Measurements of the diffraction and absorption cross sections of nuclei for negative pions at kinetic energies between 0.6 and 1.4 Bev are described. They include the absorption cross section (1) in selected nuclei from Be to Pb at 0.97 Bev, (2) in C between 0.6 and 1.2 Bev, and (3) in Al, Ca, and Pb for 1.5-Bev/c momentum ${\pi }^{-}$ and protons. Diffraction cross sections were obtained for (1) Be, C, Al, and Ca at 0.97 Bev and (2) C at 0.6, 0.8, and 1.2 Bev.

The data are compared to the optical model of the nucleus. Detailed computations are described both for a tapered Fermitype distribution of nucleons which fits the high-energy electron scattering data and for a uniform square-well nucleon distribution of the form $R=r_0{A}^{\frac{1}{2}}$. All of the absorption cross sections are shown to be in excellent agreement for a Fermi distribution with a single radial parameter $c=(1.14\mathrm{}\pm 0.04)A^{\frac{1}{3}}\times {10}^{-13\mathrm{}}$ cm, which is 6% larger than that required by electromagnetic measurements. The data are also consistent with the same value of the radial parameter as that which fits the electron-scattering data if the range of the pion-nucleon force is taken to be ≈1.0×${10}^{-13\mathrm{}}$ cm. This range is equal to the range required by pion-nucleon scattering data. A uniform distribution $R=r_0{A}^{\frac{1}{3}}$ is not consistent with the data.

The diffraction cross sections appear to be 20-30% higher than those predicted by the optical model and the dispersion relations. The implications of this discrepancy are discussed.

• Received 14 May 1957

DOI:https://doi.org/10.1103/PhysRev.107.1121