Details are given about the preparation of suitable aluminum samples for studying the effects of electron irradiation of single crystals. The observed annealing spectra of stage I differ for samples irradiated along different crystallographic directions. Results show that when the atomic‐recoil energy is slightly greater than the threshold energy, the IBsubstage is enhanced for irradiations parallel to the ⟨100⟩ but is suppressed for the ⟨110⟩. Evidently, the most favorable conditions for producing IB‐type defects occur when the initial atomic displacements cause atoms to move in the ⟨100⟩. A qualitative discussion is given which explains the observed energy dependence of the single‐crystal samples in terms of atomic displacements along ⟨100⟩ and ⟨110⟩ directions.