Nuclear structure effect on internal conversion ofl-forbidden transitions in139La,141Pr and203Tl

Accurate experimental internal conversion data have been used to study the effect of nuclear penetration in the case of thel-forbidden transitions in¹³⁹La (165.8 keV),¹⁴¹Pr (145.4 keV) and²⁰³Tl (279.2 keV). The nuclear penetration parameterλ and theE2/M 1 mixing ratioδ ² have been deduced by graphical analysis. Following results were obtained:λ=2.8±1.3,δ ² =(8.4 _?8.4 ^+14.0 )·10^?4 for¹³⁹La,λ=1.2±0.6,δ ²=(4.8±0.5)·10^?3 for¹⁴¹Pr, andλ=6.4±1.1,δ ²=1.36±0.12 for²⁰³Tl.