On Tue, Oct 1, 2013 at 10:36 AM, David Roberson <[email protected]> wrote:
Eventually the energy would become heat which I assume appears like > incoherent phonons, but initially it would be generated as waves > propagating outwards from the point at which it is thermalized. Here > outwards should be interpreted as more like a circular wave front emitted > from that point in space due to the conservation of momentum. Any motion > of atoms as a whole in one direction must have a balancing set traveling at > 180 degrees. > The idea of a wavefront is an interesting one. I seems likely that there would be one initially. One question I have is how far it would travel as a clearly-identifiable wavefront. Imagine having 5.5 MeV of mass energy to get rid of as quick as you can. If I were the one with the money, I would try spend it on as many electrons in the immediate vicinity as I could. It would not matter to me if they were cheap ones (outer shell electrons) or expensive ones (inner shell electrons). With 5.5 MeV, you can buy whatever electrons you want, and as many of them as you want, since you're a millionaire, and electrons generally cost less than 30 keV to excite. Perhaps there would be a diminishing payout a function of the radius from wherever you were. So the closer the electrons were, the more likely they would get some mass energy, and the further out, the less likely. In this thought experiment, then, there's an initial impulse of an incredible amount of energy that is delivered pretty much indiscriminately to the electrons in the immediate area. They would all presumably travel outwards, forming the initial shock front. Some energy might also go to the metal ion cores of the lattice sites. All of the electrons that were not somehow delivered from the metal would eventually return to fill some vacancy that was created, emitting a photon in the process. Photons emitted by outer shell and sea electrons would be of longer wavelength, for which the material would be opaque, and they would be reabsorbed. Photons emitted by the inner shell electrons would result in x-rays, and presumably a fraction of them would escape a nickel substrate, assuming we're not too far into the bulk, although I am not sure what fraction be stopped as well -- perhaps nearly all of them. While the electrons that were part of the initial wavefront will have been moving outwards from the initial event, as a result of conservation of momentum, I believe the photons will have been emitted in random directions. They will go on to excite electrons along their path of travel, and these in turn will fall back to ground state and emit photons in random directions. So I wonder how far the shock wave would travel. Eric
