Elastic and Inelastic Scattering of 187-Mev Electrons from Carbon-12

The scattering of 187-Mev electrons from C¹², reported previously, has been extended to 138^∘{}. It has been possible to separate the elastic scattering from the inelastic scattering and to resolve the inelastic groups from the 4.43-, 7.65-, and 9.61-Mev nuclear levels. "Absolute" values were obtained by comparing the scattering from carbon with the scattering from hydrogen and computing the proton cross section. The angular distribution of the elastically-scattered electrons falls off more steeply than the angular distribution of the inelastically-scattered electrons. Analysis of the data, using the Born approximation, shows that the root-mean-square radius of C¹² (corrected for breakdown of the Born approximation) is (2.37±{}0.05)×{}10^-13 cm with a surface thickness of (2.0±{}0.4)×{}10^-13 cm. The corresponding value of r₀, the "classical" radius parameter, is (1.33±{}0.02)×{}10^-13 cm which is larger than that found from electron-scattering measurements for the heavy nuclei and is in agreement with the trend for light nuclei. The scattering from the 4.43-Mev and 7.65-Mev levels is larger than that predicted by some shell-model calculations. The transition from the ground state to the 9.61-Mev level appears to be either quadrupole or electric monopole, which gives a spin and parity assignment of either 2⁺ or 0⁺.