High Spin Suppression of Decay
The most common mechanism for suppression of gamma decay of excited nuclei, and thus the existence of a metastable isomer for the nucleus, is lack of a decay route for the excited state that will change nuclear angular momentum (along any given direction) by the most common amount of 1 quantum unit of spin angular momentum. Such a change is necessary to emit a gamma photon, which has a spin of 1 unit in this system. Integral changes of 2,3,4, and more units in angular momentum are possible (the emitted photons carry off the additional angular momentum), but changes of more than 1 unit are inhibited by about 5 orders of magnitude in rate for every additional unit of spin change larger than 1, that the emitted gamma ray must carry. The highest known spin change of 8 units occurs in the decay of Ta-180m, which suppresses its decay by a factor of 1035 from that associated with 1 unit, so that instead of a natural gamma decay half life of 10−12 seconds, it has a half life of more than 1023 seconds, or at least 3 x 1015 years, and thus has yet to be observed to decay.
Read more about this topic: Nuclear Isomer
Famous quotes containing the words high, spin, suppression and/or decay:
“The high plains, the beginning of the desert West, often act as a crucible for those who inhabit them. Like Jacob’s angel, the region requires that you wrestle with it before it bestows a blessing.”
—Kathleen Norris (b. 1947)
“Words can have no single fixed meaning. Like wayward electrons, they can spin away from their initial orbit and enter a wider magnetic field. No one owns them or has a proprietary right to dictate how they will be used.”
—David Lehman (b. 1948)
“Rationalists are admirable beings, rationalism is a hideous monster when it claims for itself omnipotence. Attribution of omnipotence to reason is as bad a piece of idolatry as is worship of stock and stone believing it to be God. I plead not for the suppression of reason, but for a due recognition of that in us which sanctifies reason.”
—Mohandas K. Gandhi (1869–1948)
“It has taken me nearly twenty years of studied self-restraint, aided by the natural decay of my faculties, to make myself dull enough to be accepted as a serious person by the British public; and I am not sure that I am not still regarded as a suspicious character in some quarters.”
—George Bernard Shaw (1856–1950)