On the role of hexadecapole forces in describing γ-band states in the rare-earth region

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Abstract
Calculations are made for the isoscalar transition rates B(IS2, GS to 2+2 gamma ) and B(IS4, GS to 4+2 gamma ) in the RPA with a common system of equations for lambda mu =22 and 42 and for the inelastic form factors in the folding model. The analysing powers and cross sections in the (p,p') reaction with Ep=65 MeV for the levels 2+2 gamma and 4+2 gamma in 168Er are calculated within the coupled-channels method by using the microscopic form factors. It is shown that extremely large values of B(IS4, GS to 4+2 gamma )exp obtained in the (p,p') and ( alpha , alpha ') reactions are mostly due to the contribution of indirect excitation channels but not to a strong hexadecapole interaction lambda mu =42. A moderate value of the hexadecapole interaction constant kappa 0(42)=0.012 fm2 MeV-1 provides a satisfactory description of the available experimental data.