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

Significance 

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.

About the author

Tetsuo Samoto is a researcher at the Institute of Multidisciplinary Research for Advanced Materials at Tokoku University in Japan. He studied sputtering mechanisms, envisioned for the Tokamak type nuclear fusion reactors, at Kyushu University. He joined a group researching perpendicular magnetic recording at Sony research center. He was involved in developing evaporated or sputtered magnetic media, from basic R&D to the consumer product “Handycam IP”. After retiring, he moved to MEMS research group at Tohoku University, and received his PhD in Mechanical Engineering from Tohoku University (2014). Now he is in charge of fabrication of diffraction gratings particularly for neutrons in the ERATO phase imaging project.

About the author

Hidekazu Takano is specially pointed Associate Professor of Institute of Multidisciplinary Research for Advanced Materials, Tohoku University in Japan.

He is working at “Momose quantum beam phase imaging project” managed by JST, Japan, and is in charge of development of X-ray phase tomographic microscope.

He received Dr. Eng. from Tsukuba University, and had worked as beamline scientist of an industrial use beamline of SPring-8 (synchrotron radiation facility in Japan) before joining current position.

His expertize is X-ray optics, X-ray optical devices, X-ray imaging, and X-ray microscopy. Especially he published lot of work about X-ray microscopy based on synchrotron X-rays.

About the author

Professor Atsushi Momose, After studying applied physics at the University of Tokyo, in 1987, he joined the team of Hitachi Ltd., which had constructed their own beamline at a synchrotron radiation facility. Soon, he gained an idea of X-ray phase imaging and has been pioneering for the imaging technology using X-ray phase information up to now. He moved to academia (Univ. Tokyo) in 1999 and sought for a next step to attain X-ray phase imaging outside synchrotron radiation facilities for practical applications in industry and medicine. In 2012, he moved to Tohoku Univ., and now he is conducting the ERATO phase imaging project, in which neutron phase imaging is added within his research scope.

Reference

Samoto, T., Takano, H., & Momose, A. (2019). Evaluation of obliquely evaporated gadolinium gratings for neutron interferometry by X-ray microtomography. Materials Science in Semiconductor Processing, 92, 91-95.

Go To Materials Science in Semiconductor Processing

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