing around. With the addition of the neutron, the nucleus wants desperately to shed energy and transition to a lower energy level. It is wobbling quite a bit and is unstable. If it is on the neutron drip line, a neutron waveform will "drip" back out of the potential barrier provided by the strong interaction, and it will be as though the neutron were never captured, except the nucleus will still be in an excited state. If the neutron stays, the excited nucleus will transition to one or more lower-energy states through other means, often through gamma emission or internal conversion. With two deuterons, there's a similar phenomenon going on. The deuterons tunnel and form a very unstable compound nucleus, like a blob of water in the space shuttle. Even though the lifetime of the unstable compound nucleus is very brief, my understanding is that the nucleons will move around the nucleus within their shells many, many, many times before the final fate of the compound nucleus is decided. I don't take this to mean that there isn't some kind of classical physics going on within the nucleus. But it suggests to me that once tunneling to the compound nucleus has occured, we're no longer talking about the neutron of one deuteron facing the proton of another, and by this means deciding the outcome of the transition. This is just an impression. Eric
