COMPARISON OF EXPERIMENT AND THEORY FOR NUCLEAR EXCITATION IN 115IN BY THRESHOLD-ENERGY ELECTRONS

The Duke inelastic-electron-scattering program provides a major step in obtaining spin-parity assignments and mixing ratios for nuclear energy levels from threshold-energy electron scattering which populates an isomer. A detailed account of the Duke distorted-wave Born-approximation calculation for threshold-energy electrons is given, and the contribution and Coulomb distortion of the partial waves for M1 and E2 transitions is quantitatively presented. The finite tip observed in threshold electroexcitation is quantitatively accounted for by Coulomb distortion of s- and d-electron waves in the M1 and E2 transitions, respectively. A detailed comparison is made between experiment and theory for the 1.078- and 1.450-MeV states of In6649115, replacing earlier semiquantitative comparisons which used plane-wave Born-approximation calculations that resulted in factors of 2-5 disagreement for 1-2-MeV electrons. The agreement between the electron excitation functions for isomer population for the 1.078- and 1.450-MeV states and the Duke calculation is well within the 35% experimental errors. M1E2 mixing ratios are extracted from the comparison. The 1.078- and 1.450-MeV states of In115 are both 72+ with M1E2 mixing ratios, a=0E20M1, given by a=0.70.3 and 0.3, respectively. The mixing ratios are from photon self-absorption and Coulomb-excitation measurements of the same transitions, and corroborate the electron-scattering results. In this regard a search for the 1.078-MeV ray following - decay of Cd115m using a Ge(Li) Duode spectrometer yielded a null result, logft>11.5 for the - transition. With the 72+ assignments made in this work, the coexistence of spherical and rotational bands in In115 is discussed. © 1968 The American Physical Society.