Measurements of mega-electron-volt charged-particle losses in the JET tokamak are reported. The technique is based on sample activation by nuclear reaction from mega-electron-volt particles. Samples are used as flux monitors for leaking fusion plasma particles in the mega-electron-volt energy range. Ultra-low-level gamma-ray measurements were performed at three underground facilities in order to significantly enhance detection levels. Two measured radionuclides (48V and 7Be) were identified as produced predominantly from charged-particle reactions. Quantitative data on charged-particle fluxes to the wall were obtained for the first time as well as angular distribution with respect to the magnetic field.