Abstract: An apparatus for irradiating a substance or object is provided. The apparatus has a source of radiation that is placed in a housing, one side of which is provided with a centrally disposed receiving chamber for the source of radiation, and the other side of which is provided with an irradiation chamber for receiving a receptacle that contains the medium that is to be irradiated, with the irradiation chamber being aligned with the receiving chamber. Disposed between the receiving chamber and the irradiation chamber is a valve provided with a through-bore for the source of radiation, which can be introduced into the irradiation chamber. The valve can be arrested in various angular positions. The irradiation chamber can be closed off by a removable plug.