Excited superdeformed Kπ=0+ rotational bands in β-vibrational fission resonances of 240Pu

The intermediate structure of fission resonances of 240Pu was observed with an experimental energy resolution of 7 keV in the excitation energy region of E ∗ =3.8 –5.6 MeV using the 239Pu(d, pf)240Pu reaction. Two-vibrational resonance groups centered at E ∗ =4.6 MeV and 5.1 MeV, and attributed to the excitation of three and four β-phonons, were resolved into individual substates, which could be assigned to the low-spin members of Kπ=0+ superdeformed (SD) rotational bands. In the region of the lower E ∗ =4.6 MeV resonance individual moments of inertia of six well separated bands could be extracted for the first time with values of Θ/ℏ2 around 157 MeV−1, close to that of the ground state band in the second well. From the level density of these Kπ=0+ band heads the excitation energy of the SD ground state was determined to (2.25±0.20) MeV, in agreement with earlier estimates from excitation functions.