Ultrahigh resolution study of collective modes in 158Gd

Ultraprecise energies and absolute B(E2) values associated with K=0(+) excitations in Gd-158, measured with the GRID technique, reveal significant information relating to the possible existence or absence of two-phonon vibrational excitations in deformed nuclei. A strong B(E2:K=0(2)(+)-->gamma) is observed but reflects band mixing rather than a gamma gamma mode. For the K=0(3)(+) band, measurement of precise gamma transition energies shows that suggested existing placements of strong deexcitation transitions are incorrect and that there is, again, no evidence for gamma gamma-phonon character in this band either. A weak B(E1:K=1(-) -->K=0(1)(+)) value is interpreted in terms of the microscopic structure of K=0(-) and K=1(-) excitations. [S0556-2813(99)06705-9].