Additive Manufacturing of Organic Glass Scintillators

Project Overview

Scintillators are a fundamental technology that enables detection of radiation. Plastic scintillators have been of particular interest due to their suitable performance, comparatively lower cost in relation to ceramic scintillators, and enhanced robustness and environmental safety compared to liquid scintillators. Organic glass scintillators (OGS) have also been of interest due to their enhanced performance as a bulk material as well as a plastic scintillator dopant. Despite these advances, fabrication of scintillators has generally remained encumbered by long fabrication times and lengthy post-processing, which includes machining. Here, we explore two additive manufacturing (AM) methods to enable plastic scintillator fabrications with OGS dopants. These methods include fused filament fabrication (FFF), which includes extrusion of a heated plastic filament, and digital light processing (DLP), which utilizes projection of an ultraviolet (UV) image onto a photosensitive resin to facilitate conversion of the liquid resin into a solid. Both of these techniques were also explored for their capability to make bulk scintillators as well as a multimaterial fabrication platform to enable all-in-one detector fabrication. The main OGS dopant here is bis(9,9-dimethylfluoren-2-yl)diphenylsilane (P2) and the secondary dye is 1,4-bis(2-methylstyryl)benzene (bis-MSB).

Each AM method is suitable for various applications, with each technique also including various hurdles that might preclude adoption of AM scintillators for scientific use. The extruded-filament approach in FFF is interesting for its ease of multimaterial printing, and through design and tailoring of various print parameters, can achieve transparency in undyed transparent filament. However, solubility of P2 OGS in plastic filament material is relatively poor, resulting in opaque filaments not-suitable for printing. Use of other traditional scintillating dyes enables transparency in plastic filaments, though care must be taken to prevent thermal degradation of dyes in the FFF extrusion process. Transparent plastics can be made with OGS through the use of photopolymer resins for use in DLP processes. Photopolymer resins can be tuned to enhance solubility of OGS in photopolymer resins. OGS-based photopolymer resins explored here are transparent and printable, and have light outputs roughly around 5,000 photons/MeV and pulse shape discrimination figure of merits around 1.46-1.56. Further research in this area should explore chemical modifications of OGS to enhance solubility in plastic filaments for FFF as well as utilization of different photopolymer resin formulations to enhance performance in DLP/other photopolymer AM approaches.

Mission Impact

Scintillators are of significant importance in Lawrence Livermore National Laboratory mission spaces. Exploring new methods for fabricating scintillators enhances mission readiness, and also enhances lab related nonproliferation efforts in addition to developing science and technology tools and capabilities to meet future national security challenges.