This article is an illustrated review of gamma ray spectroscopy with NaI(Tl) which fills in the gaps between theoretical treatments and the knowledge of experienced users. Practical Considerations for Gamma Ray Spectroscopy with NaI(Tl): A Tutorial Travis Smith and Kimberlee J. Kearfott* Abstract: Gamma ray spectroscopy enables the identification of radioactive sources, and, with proper calibration, their activities. In use since the 1950s, NaI(Tl) spectroscopic systems remain popular due to their affordability and high detection efficiency. The crystals and ac- companying electronics may vary, and there are practical choices necessary to produce the best possible spectra for a given application or correctly interpret system performance. An over- view of the scintillation mechanism as well as the common features of a gamma ray spectrum are presented in this paper. This includes a dis- cussion of the impacts of the size and shape of detector crystals on the spectrum and counting efficiency. A description of supporting electronics is included along with techniques for arranging and optimizing them. Coaxial cables become part of the circuit and can degrade the detector signal if they have mismatched impedance or excessive length. A discussion is included of tradeoffs involved in selecting combinations of individual electronics components for NaI(Tl) spectroscopic applications. Lastly, a comprehen- sive energy calibration procedure is provided. This paper thus serves as a tutorial on several practical aspects of a NaI(Tl) gamma ray spec- troscopy system. Health Phys. 114(1):94–106; 2018 Key words: operational topics; dosimetry, gamma; education, health physics; spectros- copy, gamma INTRODUCTION In radioactive decay, radionuclides can decay with the emission of an alpha particle, beta particle, or a nucleon (proton or neutron). Each particle requires different styles of detectors in order to record consis- tent, accurate measurements. For example, a sheet of paper can stop an alpha particle and few millime- ters of plastic can stop a beta particle. This makes it exceedingly difficult to measure these types of radioac- tive particles at a reasonable distance. Fortunately, most radionuclides emit gamma rays. Due to gamma rays having such high energies and no mass, they are far more pene- trating than alpha and beta parti- cles and can be detected from many meters away. Gamma rays from a particular radioisotope are monoenergetic, meaning they are all the same energy. In the case where a radioisotope emits multi- ple different gamma rays, there are two or more specific energies at which gamma rays are emitted. Using this information, if one can accurately measure the energy of nearby gamma rays, they would be able to tell which radioactive ele- ments are nearby. NaI(Tl) detectors are commonly used for gamma ray spectroscopy because they can mea- sure gamma rays and their respective energies with acceptable uncertainty. Uncertainty in gamma ray spec- troscopy is often quoted as an energy resolution, which is an important metric for spectroscopy systems. NaI(Tl) detectors are cost effective and practical spectroscopic radia- tion detectors. Due to their preva- lence, it is important for anyone who works in a radiation field to understand how to operate a NaI (Tl) detection system. Radiation detection is a complex process, and it requires knowledge of gamma ray interactions as well as the de- tection system in order to produce meaningful data. This reference introduces how NaI(Tl) detects ra- diation as well as a comprehensive documentation of all parts neces- sary for assembling and calibrat- ing a NaI(Tl) spectroscopy system. To understand how gamma spectroscopy works, it is important to understand the type of informa- tion produced by the detector. The gamma ray spectrum has a variety *Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109‐2104. The authors declare no conflicts of interest. Travis Smith is an aspiring health physicist who graduated from the University of Michigan with a bachelor’s degree in Nuclear Engineering and Radiological Sciences in May 2017. He is currently pursuing a doctoral degree in nuclear engineering at University of Tennessee, where he is the recipient of a Tennessee Fellowship for Graduate Excellence. His current research interests involve methods of radiation detection and public health applications of radiation safety. His email address is travissm@umich.edu. For correspondence contact: Kimberlee J. Kearfott, Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109‐2104, or email at kearfott@umich.edu. (Manuscript accepted 11 October 2017) Operational Topic 94 www.health-physics.com January 2018 Copyright © 2017 Health Physics Society. Unauthorized reproduction of this article is prohibited.