The invention relates to activatable novel particles which can be used in the health sector. The invention more particularly relates to composite particles which can generate free radicals or heat when excited by X-rays. The invention also relates to the uses thereof in human health. The inventive particles comprise an inorganic-based, and optionally organic-based, nucleus and can be activated invivo in order to mark or affect cells, tissue or organs. The invention further relates to methods for the production of said particles, and pharmaceutical or diagnostic compositions containing them.