Shape Changes in the Mirror Nuclei Kr-70 and Se-70

6 pags., 3 figs., 2 tabs.
We studied the proton-rich T-z = -1 nucleus Kr-70 through inelastic scattering at intermediate energies in order to extract the reduced transition probability, B(E2; 0+ -> 2+). Comparison with the other members of the A = 70 isospin triplet, Br-70 and Se-70, studied in the same experiment, shows a 3 sigma deviation from the expected linearity of the electromagnetic matrix elements as a function of T-z. At present, no established nuclear structure theory can describe this observed deviation quantitatively. This is the first violation of isospin symmetry at this level observed in the transition matrix elements. A heuristic approach may explain the anomaly by a shape change between the mirror nuclei Kr-70 and Se-70 contrary to the model predictions.
We would like to thank the RIKEN accelerator and BigRIPS teams for providing the high intensity beams. This work has been supported by UK STFC under Grants No. ST/L005727/1 and No. ST/P003885/1, the Spanish Ministerio de Economía y Competitividad under Grants No. FPA2011-24553 and No. FPA2014-52823-C2-1-P, the Program Severo Ochoa (SEV-2014-0398), and the Spanish MICINN under PGC2018-094583-B-I00. K. W. acknowledges the support from the Spanish Ministerio de Economía y Competitividad RYC-2017-22007. A. O. acknowledges the support from the European Research Council through the ERC Grant No. MINOS-258567