https://doi.org/10.1140/epjc/s10052-022-10112-7
Regular Article - Experimental Physics
Study of naturally occurring radionuclides in the ECHo set-up
1
Physics Institute, University of Tübingen, Tübingen, Germany
2
Kirchhoff Institute for Physics, Heidelberg University, Heidelberg, Germany
a
alexander.goeggelmann@uni-tuebingen.de
Received:
11
November
2021
Accepted:
7
February
2022
Published online:
15
February
2022
The determination of the effective electron neutrino mass by analyzing the end point region of the 
Ho electron capture (EC) spectrum relies on the precise description of the expected Ho events and background events. In the ECHo experiment, arrays of metallic magnetic calorimeters, implanted with Ho, are operated to measure the Ho EC spectrum. In an energy range of 10 eV below 
, the maximum available energy for the EC decay of about 2.8 keV, a Ho event rate of the order of 
day
pixel is expected for an activity of 1 Bq of Ho per pixel. This means, a control of the background level in the order of 
day pixel is extremely important. We discuss the results of a Monte Carlo study based on simulations, which use the GEANT4 framework to understand the impact of natural radioactive isotopes close to the active detector volume in the case of the ECHo-1k set-up, which is used for the first phase of the ECHo experiment. For this, the ECHo-1k set-up was modeled in GEANT4 using the proper geometry and materials, including the information of screening measurements of some materials used in the ECHo-1k set-up and reasonable assumptions. Based on the simulation and on assumptions, we derive the expected background around and give upper limits of tolerable concentrations of natural radionuclides in the set-up materials. In addition, we compare our results to background spectra acquired in detector pixels with and without implanted Ho. We conclude that typical concentration of radioactive nuclides found in the used materials should not endanger the analysis of the endpoint region of the Ho EC spectrum for an exposure time of half a year.
© The Author(s) 2022
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