Measurements of the total internal conversion coefficient and probability in the decay of 139Ce

The total conversion coefficient of the 165.853 keV transition in 139 La has been determined to be 0·251 ± 0·002 from measurements of the electron and gamma-ray intensities and the source activity. From the X-ray and γ-photon spectra the probability P K ω K has been determined to be 0·639 ± 0·006. Using α T = 0·251 ± 0·002, α K = 0·214 ± 0·002, ω K = 0·906 ± 0·026 and P K ω K = 0·639 ± 0·006 the number of K -X rays and 166 keV photons per disintegration has been calculated to be 0·794 ± 0·009 and 0.799 ± 0·001 respectively, giving a K -X ray to γ-photon ratio of 0·99±0·01. The discrepancy between the experimental and theoretical conversion coefficients is explained by taking the nuclear structure effect into account.