RA-223 LEVELS FED IN THE FR-223 BETA-DECAY

The Fr-223 beta decay was reinvestigated using high-resolution single y spectrometry as well as gamma-gamma coincidence techniques. For single gamma-spectra measurements, radiochemically pure Fr-223 sources were obtained by chromatographic separation from a 75 MBq activity Ac-227 parent source and continuously purified of Ra-223 and daughters. The analysis of the gamma spectra of 30 sources showed the existence of 131 gamma lines, of which 87 are reported for the first time in the Fr-223 beta decay although many of them are observed following the Th-227 alpha decay. The Fr-223 half-life was remeasured and found to be T1/2=22.00+/-0.07 min. Gamma-gamma-t coincidence measurements were also carried out with Fr-223 purified sources. The Ra-223 level scheme was built on the basis of our gamma data, as well as Th-227 alpha-decay data. Among the 32 excited Ra-223 levels, of which 22 were also known from Th-227 alpha decay, 13 are newly reported from Fr-223 beta decay. Low energy levels (E < 400 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.