Abstract
The use of neutron sensors is a key requirement across many technology areas, including medical particle accelerators, nuclear power technologies, personnel dosimetry, national defence, and a wide range of scientific experiments. With a zero electric charge, neutrons present particular challenges for their effective detection. In the present study I report the first demonstration of a solid-state, direct conversion sensor for thermal neutrons based on a polymer/inorganic nanocomposite. Sensors were fabricated from ultra-thick films of poly(triarylamine) (PTAA) semiconducting polymer, with thicknesses up to 100 micrometres. Boron nanoparticles were dispersed throughout the PTAA film to provide the neutron stopping power arising from the high thermal neutron cross-section of the isotope Boron-10. To maximise the quantum efficiency of the sensor to thermal neutrons, a high volume fraction of homogeneously dispersed boron nanoparticles was achieved in the thick PTAA film using an optimised processing method. Thick active layers were realised using a high molecular weight of the PTAA (Mw=350 kg/mol), so that molecular entanglements provide a high cohesive strength. A non-ionic surfactant was used to stabilise the boron dispersion in solvent and hence suppress the formation of agglomerates and associated electrical pathways. Boron nanoparticle loadings of up to 17 vol.% were achieved, with thermal neutron quantum efficiency estimates up to 6 % resulting. The sensors’ neutron responses were characterised under a high flux thermal neutron exposure, showing a linear correlation between the response current and the thermal neutron flux. The sensitivity reached up to 194 pC at maximum thermal neutron flux. 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 Helium-3.