Anomalous Electric Dipole Conversion Coefficients in Odd-Mass Isotopes of the Heavy Elements

Abstract

A detailed review is given of experimental data on the anomalous $L$- and $M$-shell conversion coefficients of low-energy electric dipole transitions observed in the decays of odd-$A$ nuclei of high atomic number.The data are consistent in every case with the interpretation that the $E1$ conversion coefficients in the ${L}_{\mathrm{III}}$ shell agree with the theoretical, model-independent coefficients calculated by Sliv and Band and by Rose. It is definitely established in several well-measured cases that the ${L}_{\mathrm{I}}$ and ${L}_{\mathrm{II}}$ coefficients are substantially larger than the theoretical values. The most striking anomaly occurs in the 84.2-kev transition in ${\mathrm{Pa}}^{231}$, where the ${L}_{\mathrm{I}}$ and ${L}_{\mathrm{II}}$ coefficients are 21 and 15 times larger than the theoretical values, respectively.The experimental ${L}_{\mathrm{I}}$ and ${L}_{\mathrm{II}}$ coefficients are correlated with the lifetimes of the transitions, and it is shown that the magnitude of the anomaly (${L}_{\mathrm{I}}$ plus ${L}_{\mathrm{II}}$) is proportional to the retardation in gamma-ray lifetime over that calculated from the single-proton formulas. No systematic trend has been observed in the deviations of the ${L}_{\mathrm{I}}$ and ${L}_{\mathrm{II}}$ coefficients individually.