Abstract: An irradiator of the type using a radioactive material as a source of radiation is combined with a gaseous liquid contact chamber. The irradiator has a casing having an input and output therefrom and a plurality of connected chambers formed in the casing and separated by walls having an opening therethrough. A plurality of gamma radiation sources are located in a plurality of the chambers, thus forming a plurality of irradiation chambers. At least one of the chambers is a gas treatment chamber having a gas input line connected thereto to provide gas liquid contact in the gas treatment chamber. The walls between the irradiation chambers and the gas treatment chambers are made of a gamma radiation blocking material, such as lead or concrete. Gas escape lines are provided for preventing the build up of gas in the chambers, so that a fluid can be treated through a series of irradiation gas contact treatments. Gas lines can also be provided directly into the irradiation chambers.