Evidence for shape coexistence and superdeformation in 24Mg

The E0transition depopulating the first-excited 0(+) state in Mg-24 has been observed for the first time, and the E0transition strength determined by electron-positron pair and.-ray spectroscopy measurements performed using the Super-e pair spectrometer. The E0 transition strength is rho(2) x 10(3)= 380(70). A two-state mixing model implies a deformation of the first-excited 0+ state of beta(2) approximate to 1 and a change in the mean-square charge radius of Delta < r(2)> approximate to 1.9fm(2), which suggests a significant shape change between the ground state and first-excited 0(+) state in Mg-24. The observed E0strength gives direct evidence of shape coexistence and superdeformation in Mg-24, bringing this nucleus into line with similar behaviour in nearby N= Znuclei. This result agrees with recent theoretical work on the cluster nature of Mg-24 and has potential ramifications for nuclear reactions of astrophysical importance. (C) 2020 The Author(s). Published by Elsevier B.V.