Calibration sources for the LEGEND-200 experiment

In the search for a monochromatic peak as the signature of neutrinoless double beta decay an excellent energy resolution and an ultra-low background around the Q-value of the decay are essential. The LEGEND-200 experiment performs such a search with high-purity germanium detectors enriched in 76Ge immersed in liquid argon. To determine and monitor the stability of the energy scale and resolution of the germanium diodes, custom-made, low-neutron emission 228Th sources are regularly deployed in the vicinity of the crystals. Here we describe the production process of the 17 sources available for installation in the experiment, the measurements of their alpha- and gamma- activities, as well as the determination of the neutron emission rates with a low-background LiI(Eu) detector operated deep underground. With a flux of ( 4.27 ± 0.60stat ± 0.92syst) × 10-4 n / (kBq·s), approximately one order of magnitude below that of commercial sources, the neutron-induced background rate, mainly from the activation of 76Ge, is negligible compared to other background sources in LEGEND-200.

[1]  K. Rielage,et al.  The Large Enriched Germanium Experiment for Neutrinoless ββ Decay (LEGEND-1000 Preconceptual Design Report) , 2021 .

[2]  M. Misiaszek,et al.  Calibration of the Gerda experiment , 2021, The European Physical Journal C.

[3]  M. Misiaszek,et al.  Final Results of GERDA on the Search for Neutrinoless Double-β Decay. , 2020, Physical review letters.

[4]  F. E. Bertrand,et al.  Search for neutrinoless double- β decay in Ge76 with 26 kg yr of exposure from the Majorana Demonstrator , 2019, Physical Review C.

[5]  R. Kouzes,et al.  A Search for Neutrinoless Double-Beta Decay in 76 Ge with 26 kg-yr of Exposure from the Majorana Demonstrator , 2019 .

[6]  S. Schönert,et al.  Virtual depth by active background suppression: revisiting the cosmic muon induced background of Gerda Phase II , 2018, The European Physical Journal C.

[7]  S. Elliott,et al.  The Majorana Demonstrator calibration system , 2017, 1702.02466.

[8]  P. Felice,et al.  Production and characterization of 228Th calibration sources with low neutron emission for GERDA , 2015, 1508.05731.

[9]  J. Erler.  On the combination procedure of correlated errors , 2015, 1507.08210.

[10]  F. V. Massoli,et al.  Response of the XENON100 Dark Matter Detector to Nuclear Recoils , 2013, 1304.1427.

[11]  M. Tarka,et al.  Monte Carlo Studies and Optimization for the Calibration System of the GERDA Experiment , 2013, 1303.6679.

[12]  B. Wiegel,et al.  Production and characterization of a custom-made 228Th source with reduced neutron source strength for the Borexino experiment , 2011, 1110.1217.

[13]  D. Radford,et al.  A novel HPGe detector for gamma-ray tracking and imaging , 2011 .

[14]  Jing Liu,et al.  MaGe-a Geant4-Based Monte Carlo Application Framework for Low-Background Germanium Experiments , 2010, IEEE Transactions on Nuclear Science.

[15]  V. Méot,et al.  Preparation of 235mU targets for 235U(n,n′)235mU cross section measurements , 2008 .

[16]  X. Liu,et al.  Monte Carlo evaluation of the muon-induced background in the GERDA double beta decay experiment , 2007 .

[17]  K. Kroeninger,et al.  MaGe: A Monte Carlo framework for the Gerda and Majorana double beta decay experiments , 2006 .

[18]  M. J. Prata.  Solid angle subtended by a cylindrical detector at a point source in terms of elliptic integrals , 2002, math-ph/0211061.

[19]  Hayes,et al.  Review of Particle Physics. , 1996, Physical review. D, Particles and fields.