# The Bimodal Neutron and X-ray Imaging Driven by a Single Electron Linear Accelerator
## 3 Results  
With the imaging sequence shown in Figure 4, the same inspected object's neutron image and photon image can be acquired successively within a single e-LINAC operation. As shown in Figure 6a, two keys clamped by an aluminum holder are inspected. Figure 6b,c shows the photon image and neutron image, respectively. The difference between Figure 6b,c is apparent. The key's plastic handle can hardly be noticed in Figure 6b, while it is evident in Figure 6c. On the contrary, the aluminum key is clear in Figure 6b, while almost transparent in Figure 6c. The underlying principle is that the cross section of \({}^{1}\)H is large (80.2 [EMAIL_ADDRESS] meV) for neutrons but very small for photons (0.406 barn@200 keV), while the opposite is true for \({}^{27}\)Al (1.68 [EMAIL_ADDRESS] meV for neutrons and 5.48 barns@200 keV for photons). Figure 7a shows the fused image from Figure 6b,c, in which the color indicates the type of the material, while the shade may reflect the mass thickness of the inspected object. There are 512 \(\times\) 512 pixels of 200-micrometer size in the image. For each pixel, its neutron attenuation and photon attenuation will determine the coordinate of a point in Figure 7b. All the pixels in Figure 6b,c, thus, help form Figure 7b, in which we can see six clusters. Cluster (1) shows a large neutron attenuation and a small photon attenuation, and Figure 7c(1) indicates it is the plastic handle of the key. Cluster (2) shows both strong attenuation for neutrons and photons, and Figure 7c(2) indicates this zone has both plastic and aluminum. Clusters (3) to (6) have the same slope, which is the ratio of neutron attenuation to photon attenuation, implying that they are the same material. Their different distances to the origin reflect the various mass thicknesses of the aluminum material in the key. The results shown in Figure 7 indicate that bimodal imaging can be a very effective method to identify different materials with various mass thicknesses. Figure 5: The 2-dimensional distributions of (**a**) neutrons and (**b**) photons observed by the detector placed 10 m away. Figure 6: (**a**) The photo of the clamped keys; (**b**) the photon image of the keys; (**c**) the neutron image of the keys. (Measuring time is 30 min). Benefitting from the drastic difference between the attenuation coefficients for neutrons and photons, this technology can help find the residual core material in the cast turbine blade [16]. Figure 8b,c is the neutron image and photon image for a blade without residual gadolinium tracer, respectively, while Figure 8d,e is that for a blade with residual gadolinium tracer (gadolinium oxide powder in this study), respectively. There is no significant difference that can be noticed between Figure 8c,e, indicating the inability of photons to investigate the residual gadolinium tracer inside the blade. On the contrary, the difference between Figure 8b,d is evident, implying that the blade with residual gadolinium tracer can be effectively discriminated by neutrons. By fusing the images of Figure 8d,e, a new image reflecting the position distribution of residual gadolinium tracer inside the blade is formed and shown in Figure 9a. To conduct a more quantitative comparison between the blades with or without gadolinium tracer, the distributions of the value, which is the ratio between the mass attenuation coefficient of neutrons and that of photons, of  
Figure 7: (**a**) The image fused from the neutron image and photon image; (**b**) the material identification based on the information from neutron attenuation and photon attenuation; (**c**) The six clusters in (**b**) are related to different zones of the inspected object, as shown in (1) to (6). Pixel density is the number of pixels in the area of 0.0075 \(\upmu\times 0.0075\)\(\upmu\)t.  
each pixel in the six squares of Figure 9a are calculated and shown in Figure 9b(1)-(6), with their counterparts for the blade without gadolinium tracer are also shown for comparison.