Reconstruction of Ge spatial distribution in ICF target using PIXE-T

Inertial confinement fusion (ICF) target is a microsphere with diameter at millimeter scale and shell thickness at micrometer scale. Ge-doped glow discharge polymer (GDP) is an ideal material for the target. The homogeneity of dopant is vital for uniform compression and minimization of Rayleigh-Taylor (RT) instabilities in ignition. However, the method of quantitative measurement of dopants' spatial distribution is still not mature. Quantitation is not accurate and image resolution is low. Particle induced X-ray emission tomography (PIXE-T) is a suitable technique for measuring trace elements' spatial distribution in small sample at micrometer scale. This paper demonstrates the capabilities of PIXE-T to obtain quantitative spatial distribution of dopant (Germanium) in ICF target for the first time. We also developed a program run in MATLAB to reconstruct Ge spatial distribution 3D image using Filtered Back Projection (FBP) algorithm. When ion beam is transmitted through the target, its energy is attenuated due to collisions. This energy attenuation causes decrease of X-ray emission cross section. For X-ray emitted from target inside, it will be absorbed by target itself before being collected by detector. Both effects cause loss of X-ray counts, especially at the rear of target toward beam. The program can compensate the loss of X-ray counts caused by these two effects, non-linear X-ray production (NLXP) along the path of the beam and X-ray attenuation (XA). This correction is based on a uniform mass density (1.08 g/cm3) and a uniform major composition (stoichiometric ratio C:H = 5:7 for GDP material) within the sample. Corrections are applied before tomographic reconstruction, producing a more accurate Ge spatial distribution image. After converting X-ray counts in every voxel to Ge concentration using standard reference material (SRM), the image shows quantitative spatial distribution.