Neutron Phase contract imaging (NPCI) is a promising technique for non-destructive imaging of large scale (meter to 10 meters in size) and thick (cm-100’s cm cross section) metal components to characterize internal structure and ensure reliability of the build. Thermal neutron penetration depth through metals is far superior compared to x-rays and offers the ability to modify the neutron to provide more or less interaction with the intended sample. One possible application is imaging of additively manufactured metals using NPCI to characterize internal porosity and defects that might arise in selective laser sintering additive manufacturing. NPCI requires High Aspect Ratio (>10:1) gratings with feature sizes around 2 µm made of high neutron absorbing materials—with gadolinium the preferred metal of choice. Current fabrication methods etch trenches in silicon and fill them with gadolinium powder/epoxy [1] or a thin metal deposition of gadolinium [2] creating a gadolinium grating. The challenge in electroplating gadolinium is in finding compatibility between the chemistry and the downstream microfabrication techniques using grating molds sensitive to heat and chemical processes. Gadolinium salts were mixed with sulfamate-based aqueous solutions, deep eutectic solvents, and organic solvents. Gadolinium deposition windows were found using cyclic voltammetry experiments and deposited films were characterized for feasibility and make-up using scanning electron microscopy, energy dispersive spectroscopy, and confocal microscopy. Chemistry efficiencies and expected lifetimes were analyzed over multiple weeks duration. Microfabrication compatibility studies were then used to find the appropriate matching template grating mold for uniformly coating the gadolinium onto the grating in future work.

1. Kim, J., et al., Fabrication and characterization of the source grating for visibility improvement of neutron phase imaging with gratings. Review of Scientific Instruments, 2013. 84(6).
2. Grunzweig, C., et al., Design, fabrication, and characterization of diffraction gratings for neutron phase contrast imaging. Review of Scientific Instruments, 2008. 79(5).

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. Department of Energy or the United States Government.