FD-3D-GX (Fully-digital 3D imager for gamma and hard-X rays) focuses on time-resolved ultrafast phenomena using radiation from hard-X to gamma-rays, with applications in scientific and medical fields such as pump-and-probe spectroscopy and Time-of-Flight Positron Emission Tomography.

To address the limitations in detectors and acquisition techniques, the study proposes an innovative fully-digital 3D imager for gamma and hard-X rays. Key improvements include enhancing time resolution, spatial resolution (limited by multipixel approaches), and quantum efficiency, particularly for silicon-based detectors facing challenges with hard-X rays and gamma photons.  The approach involves using Separate Absorption and Multiplication regions Avalanche PhotoDiode (SAM-APD) based on III-V semiconductors, specifically GaAs-based materials. These materials offer higher efficiency and speed in absorbing hard-X rays compared to silicon. Capacitive coupling of a large-area GaAs SAM-APD to Cross Delay-Lines (CDLs) connected to Time-To-Digital-Converter (TDC) achieves spatial and temporal resolutions below 100 µm and 10 ps.

For gamma-rays, the same setup is employed by attaching a matrix of fast scintillator crystals to the GaAs SAM-APD, resulting in spatial and temporal resolutions limited by crystal geometry and jitter (500 µm and 200 ps, respectively). This approach, requiring only four channels and avoiding aggressive lithography, is considered a powerful alternative to pixelation both technologically and in terms of processing efficiency.