Building a High-Resolution Alpha Spectrometer with Red Pitaya

Alpha spectrometry remains one of the most precise and challenging methods for studying radioactive decay. From understanding heavy nuclei to tracking isotopes in research and education, the technique demands extremely sensitive instrumentation, low-noise electronics, and carefully prepared samples.

This project, made by Lappetito Lodovico, explores how a DIY alpha spectrometer can be significantly improved by combining professional-grade detector modules with the versatile Red Pitaya STEMlab board. The result is an instrument capable of delivering high-resolution alpha spectra—at a fraction of the cost of commercial systems.

Why Alpha Spectroscopy Is Challenging

Unlike gamma spectroscopy, alpha spectroscopy pushes the limits of detection. The weak signals produced by alpha interactions require:

• High-sensitivity solid-state detectors (such as silicon PIPS sensors)
• Ultra-low-noise preamplifiers to capture faint pulses
• Vacuum conditions, since even air can attenuate alpha particles
• Thin, homogeneous samples, to minimize self-absorption

Despite these challenges, Lodovico’s work shows that with patience, expertise, and the right tools, a DIY setup can achieve excellent results.

Detector: The Silicon PIPS Sensor

At the heart of the spectrometer is a Canberra PIPS SPD-100-12 detector with a 100 mm² active surface. This solid-state sensor works by reverse-biasing a p-n junction, creating a depletion zone where alpha particles generate measurable charges.

Key specifications:

• Active surface: 100 mm²
• Thickness: 100 μm
• Resolution: 12 keV at 5 MeV
• Bias voltage: 40 V

This makes the PIPS sensor an ideal choice for detecting low-energy alpha signals with precision.

Signal Processing Chain

The detector output is extremely weak, so low-noise amplification and pulse shaping are critical. Lodovico’s design used:

1. Charge-Sensitive Preamplifier (CSP) – Cremat CR-110 module, converting current pulses into voltage signals.
2. Shaping Amplifier – Filtering noise and transforming signals into Gaussian pulses for digitization.
3. Shielded Electronics – All modules enclosed in grounded metal boxes to reduce interference.

The shaping amplifier was configured with a 1 μs shaping time, striking a balance between resolution and pulse separation.

Basic Schematic of a Shaping Amplifier

Red Pitaya as the Acquisition System

Instead of expensive commercial analyzers, the Red Pitaya STEMlab 125-14 board was used for data acquisition. With its:

• 125 MS/s sampling rate
• 14-bit ADC resolution
• FPGA reconfigurability
• Built-in oscilloscope and spectrum analyzer apps

…it proved to be an ideal platform for spectroscopy research.

The open-source MCA (Multichannel Analyzer) software by Pavel Demin was deployed on a dedicated SD card, enabling real-time acquisition and energy spectrum visualization.

Results

The improved spectrometer successfully captured well-resolved alpha energy peaks from various radioactive sources. Compared to earlier DIY versions, the enhancements in shielding, electronics, and shaping delivered:

• Better energy resolution
• Reduced background noise
• Stable and repeatable measurements

This makes the system suitable not just for hobby projects, but also for educational labs and low-activity isotope studies.

Educational & Research Impact

By combining commercial detector modules with open-source tools like Red Pitaya, Lodovico’s project demonstrates how advanced nuclear measurement techniques can be made accessible to:

• University physics labs
• Student research projects
• Citizen science initiatives
• Low-budget research groups

It bridges the gap between high-cost commercial instruments and DIY experimentation, making alpha spectroscopy more approachable.

Charge Preamplifier and Detector (on the left) – Shaping Amplifier (on the right)

Detail of Front-End Electronics and Detector

Conclusion

The improved alpha spectrometer designed by Lappetito Lodovico is proof that precision nuclear measurements can be achieved with creativity, open-source tools, and modern hardware platforms like Red Pitaya.

By leveraging a PIPS sensor, low-noise electronics, and Red Pitaya’s flexible FPGA-based acquisition, this project brings alpha spectroscopy into reach for students, educators, and researchers worldwide.

Click here, to find out more about the Improved Alpha Spectroscopy with Red Pitaya.

Frequently Asked Questions (FAQ)

Q1: Why is Red Pitaya a good choice for alpha spectroscopy?
Because it combines oscilloscope, spectrum analyzer, and data acquisition in one FPGA-based platform, reducing the need for multiple expensive instruments.

Q2: What detector was used in this project?
A Canberra PIPS SPD-100-12 solid-state silicon detector with a 100 mm² active surface and 12 keV resolution at 5 MeV.

Q3: Why do alpha spectroscopy experiments require vacuum conditions?
Air attenuates alpha particles significantly, so even low-pressure environments greatly improve measurement accuracy.

Q4: What software is needed for Red Pitaya-based spectroscopy?
The MCA (multichannel analyzer) application developed by Pavel Demin, available as open-source software.

Q5: Can students or hobbyists replicate this setup?
Yes, with patience and some technical expertise. The project combines commercially available components with open-source software and Red Pitaya’s accessible platform.