Simulation of background from low-level tritium and radon emanation in the KATRIN spectrometers

Journal Article · Thu Aug 08 00:00:00 EDT 2013 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.4818118· OSTI ID:22218191

Leiber, B. ^[1]

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1. Institute for Nuclear Physics (IKP), Karlsruhe Institute of Technology (KIT), 76021 Karlsruhe (Germany)

The KArlsruhe TRItium Neutrino (KATRIN) experiment is a large-scale experiment for the model independent determination of the mass of electron anti-neutrinos with a sensitivity of 200 meV/c{sup 2}. It investigates the kinematics of electrons from tritium beta decay close to the endpoint of the energy spectrum at 18.6 keV. To achieve a good signal to background ratio at the endpoint, a low background rate below 10{sup −2} counts per second is required. The KATRIN setup thus consists of a high luminosity windowless gaseous tritium source (WGTS), a magnetic electron transport system with differential and cryogenic pumping for tritium retention, and electro-static retarding spectrometers (pre-spectrometer and main spectrometer) for energy analysis, followed by a segmented detector system for counting transmitted beta-electrons. A major source of background comes from magnetically trapped electrons in the main spectrometer (vacuum vessel: 1240 m{sup 3}, 10{sup −11} mbar) produced by nuclear decays in the magnetic flux tube of the spectrometer. Major contributions are expected from short-lived radon isotopes and tritium. Primary electrons, originating from these decays, can be trapped for hours, until having lost almost all their energy through inelastic scattering on residual gas particles. Depending on the initial energy of the primary electron, up to hundreds of low energetic secondary electrons can be produced. Leaving the spectrometer, these electrons will contribute to the background rate. This contribution describes results from simulations for the various background sources. Decays of {sup 219}Rn, emanating from the main vacuum pump, and tritium from the WGTS that reaches the spectrometers are expected to account for most of the background. As a result of the radon alpha decay, electrons are emitted through various processes, such as shake-off, internal conversion and the Auger deexcitations. The corresponding simulations were done using the KASSIOPEIA framework, which has been developed for the KATRIN experiment for low-energy electron tracking, field calculation and detector simulation. The results of the simulations have been used to optimize the design parameters of the vacuum system with regard to radon emanation and tritium pumping, in order to reach the stringent requirements of the neutrino mass measurement.

• OSTI ID: 22218191
• Journal Information: AIP Conference Proceedings, Vol. 1549, Issue 1; Conference: LRT 2013: 4. international workshop on low radioactivity techniques, Assergi (Italy), 10-12 Apr 2013; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ALPHA DECAY
BETA DECAY
DE-EXCITATION
DESIGN
ELECTRON SPECTROMETERS
ENERGY SPECTRA
INELASTIC SCATTERING
INTERNAL CONVERSION
MAGNETIC FLUX
MILLI EV RANGE
MULTIPARTICLE SPECTROMETERS
NEUTRINO DETECTION
NEUTRINOS
PARTICLE IDENTIFICATION
RADON 219
REST MASS
SENSITIVITY
TRAPPED ELECTRONS
TRITIUM
VACUUM SYSTEMS