The present invention relates to a process for decontaminating by irradiation the interior of a thermoplastic preform (10) intended for manufacturing a container, said process comprising at least steps consisting in succession in: (a) making at least one source (32) emit at least one ultraviolet (UV) emission； (b) reflecting said at least one emitted ultraviolet (UV) emission in order to direct it in the direction of the neck (18) of a preform (10)； and (c) concentrating said at least one reflected ultraviolet (UV) emission by focusing it to obtain a beam that penetrates into the interior of the preform (10).
