Proton-Proton Scattering at 40 Mev

Differential cross sections have been measured for the scattering of 39.4-Mev protons by hydrogen gas at angles from 45° to 4° in the laboratory system, with ±½° angular resolution at small angles. Data are given for every half degree near the interference minimum. The relative and absolute probable errors given are respectively ±0.5% and ±0.8% from 45° to 8°. The corresponding probable errors at 4° are ±4.0% and ±4.1%. The cross-section curve is essentially flat at 11.15 millibarns from 90° to 55° in the center-of-mass system. It falls to a minimum of 9.80 millibarns at 21°, and rises rapidly to 104 millibarns at 8°. A typical but not unique set of phase shifts which fit the data is: ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$, 40°; ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$, 16.90°; ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$, -6.93°; ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$, 3.04°; ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$, 2.16°; coupling parameter between ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}F_2^{}{}_{}{}^{}$ as defined by Stapp, -2.21°.