3D Printing of Scintillating Materials
Scintillating materials are commonly used in charged particle detectors as detector elements due to their ease of manufacture, relatively low cost, and good timing resolution. The most common type of scintillator is the plastic scintillator, in which wavelength shifting dopants are embedded in a polystyrene matrix. A charged particle, traversing the polystyrene base excited some of the polymer molecules, causing them to emit UV light upon recombination. Typically, 2,5-diphenyloxazole (PPO) is used as a first step to down-convert the UV light to longer wavelength, peaking at 350nm. Due to the short absorption length of the polymer base in the UV range, a second wavelength shifting dopant, typically 1,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), with an emission wavelength peak at 410 nm is used to further shift the emitted light to the visible range, while keeping the wavelength short enough to be effectively detected by the detection element (usually a photocathode). Scintillators are nowadays typically made by either casting of a resin+hardener combination, or by extrusion of a molten scintillator. These cast or extruded scintillator bar are t hen machined to the required geometry using standard machining techniques (note that the low melting/softening point of scintillators and to the requirements of a clean surface for ligh t collection places severe constraints on the requirements f rom the machine shop, i.e., low temperature machining and extreme cleanliness with the additional need to polish the sci ntillator parts after machining). We note that while cast sci ntillators are more versatile in their possible designs, they su ffer from long production times (up to 2 weeks for polymerization) and are also not amenable to complex geometries due to the requirement of producing a complicated mold. We approach the problem of scintillator manufacturing differently. Rather than taking a top-down approach (i.e. machining a solid block into a preferred shape subtractive manufacturing), we take a bottom-up approach, using newly developed 3D printing techniques to directly print the requir ed