On the basis of the radiation thermal approach, developed earlier by the authors, it is shown by calculation that the character of the defect formation in Nb‐based superconductors with A‐15 structure differs according to whether they are irradiated by fast neutrons or by high‐energy oxygen ions and by α‐particles. In the first case the “antistructural” defects should appear in the main, while in the second case and in the third the formation of the “antistructural” defects is less probable and point defects, vacancies and interstitial atoms, should appear. It is probable that this difference causes the different saturations of degradation of the superconducting transition temperature. The results of X‐ray and neutronographic studies are analysed and they quantitatively agree with the calculated results.

Atomic configurations of vacancies, antisite replacements, and interstitials in Mo3Si are studied by molecular dynamics. According to calculations, distortions of the crystal lattice around antisite replacements and vacancies are the same. Dumb‐bells of the Si atoms and the complexes antisite replacement‐dumb‐bells are found while simulating interstitials.

Defect formation in Mo3Si irradiated with fast neutrons is studied by the molecular dynamics technique. It is shown that within a cascade region of the thermal stage Mo atoms form an amorphous phase, while Si atoms form dendrites. This phenomenon is associated with interatomic potentials of the compound components. It is concluded that the peculiarities of interatomic potential in complex structures may affect the percolation character of the radiatiowinduced processes as well as the finite defect structure.

Configurations of antisite defects and vacancies in Nb,Sn are calculated by molecular dynamics technique with the help of Buckingham empiric potentials and the ones calculated by the pseudopotential scheme using the Heine-Abarenkov-Animalu pseudopotential. I n the case of Buckingham potentials the displacements do not exceed 1% of the value of the constant lattice; and in the latter case they reach z 10%. This discrepancy accounts for the structural differences observed a t irradiation of Nb,Sn by fast neutrons and a-particles. Es werden die Konfigurationen vonAntiplatzdefekten und Leerstellen in Nb,Sn mittels dynamischer Molekulartechnik unter Benutzung des empirischen Buckingham-Potentials und den Potentialen, die mit der Pseudopotentialmethode nach dem Heine-Abarenkov-Animalu-Pseudopotential berechnet werden, ermittelt. Fur den Fall des Buckingham-Potentials ubersteigen die Verlagerungen nicht 1% des Wertes des konstanten Gitters; und im letzteren Fall erreichen sie = 10%. Diese Diskrepanz erklart die strukturellen Differenzen, die bei der Bestrahlung von Nb,Sn durch schnelle Neutronen und a-Teilchen beobachtet werden.

The behaviour of heavy impurity replacement in a f.c.c. metal at the thermal stage under radiation is studied by the molecular dynamics technique. It is shown that vacancies formed as a result of collision cascade diffuse preferentially towards the cascade region centre at the initial stage because of the presence of enormous temperature gradients and form a void. At the second stage impurity atoms are adsorbed by the surface, while at the third one a void transforms into a dislocation loop. Impurity concentration near its plane increases strongly by tenths to hundredths times and formation of a new phase becomes significantly easier. The results are compared with the experimental data received during the investigation of the radiation heredity phenomenon.