Nanocomposite Radiation Detectors for Gamma-Ray Spectroscopy

The development of spectroscopic gamma-ray detectors requires the optimization of several factors, such as the growth of a relatively thick (>1 mm), defect-free, and compositionally uniform radiation-sensitive medium, the extraction of radiation-induced carriers from the medium without loss, a good response linearity between the radiation energy and the number of collected carriers, and the long-term stability in an ambient environment. We review recent advances in the structural design of novel gamma detector systems based on nanoparticles (NPs), including nanocrystals (NCs). The use of NPs in gamma-ray detection has been attracting great attention recently, due to their enhanced optical properties, favorable carrier multiplication condition, low-cost fabrication, and improved chemical properties with stability. Many different fabrication approaches have been adopted for indirect and direct detectors. The indirect detector can be realized by both luminescent NCs and non-luminescent (or weakly luminescent) NPs with high atomic numbers. A proper polymerization process leads to a uniform and high loading of NPs in a large volume, which protects the NPs from oxidation. Furthermore, additional types of composites, including fluorescent dyes or cosolvent, may facilitate efficient charge carrier transfer to linearly convert the incident gamma-ray energy into the number of scintillation photons with negligible loss. The direct detector is implemented by interconnecting NCs with high packing density and mitigating crack formation to extract radiation-induced charge carriers to electrodes across millions of NCs and interfaces. In addition, controlling the NC size, ligand chain length, and NC dispersion state determines the leakage current level. To the best of our knowledge, several studies of NC-based gamma-ray detectors have recently demonstrated gamma spectroscopy capability in the last 10 years, showing improved energy resolution comparable to single-crystal gamma-ray detectors. This review will provide an in-depth overview of the current status and challenges in developing NP-based gamma detectors.