Design, modeling and reconstruction method research of a 14.1Â MeV neutron imaging system suitable for low yield Z-Pinch diagnosis

In this article, we present the optimization of a neutron imaging system for Z-Pinch driven fusion experiment with large field of view (FOV) 5 mm in diameter and low neutron yields 1010 to 1012. The Inverse Radius Curvature (IRC) penumbra aperture design method was employed to yield thick aperture suitable for the large FOV. A preliminary optimal radius of the aperture which makes a tradeoff between spatial resolution and image SNR is given. The dependence of imaging signal to noise (SNR) and isoplanatism of point spread function (PSF) on the aperture thickness is discussed. A suitable compromise of aperture thickness was made between these two issues. With respect to the scintillation fiber array, the spatial resolution of the array is influenced by the diameter of fibers and the range of recoil protons. The relationships between fiber length, neutron sensitivity, temporal response and crosstalk effect are studied. And the features of three commonly used fiber arrays such as packing fraction and trapping fraction are taken into consideration as well. The optimized imaging system was simulated using GEANT4. A coded image of “E” character with 2 × 1010 neutrons is acquired and unfolded by five image reconstruction algorithms, i.e. Wiener Filtering, Richardson-Lucy, Maximum Entropy, Total Variation and Genetic algorithm. Only Genetic algorithm shows certain robustness in this condition. The reconstruction performance of Genetic algorithm is affected by the neutron yield.