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  1. First identification of large electric monopole strength in well-deformed rare earth nuclei

    E-Print Network [OSTI]

    K. Wimmer; V. Bildstein; K. Eppinger; R. Gernhäuser; D. Habs; Ch. Hinke; Th. Kröll; R. Krücken; R. Lutter; H. -J. Maier; P. Maierbeck; Th. Morgan; O. Schaile; W. Schwerdtfeger; S. Schwertel; P. G. Thirolf


    Excited states in the well-deformed rare earth isotopes $^{154}$Sm and $^{166}$Er were populated via ``safe'' Coulomb excitation at the Munich MLL Tandem accelerator. Conversion electrons were registered in a cooled Si(Li) detector in conjunction with a magnetic transport and filter system, the Mini-Orange spectrometer. For the first excited $0^+$ state in $^{154}$Sm at 1099 keV a large value of the monopole strength for the transition to the ground state of $\\rho^2(\\text{E0}; 0^+_2 \\to 0^+_\\text{g}) = 96(42)\\cdot 10^{-3}$ could be extracted. This confirms the interpretation of the lowest excited $0^+$ state in $^{154}$Sm as the collective $\\beta$-vibrational excitation of the ground state. In $^{166}$Er the measured large electric monopole strength of $\\rho^2(\\text{E0}; 0^+_4 \\to 0^+_1) = 127(60)\\cdot 10^{-3}$ clearly identifies the $0_4^+$ state at 1934 keV to be the $\\beta$-vibrational excitation of the ground state.