Yoshichika Seki

Development of Multi-colored Neutron Talbot–Lau Interferometer with Absorption Grating Fabricated by Imprinting Method of Metallic Glass

For the effective interferometric imaging at pulsed neutron sources, we have developed the Talbot–Lau interferometer which works at several wavelengths, and demonstrated its operation by observing the visibilities of moire fringes in different wavelength conditions. An absorption grating as an analyzer was fabricated by imprinting of metallic glass for the first time, and showed a well-controlled shape. Using such a grating, we have succeeded in interferometric imaging for the samples of metal rods at a wavelength of 5 A.

Demonstration of optical thickness measurement using multilayer cold neutron interferometer

We have measured the optical thickness of a phase object for the first time using multilayer cold neutron interferometer. The measured phase shift of 15.1 ± 1.9 wavelength agreed with the expected value of 17.4 ± 0.7 wavelength due to an about 600-μm-thick silicon plate. This demonstration reconfirmed that two paths in our new interferometer were completely separate, and showed its applicability into various precise measurements.

Moire fringes in a neutron spin interferometer

We have revealed the criterion to observe moire fringes in a neutron spin interferometry. In former studies using wave front division, neutron beam had to be collimated by fine slits. On the other hand, we have succeeded to observe moire fringes with divergence angle of 8.3 mrad using spin polarization division. A model based on partial coherence theory has been developed and verified experimentally. These results will be the basis for neutron wave front manipulation technique using magnetic birefringence.

Development of a simulation for measuring neutron electric dipole moment

The neutron electric dipole moment (nEDM) is sensitive to new physics beyond the standard model and could prove to be a new source of CP violation. Several experiments are being planned worldwide for its high-precision measurement. The nEDM is measured as the ultracold neutron (UCN) spin precession in a storage bottle under homogeneous electric and magnetic fields. In nEDM measurement, the systematic uncertainties are due to the motion of the UCNs, the geometry of the measurement system, and inhomogeneous electric and magnetic fields. Therefore, it is essential to quantitatively understand these effects in order to reduce them. Geant4UCN is an ideal simulation framework because it can compute the UCN trajectory, evaluate the time evolution of the spin precession due to arbitrary electric and magnetic fields, and define the storage geometry flexibly. We checked how accurately Geant4UCN can calculate the spin precession. We found that because of rounding errors, it cannot simulate it accurately enough for nEDM experiments, assuming homogeneous electric and magnetic fields with strengths of 10 kV/cm and 1 μT, respectively, and 100 s of storage. In this paper, we report on its discrepancies and describe a solution.

Research toward the development of compact neutron interference imaging instrument with gratings

The neutron interference imaging experiment with two absorption gratings has been done. We develop new way to fabricate absorption gratings for neutron with the pitch of 150 μ m, 180 μ m, and 200 μ m. Compact imaging detector system is developed, whose weight is 2kg. Small break in an acrylic plate, the welded place of Nb plate were observed, it reveals that the neutron interference imaging method can become new method of a nondestructive inspection for reinforced plastics and composite material such as CFRP and so on.

Multilayer Neutron Interferometer with Complete Path Separation

We have developed a new multilayer cold-neutron interferometer using a pair of beam splitting etalons (BSEs) with an air gap of 189 µm in spacing. This is the first multilayer neutron interferometer that separates two paths from each other completely without an overlap. Clear interference fringes with a contrast of 67% have been observed using a monochromatic cold-neutron beam with a wavelength of 0.88 nm.

Efficient phase imaging using wavelength-resolved neutron Talbot-Lau interferometry with TOF method

For efficient differential-phase-contrast imaging, we have demonstrated the wavelength-resolved neutron Talbot-Lau interferometry with the wavelength resolution of 0.11 A over a wide wavelength range of 2.5–7.5 A at RADEN in the J-PARC Materials and Life Science Experimental Facility. The time-of-flight measurement has clearly showed that the visibility of moire fringes and intensity oscillations of the interferometer varied continuously with the wavelength, and the wavelength dependence of the differential phase of metal samples was measured. Based on the analysis utilizing this wavelength dependence, we achieved both high statistical precision and high accuracy in the differential-phase-contrast imaging, and succeeded in the quantitative evaluation of the optical potentials of metals.

Simulation Study for Systematic Uncertainty Suppression in nEDM Experiment Assuming Various Surfaces Roughness

Ryo Katayama1, Kenji Mishima2,3, Masaaki Kitaguchi4, Masakazu Kurata2, Dai Sakurai5, Yoshichika Seki6, Satoru Yamashita2, Tamaki Yoshioka7 1School of Science, The University of Tokyo, Tokyo, 113-0033, Japan 2ICEPP, The University of Tokyo, Tokyo, 113-0033, Japan 3KEK, Tokai, Ibaraki, 319-1118, Japan 4KMI, Nagoya University, Nagoya, 464-8602, Japan 5Department of Physics, Tokyo University of Science, Noda, Chiba, 278-8510, Japan 6RIKEN, Wako, Saitama, 351-0198, Japan 7RCAPP, Kyushu University, Fukuoka, 812-8581, Japan

Development of a new neutron mirror made of deuterated Diamond-like carbon

We developed a new neutron mirror made of Diamond-like carbon (DLC). DLC is a film of amorphous carbon that has characteristics of both diamond and graphite. We produced DLC mirrors by ionization deposition method which is one of the chemical vapor deposition (CVD). Generally, DLC made by CVD contents a few tens of percentages of hydrogen. It decreases the Fermi potential of the DLC coating because hydrogen has negative Fermi potential. In order to increase the Fermi potential of the coating, we deuterated the DLC by using deuterated benzene for the source gas. The characteristics of the deuterated DLC(DDLC) coating was evaluated by RBS, ERDA, x-ray reflectivity, AFM. As a result, DDLC coating has 243neV due to deuteration, which is the same level as Ni. The RMS of height of the DDLC was 0.6nm so that the DDLC coating can be applied for a focusing mirror or specular transportation of pulsed neutron. Besides, we also develop Hydrogen/Deuterium DLC multiple layer mirror. So far, 4 layers mirror has been succeeded.

Development of Neutron Interferometer with Wide-Gapped ''BSE''s for Precision Measurements

We are developing large‐dimensional cold‐neutron interferometers with multilayer mirrors in order to investigate small interactions. In particular Jamin type interferometers composed of wide‐gapped “BSE”s, which divide the beam completely, can realize the precision measurement of topological Aharonov‐Casher effect. We have made a prototype with 200 μm gapped BSEs and confirmed the spatial separation of its two paths at monochromatic cold‐neutron beamline MINE2 on JRR‐3M reactor in JAEA.