Contents lists available at ScienceDirect Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso Validation of gamma scanning method for optimizing NaI(Tl) detector model in Monte Carlo simulation Huynh Dinh Chuong a , Nguyen Quoc Hung b , Nguyen Thi My Le b,c , Vo Hoang Nguyen b , Tran Thien Thanh a,b,∗ a Nuclear Technique Laboratory, University of Science, VNU-HCM, Viet Nam b Department of Nuclear Physics, Faculty of Physics and Engineering Physics, University of Science, VNU-HCM, Viet Nam c Faculty of Applied Sciences, Ho Chi Minh City University of Technology and Education, Viet Nam HIGHLIGHTS • A model for NaI(Tl) detector was optimized according to the experimental results of the scanning on front and lateral surfaces of the detector with a collimated low-energy photon beams. • The measured efciencies with energies between 30 and 1408 keV for point sources at distances of 0 cm and 30 cm from source to detector were determined. • The simulated efciencies were calculated using MCNP6 code. • Good agreement was obtained between measured and simulated efciencies for the optimized model. ARTICLEINFO Keywords: NaI(Tl) detector Gamma scanning Monte Carlo simulation MCNP6 code Efciency calibration ABSTRACT The aim of this study is the validation of gamma scanning method for optimizing NaI(Tl) detector model in Monte Carlo simulation. The experimental procedure involved: scanning on front and lateral surfaces of the detector with collimated low-energy photon beam; calibrating the efciency with energies between 31-1408 keV for point sources at distances of 0 cm and 30 cm from source to the detector. The Monte Carlo code used for the simulations was MCNP6. The diameter and the length of crystal were determined according to the measured results of gamma scanning with a collimated 241 Am radioactive source. The distance from window to crystal was estimated using transmission measurement recorded on a second detector. The density of refector was adjusted to obtain the match between measured and simulated values of efciency ratio of 81 and 31 keV from a 133 Ba radioactive source. The optimized model was applied in Monte Carlo simulations to determine the efciency and energy spectrum response function of NaI(Tl) detector for point source measurements in two confgurations. Good agreement was obtained between measured and simulated results. 1. Introduction Thallium-activated sodium iodide – NaI(Tl) detectors are commonly used for gamma-ray spectroscopy, mainly because of their high detec- tion efciency, easy maintenance and cost efectiveness. The important features of these detectors are the energy spectrum response function and the efciency, including full energy peak efciency (FEPE) and total efciency (TE). The accurate FEPE calibration curve of NaI(Tl) detectors is required for most of the radioactive monitoring applications (Grujic et al., 2013; Hung et al., 2016; Thanh et al., 2016). The TE calibration curve must be determined for several algorithms of true coincidence summing correction (Kanisch et al., 2009). Some applica- tions, such as full spectrum analysis (Caciolli et al., 2012) and spectral unfolding algorithm (Baré and Tondeur, 2011), demand also a good database of the energy spectrum response function generated by photon sources. The experimental determination of these features requires the preparation of standard sources, which is quite expensive and time consuming for the laboratories. Especially for in-situ measurements with large samples, such as the monitoring of radioactivity levels in the feld, marine environment, waste drum, surface contamination etc., the experimental calibration is very difcult. In such cases, the simulation techniques are more suitable. https://doi.org/10.1016/j.apradiso.2019.04.009 Received 19 August 2018; Received in revised form 7 March 2019; Accepted 5 April 2019 ∗ Corresponding author. Department of Nuclear Physics Faculty of Physics and Engineering Physics University of Science, VNU-HCM, 227, Nguyen Van Cu Street, District 5, Ho Chi Minh City, Viet Nam. E-mail address: ttthanh@hcmus.edu.vn (T.T. Thanh). Applied Radiation and Isotopes 149 (2019) 1–8 Available online 10 April 2019 0969-8043/ © 2019 Elsevier Ltd. All rights reserved. T