Cultural heritage investigations using cosmic muons

Cosmic rays are a constant, free source of radiation that can be exploited in various ways to probe heavy and extended objects. Analyzed with proper detection systems, they can produce radiographic as well as tomographic images of bulky materials. Several applications have been proposed, in particular in the domain of security checks, and some are presently fielded for routine use. In this paper, cosmic muon technology is presented, there are two different ways of using cosmic muons in order to produce images of massive objects, namely the absorption method and the Muon Scattering Tomography (MST) method. The absorption method requires a single detector located in general below or on the side of the volume to investigate, the MST method needs two detectors to measure the position and the direction of the muons both when they enter the volume to be inspected and when they exit. Absorption can be applied to the investigation of very large objects (volcanoes, mines, buildings, etc.) while MST is an adequate tool to investigate the content of volumes not too large with respect to the reasonable dimensions of the detectors and, considering in particular cultural heritage applications, not exceeding a few meters such as small vaults in buildings, sarcophaguses, or any other thick and heavy object whose contents are not readily reachable. MST offers the possibility of discriminating different material composing the inspected object with a good degree of resolution