Introducing Timepix2-Lite: A Miniaturized Readout Interface Enabling Nanosecond-Scale Half-Life Measurement

This paper introduces Timepix2-Lite, a compact readout interface for the Timepix2 detector that enables nanosecond-scale timing and energy measurements, demonstrating its versatility through successful integration into diverse applications and the precise determination of the 67.5 ns half-life of the 59.5 keV transition in 237Np.

The Gist

The Big Idea: A Tiny, Super-Fast Camera for Radiation

Imagine you have a camera that doesn't take pictures of people or landscapes, but instead captures radiation particles (like tiny, invisible bullets of energy) as they fly through the air.

The paper introduces a new device called Timepix2-Lite. Think of this as a "miniaturized control box" for a high-tech radiation sensor. Before this, the equipment needed to read data from these sensors was often bulky, heavy, and required a tangle of wires. The Timepix2-Lite is the size of a small smartphone (about 73mm long) and weighs only 32 grams (less than a AA battery). It connects to a computer with a single USB-C cable, making it as easy to set up as plugging in a webcam.

How It Works: The "Stopwatch and Scale" Combo

The sensor inside this device is a grid of 256 x 256 tiny squares (pixels). When a particle hits a square, the device does two things simultaneously:

1. It weighs the hit (Energy): Like a scale measuring how heavy a raindrop is, it measures how much energy the particle deposited.
2. It times the hit (Timing): Like a stopwatch that can measure time down to the nanosecond (one billionth of a second), it records exactly when the particle arrived.

The paper claims this system is fast enough to see events happening in the blink of an eye, specifically on a scale of nanoseconds. It also comes with special software called TrackLab, which acts like a live dashboard, letting scientists watch the particles move and interact in real-time on their computer screen.

The "Test Drive" at CERN

To prove this tiny device works under extreme conditions, the team took it to CERN (the European Organization for Nuclear Research), where they have a massive machine that shoots high-energy particles at incredible speeds.

• The Analogy: Imagine testing a new sports car on a professional race track.
• The Result: They pointed the Timepix2-Lite at a beam of particles moving at 180 GeV/c. The device successfully captured clear "photos" of the particle tracks. By tilting the device at different angles, they showed it could distinguish between primary particles and secondary ones based on when they arrived and how much energy they left behind. This proved the device is robust enough for high-level physics experiments.

The Main Experiment: Timing a Nuclear "Heartbeat"

The most impressive part of the paper is a specific experiment where they used this device to measure the half-life of a specific nuclear state.

• The Setup: They used a common radioactive source (Americium-241, found in some smoke detectors) and placed it very close to the sensor.
• The Process:
  1. The source emits an alpha particle (a heavy, fast-moving particle).
  2. This alpha particle hits the nucleus of a Neptunium atom, exciting it (like hitting a bell).
  3. The excited nucleus immediately relaxes by emitting a gamma ray (a photon of light).
  4. The Timepix2-Lite acts as a super-precise referee, catching both the alpha particle and the gamma ray in the same "frame" and measuring the tiny time gap between them.
• The Goal: They wanted to see how long the nucleus stayed "excited" before releasing the gamma ray. This duration is incredibly short—measured in nanoseconds.

The Results: A New Record for a Tiny Device

By analyzing thousands of these events, the team calculated the time it took for the nucleus to settle down.

• Their Finding: They determined the half-life of this specific state to be 67.5 nanoseconds.
• The Comparison: This number matches perfectly with the most accurate measurements previously done in massive, expensive laboratories.
• Why it matters: The paper highlights that they achieved this level of precision using a compact, portable device rather than a room-sized setup. They successfully measured a "nanosecond-scale half-life" in a tabletop experiment.

Summary

The paper claims that the Timepix2-Lite is a breakthrough because it packs the power of a massive nuclear physics lab into a device small enough to hold in one hand. It can:

• Connect easily to a computer via USB.
• Measure energy and time simultaneously with nanosecond precision.
• Perform complex experiments, like measuring the fleeting existence of excited atomic states, with accuracy that rivals the world's largest research facilities.

The authors conclude that this tool opens the door for both advanced laboratory research and portable, field-deployable nuclear instruments, proving that you don't need a giant machine to do giant science.

