On Mon, Jan 18, 2016 at 9:47 AM, Bob Cook <[email protected]> wrote:
I have always considered any excited nuclear state to be a nuclear isomer. > I do not know what the elevated energy nuclear state which is due to spin > energy as established during an NMR energy addition would be called. I > think it fits the general definition of an excited state with a lifetime > less than 10-9 sec., and, thus, it is not metastable from that standpoint. > In the case of a nuclear isomer, the potential energy is held within the nucleus itself, as a local minimum in energy that is above the global minimum (along the lines of Bob Higgins's description). The system boundary can be drawn around the nucleus. I think of nuclei as clumps of spherical, frictionless neodymium magnets that arrange in various ways, perhaps with segments rotating in relation to one another. In the case of an isomer, you have an arrangement that might eventually shift to a more stable one later on. With NMR, you have the perturbation of the alignment of a nucleus with a magnetic moment in an external magnetic field by an electromagnetic pulse. In this second case, unlike in the case of the nuclear isomer, the system boundary can no longer be drawn solely around the nucleus but instead must include the external fields. I don't think you'd say that the nucleus in this second case is an "isomer," or that in general it is in an excited state. Eric
