The characterization of the neutron flux in a beamline is a crucial information for many experiments. The activation technique allows to measure the neutron flux in a broad energy range from thermal region up to about 100 MeV. This technique is suitable for measuring high instantaneous fluxes, because is based on passive detectors (activation foils). We plan to irradiate 10-20 samples to measure the activation rates of many reactions that are induced with different probabilities by neutrons with different energies. In this way, we can finally unfold the neutron flux spectrum and determine its absolute intensity. Testing this methodology in a beamline, like Vesuvio, where independent neutron flux measurements are available and can be used as a benchmark, is an important step to prove the accuracy and reliability of this experimental techinque.