Ra223levels fed in theFr223β decay

Abstract

The $^{223}\mathrm{Fr}$ \ensuremath{\beta} decay was reinvestigated using high-resolution single \ensuremath{\gamma} spectrometry as well as \ensuremath{\gamma}-\ensuremath{\gamma} coincidence techniques. For single \ensuremath{\gamma}-spectra measurements, radiochemically pure $^{223}\mathrm{Fr}$ sources were obtained by chromatographic separation from a 75 MBq activity $^{227}\mathrm{Ac}$ parent source and continuously purified of $^{223}\mathrm{Ra}$ and daughters. The analysis of the \ensuremath{\gamma} spectra of 30 sources showed the existence of 131 \ensuremath{\gamma} lines, of which 87 are reported for the first time in the $^{223}\mathrm{Fr}$ \ensuremath{\beta} decay although many of them are observed following the $^{227}\mathrm{Th}$ \ensuremath{\alpha} decay. The $^{223}\mathrm{Fr}$ half-life was remeasured and found to be ${\mathit{T}}_{1/2}$=22.00\ifmmode\pm\else\textpm\fi{}0.07 min. \ensuremath{\gamma}-\ensuremath{\gamma}-t coincidence measurements were also carried out with $^{223}\mathrm{Fr}$ purified sources. The $^{223}\mathrm{Ra}$ level scheme was built on the basis of our \ensuremath{\gamma} data, as well as $^{227}\mathrm{Th}$ \ensuremath{\alpha}-decay data. Among the 32 excited $^{223}\mathrm{Ra}$ levels, of which 22 were also known from $^{227}\mathrm{Th}$ \ensuremath{\alpha} decay, 13 are newly reported from $^{223}\mathrm{Fr}$ \ensuremath{\beta} decay. Low energy levels (E400 keV) may be classified as parity doublet bands according to the predictions of the reflection asymmetric rotor model. Above a 700 keV gap, a coexistence of symmetric and asymmetric shapes including both static and dynamic octupole correlations is suggested.