Pomelo: Affordable and Versatile Gamma Spectroscopy Module for Hobbyists and Developers

Pomelo is an innovative radiation detector tailored for hobby-level gamma spectroscopy, designed to be both accessible and versatile. Developed to provide a complete low-power gamma-ray spectrometer, Pomelo can function independently or be seamlessly integrated into other projects, offering a broad range of applications for enthusiasts and developers alike.

The Pomelo gamma spectroscopy module is built around a set of well-defined requirements, prioritizing low cost and low power consumption. The target is to keep the component cost below 150 euros, making it an affordable option for hobbyists and educational purposes. At its core, the module utilizes a commercial off-the-shelf (COTS) scintillator and a silicon photomultiplier (SiPM), ensuring reliability and performance.

The detector assembly, branded as Pomelo Physics, comprises a CsI(Tl) scintillator measuring 10mm x 10mm x 30mm from OST Photonics and a Broadcom AFBR-S4N44P014M SiPM. This combination effectively detects gamma rays within an energy range of 50 keV to 3 MeV. To maintain accuracy and protect the SiPM from stray light, the scintillator is housed in a 3D printed dark box. Additionally, the module includes a Texas Instruments TMP126 temperature sensor to provide temperature compensation, ensuring consistent performance across varying environmental conditions.

Pomelo Core, the accompanying electronics module, integrates several features that enhance its functionality and ease of use. It includes a bias supply, an analog front end, and digital electronics, all essential for effective gamma ray detection and data processing. One of the standout features of Pomelo is its versatile connectivity options. The module supports USB connectivity (CDC) for data dumping to a terminal, making it straightforward to interface with laptops and other USB-equipped devices. Additionally, it features UART for interfacing with external microcontroller units (MCUs), such as Arduinos or Raspberry Pis. The onboard level shifter on the UART lines ensures compatibility with both 3.3V and 5V systems.

Pomelo is designed to be user-friendly while offering robust performance. It supports onboard histogramming and run control, enabling spectrum readout, reset functions, and timed measurements directly from the device. For more advanced applications, the module provides a list-mode data option, allowing detailed analysis of individual gamma events.

Furthermore, Pomelo includes dedicated hardware handshaking for coincidence measurements with two devices, enhancing its capability for complex experiments. The software-configurable energy threshold adds another layer of customization, allowing users to tailor the module’s sensitivity to specific requirements.

Pomelo stands out as a comprehensive solution for gamma spectroscopy, combining affordability, low power consumption, and versatile connectivity in a compact design. Its integration of commercial scintillator and SiPM components, coupled with thoughtful features like temperature compensation and coincidence measurements, makes it a powerful tool for hobbyists, educators, and developers exploring the fascinating world of gamma spectroscopy. Whether used as a standalone device or integrated into larger projects, Pomelo offers everything needed for effective gamma ray detection and analysis.

more information: https://hackaday.io/project/194457-pomelo-gamma-spectroscopy-module

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