Development of an Electron-Tracking Compton Camera using CF4 gas at high pressure for improved detection efficiency

We have developed an Electron-Tracking Compton Camera (ETCC) for medical imaging and MeV gamma-ray astronomy. The ETCC consists of a gaseous Time Projection Chamber (μμ-TPC) and pixel scintillator arrays. To improve the detection efficiency, we have optimized the gas mixture in the μμ-TPC and operated the ETCC at high pressure. Basic characteristics such as the gas gain, drift velocity, energy resolution, and position resolution of the μμ-TPC were examined, and using this optimization, both the efficiency and the angular resolution of the ETCC were measured. We achieved a steady gas gain of ∼20,000∼20,000 in Ar/CF4/isoC4H10 (54:40:6) at 1.4 atm. The diffusion constant in Ar/CF4/isoC4H10 (54:40:6) at 1.4 atm was ∼2∼2 times better than in Ar/C2H6 (90:10) at 1 atm. The efficiency in Ar/CF4/isoC4H10 (54:40:6) at 1.4 atm was also ∼2∼2 times higher than in Ar/C2H6 (90:10) at 1 atm.