Neutron Cross-Section Measurements ofC12between 14 and 25 MeV

Measurements of the elastic and nonelastic cross sections for neutrons on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ have been made over the energy range between 14 and 25 MeV using a spherical shell of scattering material surrounding a stilbene detector. In addition to the known peak in the elastic scattering at 19.5-MeV neutron energy, another has been found at 15.8 MeV. The widths of these peaks at half-maximum are 2.0 and 0.5 MeV, respectively. No resonance structure in the nonelastic scattering cross section was found. With specially designed scatterers, the differential elastic scattering was measured at angles which correspond to the zeros of the first four Legendre polynomials, viz., at 90°, 54.8°, 39.2°, and 30.5°. The excitation function of elastic scattering at these angles showed a similar resonance structure in each case, the weakest being at 90°. Inelastic neutron scattering to the first excited state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ was determined between 14 and 21 MeV by measuring the 4.43-MeV $\gamma$ rays produced by the decay of this state. A very small peak was found at 15.8 MeV and a broader rise near 19 MeV. The low level of resonant effects in the nonelastic channels suggests that the resonances observed in the elastic cross section are caused by single-particle states, and the differential measurements indicate that they are caused by $p$ waves.