Shape-driving effect of the proton 1/2[541] band in 171Ta

High-spin states in 171Ta were populated through the heavy-ion fusion-evaporation reaction 157Gd (19F, 5n)171Ta at 105MeV beam energy. Lifetimes of the levels of the πh 9/21/2[541] band have been measured by using the Doppler shift attenuation method. The transition quadrupole moments ( Q t) and the quadrupole deformation (β2) have been extracted. Both β2 and Q t values decrease slightly with increasing rotational frequency. The average β2 value of 0.26 is 18% larger than that of the πh 11/2 9/2[514] band. Total Routhian Surface calculations have been performed with the non-axial deformed Woods-Saxon potential and the predicted values of the quadrupole deformation β2 are in good agreement with that deduced from our lifetime measurement. The shape-driving effect is discussed.