B(E1) rates in $^{229}Ra$ and traces of octupole correlations at the upper border of the A=225 island

The introduction of the fast timing beta gamma gamma (t) method at ISOLDE (CERN) has opened the heavy actinide region to lifetime measurements down to tenths of picoseconds, providing a direct experimental means of measuring the E1 rates. Recently, this method has been successfully applied to /sup 229/Ra, located at the border of the A=225 island of octupole deformation. In the light of the new results, structural similarities are established between /sup 229/Ra and its N=141 isotone /sup 231/Th, investigated with the same technique. The comparison shows that some collective aspects of both nuclei are related, but that the strength of the El transitions presents interesting differences. The collective B(E1) rates are also discussed in comparison with neighbouring nuclei in the upper border of the island of octupole deformation at A=225. (8 refs).