Multi-MeV Gamma Interaction Position Estimation in Large Pure Cherenkov Emitter Crystals

In this work, we study the Cherenkov light created by prompt-gammas in a monolithic and pure Cherenkov emitter crystal to achieve position estimation for Prompt-gamma Imaging (PGI). This approach relies in the exclusive use of Cherenkov light and could lead to a novel system concept with an effective background discrimination at a relatively low production cost. The detector consisted of a $25 \times 25 \times 10 \mathrm{~mm}^{\wedge} 3 \mathrm{PbF} 2$ crystal coupled to a $8 \times 8$ SiPM array and was mounted on a 2 D translation stage. Two tungsten blocks were used to form a 3 mm slit to collimate a 228 Th gamma source. The detector was shifted in increments of 3 mm in the Y -axis direction, while the collimation system and source were fixed. Four datasets were acquired at four different detector positions: $0 \mathrm{~mm}, 3 \mathrm{~mm}, 6 \mathrm{~mm}$, and 9 mm. The floodmaps from each dataset showed consistent distribution shifts across the four positions. However, the presence of noise/background in the results was significant and did not allow to achieve an accurate position estimation. The low signal-to-noise ratio and readout electronics used in the current setup pose limitations to the full potential of this approach. Next steps include the development of tailored readout electronics to enhance the Cherenkov light collection and testing the set-up in a proton beam line.