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Nuclear field theory (Bohr-Mottelson, II). Equivalent to RPA with dipole-dipole interaction. Shifts of the lines are smaller than the uncertainty of the 2 qp energies. M1?. E1. B(E1)[arb. units]. screening. enhancement. Transitional (X(5)). deformed. 88. 90. Two-neutron
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Nuclear field theory (Bohr-Mottelson, II) Equivalent to RPA with dipole-dipole interaction
Shifts of the lines are smaller than the uncertainty of the 2 qp energies.
M1? E1
B(E1)[arb. units] screening enhancement
Transitional (X(5)) deformed
88 90
Two-neutron transfer crossections
Shape coexistence analysis by Zielinska et al. Collective degrees of freedom by IBA Good fit to energies, reasonable fit to E2 matrixelements Strong mixing
2 shell correction, zero pairing 1 3 4
1 and 2 merge into a state with 56 neutrons protons 42
3,4 3 1 4
Two-state mixing Origin of mixing: pair scattering Size of the coupling: few 100 keV strong mixing E1 operator cannot move 2 particles
Two-level mixing model strong branching very different M very different mixing
i no mixing experiment 3:1 Zielinska et al 1.33:1
nb pb b nb Pair scattering blocked: b partially blocked: pb not blocked: nb
2qp octupole collective octupole Collective dipole Sensitive to deformation yes no yes no no Relation between the E1 matrix elements B(E1,low):B(E1,8 MeV) experiment: 1:10 2qp- calculations: <1:1000 Coupling to other degrees of freedom Soft octupole mode
Relation between M1 matrix elements M1 matrix elements are weakly deformation dependent
2 1 3 4
Conclusions Origin of low-lying dipole strength? M1 or E1 by coupling to octupole Dipole branch to second 0+ new evidence for shape coexistence Occurrence for only few states is a consequence of Pauli Principle. Information about the microstructure. Derivation of mixing amplitudes problematic