The scattering of alpha particles by helium

In order to obtain information about the levels of even spin and parity of ⁸Be at energies above 11 MeV, the differential cross-section for the α-particle-helium elastic scattering has been measured at a series of beam energies from 23·1 to 38·4 MeV, for many c.m.s. angles between 30 and 90°. Phase shifts up to L = 8 have been calculated for each energy. Combining these results with previous figures for lower energies, the phase shifts δ₀, δ₂ and δ₄ are thus known as functions of incident energy from 0·15 MeV to 38·4 MeV. The behaviour of the phase shift δ₄ confirms the existence of a previously suggested level with I = 4 at an excitation energy of about 11·4 MeV in ⁸Be. The phase shifts δ₆ and δ₈ are small, as expected if the rotational series of levels in ⁸Be term inates with I = 4.