Search for stable octupole deformation in Fr-225

Abstract

Levels in Fr-225 have been studied by gamma-ray and conversion-electron spectroscopy following the beta-decay of Rn-225 and by the Ra-226(t,alpha)Fr-225 single-proton-pickup reaction. Multipolarities were obtained for ~ 50 gamma-transitions, and a level scheme was established in which definite spin-parity values were determined for over 20 of the 48 levels. Although low-lying rotational bands of both parities exist for K = 1/2 and K = 3/2, there is no experimental evidence to claim these are parity doublets. E1 strengths connecting the K-π = 3/2(±) bands are intermediate between those for nuclides which are reflection symmetric and those claimed to be octupole deformed. The (t,α) cross sections are in better agreement with those predicted for the reflection-symmetric case than with those from an octupole-deformed description. These observations may be confirming theoretical predictions that octupole correlations are important in Fr-225, but that there is no large stable octupole deformation.