For study of states with a large reduced alpha width the method of measurement of the excitation function of elastic scattering of alpha particles is proposed, but in a geometry which is the reverse of the traditional experimental arrangement. The targets are helium gas which is simultaneously a moderator for the primary beam of heavy ions and an absorber which shields the detector from the direct beam. The advantages of the method are obvious in those cases in which in the usual experimental arrangement the need arises of using gas targets of rare isotopes or of measurements at an angle 180-degrees. To check the method we have carried out a comparison with the known alpha + C-12 interaction. New results are obtained in the interaction N-15 + alpha.