[M-IS26] Gas hydrates in environmental-resource sciences

[MIS26-09] Three-dimensional nondestructive observation of natural methane hydrate

*Satoshi Takeya¹, Akihiro Hachikubo², Satoshi Yamashita², Hirotsugu Minami², Hirotoshi Sakagami², Kazuyuki Hyodo³, Akio Yoneyama⁴ (1.National Institute of Advanced Industrial Science and Technology, 2.Kitami Institute of Technology, 3.High Energy Accelerator Research Organization, 4.SAGA Light Source)

Keywords:clathrate hydrate, natural gas hydarte, Hydrate sediment, X-ray CT

The density of gas hydrates varies depending on the type of guest spices encapsulated in the hydrate crystal, but is generally about the same as ice or water (0.9~1.1 g/cm³). A material with such a relatively small density has a small absorption rate of X-rays. For this reason, it is difficult to visualize the internal structure using the X-ray absorption contrast caused by the slight difference in density within the material, which is the visualization principle of medical and industrial X-ray computed tomography (CT) systems. On the other hand, the phase of X-rays shifts significantly even in materials with small density. Therefore, if we can detect the phase shift of X-rays in a material, it is possible to observe the small density difference in the material with high sensitivity 1).

In this study, we used diffraction contrast (DEI) method2) as a method to detect the phase shift; the DEI method can detect density differences of about 0.01 g/cm³. The DEI method can detect a density difference of about 0.01 g/cm³ and has a relatively wide dynamic range of density (density difference: ~1 g/cm³).3) It is also effective for high-sensitivity measurement of samples with coexisting gas (voids) in addition to gas hydrate and ice (water).3) We also performed absorption-contrast X-ray CT measurements on a sample of natural sediment. The results will be reported.