X-ray microtomography: A powerful tool for designing evaporated gadolinium gratings for neutrons

Neutron imaging achieves the optimal benefit for the industrial use of neutrons. In Japan, the strongest pulsed neutron source is available at J-PARC for various measurements. Recently, a new method for visualizing the phase changes of neutrons called “Neutron Phase Imaging” is an emerging technique in the field of neutron imaging. Although the optical system is the same as that of X-ray phase imaging using gold gratings, gadolinium absorption gratings with a large size and high-aspect-ratio are needed for neutron phase imaging, the fabrication technique of which has not been established fully.

To this end, Tohoku University researchers: Dr. Tetsuo Samoto, Dr. Hidekazu Takano and Prof. Atsushi Momose evaluated the feasibility of oblique evaporation of Gd on to a Si grating. A concern was how the density of deposited Gd is affected due to the oblique incident angle.

They used X-ray microtomography to visualize 3D density distributions of the deposited Gd films (See the figure movies on the headline). They discussed evaporation conditions in connection with estimated performance as a neutron absorption grating. Their research work was published in the research journal, Materials Science in Semiconductor Processing.

In brief, the research team fabricated test Gd gratings using the oblique evaporation method, which involves a sequence of evaporation by changing geometrical parameters. After fabrication, a three-dimensional X-ray microtomography was used to measure the density distributions in deposited Gd patterns.

The authors observed a layered Gd density distribution consistently with the Gd evaporation sequence. This was attributed to the void formation process. From the density distribution, the effective height of Gd pattern was evaluated, allowing the estimation of its performance as a neutron absorption grating successfully.

In summary, Dr. Tetsuo Samoto and colleagues successfully fabricated and evaluated Gd density deposited on Si gratings by X-ray microtomography, allowing estimation of its performance as a neutron absorption grating. In addition, the result was valuable in establishing the sequence of the oblique evaporation method.