Development and experimental validation of a symmetrical dual-chamber time projection chamber for high-precision neutron-induced fission cross-section measurement

Exploring the Core Design and Technological Breakthroughs of INPC-TPC
The research team innovatively designed the INPC-TPC with a symmetrical dual-chamber structure to overcome the 3%-5% measurement uncertainty limitation of traditional fission chambers. This structure spatially separates fission fragments and recoil protons, reducing the dynamic range requirement of a single chamber from 4000-fold to a manageable level. Meanwhile, it adopts GEM readout technology, which achieves sub-millimeter spatial resolution (122 μm in the X-Y plane) and stable gain through its cascaded amplification architecture, effectively suppressing sparking risks—outperforming traditional MICROMEGAS technology. Each chamber of the detector is equipped with 4608 readout pads, enabling powerful particle identification via 3D particle track reconstruction and energy deposition (dE/dx) measurement.

From Technical Scheme to Experimental Validation
The design of INPC-TPC stems from the core advantages of Time Projection Chambers (TPC)—capable of both track reconstruction and energy measurement—previously widely used in large-scale high-energy physics experiments. The research team further optimized the design: adopting the H(n,n) cross-section (with an uncertainty of only 0.2%) as the reference standard to break through the precision bottleneck of traditional relative measurement; using a partitioned target design to enable simultaneous measurement of ²³⁵U and ²³⁸U; and integrating a low-noise electronics system (noise level 0.6 mV, dynamic range 3000:1) to ensure data acquisition accuracy. In experiments at the CSNS Back-n neutron source, the detector successfully identified fission fragments in a wide energy range (0.5 eV-200 MeV) and accurately measured a 30 mm-diameter neutron beam spot, verifying the feasibility of the technical scheme.

Experimental Innovation: Multi-Track Event Processing and Performance Validation
To address the challenge of overlapping multi-particle tracks in white neutron experiments, the research team adopted a weighted iterative Hough transform algorithm to effectively separate and reconstruct 3D point clouds, improving identification accuracy through signal amplitude weighting correction. Experimental results show that fission fragments, protons, and light charged particles can be clearly distinguished based on the energy-length 2D distribution graph. The track start positions of fission fragments precisely match the shape of the partitioned target, confirming detection specificity. In neutron beam spot measurement, Gaussian fitting yielded diameters of 30.52 mm (X-axis) and 29.43 mm (Y-axis), with relative errors both less than 2%—surpassing similar research outcomes.

Far-Reaching Significance for Nuclear Science and Technology
This research not only advances the development of high-precision fission cross-section measurement technology but also holds significant practical application value. Accurate fission cross-section data are the core foundation for nuclear reactor design, nuclide synthesis calculations, and astrophysical nuclear process simulations. The breakthrough of INPC-TPC is expected to meet the demand for 1%-level measurement precision in related fields. Additionally, the detector’s supporting designs, such as the gas system, high-voltage voltage divider circuit, and LabVIEW-based data acquisition software, provide a reusable technical framework for future nuclear physics experiments.

Future Research Directions and Outlook
The research team will next complete the dual-chamber assembly and neutron energy calibration experiments in single-bunch mode, while simultaneously conducting reference target nuclide count measurements. The goal is to achieve accurate measurement of the cross-section ratios ²³⁵U(n,f)/H(n,n) and ²³⁸U(n,f)/H(n,n). In the future, the detector’s application will be expanded to higher energy ranges and more actinide nuclides (e.g., ²³⁹Pu), further improving nuclear physics theoretical models and advancing the construction of high-precision nuclear databases.

"Through structural innovation and technological integration, INPC-TPC pushes the precision of fission cross-section measurement to a new height," the research team stated. "This achievement not only verifies the performance potential of the new detector but also provides more reliable technical support for basic research and practical applications in the nuclear science field."

The complete study is via by DOI: https://doi.org/10.1007/s41365-025-01873-3