The activation contamination in the metal-based ionization chambers as gamma dosimeters in the mixed filed dosimetry

This study aims to determine the activation contamination in the metal-based ionization chambers, i.e. Mg(Ar)- and Al(Ar)-chambers. The contamination was estimated by directly measuring the signal caused by the radioactive nuclides after the irradiation. The INAA gamma ray spectra clearly showed that the ionization chambers were activated. The activation contamination could comprise more than 2% of the total measured current of the Mg(Ar)-chamber, and more than 50% of the Al(Ar)-chamber, both irradiated free-in-air at the THOR epithermal neutron beam. The activation contamination provides concrete evidence of the necessity of the thermal neutron sensitivity correction.