This SBIR project will develop a non-hygrocopic amorphous glass scintillator for neutron/gamma dual particle sensing that possesses a high loading of transparent lead (Pb) nanoparticles. Dual-particle detection and imaging in a mixed field is currently based largely on liquid scintillators or trans-stilbene single crystals that exhibit a pulse-shape response that differs depending on the energy loss characteristics of the interacting neutron or gamma-ray. Both of these organic systems depend on differences in the relative fraction of light produced via either prompt singlet fluorescence or triplet-triplet annihilation. Typically, neutron interactions are distinguished by a greater portion of delayed luminescence in the optical pulse shape compared with equivalent pulses derived from gamma-ray interactions. However, degraded performance in the solution-grown stilbene crystals due to imperfections in the lattice, along with the high-cost, limited size, and low-fracture toughness has led to interest in non-crystalline organic scintillators, noting that we manufacture hand-held dual-particle imagers for which the stilbene scintillator crystals are by-far the largest cost-driver in the instrument. Recently, Sandia National Labs developed stable small-molecule organic glass scintillators (OGSs) based on fluorine chromophores that have a fast luminescent response (< 300 ps), high light yield (~20,000 ph/MeV), and importantly, the ability to be melted and cast into transparent glasses via a relatively low-temperature process. Furthermore, tin-OGS has been developed that has a better photoelectric response than the equivalent pure organic. However, its tin loading is poor and the gamma-ray spectra is still dominated by the Compton continuum. The optical responses of lead nanoparticles are governed by their surface plasmon resonances, whose wavelength can modulated by varying the particle size. For our typical aqueous hydrothermal synthesis approaches that produce < 20 nm Pb quantum dots, the absorbance peak of the Pb-colloidal solution is at 300 nm, which is sufficiently far below the emission wavelength of the scintillating matrix that self-absorption can be minimized. Nevertheless, the degree of Pb-loading possible in the OGS solid has not yet been measured. During Phase I, we will quantify the scintillator performance (PSD figure of merit, gamma-ray and neutron light yields, luminescence decay, spectral characteristics) as the loading percentage is varied so that imaging prototypes can be fabricated during Phase II.
