Beta and Gamma Decay Contents Beta What it
Beta and Gamma Decay Contents: Beta • What it is and the Neutrino Hypothesis • Reverse decay: electron capture • Enrico Fermi, Wolfgang Pauli, and the “little neutral one” Gamma • What it is • Being Discrete • Whiteboards
Beta Decay: 60 Co 27 60 Ni 28 13 N 7 13 C 6 + + - + e + + e Conservation of charge Beta minus - electron “As if” neutron -> proton + electron Beta plus - positron “As if” proton -> neutron + positron Particles are “of the nucleus” (not orbital) (electron capture) - Neutrino, (anti neutrino) – fudge (Conserve lepton number) Energy is continuous (i. e. neutrino gets random share)
Why the shape? Why - or +
Pauli, Fermi, and the little neutral one Wolfgang Pauli 1900 -1958 Enrico Fermi 1901 -1954 Beta decay products were missing energy Pauli proposes a particle is carrying away energy Fermi names it Neutrino - “Little neutral one” - It. Neutrinos confirmed in 1956, no surprise
e e
Gamma Decay: 239 Pu 94 239 94 Pu + Nucleus has energy levels Energy of transition emitted as a high energy photon ( ≈ 5 -. 05 nm) Usually after a beta or alpha decay Many energies possible Stopped by meters of lead Used for food irradiation
Example: Tl-208 emits a 0. 6210 Me. V gamma and the neutral (un -excited) atom has a mass of 207. 9820047 u. What was the mass before the gamma was emitted? Gamma ray energies associated with alpha and beta decays – so Alpha and Gamma energies are discrete. (Like spectral lines we saw)
Example: Tl-208 emits a 0. 6210 Me. V gamma and the neutral atom has a mass of 207. 9820047 u. What was the mass before the gamma was emitted? Well, 0. 6210 Me. V has a mass of (0. 6210 Me. V)/(931. 5 Me. V) = 0. 000666667 u So the parent is this much more massive: 207. 9820047 + 0. 000666667 = 207. 9826714 u
Whiteboards: Gamma Decay 1|2
239 Pu 94 --> 239 Pu 94 + 239. 052464 --> 239. 052157 What is the energy of the gamma emitted? Parent mass = 239. 052464 u Product mass = 239. 052157 u Mass defect = parent - products = 0. 000307 u Energy of radiation = (0. 000307 u)(931. 5 Me. V/u) = 0. 2860 Me. V
245 Cm 96 --> 245 Cm 96 + ? ? ? --> 245. 065486 What is the excited mass of the parent, if a 0. 2957 Me. V gamma photon is emitted? Mass of 0. 2957 Me. V = (0. 2957 Me. V)/(931. 5 Me. V/u) = 0. 000317445 u Excited parent is more massive than this by that amount Parent mass = 245. 065484 + 0. 000317445 u = 245. 0658034 u
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