Eur. Phys. J. C (2025) 85: 1080
https://doi.org/10.1140/epjc/s10052-025-14333-4

Regular Article - Computing, Software and Data Science

Simulation of the background from $_{}^{13}$C${(\alpha ,n)}^{16}$O reaction in the JUNO scintillator

¹ Yerevan Physics Institute, Yerevan, Armenia
² Université Libre de Bruxelles, Brussels, Belgium
³ Universidade Estadual de Londrina, Londrina, Brazil
⁴ Pontificia Universidade Catolica do Rio de Janeiro, Rio de Janeiro, Brazil
⁵ Millennium Institute for SubAtomic Physics at the High-Energy Frontier (SAPHIR), Anid, Chile
⁶ Universidad Andres Bello, 700, Fernandez Concha, Chile
⁷ Beijing Institute of Spacecraft Environment Engineering, Beijing, China
⁸ Institute of High Energy Physics, Beijing, China
⁹ North China Electric Power University, Beijing, China
¹⁰ Tsinghua University, Beijing, China
¹¹ University of Chinese Academy of Sciences, Beijing, China
¹² College of Electronic Science and Engineering, National University of Defense Technology, Changsha, China
¹³ Chongqing University, Chongqing, China
¹⁴ Dongguan University of Technology, Dongguan, China
¹⁵ Jinan University, Guangzhou, China
¹⁶ Sun Yat-Sen University, Guangzhou, China
¹⁷ Harbin Institute of Technology, Harbin, China
¹⁸ The Radiochemistry and Nuclear Chemistry Group in University of South China, Hengyang, China
¹⁹ Wuyi University, Jiangmen, China
²⁰ Key Laboratory of Particle Physics and Particle Irradiation of Ministry of Education, Shandong University, Jinan, Qingdao, China
²¹ Nanjing University, Nanjing, China
²² Guangxi University, Nanning, China
²³ School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
²⁴ Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, China
²⁵ Nankai University, Tianjin, China
²⁶ Wuhan University, Wuhan, China
²⁷ Xi’an Jiaotong University, Xi’an, China
²⁸ Xiamen University, Xiamen, China
²⁹ School of Physics and Microelectronics, Zhengzhou University, Zhengzhou, China
³⁰ Institute of Physics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
³¹ National United University, Miao-Li, Taiwan
³² Department of Physics, National Taiwan University, Taipei, Taiwan
³³ Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
³⁴ Department of Physics, University of Jyvaskyla, Jyvaskyla, Finland
³⁵ IJCLab, CNRS/IN2P3, Université Paris-Saclay, 91405, Orsay, France
³⁶ CNRS, LP2I, UMR 5797, Univ. Bordeaux, 33170, Gradignan, France
³⁷ IPHC, CNRS/IN2P3, Université de Strasbourg, 67037, Strasbourg, France
³⁸ CNRS/IN2P3, CPPM, Aix Marseille Univ, Marseille, France
³⁹ SUBATECH, IMT Atlantique, CNRS-IN2P3, Université de Nantes, Nantes, France
⁴⁰ III. Physikalisches Institut B, RWTH Aachen University, Aachen, Germany
⁴¹ Institute of Experimental Physics, University of Hamburg, Hamburg, Germany
⁴² Forschungszentrum Jülich GmbH, Nuclear Physics Institute IKP-2, Jülich, Germany
⁴³ Institute of Physics and EC PRISMA+, Johannes Gutenberg Universität Mainz, Mainz, Germany
⁴⁴ Technische Universität München, Munich, Germany
⁴⁵ Helmholtzzentrum für Schwerionenforschung, Planckstrasse 1, 64291, Darmstadt, Germany
⁴⁶ Eberhard Karls Universität Tübingen, Physikalisches Institut, Tübingen, Germany
⁴⁷ INFN Catania and Dipartimento di Fisica e Astronomia dell Università di Catania, Catania, Italy
⁴⁸ Department of Physics and Earth Science, University of Ferrara and INFN Sezione di Ferrara, Ferrara, Italy
⁴⁹ INFN Sezione di Milano and Dipartimento di Fisica dell Università di Milano, Milan, Italy
⁵⁰ INFN Milano Bicocca and University of Milano Bicocca, Milan, Italy
⁵¹ INFN Milano Bicocca and Politecnico of Milano, Milan, Italy
⁵² INFN Sezione di Padova, Padua, Italy
⁵³ Dipartimento di Fisica e Astronomia dell’Università di Padova and INFN Sezione di Padova, Padua, Italy
⁵⁴ INFN Sezione di Perugia and Dipartimento di Chimica, Biologia e Biotecnologie dell’Università di Perugia, Perugia, Italy
⁵⁵ Laboratori Nazionali di Frascati dell’INFN, Rome, Italy
⁵⁶ University of Roma Tre and INFN Sezione Roma Tre, Rome, Italy
⁵⁷ Pakistan Institute of Nuclear Science and Technology, Islamabad, Pakistan
⁵⁸ Joint Institute for Nuclear Research, Dubna, Russia
⁵⁹ Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia
⁶⁰ Lomonosov Moscow State University, Moscow, Russia
⁶¹ Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava, Bratislava, Slovakia
⁶² High Energy Physics Research Unit, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
⁶³ National Astronomical Research Institute of Thailand, Chiang Mai, Thailand
⁶⁴ Suranaree University of Technology, Nakhon Ratchasima, Thailand
⁶⁵ Department of Physics, Oliver Lodge Laboratory, The University of Liverpool, Oxford Str., L69 7ZE, Liverpool, UK
⁶⁶ University of Warwick, CV4 7AL, Coventry, UK
⁶⁷ Department of Physics and Astronomy, University of California, Irvine, CA, USA
⁶⁸ Emirates Nuclear Technology Center (ENTC), Khalifa University, Abu Dhabi, United Arab Emirates
⁶⁹ Joint Institute for Nuclear Research, Dubna, Russia

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Received: 9 March 2025
Accepted: 20 May 2025
Published online: 30 September 2025

Abstract

Large-scale organic liquid scintillator detectors are highly efficient in the detection of MeV-scale electron antineutrinos. These signal events can be detected through inverse beta decay on protons, which produce a positron accompanied by a neutron. A noteworthy background for antineutrinos coming from nuclear power reactors and from the depths of the Earth (geoneutrinos) is generated by ($\alpha ,n$) reactions. In organic liquid scintillator detectors, $\alpha$ particles emitted from intrinsic contaminants such as $_{}^{238}$U, $_{}^{232}$Th, and $_{}^{210}$Pb/$_{}^{210}$Po, can be captured on $_{}^{13}$C nuclei, followed by the emission of a MeV-scale neutron. Three distinct interaction mechanisms can produce prompt energy depositions preceding the delayed neutron capture, leading to a pair of events correlated in space and time within the detector. Thus, ($\alpha ,n$) reactions represent an indistinguishable background in liquid scintillator-based antineutrino detectors, where their expected rate and energy spectrum are typically evaluated via Monte Carlo simulations. This work presents results from the open-source SaG4n software, used to calculate the expected energy depositions from the neutron and any associated de-excitation products. Also simulated is a detailed detector response to these interactions, using a dedicated Geant4-based simulation software from the JUNO experiment. An expected measurable $_{}^{13}$C${(\alpha ,n)}^{16}$O event rate and reconstructed prompt energy spectrum with associated uncertainties, are presented in the context of JUNO, however, the methods and results are applicable and relevant to other organic liquid scintillator neutrino detectors.