X-ray attenuation strictly depends on the number of electrons in the sample materials, and thus on their position in the periodic system. Hydrogen and organic materials are hardly visible, and metals are impenetrable for X-rays. Neutrons interact with the nuclei, and their attenuation often shows complementary behaviour to X-rays: Hydrogen and many light elements deliver high contrast, while many metals, especially aluminium and lead, are easily penetrated. Organic materials like bones can be detected in metal casings like relic containers.
Because of the high penetration of neutrons, they can reach deep into the bulk of materials, and the gamma cascade emitted on neutron absorption can measure elemental, even isotopical composition in the bulk material by Promt Gamma Activation Analysis (PGAA), other than X-ray fluorescence, which only delivers information about surfaces.
PGAA and neutron imaging are available at the FRM II reactor of Technische Universität München which will resume operation in early 2025, but neutron imaging, including computed tomography is also available at the reactor of Atominstitut in Vienna.
The talk will show several examples to illustrate neutron methods, many of them from cultural heritage.