RESONANT DIFFERENTIAL SCATTERING OF ELECTRONS BY HELIUM

The resonant differential scattering of electrons by helium has been investigated for energies close to 19·3 ev. A data-logging technique was used to obtain exceptionally high signal-to-noise ratios. Analysis of the results gave δ0 similar,equals 111°, δ1 similar,equals 17°and δ2 similar,equals 3°for the first three phase shifts for potential scattering at the resonance energy, and 8 mev for the natural width at half-height. Structure was observed at 19·45 ± 0·05 ev which had the properties of a p-wave resonance with a natural width of order 0·25 mev.