The XTRA Option at the NEUTRA Facility—More Than 10 Years of Bi-Modal Neutron and X-ray Imaging at PSI

Just after the start into the new millennium the concept for combined neutron and X-ray imaging was introduced by extending the standard configuration of the thermal neutron imaging NEUTRA instrument with a complementary 320 kV X-ray tube setup. Using essentially the same detector configuration for both neutron and X-ray imaging enables a pixel-wise (in radiography) and a voxel-wise (in tomography) correlation and combination of attenuation data. The optimal use and analyses of such complementary data sets depend on the specific investigation and research question and range from a combinatory interpretation of separately analyzed images to full data fusion approaches. Here, several examples from more than a decade of bimodal neutron and X-ray imaging at NEUTRA at PSI shall be reviewed.

Using Thermal Neutron Imaging in Forest Products Research

Neutron imaging is a nondestructive evaluation technique with enhanced hydrogen sensitivity that allows researchers to monitor water content and transport in materials. In lignocellulosic research, this technique has typically been used to measure changes in moisture content, water transport and even local changes in the density of wood. Yet, studies looking into the combined effects of moisture-uptake, chemical modifications and thermal degradation are still lacking. This is perhaps due to the inherent limited availability of these instruments and their lesser spatial resolution compared to X-ray imaging. While recent advances in detector technology and neutron production have led to continued improvements in both instrument availability and spatial resolution, the technique remains underutilized in forest products research. Here, we used thermal neutron imaging to measure differences in the attenuation of the neutron beam due to acetylation in both solid wood samples and wood−plastic composite samples, as well as a thermally degraded wood sample. Our results show that moisture plays a key role in the contrast. Moreover, we showed that the attenuation coefficient is particularly sensitive to changes in density and/or local hydrogen content caused by thermal degradation of the wood polymers.