Intruder States and the Onset of Deformation in the Neutron-Deficient Even-Even Polonium Isotopes

Shape coexistence in the light Po isotopes

“…Another interesting point is that the decay pattern of the 2 + 2 state, as observed in Refs. [25,28], is di erent from the one seen in the heavier isotopes; notably, the transition to the rst excited 2 + state has an E0 component. It seems that 200 Po marks the end of a 'regular regime', which is replaced, starting with 198 Po, by an abrupt downsloping trend for nearly all the states, as seen from the systematics.…”

“…The energy of the rst 6 + and 8 + states increases with decreasing mass and the states remain very close together. The one exception from this very smooth variation is the behavior of the 0 + 2 state, identi ed in + /EC decay experiments [25,28]. This state drops in energy by 600 keV between 202 Po and 200 Po, becoming the second excited state in the latter nucleus.…”

“…It is concluded that the model can reproduce the experimental trend of the yrast levels, together with the yrare 2 + and 4 + states, via an increase in the particle-vibration coupling. The second excited 0 + states, which were identi ed in the light Po isotopes down to A=196, from + /EC and decay studies [25,28], are nonetheless not reproduced by the model. The alternative i n terpretation is heavily based on the observed low-lying 0 + 2 states, which are discussed in terms of intruder con guration [25,11].…”

“…The second excited 0 + states, which were identi ed in the light Po isotopes down to A=196, from + /EC and decay studies [25,28], are nonetheless not reproduced by the model. The alternative i n terpretation is heavily based on the observed low-lying 0 + 2 states, which are discussed in terms of intruder con guration [25,11]. The perturbation in the systematics below A=200 is described qualitatively as being due to the mixing of the associated intruder band with the regular structures.…”

“…The g-factor of the 8 + 1 state in 198 Po is also known [27] and is consistent with a ( 1h 9=2 ) 2 structure. The interpretation of the light Po isotopes must, therefore, rely upon the energy systematics and additional information obtained in decay measurements [25], which will be discussed later.…”