Boron-Loaded Polymeric Sensor for the Direct Detection of Thermal Neutrons

We report the first demonstration of a solid-state, direct-conversion sensor for thermal neutrons based on a polymer/inorganic nanocomposite. Sensors were fabricated from ultrathick films of poly(triarylamine) (PTAA) semiconducting polymer, with thicknesses up to 100 μm. Boron nanoparticles (NPs) were dispersed throughout the PTAA film to provide the neutron stopping power arising from the high thermal neutron cross section of the isotope ¹⁰B. To maximize the quantum efficiency (QE) of the sensor to thermal neutrons, a high volume fraction of homogeneously dispersed boron nanoparticles was achieved in the thick PTAA film using an optimized processing method. Thick active layers were realized using a high molecular weight of the PTAA so that molecular entanglements provide a high cohesive strength. A nonionic surfactant was used to stabilize the boron dispersion in solvent and hence suppress the formation of agglomerates and associated electrical pathways. Boron nanoparticle loadings of up to ten volume percent were achieved, with thermal neutron quantum efficiency estimates up to 6% resulting. The sensors' neutron responses were characterized under a high flux thermal neutron exposure, showing a linear correlation between the response current and the thermal neutron flux up to ∼10⁷ cm^-2 s^-1. Polymer-based boron nanocomposite sensors offer a new neutron detection technology that uses low-cost, scalable solution processing and provides an alternative to traditional neutron sensors that use rare isotopes, such as ³He.