  Plastic scintillator detectors are used in high energy physics as well as for
diagnostic imaging in medicine, beam monitoring on hadron therapy, muon
tomography, dosimetry and many security applications. To combine particle
tracking and calorimetry it is necessary to build detectors with
three-dimensional granularity, i.e. small voxels of scintillator optically
isolated from each other. Recently, the 3DET collaboration demonstrated the
possibility to 3D print polystyrene-based scintillators with a light output
performance close to that obtained with standard production methods. In this
article, after providing a further characterization of the developed
scintillators, we show the first matrix of plastic scintillator cubes optically
separated by a white reflector material entirely 3D printed with fused
deposition modeling. This is a major milestone towards the 3D printing of the
first real particle detector. A discussion of the results as well as the next
steps in the R&D is also provided.
