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Ionisation is the process bi that an atom or a molecule acquires a negative or positive chairge bi gainin or losin electrons. Ionisation, eften, results frae the interaction o an atom or a molecule wi an ionisin pairticle, includin chairged pairticles wi sufficient energies an energetic photons. A rare case o ionisation in the absence o an freemit pairticle is the internal conversion process, throu that an excitit nucleolus transfers its energy tae ane o the inner-shell electrons an ejects it wi heich kinetic energy.