Back to Basics: Energy Resolution of Room Temperature Semiconductor Detectors Through the Lens of BiI ₃

Abstract The energy resolution of the prototype spectrometer is one of the most cited figures when reporting the development of new promising room‐temperature semiconductor detectors (RTSDs) for gamma‐ray spectroscopy. As the search for new materials has expanded beyond the traditional nuclear field, it is important to recall best practices on how to characterize the energy resolution of a detector so that it can be properly compared with previously reported data in the literature and more effectively advance the field forward. Here, as part of this special edition, the path toward reporting comparable energy resolution is presented through the case study of BiI ₃ . Notwithstanding the essential optimization of single crystal growth, and detector manufacturing processes, as well as the fine‐tuning of detector electronics required for taking a promising material into a deployable detector, the evolution that took BiI ₃ single crystals detectors from barely able to collect a ²⁴¹ Am alpha spectrum to a first‐ever ²⁴¹ Am gamma spectrum, and eventually to demonstrate a ¹³⁷ Cs 662 keV gamma spectrum with 2.2% energy resolution is reviewed as a case study of RTSD research and development.