Direct Detection of Fast Neutrons by Organic Semiconducting Single Crystal Detectors

Fast neutron detection is significant for neutron imaging and flux monitoring but cannot be directly achieved by inorganic semiconductors. The traditional detection is mainly mediated by an organic scintillator and a coupled photodetector, resulting in signal losses. Here, a direct detection method for fast neutrons is demonstrated based on organic semiconducting single crystals (OSSCs) detectors. Methyl 4-hydroxybenzoate (4MHB, C₆H₅O-COOCH₃) and 4-hydroxycyanobenzene (4HCB, C₆H₅O-CN). The organic semiconductor acts as a fast neutron sensitive material due to its high hydrogen density, simultaneously as a semiconductor that generates the electric signal. The detectors based on 4MHB crystals can quantitatively measure the dose and energy of the fast neutron flux with a response time of 0.5 µs and detection efficiency of 78.5% cm⁻³. Effects of functional groups on fast neutron detection performances are also investigated as a guideline to synthesis new molecules for this purpose. Furthermore, neutron radiation effects on these detectors are investigated. Hydrogen-related point defects are generated by fast neutrons, but device performances remain robust after irradiation of 10¹³ n cm⁻² fast neutrons. This study demonstrates that OSSCs show great potential as direct fast neutron detectors and particularly have highly-localized and tissue-equivalent properties that benefit neutron imaging and cancer therapy applications.