Scattering of High Energy Protons in Hydrogen

Abstract

7340 photographs of high energy proton tracks in hydrogen were taken and the observed frequency of scattering was compared with Mott's wave-mechanical treatment. Strong anomalies were found when the energy of the incident proton exceeded 600 kv. The anomalies consisted chiefly in finding about ten times too much scattering in the angular range 40\ifmmode^\circ\else\textdegree\fi{}-45\ifmmode^\circ\else\textdegree\fi{}, where this angle is the angle of scattering of the longer tine as measured in the observer's coordinate system. The angular distribution for energies less than 600 kv was found to be in accord with Mott's expression to within the rather large statistical fluctuations. Although only 74 collisions with an energy greater than 600 kv were observed it seems very improbable that the distribution can be entirely accounted for by statistical fluctuations. Since Mott's formula is based upon the assumption of Coulomb forces the experimental discrepancies indicate a departure from the inverse square law when the energy of the incident proton exceeds about 600 kv. This means that for a classical distance of closest approach of about 6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ the two protons can no longer be treated as classical point charges, whereas on purely classical grounds there should be no such difficulties down to 1/1846 the electron radius or about ${10}^{\ensuremath{-}16}$ cm.