Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 6 1 2019 03 30 22 27 EN Iran Hassanzadeh Department of Nuclear Physics, School of Physics, University of Tabriz, Tabriz, Iran Armin Allahverdy Radiology Department, Sari School of Allied Medical Sciences, Mazandaran University of Medical Sciences Okhtay Jahanbakhsh Department of Nuclear Physics, School of Physics, University of Tabriz, Tabriz, Iran Alireza Khorrami Moghaddam Radiology Department, Sari School of Allied Medical Sciences, Mazandaran University of Medical Sciences 2018 07 31 2019 02 19 Purpose: In some gamma spectroscopy experiments, neutrons may also be present, so depending on experimental conditions, Gamma spectroscopy can be influenced by the presence of neutrons. Materials and Methods: In this study, a NaI(Tl)(63 mm×63 mm) detector is used to investigate the effects of fast neutrons on the spectrum of gamma photons. The radiation source used in these experiments is made up of two point sources: an AmBe (50 mCi) neutron source and a 137Cs(10 mCi) gamma source. Results: Results were determined through both measurements and Monte Carlo simulation (MCNPX) under two different experimental conditions and were compared. When the detector is placed under an angle to the source, gamma photon energy peaks resulting from inelastic interactions of the fast neutrons with the detector materials and surrounding materials in the energy range of 0.1-0.9(MeV) are pretty visible in the gamma main spectrum. These results can be used to optimize industrial tomography experiments carried out with NaI(Tl) scintillators. Conclusion: Also, the results show that the detection of fast neutrons with a NaI(Tl) scintillator is possible with low efficiency. https://fbt.tums.ac.ir/index.php/fbt/article/view/184 https://fbt.tums.ac.ir/index.php/fbt/article/download/184/119