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An experimental method for the simultaneous determination of energy and intensity of a charged particle beam is presented and results obtained with proton, 3He2+ and α particle beams in the energy range below 40 MeV are reported. The method is based on activity measurements of at least two radioisotopes produced simultaneously in a thin target sample. The beam energy is deduced from the activity ratio of the two radioisotopes while the intensity may then be calculated from the activity of one of the two considered radioisotopes. The target materials used in this work are those for which recommended excitation functions for the radioisotopes are available from the IAEA data base. Copper foils were irradiated with protons and α particles while aluminium foils were used for irradiation with 3He2+ particles. The range of beam energies investigated in this work are those available at the Scanditronix MC 40 (K=40) cyclotron for which the maximum energy for both protons and α particles is 40 MeV, while for 3He2+ particles it is 53 MeV. With respect to the nominal settings of the cyclotron, the results obtained are very satisfactory; being in agreement within 1%, 5% and 7% for beams of protons, α and 3He2+ particles respectively. The method is easy to apply, economic and also relatively accurate and precise, provided that precise cross section data of the considered nuclear reactions are available. It can be applied for various energy ranges of charged particle beams from cyclotrons or linear accelerators and is especially useful for the determination of beam energy and intensity after transmission through material with inaccurately known characteristics and properties such as powders or porous matter, or after transmission through complex target systems.