Hamburg 2016 – wissenschaftliches Programm
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T: Fachverband Teilchenphysik
T 6: Neutrinomasse I
T 6.6: Vortrag
Montag, 29. Februar 2016, 12:20–12:35, VMP5 SR 0079
Vacuum simulation of the KATRIN radon background — •Joachim Wolf for the KATRIN collaboration — Karlsruher Institut für Technologie (KIT), IEKP, Postfach 3640, 76021 Karlsruhe
The objective of the KATRIN experiment at KIT is the measurement of the electron neutrino mass. A central component is the Main Spectrometer (1240 m3), where the energy of the β-electrons from tritium decay (18.6 keV) will be measured close to the endpoint of the spectrum. The pumping system of the ultra-high vacuum vessel consists of turbo-molecular pumps, a large-scale getter pump (up to 3000 m NEG strips, St707) and three cryo-baffles at LN2 temperature, designed to maintain a pressure in the range of 10−11 mbar. The NEG strips, as well as the stainless steel walls are known to emanate small amounts of radon atoms, increasing the intrinsic background rate, which would limit the sensitivity for the neutrino mass. The cryogenic copper baffles in front of the NEG pumps capture most of the radon, before it decays in the main volume. However, radon does not stick to the cold surface indefinitely. If it desorbs after a limited residence time, it can contribute again to the background rate.
This talk describes the simulation of this radon background with the Test-Particle Monte Carlo (TPMC) code MolFlow+ and compares the results with measurements. We modified the original MolFlow+ code, and added two new, time-dependent features, (i) a finite residence time for all adsorbing surfaces, and (ii) a finite half-life of the test particles. Results are presented for different radon isotopes. This work has been supported by the German BMBF (05A14VK2).