lecture_19_07b

lecture_19_07b - Nuclear decays : (Z,A) (Z-2,A-4)+24He...

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05/12/09 Physics 13 - Fall 07 - G.R. Goldstein 1 Nuclear decays 2200 α : (Z,A) (Z-2,A-4)+ 2 4 He Strong or nuclear glue and quantum tunneling 2200 β : (Z,A) (Z+1,A)+ e - also have (Z-1,A)+ e + Weak and based on n p+e - + ν (anti-neutrino) 2200 γ : (Z,A)* (Z,A)+ γ EM quantum transition Each with characteristic decay time and energy release (Q value)
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05/12/09 Physics 13 - Fall 07 - G.R. Goldstein 2 Radioactivity All decays occur randomly - probability distribution characteristic of nuclide and decay products Activity=rate of decrease in time=-dN/dt= A (t) A in units of Curies=3.7 × 10 10 disintegrations/sec or Becquerels (Bq) SI units A N(t) (each decay is independent of others) with A = λ N(t) λ =decay constant How does N change in time?
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05/12/09 Physics 13 - Fall 07 - G.R. Goldstein 3 Exponential decay A ( t ) = - dN dt = l N ( t ) So dN N = - l dt and dN N N 0 N ( t ) = - l dt 0 t or ln( N ( t )) - ln( N 0 ) = - l t or N ( t ) = N 0 e - l t and A ( t ) = A 0 e - l t Hence 1 l = t mean lifetime Note also that A ( t ) will be 1 2 A 0 for e - l t = 1 2 or t 1/ 2 = ln2 l t 1/2 is the half-life. Exponential decay law for many phenomena, especially QM decays and heat transfer.
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lecture_19_07b - Nuclear decays : (Z,A) (Z-2,A-4)+24He...

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