# VCI2019 - The 15th Vienna Conference on Instrumentation

18-22 February 2019
Vienna University of Technology
Europe/Vienna timezone

## Innovative $\gamma$ detector filled with high-density liquid for brain PET imaging

21 Feb 2019, 11:55
20m
EI8 ()

### EI8

Talk Medical Applications

### Speaker

Morgane Farradèche (IRFU / CEA Saclay, France)

### Description

CaLIPSO is an innovative $\gamma$ detector designed for high precision cerebral PET imaging. For the first time, liquid trimethylbismuth is used as sensitive medium. The detector operates as a time-projection chamber and detects both Cherenkov light and charge signal. Indeed, each 511-keV photon releases a single primary electron that triggers a Cherenkov radiation and ionizes the medium. As trimethylbismuth has never been studied before, we measured its free ion yield that represents the number of electron-ion pairs released by the primary electron. To do so, we developed a low-noise measuring system to determine the weak current induced by a $^{60}$Co source in the liquid with an accuracy better than 5 fA for a strong electric field up to 7 kV/cm. We used tetramethylsilane as benchmark liquid to validate the apparatus and we measured a zero-field free ion yield of $0.53 \pm 0.03$ in agreement with measurements in literature. However, we found a zero-field free ion yield of $0.083 \pm 0.003$ for trimethylbismuth, which is a factor 7 lower than the typical values for similar dielectric liquids. Quantum chemistry computations on heavy atoms tend to demonstrate the high ability of trimethylbismuth to capture electrons, which could explain this weak value. This recombination mechanism marks a new step in understanding charge transport in liquid detectors.

### Primary authors

Morgane Farradèche (IRFU / CEA Saclay, France) Gérard Tauzin (IRFU / CEA Saclay, France) Jean-Philippe Mols (IRFU / CEA Saclay, France) Jean-Pierre Bard (IRFU / CEA Saclay, France) Jean-Pierre Dognon (IRAMIS / CEA Saclay, France) Viatcheslav Sharyy (IRFU / CEA Saclay, France) Dominique Yvon (IRFU / CEA Saclay, France)