High-resolution 3D-printed plastic scintillators with tertiary dye

TL;DR

The study addresses the trade-off between geometric resolution and scintillation performance in additive manufacturing of plastic scintillators by introducing a tertiary dye, coumarin 450, to limit cure depth at 405 nm. By comparing two-dye and three-dye formulations under bulk curing and vat-based 3D printing, the authors demonstrate substantial improvements in print fidelity (down to 0.7 mm external, 0.1 mm internal features) with minimal loss in light output or PSD performance. The resulting materials yield LO up to ~50% of EJ-200 and PSD FoM up to 1.35 in the 0.9–1.1 MeVee range, while enabling complex geometries such as sub-millimeter internal channels and embedded structures. This approach expands the design space for custom radiation detectors, particularly where conventional machining is impractical, and points to future work in inert environments and optimized resin chemistries to further close the gap with commercial scintillators.

Abstract

Additive manufacturing offers efficient production of plastic scintillators with nontrivial geometries using vat polymerization, allowing fabrication of geometries which would be difficult or even impossible to produce using conventional subtractive manufacturing. This work presents a novel photocurable scintillator formula that includes coumarin 450 as a tertiary dye to enable high-resolution 3D printing via the manipulation of the 405 nm cure light. Bulk photocured and 3D printed (with and without tertiary dye) samples were compared through observational assessment and spectral response. All samples showed pulse shape discrimination between neutron and gamma events. Inclusion of the tertiary dye has minimal impact on emission spectrum and light output, but significant impact on print resolution as shown by comparison of printed high-complexity geometries and feature resolution test objects. With the use of a cure-limiting dye, unsupported features, such as freestanding pillars, were resolvable down to 0.7 mm. Even finer resolution at or below 0.1 mm was achieved in fully supported, integrated structures printed with off-the-shelf 405 nm desktop 3D printer. Scintillators demonstrated a light output up to 50% of EJ-200 with a PSD figure of merit up to 1.35 at 0.9-1.1 MeVee.

Figures (15)

• Figure 1: Printer assembly setup with vat polymerization SL1S 3D printer (center left), CW1S (far left), and post-curing FX-1250 lamp (center right and far right).
• Figure 2: Models for 3D printing resolution test samples featuring a) a model with external pins and internal holes that have diameters ranging from 1.5 mm to 0.5 mm in steps of 0.05 mm, internal horizontal holes with diameters ranging from 3.5 to 1.0 mm in steps of 0.25 and 0.10 mm, and b) a model with internal vertical hole features with diameters from 3.5 to 1.0 mm in steps of 0.25 and 0.10 mm.
• Figure 3: Absorption & emission spectra for a) each major fluorescent component of the resin formulas and b) the interaction between PPO emission & exalite 416 absorption, PPO emission & coumarin 450 absorption, and coumarin 450 absorptions & TPO absorption.
• Figure 4: Decay of purple discoloration over 14 days, shown by a) a 3D printed scintillator immediately after printing, b) the same geometry 3 days after printing, c) the now cut and polished geometry 7 days after printing, and d) the same scintillator 14 days after printing with no purple discoloration.
• Figure 5: Comparison of final bulk photocured and 3D printed scintillators: a) a commercially thermal cured EJ-200 for comparison, b) the two-dye formula after bulk curing and polishing, c) the same two-dye formula after 3D printing and polishing, and d) the three-dye formula after 3D printing and polishing.