Investigation of the Resonant Vibration Modes of Radiation Induced Interstitial Atoms in Aluminum by Diffuse Inelastic Neutron Scattering

Diffuse inelastic neutron scattering measurements are reported which are used, for the first time, to study the dynamics of radiation‐induced self interstitial atoms. Large single crystalline aluminum samples are electron‐irradiated in a specially built facility at T ≦ 20 K to defect concentrations of up to 500 at ppm and subsequently transported in the cold state to the high flux reactor at Grenoble. The measurements are done at T = 6 K on the triple axis spectrometer IN3 and are repeated after annealing at T = 46 K (above stage I) and at T ≈ 300 K (after complete recovery). The irradiated samples show a significant increase of the inelastic scattering intensity at transferred energies between 0.7 and 2 THz. By comparison with the results of computer calculations the different frequencies of the energy loss spectrum can be attributed to the different vibration modes of interstitial atoms. The frequencies of the most significant modes of the self interstitial atom are determined to be ν = 0.75 THz and ν = 1.35 THz for the translation‐(A 2u )‐and libration‐(E g )‐mode, respectively.