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Depth profile study of Pb-210 in the surface of an NaI(Tl) crystal

Authors
Yu, G. H.Ha, C.Jeon, E. J.Kim, K. W.Kim, N. Y.Kim, Y. D.Lee, H. S.Park, H. K.Rott, C.
Issue Date
3월-2021
Publisher
ELSEVIER
Keywords
Surface contamination; Depth profile; (210) Pb; (210) Po; NaI(Tl) crystal
Citation
ASTROPARTICLE PHYSICS, v.126
Indexed
SCIE
SCOPUS
Journal Title
ASTROPARTICLE PHYSICS
Volume
126
URI
https://scholar.korea.ac.kr/handle/2021.sw.korea/49538
DOI
10.1016/j.astropartphys.2020.102518
ISSN
0927-6505
Abstract
The surface Pb-210 is one of the main background sources for dark-matter-search experiments using NaI(Tl) crystals, and its spectral features associated with the beta-decay events for energies less than 60 keV depends on the depth distribution of Pb-210 in the surface of an NaI(Tl) crystal. Therefore, we must understand the profile of surface Pb-210 to precisely model the background measurement in the low-energy region for the low-background experiment using NaI(Tl) crystals. We estimate the depth profile of the surface Pb-210 contamination by modeling the measured spectrum of the alpha emission from the decay of Po-210 at the decay sequence of the surface Pb-210 contamination that is obtained using an Rn-222-contaminated crystal. In order to describe the energy spectra of the surface contamination we perform a log-likelihood fit of the measured data to a sum of Geant4 Mote Carlo simulations, weighted by an exponential curve as a function of the surface depth. The lowand high-energy events from the beta decay of surface Pb-210 are also modeled to improve the depth profile for shallow depths. We simulate the energy spectra from beta decays of Pb-210 that are exponentially distributed in the surface by following two exponential functions where the mean-depth coefficients are free parameters in the data fitting; we observed that the energy spectra are in good agreement with the measured data. (C) 2020 Elsevier B.V. All rights reserved.
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