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Nuclear Physics
PHY 361
2008-04-21
Outline
history
structure of the nucleus• nuclear binding force• liquid drop model• shell model – magic numbers
binding energy• chart of nuclides• line of stability, drip line, island of stability
radioactivity• ,, decay• fission, fusion
History
Becquerel – discovered radioactivity (1896)
Rutherford – nuclear model• classified ,, radiation, particle = 4He nucleus• used scattering to discover the nuclear model• postulated ‘neutrons’ A=Z+N (1920); bound p+ e- state?
Mosley – studied nucleus via X-ray spectra• correlated (Z = charge of nucleus) with periodic table• extra particles in nucleus: A = Z + ?
Chadwick – discovered neutron (1932)
Pauli – postulated neutral particle from -decay (1930)
Fermi – theory or weak decay (1933) ‘neutrino’
Fission – Hahn, Strassmann, (&Meitner!) (1938)• first reactor (chain reaction), Fermi (1942)
Bohr, Wheeler – liquid drop model
Mayer, Jensen – shell model (1949)
Hofstadter – electron scattering (1953-)• measured the charge density of various nuclei• discovered structure in the proton (not point-like particle)
Nuclear potential
strong force + Coulomb repulsion (p-p)
~ finite square potential
hard core – const. density
Hofstadter, electron scattering
Liquid drop model of the nucleus
constant density like a liquidR = R0 A1/3 where R0 ~ 1.2 fm = A / (4/3 R3) = 1014 g/cm3 !
finite square potential• p,n act as free particles inside of drop• states filled to Fermi energy
‘surface tension’ • normally prevents breakup• excitation can induce split into smaller
drops with lower overall energy
nucleus atom
Shell model of the nucleus
1949 – M. Mayer, J.H.D. Jensen
similar to atomic orbitals• quantized angular momentum• energy levels• multi-particle wave function
difference:• no ‘central’ potential (nucleus)• effective finite square potential• complicated nuclear force• strong dependence on spin• two particles: p, n• more types of decays
Chart of Nuclides – binding energy
AZXN
q ex. 1H, 2H, 3He, 4He
A = Z + N = # protons + # neutrons
B = Z MHc2 + N mnc2 - MAc2
nuclides – Z,N• isotope – constant Z (‘same place’)• isotone – constant N (isoto‘n’e)• isobar – constant A (‘same weight’)• isomer – excited state or nuclide
Chart of Nuclides – lifetime
http://www.nndc.bnl.gov/chart
magic numbers
Chart of Nuclides – decay mode
http://www.nndc.bnl.gov/chart
stable nuclide- decay, electron capturedecayp decayn decayspontaneous fission
magic numbers
Chart of Nuclides – island of stability
http://en.wikipedia.org/wiki/Island_of_stability
magic numbers
N
Z
Nuclear decay modes:
++ decay
- decay (isobar)
+ decay (isobar)
electron capture (isobar)
p decay (isotone)
n decay (isotope)
decay (isomers)
electron conversion (EC)
spontaneous fission (SF)
double beta decay (2)
neutrino-less double beta decay (0)
beta-delayed n,p, decay
ISOBARS
ISOTOPES
ISOT
ON
ES
ISOMERS
Alpha-decay
Beta-decay
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