The development of a high granular crystal calorimeter prototype of VLAST

TL;DR

This work presents the HEIC-Cube, a high-granularity BGO calorimeter prototype for the VLAST gamma-ray observatory, designed to cover $0.1$ GeV to $20$ TeV with a dynamic range of $10^6$ using a dual-APD dual-gain readout and attenuation filters. The prototype features 10 longitudinal layers of $5 imes5$ cubic BGO crystals ($3 ext{ cm}$ side), each read out by two APDs, with embedded PAM/ADM electronics and a DCM for data handling, enabling detailed imaging of showers and improved particle identification. LED-based tests and two months of cosmic-ray data validate the large dynamic range (exceeding $2.4\times10^6$) and MIP-level signals (~$18$ fC MPV), while revealing temperature-related performance variations that inform thermal control needs. The results provide a concrete path toward optimizing the final VLAST calorimeter design, including calibration, attenuation-filter tuning, and beam testing, to achieve precise electron/gamma energy measurements across a vast energy spectrum.

Abstract

Very Large Area gamma-ray Space Telescope (VLAST) is the next-generation flagship space observatory for high-energy gamma-ray detection proposed by China. The observation energy range covers from MeV to TeV and beyond, with acceptance of 10 m^2sr. The calorimeter serves as a crucial subdetector of VLAST, responsible for high-precision energy measurement and electron/proton discrimination. This discrimination capability is essential for accurately identifying gamma-ray events among the background of charged particles. To accommodate such an extensive energy range, a high dynamic range readout scheme employing dual avalanche photodiodes (APDs) has been developed, achieving a remarkable dynamic range of 10^6. Furthermore, a high granular prototype based on bismuth germanate (BGO) cubic scintillation crystals has been developed. This high granularity enables detailed imaging of the particle showers, improving both energy resolution and particle identification. The prototype's performance is evaluated through cosmic ray testing, providing valuable data for optimizing the final calorimeter design for VLAST.

Figures (14)

• Figure 1: Architecture of the payload of VLAST.
• Figure 2: (a) 30 mm side length BGO cubic crystal, coated with white reflective film. (b) The HAMAMATSU S8664-0505 type APD. (c) Vertical structure diagram of the APD.
• Figure 3: A typical MIPs distribution from a detector unit.
• Figure 4: Block diagram of electronic pre-amplifier module (PAM) and analog to digital module (ADM).
• Figure 5: Block diagram of the devices that utilizes a LED for measuring gain ratio.