Thin coded apertures for high-energy neutron and x-ray imaging

The passive imaging of high-energy x-rays and neutrons is a useful diagnostic in laser-driven fusion as well as laboratory astrophysics experiments which aim to study small samples at high resolutions. Typical pinhole imaging systems require high attenuation for adequate image contrast. When high-resolution is also required, high aspect ratio pinholes are necessary and result in narrow fields of view and difficult to align diagnostics.

Here we demonstrate a coded aperture with scatter and partial attenuation included (CASPA) and compare it to the more common method of pinhole imaging. We confirm the well-known throughput increase of coded apertures, and show that the decoding algorithm relaxes the need for a thick substrate. This may allow for thinner, easier to align and potentially cheaper alternatives to be fielded. We explore CASPAs for ICF experiments fielded at the NIF using Geant4 simulations to discuss the viability of this technique to measure neutron or x-ray implosion asymmetries, and test the feasibility of using these CASPAs for high repetition rate, short pulse laser-driven neutron experiments.