[cronopios]

There are two of them, but I think they are both at the CERN.

One is displayed to the public, and, IIRC, the other one is in a showcase at the entrance of a lab.

[mino]

I also see it at the Science Museum London in this gallery:

http://www.sciencemuseum.org.uk/visitmuseum/plan_your_visit/...

Was it a loan then? It looked like part of the permanent collection.