Isotopic imaging with epithermal neutrons at the ISIS Neutron and Muon Source.

An advanced non-invasive isotopic imaging technique based on Neutron Resonance Transmission Imaging (NRTI) has been implemented at the INES beamline of the ISIS Neutron Muon Source (UK), featuring high sensitivity to isotopes and enabling enhanced contrast in bulk radiography. NRTI relies on the neutron resonant absorption reactions occurring at epithermal energies. Nuclear resonance energies are isotope fingerprints, since the energy position of resonance dips in the transmitted neutron spectrum is uniquely associated with the individual isotopes present in the sample. Using a time and space-resolved detector with an event-mode acquisition system it is possible to conduct simultaneous spectroscopy and imaging investigation by recording the transmitted spectra in each pixel. Resonance selections can be performed post-processing through specific data analysis tools to enhance the absorption contrast of selected isotopes and visualise their distribution in the bulk. A pilot study with samples enriched with Ag-109 and Ag-107 is presented to demonstrate the potential of NRTI at the ISIS facility as a powerful and competitive tool for isotopic imaging. Future quantitative calibration for accurate isotopic ratio evaluation will expand its utility across various fields, such as nuclear engineering and archaeology, enabling detailed non-invasive analysis of complex materials previously challenging with conventional methods.