UW, Warsaw

DSAM lifetimes measurements of 132La hypothetical chiral bands

Level lifetimes in three bands of 132La as well as in yrast band of 131La were measured using the Warsaw University cyclotron. The 132La and 131La excited states were populated in 122Sn(14N,4n)132La and 122Sn(14N,5n)131La reaction respectively, with 14N beam energy equal 70MeV. 10mg/cm2 thick 122Sn target was used, what allows to stop the recoiling La inside thetarget. Lifetimes of the excited levels were determined from the gamma-lineshape analysis of the Doppler disturbed gamma transitions, taking into account several important phenomena for the Doppler Shift Attenuation Method:

- reaction kinematics: distribution of the initial velocity and entry state distribution.
- slowing down process of recoils in the target matter
- analysing the levels lifetimes "step by step" going down ni the excitation energy.Any constrains about fixed quadrupole moment along the band was not assumed.

In case of 132La, it is the first measurement of lifetimes in any nucleus with supposed chiral band structure. More then 40 absolute values of B(M1) and B(E2) have been deduced. New band have been found 1MeV above the yrast levels with intraband M1 transitions about 0.5 W.u. and E2 about 10-20 W.u.