# Conference on Science at the Sanford Underground Research Facility 2017

12-16 May 2017
South Dakota School of Mines and Technology
US/Mountain timezone
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Reduction of radon background in the KATRIN experiment

Content: The objective of the Karlsruhe Tritium Neutrino experiment (KATRIN) at the Karlsruhe Insti-tute of Technology (KIT) is the measurement of the effective electron neutrino mass with a sensitivity of 200 meV/c$^2$. A central component is the Main Spectrometer (MS), a MAC-E filter type electrostatic high pass filter for electrons. It measures the energy of $\beta$-electrons from tritium decay close to the endpoint at 18.6 keV with high precision, but a low count rate. Short-lived radon isotopes are a serious source of background for the measurement of the neutrino mass with the KATRIN experiment. The target value for the background rate in the KATRIN design is $10^{-2}$ cps. The large ultra-high-vacuum chamber of the MS has a volume of 1240 m$^3$ and is operated at an ultra-low pressure in the range of $10^{-11}$ mbar, which is required to reduce the background rate. The pumping system of the MS consists of turbo-molecular pumps and large-scale getter pumps (SAES St707 non-evaporable getter (NEG) strips). The NEG strips ($^{219}$Rn, t$_{1/2}$ = 3.9 s), as well as the stainless steel walls ($^{220}$Rn, t$_{1/2}$ = 56 s) are known to emanate small amounts of radon atoms, increasing the intrinsic background rate by 0.5 cps, if no further countermeasures are taken. Therefore, three LN$_2$-cooled cryogenic baffles (1.7-m diameter), made of L-shaped copper panels, have been installed in front of the NEG-pumps, reducing the transmission of radon into the main volume. Radon from the walls and welds of the vacuum chamber, which is directly emanated into the main volume, has to be removed quickly enough before it decays. However, radon does not stick to a cold surface indefinitely. It either desorbs after a limited sojourn time, or it decays into polonium while still on the cold baffle. This talk describes the simulation of the effectiveness of the radon suppression with the Test-Particle Monte Carlo (TPMC) code MolFlow+ and presents data from an extensive measurement program. We acknowledge the support of the Helmholtz Association (HGF), the German Ministry for Education and Research BMBF (05A14VK2) and the Helmholtz Alliance for Astroparticle Physics (HAP).
Id: 47
Place: South Dakota School of Mines and Technology
501 East Saint Joseph Street
Rapid City, SD 57701

Room:
Starting date:
 15-May-2017 16:40 (US/Mountain)
Duration: 20'
Contribution type: Presentation
Primary Authors: Dr. WOLF, Joachim (Karlsruhe Institute of Technology (KIT))
Presenters: Dr. WOLF, Joachim
Material: Slides
Included in session: Low-Background Workshop
Included in track: Low-background Workshop