An ADVENTURE project
Ancient Charm is an ADVENTURE project, an action line of NEST (New and Emerging Science and Technology) is an activity in the Sixth Framework Programme (FP6) to support unconventional and visionary research with the potential to open new fields for European science and technology, as well as research on potential problems uncovered by science.
"Integrating and strengthening the European Research Area"
A large variety of chemical, physical and microstructural techniques are employed to characterize objects of cultural significance. Most of these methods are invasive and probes like X-rays and charged particles have limited penetration power in matter.
Neutrons, on the other hand, can penetrate thick layers without substantial scattering or absorption depending on their energy. Until now, thermal (i.e. low energy) neutrons had been used to perform neutron tomographies on cultural heritage samples, showing for instance the interior of hollow objects. However, thermal neutron tomographies do not give indication on the chemical nature of the sample.
Many elements have neutron absorption resonances in the epithermal energy range (1 eV < E < 1 keV). Neutron absorption is followed by the prompt emission of a gamma-ray cascade, and both the gamma emission and the neutron transmission can be measured. Neutron absorption resonances are characteristics for every isotope, and they constitute a useful fingerprint for chemical analysis of the bulk of the sample. Absorption resonances of different energies can be easily identified via the time-of-flight (TOF) technique.
Spatially resolved information can be obtained in transmission geometry via the use of pixelated detectors; measurement of neutron resonances with different strengths can provide an indication of the chemical composition of the bulk of the sample in a completely non-destructive way. Multiple positioning (translation/rotation) of the sample and simultaneous transmission measurements can provide many element-resolved neutron radiographies of bulky samples.
An alternative approach is to make use of a collimated neutron beam to locally irradiate a selected region of the sample, and measure the gamma-ray emission following neutron capture to identify (again through the TOF technique) the emitting elements.
Developing the Neutron Resonant Capture Imaging combined with Neutron Resonance Transmission (NRCI/NRT) as a non-invasive technique for imaging and its use in cultural heritage research was the ultimate aim of the ANCIENT CHARM project.
The idea of developing an imaging technique based on epithermal neutron absorption was totally new and presented a number of scientific and technical challenges which were best addressed by the joint development of two related imaging methods:
• Prompt Gamma Activation Imaging combined with cold Neutron Tomography (PGAI/NT) and
• Neutron Diffraction Tomography (NDT).
The combined use of the three new imaging methods provide a new, comprehensive neutron-based imaging approach to the non-destructive analysis of cultural heritage samples whose integrity must be preserved, like for instance archaeological findings, relieves, ancient jewels.