No abstract

The neutron imaging facility at Thai Research Reactor-1/Modification 1 (TRR-1/M1), located at Thailand Institute of Nuclear Technology (Public Organization) has been improved for non-destructive characterization of internal structure of materials. The aims are to study the beam characteristic after an installation of the external collimator, and to optimize the exposure condition for a new setup. The neutron imaging setup was modified to increase the L/D ratio. As a consequence of the extended distance from the beam port to the sample position, an external collimator was installed to focus the neutron beam since 2018. Moreover, a new sample holder was installed to support sample rotation and translations with increased stability. The experiment was performed at the TRR-1/M1 reactor with 1 MW-reactor power. The neutron beam at the 8-inches south beam port of the TRR-1/M1 was evaluated in terms of beam homogeneity and the relationship between the grayscale value and image quality obtained from a CCD camera. The present performance of the neutron imaging system was tested with an ASTM standard sample, called sensitivity indicator. The results are shown in terms of image contrast and sharpness.

It is well known that neutron imaging is a powerful nondestructive technique in archaeological studies, especially for visualization of organic contents or low-density parts inside antiques. In Thailand, the neutron imaging system has been developed to perform neutron tomography (NT) for archeological studies since 2015. A compact NT system, which is composed of a CCD camera coupled with a LiF/ZnS fluorescence screen and an in-house developed rotation stage, was used to investigate the internal structure of an object. The experiment was set up at Thai Research Reactor (TRR-1/M1) of Thailand Institute of Nuclear Technology (Public Organization) with the power of 1.2 MWth. The neutron intensity at the radiographic position was about 10 6 n.cm -2 s -1 . In this work, an ancient sample of interest, namely, the 15 th -18 th century terracotta doll was investigated to perform the developed NT system. The resulting 2D neutron image showed a crack at the neck and a small gravel inside the body. Then, the projections were reconstructed by means of the Octopus Imaging software. Even with the compact NT system (L/D: 50), the 3D neutron image of the ancient doll was successfully reconstructed. The image revealed some hidden organic materials coated on the neck of the doll. Moreover, the elemental composition of the terracotta doll was analyzed by using X-ray fluorescence technique. The result could further inform the historical records of the ancient doll.

Neutron imaging, based on a digital-based detector system, was developed for non-destructive internal inspection at the Thai Research Reactor-1/Modification 1 (TRR-1/M1). Neutron activation analysis was employed to determine thermal-neutron flux at the imaging position. The facility provided flux of thermal neutrons at 2.5× 105 cm−2s−1. Several standard samples were used to evaluate the collimation ratio (L/D), resolution, and unsharpness for the current setup of neutron imaging. An analytical method was employed to determine image quality parameters to moderate neutron flux. The L/D ratio depends on the aperture size of the divergent collimator and can be amended by using appropriate sample shape, resulting in more accurate estimate of collimation parameters. Resolution and unsharpness for neutron tomography were 0.5 mm and 1 mm, respectively. Results suggested the possibility of evaluating image quality using samples with non-complex structure.