Design of a scattering-assisted thick pinhole imaging system for indirect spatially resolved diagnosis of intense...

Spatially resolved diagnosis of intense pulsed gamma radiation fields is important for characterizing both the intrinsic non-uniformity of the radiation field and the local irradiation conditions. However, under high transient dose-rate conditions, conventional detectors are prone to signal saturation and radiation-induced damage, making direct measurement difficult. To address this issue, a scattering-assisted thick pinhole imaging system is proposed for indirect imaging of radiation field intensity distributions. In this system, a thin scattering target is introduced to generate measurable scattered-photon signals, and a thick pinhole is used to spatially modulate these signals. To improve imaging performance, a multi-metric objective function integrating the coherence, mean coherence, and signal acquisition factor is constructed, and a genetic algorithm coupled with Monte Carlo simulation is employed to optimize the thick pinhole geometry. For image reconstruction, a sparsity-prior reconstruction method based on the alternating direction method of multipliers is developed. The results show that the optimized thick pinhole achieves better reconstruction quality than a randomly selected thick pinhole and a double-cone aperture, while the proposed reconstruction method outperforms established iterative reconstruction algorithms in both reconstruction quality and iterative stability. In addition, the proposed system and reconstruction method retain good robustness under representative noise and practical system perturbation conditions, with the main spatial distribution features remaining distinguishable. This study provides a feasible indirect imaging approach for spatially resolved diagnosis of intense pulsed gamma radiation fields.