Muons reveal the interior of volcanoes
The MU-RAY project has the very challenging aim of providing a “muon X-ray” of the Vesuvius volcano (Italy) using a detector that records the muons hitting it after traversing the rock structures of the volcano. This technique was used for the first time in 1971 by the Nobel Prize-winner Louis Alvarez, who was searching for unknown burial chambers in the Chephren pyramid.
Muons come from the interaction of cosmic rays with the Earth's atmosphere. They are able to traverse layers of rock as thick as one kilometre or more. During their trip, they are partially absorbed by the material they go through, very much like X-rays are partially absorbed by bones or other internal structures in our body. At the end of the chain, instead of the classic X-ray plate, is the so-called 'muon telescope', a special detector placed on the slopes of the volcano.
As for ordinary X-ray radiography, a larger muon absorption corresponds to a higher density in the volcano. The flux of backward muons can be used for normalization.
[From H.K.M. Tanaka et al., Earth and Planetary Science Letters 263 (2007) 104]
Reconstructed average density distribution of the summit of Mt. Asama in Japan.
[From H.K.M. Tanaka et al., Earth and Planetary Science Letters 263 (2007) 104]
The thicker the layer of rock, the larger the detector area must be, otherwise it would take too long to take the data. “We are working on a prototype of a new detector,” says Paolo Strolin. “The new system will be modular to globally cover surfaces of the order of tens of square metres. The detectors will have good angular resolution and an improved signal-to-background ratio.” The R&D project on the new generation ‘muon telescopes’ is supported by INFN, the Italian National Institute of Geophysics and Volcanology (INGV), the Italian Government and the University of Naples Federico II.
The MU-RAY collaboration involves physicists and volcanologists from the Universities of Florence, Naples, Perugia and Tokyo, as well as from INFN, the Vesuvius Observatory of the INGV, Fermilab and LAL-Orsay. Other volcanoes are being studied with this technique in Japan and in the Lesser Antilles. |
With this article, the Bulletin begins a new series providing readers with a look "outside CERN". We will regularly feature scientific activity going on in CERN's Member States. |