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NUCLEAR STRUCTURE PHENOMENOLOGICAL MODELS
From molecules to atomic nuclei. Standard model Basic concepts of nuclear physics. Units Properties of nucleons Liquid drop model Surface vibration and rotation MICROSCOPIC MODELS Nuclear force Nuclear mean field Shell model Second quantisation in the mean field Residual interaction. Collective excitations Collective model. Nilsson model
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From molecules to atomic nuclei
10-15m=1fm
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Standard model
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Basic concepts of nuclear physics
nucleon: proton or neutron nuclide: nucleus uniquely specified by number of protons (Z) and neutrons (N) mass number: A=Z+N isotopes: nuclides with the same Z ex: 235U and 238U isotones: nuclides with the same N ex: 2H, 3He isobars: nuclides with the same A atomic mass unit: 1u=1/12 m(12C) = kg=931.5 MeV/c2
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Basic physical observables in nuclei
Electric quadrupole momentum Angular momentum Magnetic dipole momentum Parity Energy levels Decay rates
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Electric quadrupole moment
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Magnetic dipole moment
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Units used in nuclear physics
Length 1 fm =10-15 m Energy 1 MeV = 106 eV 1 eV = 1, J Basic constants MN=938,90 MeV/c2 ħc=197,33 MeV fm e2=ħc/137=1,44 MeV fm
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Properties of nucleons
proton neutron mass = MeV/c2 = MeV/c2 charge +1 spin 1/2 magnetic moment μN μN parity
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Nuclear chart stability of nuclei
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Limits of stable nuclei exotic nuclei
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Nuclear size from electron scattering experiments
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Binding energy Mass defect
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Example
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Binding energy/nucleon: B/A
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Liquid drop model Weizsäcker semiempirical formula (1935)
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Symmetry energy
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Liquid drop energy versus (Z,N)
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Surface vibration and rotation Deformation parameters of the nuclear surface
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Vibrational states
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Rotational states
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Total spin I and its projections to laboratory (M) and intrinsic (K) systems
Ω
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Parameters in the intrinsic system
Ω is the rotation angle
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β & γ vibrations of a deformed shape
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Rotational-vibrational model Rotational bands
built on top of the vibrational band head
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Sakai-Sheline rule vibrational states → rotational bands
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Nuclear force
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Deuteron: the simplest nuclear system
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Deuteron spin & magnetic moment
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Electromagnetic versus strong field
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Yukawa potential
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Shell model
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Nuclear mean field: the selfconsistent single particle potential created by all nucleons
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Mean field potential for protons and neutrons
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Spin-orbit interaction
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Example
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Shell model magic numbers appear due to the spin-orbit interaction
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Spherical shell model scheme
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The last nucleon of an odd-even (even-odd) nucleus determines the nuclear properties (spin, quadrupole and magnetic moments)
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Schmidt limits for magnetic moments
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Schmidt limits for quadupole moments
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creation/annihilation
Second quantisation in the mean field Each spherical level is filled by 2j+1 nucleons with different projections creation/annihilation operators for nucleons (fermions) Fermi level Ground state is a Slater determinant obeying the Pauli exclusion principle
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Particle (croses) and hole (open circles) states
p-h excitation:
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(p,2p) reaction in the shell model
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Residual interaction among nucleons in the mean field
Multipole expansion l=0 : pairing l=2 : quadrupole-quadrupole
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Quasiparticle Hamiltonian approximation Ground state =BCS vacuum
Particle-particle (p-p) short-range interaction describes pairing correlations Quasiparticle approximation Hamiltonian Ground state =BCS vacuum
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Occupation probabilities Gap parameter
Normal system Superfluid system Fermi level
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Proton gap versus Z
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Particle-hole (p-h) long-range interaction describes collective excitations: 1) low-lying surface vibrations 2) giant resonance of protons against neutrons Hamiltonian p-h excitation p h
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Distribution of collective excitations for various multipolarities versus energy
Giant resonance Low-lying vibrational state
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Collective model
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Nilsson model of single particle states in the deformed intrinsic system
Single particle energy versus deformation Deformed Hamiltonian
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DECAY PROCESSES Alpha decay, cluster emission Beta decay Gamma decay
Fission and fusion
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Nuclear decay modes
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Decay law Decay width Γ=ħλ
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Narrow decaying resonance (Γ is small) is a quasi-stationary process
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Decay rate (activity)
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Alpha decay
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The first probabilistic interpretation
G. Gamow "Zur Quantentheorie des Atomkernes" (On the quantum theory of the atomic nucleus), Zeitschrift für Physik, vol. 51, (1928). The first probabilistic interpretation of the wave function Rext ↓ Internal region External region
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Quantum penetration explains Geiger-Nuttall law for α and cluster decays (C, O, Ne, Mg, Si)
Coulomb parameter
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Beta decay
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Fermi & Gamow-Teller transitions
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Gamma decay
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Parity rules for gamma transitions
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Decay operators in second quantisation: gamma transitions beta transitions
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Fission & fusion
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Fission - liquid drop model
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Energy release for various processes
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Strutinsky shell-model correction The double humped barrier determines the occurrence of superhevy nuclei Density of levels liquid drop shell model
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Superheavy nuclei are formed by fusion and detected by alpha decay chains
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Fusion energy
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The Sun
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