Speaker
Description
All-sky observations of MeV gamma rays are expected to play a crucial role in solving unresolved questions in high-energy astrophysics, such as the emission mechanisms of gamma-ray bursts and blazars. To that end, we propose an MeV gamma-ray mission concept, AMEGO-X. The gamma-ray detector onboard AMEGO-X consists of a silicon tracker and a CsI calorimeter. The silicon tracker is composed of an active target detector called AstroPix, which is currently under development and is expected to feature low power consumption (< 1.5 $mW$/$cm^2$) and a large depletion depth (500 $\mu m$) compared to other sensors. The third version of this sensor, AstroPix3, has a large pixel size of 500 × 500 $\mu m^2$ compared to other pixel sensors. Its depletion depth is estimated to be about 70 $\mu m$ under a bias voltage of 200$ V$, and it is important to investigate the distribution of the depletion depth in detail. However, such investigations have not yet been conducted. To address this, we conducted a scanning test using a collimated X-ray beam, generated from radioisotope source, which had a spot size of approximately $\sigma \sim$180 $\mu m$ on the sensor surface. The beam scanned across the chip in both horizontal and vertical directions at 100 $\mu m$ intervals, aligned with the pixel grid. As a result, we observed a Gaussian-like distribution of count rates within individual pixels. Furthermore, a Monte Carlo simulation based on Geant4 showed that the shape of the simulated count rate distribution closely matched the experimental data.
In this work, we report on the X-ray scanning evaluation of the AstroPix3 chip and comparisons with the results of the Monte Carlo simulations.
