Hydrogen Scattering Correction Method for Neutron Imaging

Abstract

Neutron imaging can nondestructively detect the composition and structure of a sample, and has been used in many fields for quantitative analysis. Neutron imaging can be used to detect elements that are difficult to detect with X-rays, such as hydrogen. When neutron imaging is used for quantitative analysis of hydrogen-containing samples, the neutron beam decays because of scattering with hydrogen rather absorption. However, neutrons scattered in the direction of the neutron beam may still reach the detector, and these scattered neutrons can bring additional intensity to the sample and its edges, bring artifacts to the image, and cause serious interference to quantitative analysis. The elimination of scattering effect is one of the most important problems in the quantitative analysis of neutron imaging. Because samples with hydrogen have a larger total scattering than absorption cross section, the influence of the scattered neutrons on the transmitted image is not negligible. The results of neutron imaging quantitative analysis are also affected by the energy spectrum effect. Since the incident neutron beam is not unienergetic, the probability of interaction between the lower energy neutrons and the sample is high, resulting in the macroscopic cross section of the neutron varying with the thickness of the sample. Several existing scattering correction methods, such as increasing the distance between the sample and the detector, the point scattered functions method, using microchannel plates, and using the blackbody grids, are not applicable to all samples, or not applicable to dynamic neutron imaging, or will increase exposure time or complicate data processing. A new scattering correction method, the double-detector method was presented. The double-detector method used two detectors at two locations to image. The close detector can obtain a high-resolution image, but the image is affected by scattered neutrons. The far detector obtain images that are unaffected by scattered neutrons, but with poor resolution. The scattering neutron distribution can be obtained by processing the two images. By subtracting the scattering neutron distribution from the close image, an image with high resolution and free from scattering neutrons can be obtained to complete scattering correction. The method was used to correct the water steps sample images. And the macroscopic cross section was corrected by the energy spectrum correction factor. The results show that the thickness of the water steps in the close-position image differs greatly from the actual thickness due to the influence of scattered neutrons. And the thickness of the water steps corrected by the double-detector method is in good agreement with the actual thickness. The double-detector method is a feasible scattering correction method.

Keywords

• neutron imaging
• quantification
• scattering correction
• spectrum effects