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

TL;DR

This paper develops detailed background models for NaI(Tl) detectors in the COSINE-100 dark matter experiment using Monte Carlo simulations, identifying key background sources and their contributions.

Contribution

It introduces comprehensive background models for COSINE-100's NaI(Tl) crystals based on simulations and measurements, including internal and external sources.

Findings

Average background level is 3.5 counts/day/keV/kg in 2-6 keV range.

Dominant background contributors are $^{210}$Pb and $^3$H.

Background sources are effectively identified and modeled.

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 $^{210}$Pb and $^3$H.