Contents lists available at ScienceDirect Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso Investigation of cosmic-ray induced background of Germanium gamma spectrometer using GEANT4 simulation Nguyen Quoc Hung a, ⁎ , Vo Hong Hai a,b , Masaharu Nomachi c a Department of Nuclear Physics, Faculty of Physics and Engineering Physics, VNUHCM-University of Science, 227, Nguyen Van Cu Street, District 5, Ho Chi Minh City, Viet Nam b Nuclear Technique Laboratory, VNUHCM-University of Science, 227, Nguyen Van Cu Street, District 5, Ho Chi Minh City, Viet Nam c Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan ARTICLE INFO Keywords: GEANT4 simulation HPGe Ge gamma spectrometer Cosmic-ray induced background Muons ABSTRACT In this article, a GEANT4 Monte Carlo simulation toolkit was used to study the response of the cosmic-ray induced background on a High-Purity Germanium (HPGe) gamma spectrometer in the wide energy range, up to 100 MeV. The natural radiation background measurements of the spectrometer were carried out in the energy region from 0.04 to 50 MeV. The simulated cosmic-ray induced background of the Ge detector was evaluated in comparison with the measured data. The contribution of various cosmic-ray components including muons, neutrons, protons, electrons, positrons and photons was investigated. We also analyzed secondary particle showers induced by the muonic component. 1. Introduction Germanium (Ge) gamma spectrometers have been useful tools for analyzing radionuclides in environmental and food samples due to high efficiency and low background. The sensitivity of a Ge spectrometer is influenced by its detection efficiency, energy resolution and the natural radiation background sources at the measurement site. The background spectrum measured by a Germanium detector results from environ- mental gamma radiation, 222 Rn and its gamma-ray-emitting daughters in the shield, cosmic rays and an intrinsic contamination of Ge detector and shield materials (Heusser, 1986; Heusser, 1993; Heusser, 1994; Vojtyla, 1996). To reduce the environmental gamma radiation, the Ge detector is mounted inside a passive shielding made of low-activity lead, iron or copper that is able to suppress most of the radiation from outside. To reduce a contribution from 222 Rn and its daughters, nitrogen gas has been used to flush the shield. Cosmic rays component can be suppressed in underground laboratories or in ground labora- tories if anticoincidence system is used Heusser (1993) and Thomas et al. (2013). More recently Cagniant et al. (2015) used a cosmic veto to design a new versatile ultralow background photon spectrometer installed in a ground laboratory level. To understand the effect of cosmic rays to the Ge gamma spectro- meters, there have been some works experimentally to study the cosmic-ray induced background to the Ge detector (Haines et al., 2011; Solc et al., 2014; Bikit et al., 2014). Cosmic rays can contribute to the background spectrum because of their penetrating power and large number of physical processes leading to background induction. An effective way to understand a contribution of cosmic rays to the Ge detector background is to use a Monte Carlo simulation of the detector background (Vojtyla, 1995; Vojtyla, 1996; Joković et al., 2009; Breier and Povinec, 2010; Solc et al., 2014). However, these studies were mostly compared without measured data (Vojtyla, 1995; Vojtyla, 1996; Joković et al., 2009; Breier and Povinec, 2010) or with the Ge-detector background measured bellow 25 MeV (Solc et al., 2014). The aim of this work was to study the response of cosmic-ray induced background in a High-Purity Germanium (HPGe) gamma spectrometer using GEANT4 simulation toolkit. The background measurements were carried out at ground laboratory level up to 50 MeV and compared with simulation data. We investigate contributions of cosmic-ray components, including muons, neutrons, protons, electrons, positrons and photons on the background spectrum. We also analyzed secondary particle showers induced by the muonic component. The simulations and analysis of the deposited energy in the Ge-detector by cosmic rays were carried out in the wide energy range, up to 100 MeV. 2. Materials and methods 2.1. Experimental set-up The HPGe detector (Canberra model GC2018) (Canberra, 2013) is of http://dx.doi.org/10.1016/j.apradiso.2016.12.047 Received 26 August 2016; Received in revised form 29 November 2016; Accepted 21 December 2016 ⁎ Corresponding author. E-mail address: nqhung@hcmus.edu.vn (N.Q. Hung). Applied Radiation and Isotopes 121 (2017) 87–90 Available online 28 December 2016 0969-8043/ © 2016 Elsevier Ltd. All rights reserved. MARK