Quote:
Originally Posted by dleviwing  I think isomers are a better analogy here.
Some units of matter have surfaces but are more analogous to soap bubbles that to particles; even these are considered particles by the particle physicists regardless of their short lifespan. |
Particle physicists 'consider' a lot of the entities they work with to be 'particles'. When they find an entity that has field and wave characteristics, the vocabulary of particle remains. 'Soap bubbles' only appear to have surfaces. When an entity appears and disappears - with a half life of fractions of nano, micro and picoseconds - it is called a particle - the proprietary word of particle physicists. Shop talk. While the question remains: What units of matter have 'surfaces' in accordance with the definition of - in absentia wave and/or field - discontinuity from surrounding space? From Wikipedia, the free encyclopedia
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A
nuclear isomer is a
metastable state of an
atomic nucleus caused by the
excitation of one or more of its
nucleons. A nuclear isomer occupies a higher energy state than the corresponding non-excited nucleus, called the
ground state. The nuclear isomer will sooner or later release the extra energy and decay into the ground state.
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[edit] Metastable isomers Metastable isomers can be produced through
nuclear fusion or other
nuclear reactions. A nucleus thus produced generally starts its existence in an
excited state that de-excites through the emission of one or more
gamma rays (or, equivalently,
conversion electrons), usually in a time far shorter than a
picosecond. However, sometimes it happens that the de-excitation does not proceed rapidly all the way to the nuclear
ground state. This usually occurs because of the formation of an intermediate excited state with a
spin far different from that of the ground state. Gamma-ray emission is far slower (is "hindered") if the spin of the post-emission state is very different from that of the emitting state, particularly if the excitation energy is low, than if the two states are of similar spin. The excited state in this situation is therefore a good candidate to be metastable, if there are no other states of intermediate spin with excitation energies less than that of the metastable state.
Metastable isomers of a particular
isotope are usually designated with an "m" (or, in the case of isotopes with more than one isomer, m2, m3, and so on). This designation is usually placed after the atomic symbol and number of the atom (e.g., Co-58m), but is sometimes placed as a superscript before (e.g., 58mCo). Increasing indices, m, m2, etc. correlate with increasing levels of excitation energy stored in each of the isomeric states (e.g., Hf-177m2 or 177m2Hf).
A different kind of metastable nuclear state (isomer) is the
fission isomer or
shape isomer. Most
actinide nuclei, in their ground states, are not spherical, but rather
spheroidal -- specifically, prolate, with an
axis of symmetry longer than the other axes (similar to an
American football or
rugby ball, although with a less pronounced departure from
spherical symmetry). In some of these, quantum-mechanical states can exist in which the distribution of
protons and
neutrons is farther yet from spherical (in fact, about as non-spherical as a American football), so much so that de-excitation to the nuclear ground state is strongly hindered. In general these states either de-excite to the ground state (albeit far more slowly than a "usual" excited state) or undergo
spontaneous fission with
half lives of the order of
nanoseconds or
microseconds -- a very short time, but many orders of magnitude longer than the half life of a more usual nuclear excited state. Fission isomers are usually denoted with a postscript or superscript "f" rather than "m," so that a fission isomer in e.g.
plutonium 240 is denoted Pu-240f or 240fPu.
________________________
An acquaintance recently and flippantly dubbed the issued 'particle', as 'Elvis', commenting on how he's frequently observed at various locations (pumping gas in a Nevada filling station?)... Adding that in this case, when he appears for an autograph or signature session, he abruptly leaves the building. "All things originate in waves and fields, and waves and fields come out of all things?" - Paraphrased
Best regards,
- RP
Linear Mode
