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 ±{}{}^∘{} 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: ¹S₀, 40^∘{}; ³P₀, 16.90^∘{}; ³P₁, -6.93^∘{}; ³P₂, 3.04^∘{}; ¹D₂, 2.16^∘{}; coupling parameter between ³P₂ and ³F₂ as defined by Stapp, -2.21^∘{}.