The VERDI detector is a passive neutron detector, based on the multi-foil activation technique, developed for measurements in harsh environments, such as those encountered in fusion devices. During the 2019 Joint European Torus (JET) Deuterium-Deuterium (DD) campaign, irradiation studies of dosimetry foils and ITER material samples were performed at the JET Long Term Irradiation Station (LTIS). VERDI detectors were used to determine the neutron fluence and energy spectrum at the irradiation position of the samples. In the present work, the VERDI detector results are used as input to FISPACT-II to predict the radionuclide product inventory of the irradiated samples. The results of the calculations are compared against activities determined by gamma spectrometry. The application of the VERDI detector is demonstrated and data for the validation of activation predictions in ITER materials irradiated in a DD fusion environment are provided.