Validation of a model for radon-induced background processes in electrostatic spectrometers

Abstract

The Karlsruhe Tritium Neutrino (KATRIN) experiment investigating tritium βdecay close to the endpoint with unprecedented precision has stringent requirements on the background level of less than 10 −2 counts per second. Electron emission during the α-decay of 219,220 Rn atoms in the electrostatic spectrometers of KATRIN is a serious source of background exceeding this limit. In this paper we compare extensive simulations of Rn-induced background to specific measurements with the KATRIN prespectrometer to fully characterize the observed Rn-background rates and signatures and determine generic Rn emanation rates from the pre-spectrometer bulk material and its vacuum components.

Simulation and measurement of the suppression of radon induced background in the KATRIN experiment

“…The secondary low-energy electrons produced in this process, can leave the trap, being counted by the detector as background events. Thus, a single radon decay, which can produce primary electrons from a few eV up to 200 keV, can lead to an elevated background rate for a limited time interval, until the energy of the primary electron is spent [5]. The length of the time interval depends on the pressure and the energy of the primary electron.…”

Status of the KATRIN Experiment and Prospects to Search for keV-mass Sterile Neutrinos in Tritium β-decay

“…A measurement with a cooled baffle system results in a background level equivalent to the one without radon induced events (blue squares). studied already in great detail in [20,21,22,23]. With test experiments at the prespectrometer it was shown that a single radon decay in the sensitive volume of the spectrometer can lead to very high background rates.…”

Modeling of electron emission processes accompanying radon-α-decays within electrostatic spectrometers

“…Our model allows for consecutive IC processes in case the initial de-excitation process does not result in a ground state configuration of the polonium daughter. We also include the rare IC process of the decay 220 Rn → 216 Po * [19], but its contribution is negligible for the investigations in [9,10]. As mentioned above, the emission Table 2.…”

“…To study the event topologies of electrons from the α-decay of 219,220 Rn atoms, and to estimate background rates and characteristics due to their subsequent trapping (for details, see [9,10]), a detailed code for particle trajectory calculations in the complex electromagnetic field configuration of the KATRIN spectrometer is required. This challenging task is met by the KATRIN simulation package Kassiopeia [32], which was validated by a variety of different measurements [10,12,13,33]. A Monte Carlo event generator was developed to model electron emission following 219,220 Rn α-decay and is described in section 3.1.…”

“…The implementation of this model into our simulation software will be discussed in section 3. Within section 4 we will outline the importance of the physics model implemented in this work in the light of our attendant publications [9,10,14].…”