Isospin mixing in the ground state of Mn-52

The presence of isospin mixing into the ground state of Mn-52 was studied v ia anisotropic positron emission from nuclei. With this method the isospin forbidden Fermi-component in the Gamow-Teller dominated beta decay was dete rmined. It is shown that sample purity and the control of positron scatteri ng is of vital importance. Comparison between theory and experiment shows t hat shell model calculations of the isospin mixing probability deviate by a factor three to seven from experiment. For more recent Hartree-Fock-RPA ba sed calculations the difference is over two orders of magnitude. (C) 2000 E lsevier Science B.V. All rights reserved.