Fig. (30) The K-shell internal-conversion electron line of the 63.1 keV transition in Tm measured with an original and modified 169Yb source [209]. The original source was prepared by vacuum evaporation onto Al backing and was contaminated by a usual hydrocarbon over layer21 (described by a 3 nm thick carbon layer in Monte Carlo calculations). In the case of the modified source a supplementary Pu layer of average thickness of 0.4 nm was evaporated where electrons of the kinetic energy of 3.7 keV suffered additional elastic and inelastic scattering. The agreement of measured and calculated (smooth curves) shapes indicates correctness of the electron loss function in plutonium applied in calculations of the 241Pu β-spectrum shape. The natural width of this conversion line is 32.0 eV [212].