Metrological characterisation of neutron and X-ray computed tomography

As additive manufacturing (AM) advances, the need for reliable, non-destructive dimensional inspection of complex internal geometries has grown. Nondestructive quality control could be performed by industrial X-ray computed tomography (XCT) in case of low-atomic-number materials (eg, engineering plastics, aluminium, titanium, steel). In contrast, neutron computed tomography (NCT) is available for inspecting certain high atomic number materials, including tungsten, tantalum, and platinum. This study presents a comprehensive metrological evaluation of three XCT systems and one NCT system, using a custom-designed multi-sphere calibration phantom and Ti6Al4V specimen. Reference measurements were obtained via a coordinate measuring machine (CMM), and a detailed measurement model was developed to support rigorous uncertainty analysis in case of XCTs and NCT. The NCT system, evaluated within a metrological framework for the first time, achieved a voxel size of 43 μ m and an expanded uncertainty of 0.107 mm (k=2), comparable to the XCT system (64 μ m voxel size). Measurement errors ranged from −0.064 mm to +0.038 mm for NCT and from −0.039 mm to +0.036 mm for XCT systems. Among the five uncertainty evaluation methods tested, the VDA 5 approach provided the most balanced and reliable estimates. The calibration phantom proved reusable for NCT due to manageable activation levels. This work underscores the importance of selecting appropriate imaging modalities and uncertainty models, particularly those incorporating bias, for traceable and reliable dimensional metrology in advanced manufacturing contexts.