NEUTRON-INDUCED COLLISION CASCADE MIXING IN NB V SUPERLATTICES/

High-angle X-ray diffraction was used to determine cascade mixing effi ciencies, Dt/dpa, in Nb/V superlattices irradiated to small doses (les s-than-or-equal-to 0.26 dpa). Samples were neutron irradiated in the c ore of the High Flux Beam Reactor at Brookhaven National Laboratory an d ion irradiated with 1.5 MeV Ne. No significant differences were obse rved in cascade mixing efficiencies between the two types of irradiati on. Values of Dt/dpa were observed to vary with the modulation wavelen gth of the superlattice, with thicker wavelength samples yielding valu es approaching that determined from ion mixing thick Nb/V bilayers (Dt /dpa almost-equal-to 110 angstrom2/dpa). The decrease in mixing effici ency observed at lower wavelengths may be related to an observed struc tural transition in which the interfaces of the superlattice become co herent.