Technical Summary

Technical Summary: Introducing Timepix2-Lite

Problem Statement
Modern particle detection and radiation measurement increasingly demand readout systems that are not only high-performance but also compact, flexible, and capable of precise temporal and spatial resolution. While hybrid pixel detectors like Timepix2 offer simultaneous Time-of-Arrival (ToA) and Time-over-Threshold (ToT) measurements, existing readout interfaces often lack the miniaturization required for diverse experimental setups, such as stratospheric balloon missions, mobile educational demonstrations, or field-deployable nuclear instrumentation. There is a need for a compact, USB-compatible platform that maintains the full functionality of the Timepix2 architecture while integrating seamlessly with advanced data acquisition software.

Methodology
The authors developed Timepix2 Lite, a miniaturized readout interface designed specifically for the Timepix2 hybrid pixel detector. The system architecture consists of two printed circuit boards (PCBs) housed in a compact aluminum enclosure (73 mm × 22 mm × 14 mm, 32 g):

• Chipboard: Houses the Timepix2 detector with a 500 µm silicon sensor, an onboard high-voltage generator (0–150 V), a temperature sensor, and power regulation for analog and digital sections.
• Mainboard: Features an STM32U5A9 microcontroller (MCU) for host communication and a CPLD (MachXO2) for logic-level translation. It utilizes a USB-C interface (RNDIS class) for plug-and-play connectivity and supports external synchronization via a flat connector.

The system operates in ToT10/ToA18 mode, allocating 10 bits for energy (Time-over-Threshold) and 18 bits for timing (Time-of-Arrival). Data acquisition is managed through the TrackLab software framework, which handles real-time processing, visualization, and clustering.

To validate the system, the authors conducted two primary experiments:

1. Functional Testing at CERN: The device was tested at the Super Proton Synchrotron (SPS) beamline using 180 GeV/c hadrons. The detector was mounted on a rotation stage to measure angular dependence, energy deposition, and track separation capabilities.
2. Half-Life Measurement: A tabletop experiment was performed to measure the half-life of the second excited state in $^{237}$Np (59.5 keV transition). Using an $^{241}$Am source, the system employed a time-delayed coincidence method. The algorithm identified $\alpha$-particles (energy 2–4 MeV) and coincident $\gamma$-photons (50–70 keV) within the same frame, analyzing the Time-of-Arrival difference ($\Delta$ToA) between them.

Key Contributions

• Miniaturized Architecture: The paper introduces the first miniaturized, USB-compatible readout interface for Timepix2, reducing cabling and space requirements significantly compared to previous systems like Katherine or Hardpix.
• Simultaneous High-Resolution Measurement: The system enables simultaneous energy and precise timing measurements on a nanosecond scale (12.5 ns resolution with an 80 MHz clock) within a single compact unit.
• Software Integration: Full integration with the TrackLab framework allows for real-time data visualization and advanced analysis, including particle tracking and clustering, directly accessible via a standard host PC.
• Demonstrated Capability: The successful determination of a nuclear half-life in a compact, educational-style setup demonstrates the system's viability for both laboratory research and field applications.

Results

• CERN Testing: The Timepix2 Lite successfully recorded particle tracks with high spatial resolution (55 µm pitch) at various incidence angles. It distinguished primary and secondary particles using ToA information and maintained a relative energy resolution ($\sigma_E/E$) of approximately 8% across different angles and gain modes.
• Half-Life Measurement: Using the delayed-coincidence method, the system measured the half-life of the 59.5 keV state in $^{237}$Np. The final result was determined to be 67.5(7) ns.
  • Statistical uncertainty: $\pm 0.65$ ns
  • Systematic uncertainty: $\pm 0.15$ ns
  • This value is consistent with previously reported literature values (ranging from 67.60 to 68.1 ns).

Significance
The paper posits that Timepix2 Lite represents a significant step forward in making advanced hybrid pixel detector technology accessible for diverse applications. By combining a compact, lightweight design with nanosecond-scale timing precision and seamless software integration, the system lowers technical barriers for experiments such as nuclear spectroscopy and educational demonstrations. The successful measurement of a nuclear half-life in a tabletop configuration confirms the detector's accuracy and highlights its potential for use in spaceborne instrumentation and field-deployable nuclear devices. The authors note that while the current 12.5 ns resolution is sufficient for this measurement, future iterations utilizing detectors with superior timing resolution (e.g., Timepix3) could further approach the precision of state-of-the-art laboratory measurements.