Electric monopole transitions in nuclei

Electric monopole, E0 transitions in nuclei are reviewed. Values for ρ²(E0)×10³, X(E0/E2) and q_K²(E0/E2) are tabulated. Particular attention is paid to a complete re-evaluation of all reported values starting from raw input data, i.e. none of the adopted values are taken from the literature without evaluation. Values for J→J transitions for J=0, J=2, and some selected J=4 transitions are given. The 2→2 transitions involve evaluation of δ(E2/M1) mixing ratios. These were usually assessed from values given in ENSDF. Asymmetric uncertainties and multiple sources of error are handled using up-to-date, Monte Carlo-based procedures. All conversion coefficients and electronic factors are taken from the latest tabulations. As a second major component of the review, a detailed illustration of the association of E0 transition strengths with the manifestation of shape coexistence in nuclei is made. This demonstrates that large E0 transition strengths are a strong indication of the presence of shape coexistence in nuclei. In many cases this is shown to be directly corroborated by B(E2) data. Some details of experimental techniques behind the input data are given. The connection between E0 transition strengths and mean-square charge radii, isotope and isomer shifts is sketched.