The object of this proposal is to measure the partial vibrational density of states (VDOS) within the incoherent approximation for the archetypal 'strong' network forming glass GeO2 by using the method of isotope substitution in neutron spectroscopy. The results will improve on previous neutron scattering work where the extreme incoherent approximation was employed in which the coherent scattering length, mass and mean square displacement (Debye-Waller factor) of Ge and O are assumed to be equal. The results will be used to find the source of significant discrepancies between the VDOS (i) previously measured for GeO2 by using neutron scattering and (ii) calculated by using ab initio molecular dynamics simulations.