# Fast-, Light-Cured Scintillating Plastic for 3D-Printing Applications
## 2 Materials and Methods
### Scintillator Characterization  
For each scintillator, the hardness of the plastic scintillators was measured using a Shore A durometer. For the curing studies, the light emission spectrum of the scintillators was measured by a Horiba (Kyoto, Japan) FluoroMax Plus with an excitation wavelength of 380 nm. The relative light yield and PSD figure of merit (FoM) were measured for each scintillator. For the scintillators that leached (see Section 3.2.2 for details), the hazy film was cleaned off using mild soap and water before the measurements. Each scintillator was wrapped with two layers of MIL-T-27730A PTFE tape and coupled to a 2\" Hamamatsu (Shizuoka, Japan) R7724 PMT biased at \(-\)1050 V.The signals were recorded using CAEN (Viareggio, Italy) CoMPASS (version 1.5.3) software on a CAEN DT5730, a 500 MS/s, 14-bit waveform digitizer. Figure 1 plots examples of neutron and gamma waveforms from the AFIT101 plastic scintillator formulation as recorded by the digitizer. The pulse shape is similar to that of other organic scintillators. For each waveform, the pretrigger was set to 48 samples (96 ns), and the baseline was calculated using the first 40 samples (80 ns). The long gate was set to 400 ns, and the short gate was varied to optimize the PSD FoM for each scintillator. The short gate averaged approximately 23 samples (46 ns). Both the long and short gates began immediately after the 40-sample baseline window. The relative light yield of the scintillators was compared to EJ-276 [13] and measured using the Compton edges from the 0.511 MeV (0.341 MeV) and 1.275 MeV (1.062 MeV) \({}^{22}\)Na gamma rays and the 0.662 MeV (0.478 MeV) \({}^{137}\)Cs gamma ray. The EJ-276 plastic scintillator was a bare 1\" diameter \(\times\) 1\" long right circular cylinder, dated 30 October 2020 from the manufacturer, which has known aging degradation [15, 19, 20]. It was removed from its nitrogen-environment shipping container on 26 April 2021 for its first use in measurements. The Compton edge location in the recorded spectrum was determined by fitting a half-Gaussian distribution to the edge as shown in Figure 2 for the \({}^{22}\)Na 0.511 MeV (0.341 MeV) gamma ray in EJ-276. The Compton edge, which was used for comparing the relative light yield between scintillators, was calculated as  
\[CE=\mu+\sigma\sqrt{2\ln 2}, \tag{1}\]  
where \(\mu\) and \(\sigma\) are the mean and standard deviation of the Gaussian distribution [21]. For each scintillator, including EJ-276, the average and standard deviation of each of the three Compton edges were calculated from multiple measurements of each scintillator. The relative light yield was then calculated as the ratio of the average Compton edge for each scintillator to EJ-276 for each of the three Compton edges. The reported relative light yield is an average of the three relative light yields obtained for each scintillator for the three Compton edges measured. This approach in locating the Compton edge introduces potential bias [22] and does not take into account effects such as multiple scattering [23]. Since this potential bias was comparable in the scintillators and EJ-276 measurements (\(<\)0.5% difference), calculating relative light yield minimizes the potential impact of this bias [22]. Second, neutron and gamma-ray induced events were discriminated using the waveform charge integration PSD as shown in Figure 3a [24]. After calibrating the energy of  
Figure 1: Example recorded waveforms for a neutron (orange) and gamma-ray (blue) event in AFIT101 using a Caen DT5730 digitizer. Each waveform is the average from all the pulses between 0.9 and 1.1 MeVee and a PSD of 0.10–0.14 for gamma rays and 0.19–0.23 for neutrons. Figure 2: An example \({}^{22}\)Na pulse integral spectrum from EJ-276 illustrating the half-Gaussian fit to the 0.511 MeV gamma-ray Compton edge (0.341 MeV). the spectrum using the Compton edges from the 0.511 MeV, 0.662 MeV, and 1.275 MeV gamma rays, a PSD histogram was generated from the events between 450 and 550 keVee.