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Figure 1.

The two timing coincidence apparatuses.

The two timing coincidence apparatuses. In (a) the standard coincidence apparatus, used in this paper to measure the timing performance with the scintillator crystal length, L is shown. In (b) the depth of interaction (DOI) coincidence apparatus is seen. In this, the measured scintillator detector is rotated 90 degrees, with respect to the reference scintillator detector. In the standard coincidence apparatus the Na22 source is placed equidistant between the two scintillator detectors, whereas in the DOI coincidence apparatus the source is placed much closer to the measured scintillator detector. This leads to electronic collimation forming a confinement region within the measured scintillator detector. The confinement region is shown in grey surrounded by a red dashed line [1].

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Table 1.

Main SiPM parameters used for standard and DOI timing coincidence measurements.

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Figure 2.

Photograph of the DOI timing coincidence apparatus.

The timing coincidence apparatus set up for DOI measurements. The reference detector, shown on the left of the image, is a 2×2×5 mm3 Agile Ca-co-doped LSO:Ce wrapped in PTFE tape coupled to a Hamamatsu MPPC S10931-050P SiPM using Rhodorsil 47 V optical grease. On the right, the source is shown close to the 3D-printed clamp holding the same photodetector coupled to the scintillator crystal under investigation.

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Table 2.

Coincidence time resolution values for two identical polished 2×2×5 mm3 Ca-co-doped LSO:Ce wrapping in PTFE tape for standard and DOI measurements.

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Figure 3.

CTR against scintillator crystal length.

The CTR with scintillator crystal length is plotted for Proteus LYSO:Ce scintillator crystals of lengths 5, 10, 15, 20 and 30 mm. All crystals possess a cross section of 2×2 mm2.

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Table 3.

Standard coincidence apparatus measurements for two identical polished Proteus LYSO:Ce scintillator crystals wrapped in PTFE tape.

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Figure 4.

Number of valid γγ events detected against DOI for 30 mm LYSO:Ce scintil- lator crystals.

The number of γγ events recorded with DOI for two Proteus 2×2×30 mm3 LYSO:Ce scintillator crystals. A uniform distribution convolved with a Gaussian distribution with FWHM of 1 mm is plotted as a dashed black line.

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Figure 5.

CTR against DOI for 30 mm LYSO:Ce scintillator crystals.

Coincidence time resolution (CTR in ps) versus the depth of interaction (DOI in mm) for two Proteus 2×2×30 mm3 LYSO:Ce scintillator crystals in the wrapped and unwrapped configurations. Measurements are alternated with increasing DOI to check for any systematic error introduced by individual LYSO:Ce scintillator crystals.

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Table 4.

Mean values for energy and timing performance of 30

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Figure 6.

Delay peak centroid against DOI for 30 mm LYSO:Ce scintillator crystals.

The delay peak centroid versus the depth of interaction plotted for two Proteus 2×2×30 mm. LYSO:Ce scintillator crystals in the unwrapped and wrapped configurations. The plateau is seen in all measurements at a DOI of approximately 20 mm.

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Figure 7.

Energy resolution against DOI for 30 mm LYSO:Ce scintillator crystals.

The energy resolution (%) versus the depth of interaction plotted for two Proteus 2×2×30 mm3 LYSO:Ce scintillator crystals in the unwrapped and wrapped configurations. For a DOI greater than 5 mm, the mean energy resolutions are 16.52±0.02% and 13.92±0.01% for the unwrapped and wrapped configurations respectively.

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Figure 8.

Light output against DOI for 30 mm LYSO:Ce scintillator crystals.

The right photopeak centroid versus the depth of interaction for two identical LYSO:Ce scintillator crystals of shape 2×2×30 mm3 in the wrapped and unwrapped configurations. The right photopeak centroid corresponds to the absolute light output of the scintillator detector under investigation.

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Figure 9.

Number of valid γγ events detected against DOI for 20 mm LSO:CeCa scintillator crystals.

Three configurations shown for a 2×2×20 mm3 LSO:CeCa scintillator crystal. In this we see that the partially wrapped and wrapped configurations shown good alignment, whereas the unwrapped shows poor. This will result in fewer events being collected and thus a larger error in higher DOI measurements.

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Figure 10.

CTR against DOI for 20 mm LSO:CeCa scintillator crystals.

The coincidence time resolution is plotted versus the depth of interaction for three configurations of a 2×2×20 mm3 LSO:CeCa scintillator crystal. Wrapped refers to covering all faces except that in contact with the photodetector in PTFE tape. Partially wrapped has only the side faces covered in PTFE tape leaving the face in contact and opposite the photodetector unwrapped. Unwrapped refers to no covering.

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Table 5.

Mean values for energy and timing performance of 20

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Figure 11.

Delay peak centroid against DOI for 20 mm LSO:CeCa scintillator crystals.

The delay peak position with depth of interaction is plotted for a LSO:CeCa scintillator crystal of shape 2×2×20 mm3 for the unwrapped, partially wrapped and wrapped configurations.

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Figure 12.

Energy resolution against DOI for 20 mm LSO:CeCa scintillator crystals.

The energy resolution (%) for a LSO:CeCa scintillator crystal of shape 2×2×20 mm3 for the unwrapped, partially wrapped and wrapped configurations.

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Figure 13.

Light output against DOI for 20 mm LSO:CeCa scintillator crystals.

The right photopeak centroid plotted against the depth of interaction for a LSO:CeCa scintillator crystal of shape 2×2×20 mm3 for the unwrapped, partially wrapped and wrapped configurations. The photopeak centroid corresponds to the light output of the scintillator detector.

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