Abstract: Extended x-ray absorption fine structure has been measured on two powdered samples of 70Ge and 76Ge
as a function of temperature from 20 to 300 K. The effect of isotopic mass difference on the amplitude of
relative atomic vibrations is neatly evidenced by the temperature dependence of the difference of Debye-
Waller factors. The isotopic effect is also detected on the difference of nearest-neighbor average
ineratomic distances, thanks to a resolution better than 10 fm.