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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Multipolarity of gamma radiation ： ウィキペディア英語版 Multipolarity of gamma radiation Transitions between excited states (or excited states and the ground state) of a nuclide lead to the emission of gamma quanta. These can be classified by their multipolarity.〔J.M.Blatt and V.F. Weisskopf: ''Theoretical Nuclear Physics'', Springer, New York (1979)〕 There are two kinds: ''electric'' and ''magnetic'' multipole radiation. (Each of these, being electromagnetic radiation, consists of an electric and a magnetic field, of course). Electric dipole, quadrupole, octupole… radiation (generally: 2$l$pole radiation) is also designated as E1, E2, E3,… radiation (generally: E$l$ radiation.〔Note: the symbol $l$ is used here to distinguish the letter "el" clearly from the numeral "one". Unfortunately, $l$ sits slightly below the main line of typing.〕 Similarly, magnetic dipole, quadrupole, octupole… radiation (generally: 2$l$pole radiation) is designated as M1, M2, M3,… radiation (generally: M$l$ radiation. For a more general theoretical description, see Multipole radiation. There is no monopole radiation ($l\; =\; 0$).〔 In quantum mechanics, angular momentum is quantized. The various multipole fields have particular values of angular momentum: E$l$ radiation carries an angular momentum $l$ in units of $\backslash hbar$; likewise, M$l$ radiation carries an angular momentum $l$ in units of $\backslash hbar$. The conservation of angular momentum leads to selection rules, i.e., rules defining which multipoles may or may not be emitted in particular transitions. To make a simple classical comparison, consider the figure of the oscillating dipole. It produces electric field lines travelling outwards, intertwined with magnetic field lines, according to Maxwell's equation. This system of field lines then corresponds to that of E1 radiation. Similar considerations hold for oscillating electric or magnetic multipoles of higher order. Conversely, it is plausible that the multipolarity of radiation can be determined from the angular distribution of the emitted radiation. == Quantum numbers and selection rules for Multipole Radiation== A state of a nuclide is described by its energy above the ground state, by its angular momentum ''J'' (in units of $\backslash hbar$), and by its parity, i.e., its behaviour under reflection (''positive'' + or ''negative'' -). Since the spin of nucleons is 1/2 (in units of $\backslash hbar$), and since orbital angular momentum has integral values, ''J'' may be an integral or half integral number. Electric and magnetic multipole radiations of the same order $l$ (i.e., dipole, or quadrupole...) carry the same angular momentum $l$ (in units of $\backslash hbar$), but differ in parity. The following relations hold for $l\; >\; 0$:〔 :::Electric multipole radiation: Parity = (-1)$l$ ::::Here, the electric field has parity -(-1)$l$, and the magnetic field (-1)$l$ ::: Magnetic multipole radiation: Parity = -(-1)$l$ ::::Here, the electric field has parity(-1)$l$, and the magnetic field -(-1)$l$ The designation "''Electric'' multipole Radiation" seems appropriate since the major part of that radiation is produced by the charge density in the source;〔 conversely, the "''Magnetic'' multipole radiation" is mainly due to the current density of the source.〔 In electric multipole radiation, the electric field has a radial component; in magnetic multipole radiation, the magnetic field has a radial component.〔 An example: in the simplified decay scheme of 60Co above, the angular momenta and the parities of the various states are shown (A plus sign means even parity, a minus sign means odd parity). Consider the 1.33 MeV transition to the ground state. Clearly, this must carry away an angular momentum of 2, without change of parity. It is therefore an E2 transition. The case of the 1.17 MeV transition is a bit more complex: going from ''J'' = 4 to ''J'' = 2, all values of angular momentum from 2 to 6 could be emitted. But in practice, the smallest values are most likely, so it is also a quadrupole transition, and it is E2 since there is no parity change. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Multipolarity of gamma radiation」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.