Performance of the AstroPix Prototype Module for the Barrel Imaging Calorimeter at the ePIC Detector and in Space-Based Payloads

TL;DR

AstroPix_v3 HV-CMOS sensors are developed for medium-energy gamma-ray detection and integrated into space- and collider-focused imaging layers such as the BIC and A-STEP. The paper reports tests on configurations from single-chip to nine-chip modules, demonstrating scalable, daisy-chained readout and synchronized Time-of-Arrival across multiple layers. Key findings include active-pixel yields around $99\%$, stable ToT in the $5$–$7\ μs$ range, and per-chip hit rates compatible with EIC and space environments (e.g., up to ~ $1.6$ kHz per chip; $925$ Hz per chip expected in EIC, $1$ Hz cm$^{-2}$ in space, $45$ Hz per chip for GRB), with a current per-pixel rate limit near $4$ Hz. The results validate AstroPix_v3 as a feasible imaging-layer technology for the BIC and A-STEP and outline plans to reach higher rates, full depletion, faster timing, and lower power.

Abstract

AstroPix is a high-voltage CMOS (HV-CMOS) monolithic active pixel sensor originally developed to enable precision gamma-ray imaging and spectroscopy in the medium-energy regime (approximately 100 keV-100 MeV) based on the groundwork laid by ATLASpix and MuPix. It features a 500 um pixel pitch, in-pixel amplification and digitization, and low power consumption (around 3-4 mW/cm^2), making it scalable for large-area, multilayer telescope detector planes. The detectors have a designed dynamic range of 25 keV to 700 keV. With these features, AstroPix meets the requirements of future space-based high-energy telescopes and the imaging layers of the Barrel Imaging Calorimeter (BIC) in the Electron-Proton/Ion Collider (ePIC) detector at the future Electron-Ion Collider (EIC). For the space-based payload, AstroPix is being integrated into sounding rocket and balloon payloads to demonstrate the technical readiness of the devices. For BIC, AstroPix-based imaging layers interleaved within the lead/scintillating-fiber (Pb/SciFi) sampling calorimeter provide granular shower imaging, enabling key performance features such as electron/pion or gamma/neutral-pion separation. As part of the ongoing detector R&D efforts, we have been testing various AstroPix v3 configurations: the single chip, a quad-chip assembly, a three-layer stack of quad chips, and a nine-chip module that represents the smallest prototype unit of the BIC imaging layer. This presentation will highlight recent performance test results from these AstroPix detector configurations.

Figures (8)

• Figure 1: Detector structure of A-STEP and ComPair-2 missions at NASA Goddard Space Flight Center (left) and Barrel Imaging Calorimeter (right).
• Figure 2: AstroPix_v3 configurations: stepwise progression from single-chip to nine-chip prototype module.
• Figure 3: Pictures of the bench test setup with AstroPix_v3 configurations.
• Figure 4: Mask map of the quad-chip module (left) and results of the injection test: hit map (middle) and ToT map (right). Each plot corresponds to one chip in the 2$\times$2 array.
• Figure 5: Cosmic-ray event display of a three-layer stack of quad-chips (left) and hit information.