The New York Times reported this week on the search for a masterpiece of Da Vinci, The Battle of Anghiari, that is presumably "buried" beneath other frescoes in the Palazzo Vecchio, Florence.
One technique uses backscattered neutrons, the other uses emitted gamma rays in a version of neutron activation analysis.
An interview with Maurizio Seracini, the lead engineer, appeared in Wired.
There is also a scientific article out discussing preliminary tests:
Neutron back scattering for the search of the Battle of Anghiari