Nuclear structure effect in internal conversion of the 166 keV hindered M1 transition in 139La

The internal conversion coefficients were calculated for the 165.853 keV 5/2+→7/2+ hindered transition in 57139La using the new computer program NICC for conversion coefficients of all atomic shells. The algorithm employed in this code is described. The analysis of precise experimental data yielded the nuclear penetration parameter lambda=4.2+-0.8. This value was found to be in agreement with theoretical estimates and to correspond to the Nilsson deformation parameter β=-0.056+-0.004 of the 139La nucleus. Using the Nilsson wave functions for above β the mixing ratio delta2=Nsub(γ)(E2)/Nsub(γ)(M1) was determined to be less than 3x10-5, which supports the assumption of a pure M1 multipolarity of this transition. (author)