Beta +/electron-capture decay of 192,194,196,198,200Bi: Experimental evidence for low lying 0+ states.

Abstract

Levels in the $^{192}$,194,196,198,200Pb isotopes were studied via the ${\ensuremath{\beta}}^{+}$/electron-capture decay of mass separated Bi isotopes. Multiscaled spectra of \ensuremath{\gamma} rays, x rays, and conversion electrons, and \ensuremath{\gamma}-\ensuremath{\gamma} and \ensuremath{\gamma}-${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ coincidences were measured. The existence of ${0}^{+}$ states in the $^{192\mathrm{\ensuremath{-}}200}\mathrm{Pb}$ nuclei is shown and evidence for the beginning of a collective band built on top of the ${0}_{2}^{+}$ states is seen in $^{192}$,194,196Pb. A discussion in terms of characteristic properties of intruder states in the even-even nuclei and in terms of a one-broken-neutron-pair formalism is given. This shows clearly the presence of both neutron and proton [\ensuremath{\pi}(2p-2h)] based states in the semimagic Pb nuclei at low excitation energy.