($alpha$,2$alpha$) REACTION ON $sup 9$Be AT 42.8 AND 49.2 MeV AND ON $sup 16$O AT 49.2 AND 52.5 MeV.

The ($\ensuremath{\alpha},2\ensuremath{\alpha}$) reactions on $^{9}\mathrm{Be}$ at 42.8 and 49.2 MeV and $^{16}\mathrm{O}$ at 46.0 and 52.5 MeV have been studied in order to test the validity of the impulse approximation. The experimental data are consistent with this approximation, but the over-all agreement is much worse than in the case of the ($\ensuremath{\alpha},2\ensuremath{\alpha}$) reaction on $^{6}\mathrm{Li}$.