Sensitized Triplet Exciton Generation in Nanostructured Polymer Scintillators: Toward Improved γ/Neutron Discrimination

Scintillating materials emit light when exposed to ionizing radiation and are particularly useful for the detection of nuclear threats, medical imaging, and high-energy physics. A subset of these materials enables the discrimination of neutrons and charged particles from gamma-rays through pulse shape discrimination (PSD). This time-gated technique exploits that in these materials, the scintillation pulse shape depends on the nature of the incident radiation. The most used PSD materials are polymeric scintillators featuring triplet-triplet annihilation (TTA) based delayed fluorescence as the radiation fingerprint. We report here that sensitive and rapid PSD is achieved in nanostructured polymeric scintillators consisting in a solid polymer matrix and liquid nanodomains in which the TTA-active dye 9,10 diphenyl anthracene is dissolved. The liquid nature of the nanodomains renders TTA highly efficient, allowing delayed fluorescence to occur at low energy densities. We demonstrate that TTA is further enhanced by the inclusion of properly selected and dosed metalated porphyrin. The latter act as gamma/neutron discrimination sensitizers, doubling the density of annihilating triplets and increasing the time discrimination capability by 30% at event rates up to 1 MHz. Interestingly, these improvements are related to a sensitization effect that does not involve triplet-triplet energy transfer from metalated porphyrins.