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