Thursday, January 18, 2018
CHEM 418 Nuclear Chemistry, Winter 2018: Lecture 5 Beta Decay
Beta decay is presented in this lecture. The neutrino hypothesis and its relationship with beta decay is discussed. A review of Q value calculations for beta decay is provided. The importance of spin and parity, and how it can be used to assess beta decay, is discussed. Modeling beta decay through the weak force is provided. The impact of Coulomb interactions on positron and electron spectral shape is presented. The use of Kurie plots in understanding beta decay is introduced. Selection rules in beta decay and beta transitions are explained. Calculating logft and its relation to spin and parity are presented. Double beta decay is discussed. The lecture time is 48 minutes. The lecture is assigned on Thursday 18 January 2018 and due Tuesday 23 January 2018.
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Lecture 5 viewed and pdf quiz submitted via email. What I was wondering is if there is a reasonable cut off between Low A and High A when evaluating relative alignments of spins in beta decay.
ReplyDeletePure Fermi and pure Gamow-Teller transition examples can be found at just about all A. However there are some trends. When we learn about the shell model the cutoff points will become clearer. As A increases, the relative number of neutrons increase.
DeleteAs good example of the transition point around Z=40. Isotopes would have 50-60 neutrons in this region. The spin at Z of 32 to 40 is 5/2 and 1/2, while the spins for 50-60 neutrons would be g 9/2, g7/2, and d5/2. So an unpair nucleon transitioning between these state would likely have a spin of 1 for an allowed transition, which would be Gamow-Teller.
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ReplyDeleteI had a hard time understanding the |M|^2 term in the beta decay equation. Is that just an innate property that that describes the probability of the decay happening/ going from the initial to final state?
Yes, what you describe is correct. It is a transition probability from the initial to the final state. This is related to the decay constant and is a unique term for each decay.
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ReplyDeleteFor the last question, we are just suppose to add up the spins and see if it is 1/0, is that right?
Ryan Cheung
Look at the chart with the question. The spin changes with 2nd forbidden are different for Fermi or Gamow-Teller. If one reads starting on page 88 in Nuclear and Radiochemistry the discussion on mixtures of Fermi and Gamow-Teller are relevant. The beta decay section in Modern Nuclear Chemistry is also informative on this discussion. For this decay it is likely a mixture of states.
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