Gamma induced background in the KATRIN main spectrometer

The KArlsruhe TRItium Neutrino experiment (KATRIN) experiment aims to measure the electron neutrino mass with a sensitivity of m(ν_e)<200 meV/c². It utilizes a MAC-E-type spectrometer for high-resolution and high-statistics spectroscopy of the β-decay of ³H close to its endpoint of 18.6 keV. The KATRIN spectrometer and detector section has undergone 3 commissioning phases in recent years, with one of the major goals being the characterization and reduction of the background level. Secondary electrons, that are created inside the main spectrometer by external radiation, e.g. cosmic muons or natural radioactivity gammas, are considered to be one of the main contributions to the remaining background level. The experimental investigation of the gamma induced background has been twofold. Firstly by exposing the spectrometer wall to an external 50 MBq ⁶⁰Co gamma source and secondly by introducing additional gamma shielding inside the experimental hall, effectively reducing the flux of natural radioactivity gammas to the spectrometer wall. This talk gives an overview of the investigations and results concerning gamma induced background in the KATRIN main spectrometer.