# Gamma-induced background in the KATRIN main spectrometer

## TL;DR

This study investigates whether gamma radiation from external sources significantly contributes to background noise in the KATRIN experiment's main spectrometer, finding that shielding effectively reduces such background events.

## Contribution

The paper provides the first detailed simulation and experimental analysis quantifying gamma-induced background in the KATRIN main spectrometer, establishing an upper limit on this background source.

## Key findings

- Gamma radiation contributes less than 0.006 counts/sec to background.
- Electrostatic and magnetic shielding effectively suppress gamma-induced secondary electrons.
- Gamma-induced background is not a significant limiting factor for KATRIN's sensitivity.

## Abstract

The KATRIN experiment aims to measure the effective electron antineutrino mass $m_{\overline{\nu}_e}$ with a sensitivity of 0.2 eV/c$^2$ using a gaseous tritium source combined with the MAC-E filter technique. A low background rate is crucial to achieving the proposed sensitivity, and dedicated measurements have been performed to study possible sources of background electrons. In this work, we test the hypothesis that gamma radiation from external radioactive sources significantly increases the rate of background events created in the main spectrometer (MS) and observed in the focal-plane detector. Using detailed simulations of the gamma flux in the experimental hall, combined with a series of experimental tests that artificially increased or decreased the local gamma flux to the MS, we set an upper limit of 0.006 count/s (90% C.L.) from this mechanism. Our results indicate the effectiveness of the electrostatic and magnetic shielding used to block secondary electrons emitted from the inner surface of the MS.