## 2 Time-of-Flight Neutron Transmission Imaging Experiment
### Experimental  
A wavelength-resolved neutron transmission imaging experiment based on the TOF method of pulsed neutrons was performed to measure the position-dependent Bragg-dip neutron transmission spectra of the sample. The experiment was performed at the  
\begin{table}
\begin{tabular}{c c} \hline
**Grain** & **[_uvw_]** \\ \hline
1 & [100 70 52] \\
2 & [100 66 38] \\
3 & [100 74 26] \\ \hline \end{tabular}
\end{table}
Table 1: Crystal orientations [_uvw_] along neutron transmission direction for Grains 1, 2 and 3.  
Figure 1: **(a)** Photograph of the Si–steel plate sample. The region surrounded by dashed black lines indicates the field of view (FOV). **(b)** IPF map of the sample, evaluated by Bragg-dip neutron transmission imaging [19]. The number indicated in the figure indicates the number of grain. The figure is reproduced with permission of the International Union of Crystallography from reference [19].  
pulsed neutron instrument, the Neutron Beamline for Observation and Research Use (NOBORU) [21] constructed at BL10 at the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). Figure 2 shows a schematic of the neutron beamline. The 3 GeV proton synchrotron of J-PARC was driven for the pulsed spallation neutron source, and the proton beam power changed from 400 to 500 kW during the experiment. Neutrons were produced by the spallation reaction at the Japan Spallation Neutron Source (JSNS), and moderated by the decoupled-type 20 K supercritical 100% para-H\({}_{2}\) moderator. The moderator surface area was 10 \(\times\) 10 cm\({}^{2}\). The neutron pulse FWHM was about 50 \(\upmu\)s for cold neutrons (0.4 nm wavelength). Therefore, the wavelength resolution could be calculated as 0.35% for cold neutrons using the neutron flight path length as described later. The neutron beam intensity and the beam angular divergence were controlled by the B\({}_{4}\)C slit. The slit size was 3 \(\times\) 3 cm\({}^{2}\), and the slit was set at 7.05 m from the neutron source. A gas electron multiplier (GEM) detector containing the \({}^{10}\)B(n,\(\alpha\))\({}^{7}\)Li converter [22] with the TOF analysis function was used as a neutron TOF-imaging detector. The pixel size was 800 \(\times\) 800 \(\upmu\)m\({}^{2}\), and 128 \(\times\) 128 pixels of the imaging detector gave an active area of 10.24 \(\times\) 10.24 cm\({}^{2}\). The detector was set at 14.26 m from the neutron source, and the sample was set at 4 cm in front of the detector. Hence, the sample was set at 14.22 m from the neutron source. Therefore, the neutron collimator ratio, L/D, was about 2400, and the neutron beam angular divergence was about 0.416 mrad. We put the sample close to the detector for avoiding the blurring effect of spatial resolution due to the neutron beam angular divergence. It is no problem in terms of the diffracted neutron background for the detector. This is because longer wavelength neutrons cause back scattering according to [PERSON]'s law, and cannot be detected by the detector [19]. The estimated cold/thermal neutron flux during this experiment was approximately 6.5 \(\times\) 10\({}^{4}\) n/cm\({}^{2}\)/s. The open beam measurement, without the sample, was about 7.2 h. The sample beam measurement was about 14.5 h. By these measurements, the neutron transmission was obtained at each wavelength position-dependently.