Eur. Phys. J. C (2018) 78: 490
https://doi.org/10.1140/epjc/s10052-018-5970-2

Regular Article - Experimental Physics

Background model for the NaI(Tl) crystals in COSINE-100

¹ Department of Physics and Astronomy, Sejong University, Seoul, 05006, South Korea
² Wright Laboratory, Department of Physics, Yale University, New Haven, CT, 06520, USA
³ Physics Institute, University of São Paulo, São Paulo, 05508-090, Brazil
⁴ Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
⁵ Korea Institue of Science and Technology Information, Daejeon, 34141, Republic of Korea
⁶ Department of Physics, Bandung Institute of Technology, Bandung, 40132, Indonesia
⁷ Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
⁸ Center for Underground Physics, Institute for Basic Science (IBS), Daejeon, 34126, Republic of Korea
⁹ Department of Science Education, Ewha Womans University, Seoul, 03760, Republic of Korea
¹⁰ Department of Physics, Sungkyunkwan University, Seoul, 16419, Republic of Korea
¹¹ Department of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin-Madison, Madison, WI, 53706, USA
¹² Department of Physics, Kyungpook National University, Daegu, 41566, Republic of Korea
¹³ Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea
¹⁴ Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
¹⁵ Department of Accelerator Science, Graduate School, Korea University, Sejong, 30019, South Korea

^* e-mail: ejjeon@ibs.re.kr

Received: 17 April 2018
Accepted: 1 June 2018
Published online: 12 June 2018

Abstract

The COSINE-100 dark matter search experiment is an array of NaI(Tl) crystal detectors located in the Yangyang Underground Laboratory (Y2L). To understand measured backgrounds in the NaI(Tl) crystals we have performed Monte Carlo simulations using the Geant4 toolkit and developed background models for each crystal that consider contributions from both internal and external sources, including cosmogenic nuclides. The background models are based on comparisons of measurement data with Monte Carlo simulations that are guided by a campaign of material assays and are used to evaluate backgrounds and identify their sources. The average background level for the six crystals (70 kg total mass) that are studied is 3.5 counts/day/keV/kg in the (2–6) keV energy interval. The dominant contributors in this energy region are found to be Pb and H.