Novel neutron imaging aperture for ICF*

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 of transient electron-positron plasmas.

Here we demonstrate a coded aperture with scatter and partial attenuation included, which we have dubbed a ‘CASPA’.  We compare CASPAs to the more common method of pinhole imaging, confirming the well-known throughput increase of coded apertures, and show that the decoding algorithm relaxes the need for a thick substrate.  This is demonstrated with a 511 keV x-ray source through ray-tracing and Geant4 simulations to show how partial attenuation of the source by the CASPA allows for a superior signal to noise ratio with respect to an equivalent standard pinhole system. 

We explore the potential applications in ICF, using NIF-like sources and geometries in Geant4 simulations to discuss the viability of this technique for measurements of implosion asymmetry.  Finally, after suggesting CASPA corrections to previous coded aperture maximum-likelihood expectation-maximization models, we discuss the reduction in substrate thickness of a CASPA based system in comparison to current NIF architecture, and its impact on imaging capabilities.