This supports what Bob Cook says. http://www.wheldon.talktalk.net/kisomers/tutorial/tut4.html
quote: A "nuclear" isomer is defined as a long-lived excited nuclear state. There is no strict definition of long-lived, but the lower limit on the half-life is normally taken to be about 5 nanoseconds [ns] (10-9 seconds). Although this is a somewhat arbitrary limit, such a lifetime is much longer than a "typical" excited nuclear state which lives for a few picoseconds [ps] (10-12 seconds). In addition, a state living longer than a few nanoseconds can easily be separated experimentally from the "typical" prompt states by pulsing the beam and selecting only those event that occur away from the beam bursts. Harry On Mon, Jan 18, 2016 at 10:47 AM, Bob Cook <[email protected]> wrote: > Eric-- > > I did misunderstand what I thought you were saying. > > I do agree with you that most people consider nuclear isomers to be > excited energy states with a large differential energy above the ground > state. > > 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. As you point out normal NMR states are not at a large energy > differential, except in large magnetic fields. The larger the field, the > greater the excited energy is above the ground state. I think that the > rule is that the changes in spin angular momentum have to be prime number > multiples of the h/2-pie quantum of angular momentum. The energy of the > elevated state results from the change of the nuclear spin magnetic moment > in the ambient B magnetic field. > > Bob Cook > > > *From:* Eric Walker <[email protected]> > *Sent:* Sunday, January 17, 2016 10:20 AM > *To:* [email protected] > *Subject:* Re: [Vo]:Re: Nuclear Isomers (2005 article in Nature) > > Hi Bob, > > On Sun, Jan 17, 2016 at 7:15 AM, Bob Cook <[email protected]> wrote: > > I agree with your thought about the role of isomers in the natural >> abundance of elements. > > > I think you accidentally mistook the quote I was quoting from Harry's > article for something I myself said. I was asking for clarification of what > they were saying. > > Isomers are what makes nuclear magnetic resonance (NMR) a valuable tool. >> The idea is that a nucleus is excited to an elevated “isomeric” energy >> state by a RESONANT radio frequency input energy in a magnetic field and >> then decays back to its initial “ground state'’ or some other ground state >> not the same as the original state. > > > Forgive my ignorance -- when we talk about NMR, I think of polarization of > nuclei with nonzero spin in an external field using radiowaves or > microwaves. When I think of an isomer, I think of a nuclear isomer, in > which the nucleons in a nucleus are in a configuration that lies keV or MeV > above the ground state. I don't think radiowaves or microwaves can do > anything to populate or depopulate these states; or am I mistaken? > > A question I have about the nuclear isomerism referred to in the opinion > piece has to do with its potential utility. It seems like it would at best > be good as a battery, or, possibly, a bomb. > > Eric >
