Level structure in the transitional nucleus 215Fr

The level scheme of Fr-215 is extended up to 55/2 h and 4.8 MeV excitation energy with the addition of 52 new gamma-ray transitions. Previously established isomers and their half-lives, except for the 47/2(+) state, are revisited. The discrepancy in the half-life of the 39/2(-) state is resolved, and its half-life is revised to 11.4(14) ns. An overall good agreement is observed between the experimental results and the shell-model calculations performed using the CD-Bonn NN interaction derived from the V-l(ow)-k renormalization approach. A weak coupling of the odd proton to the even-even core is observed to account for the level structure at lower energies, which strongly resembles a decoupled nonrotational band. A new positive-parity sequence is also established which is observed to originate from the coupling of the i(13/12) proton at low excitation energy.

Automated summary

The level scheme of Fr-215 is extended with the addition of 52 new gamma-ray transitions, and the previously established isomers and their half-lives are revisited. A good agreement is observed between the experimental results and the shell-model calculations. The weak coupling of the odd proton to the even-even core and the establishment of a new positive-parity sequence are also observed.