While I do not believe that this series of posts can be really useful to my younger colleagues, who will in a month have to participate in a tough selection for INFN researchers in Rome, I think there is some value in continuing what I have started last month. 
After all, as physicists we are problem solvers, and some exercise is good for all of us. Plus, the laypersons who occasionally visit this blog may actually enjoy fiddling with the questions. For them, though, I thought it would be useful to also get to see the answers to the questions, or at least _some_ answer.
Indeed, many of the questions I have put together in this series have multiple possible solutions, or are sufficiently ill-posed to lend themselves to criticism. This is in fact exactly what they are meant to do: as an examiner, you learn quite a lot from a critical answer and much less so from a correct unique solution to a dull exercise.

So let's go on with the series, with the understanding that I will post some answers to the questions, in the comments thread, unless some tidy reader decides to do so before me (please do, I'm very lazy this summer).

The problems of today have to do with the interactions of particles with matter.

13 - Discuss what physical changes are expected if a 1 inch thick disk of iron weighing 1kg receives a flux of a triillion charged pions with an energy of 5 GeV each. How does the answer change if the energy goes to 50 GeV per pion? And for 0.5 GeV per pion?

14 - Explain very briefly the concept of compensation in a hadronic calorimeter for a particle physics experiment.



I offer these questions as a self-test of one's knowledge in particle physics. I am not part of the INFN selection committee. I have no connection to the selection committee, nor any insider information on how the exam will be structured. All I know about it is what is contained in the official call, available to everybody. I do have some previous experience with INFN selections of researchers, but this needs not be relevant for this year's selection.