A neutral particle analyzer (NPA) was deployed on JET for measurement of distribution function of MeV energy protons driven by high power ion cyclotron resonance frequency heating of deuterium plasmas in the hydrogen minority scheme (D(H) ICRF heating). Unexpectedly, efficient neutralization of Me V energy protons was observed in the plasma center, without recourse to injection of a beam of atoms to provide charge donors for charge­exchange (CX) neutralization reactions. This paper presents a model elucidating the role of carbon and beryllium, the main impurities in JET plasmas, in this process and establishes charge exchange between hydrogen-like ([HJ) ions of the impurities and protons as the main neutralization process. A model calculation for deducing the proton energy distribution function f(Ep) from measured hydrogen flux is described. Uncertainties in cross-sections and their effect on the inferred f(Ep) are examined. Validity of this model of Impurity Induced Neutralization (IIN)[l] is tested by using it to describe the measured hydrogen flux in different conditions of plasma heating and fueling. Using this model and a procedure in which a known change in density of deuterium atoms at the plasma center is made by applying neutral beam injection (NBI), we have deduced the background thermal deuterium atom density at the plasma center, which is an important new diagnostic result. Concerning future experiments, the model predicts that carbon and beryllium impurities will be major contributors to neutralization of hydrogenic ions in ITER, for ion energies Er≤ lMeV/u. According to these estimates measurement of ICRF driven hydrogenic ions in ITER plasmas will be possible without recourse to injection of atomic beams, using an NPA instrument similar to that used on JET.