Gamma-Ray Excitation of the 15.1-Mev Level inC12

Abstract

The parameters of the 15.1-Mev level in ${\mathrm{C}}^{12}$ have been determined. The angular distribution of scattered photons has been determined to be dipole. A scatter-associated background to the scattering from this level has been demonstrated. The peak absorption cross section of 29.7\ifmmode\pm\else\textpm\fi{}1.1 barns has been determined from a self-absorption experiment. The self-absorption measurement and a production experiment combine to give values of 64.5\ifmmode\pm\else\textpm\fi{}10.4 ev and 59.2\ifmmode\pm\else\textpm\fi{}9.7 ev for the total level width and radiative width to the ground state, respectively. The combination of the value of the integrated elastic scattering cross section from the absolute measurement, and those values calculated from the self-absorption and production experiments gives for this integrated cross section the value 2.33\ifmmode\pm\else\textpm\fi{}0.19 mb-Mev. The radiation width to the 4.43-Mev state of ${\mathrm{C}}^{12}$ is determined to be 3.2\ifmmode\pm\else\textpm\fi{}2.5 ev by fitting the detector resolution function to observed pulse-height spectra. A value for the inelastic scattering in the giant resonance region of ${\mathrm{C}}^{12}$ is determined.