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Alessandro Fornaini (promotion date: 2 June 2005)

X-ray imaging and read out of a TPC with Medipix CMOS Asic.

Promotion Date: 2 June 2005

MESA+

I’ll start by explaining something about the title. Medipix is a European collaboration of about 15 institutes all over Europe. Its goal is to develop a new technology for radiographies, basically a new type of instrument to detect X-rays. The reason for this is that with this new technology you need much less (20 times!!) radiation. But also these devices can make images that are impossible to make with the current technology and the images can be stored in a computer, which is an advantage as opposed to the bulky X-ray charts you have to mail around if another doctor needs the patient’s data. You can compare our new technology with a digital camera, that however does not see the light but the X-rays.

What was your thesis about?

I’ll start by explaining something about the title. Medipix is a European collaboration of about 15 institutes all over Europe. Its goal is to develop a new technology for radiographies, basically a new type of instrument to detect X-rays. The reason for this is that with this new technology you need much less (20 times!!) radiation. But also these devices can make images that are impossible to make with the current technology and the images can be stored in a computer, which is an advantage as opposed to the bulky X-ray charts you have to mail around if another doctor needs the patient’s data. You can compare our new technology with a digital camera that however does not see the light but the X-rays.

And this is completely new technology?

Yes. Actually the fundamental physics was used for experiments at CERN to detect elementary particles. We transferred the world of high energy physics to daily life.

The name of the collaboration is also the name of the new instrument we developed: Medipix.

Can you briefly explain the underlying principle?

Basically there is a thin layer of silicon. If an X-ray hits the silicon, it is converted into electrons. Connected to this layer of silicon there is an electronic chip detecting the electrons like an electrical current. Then specific computer software ‘translates’ this input into a set of data reconstructing the image. We also went back to fundamental physics by developing a new standard of detection, the TPC (Time Projection Chamber), for elementary particles.

You spent the larger part of your research in Amsterdam. Why was that?

It is quite simple really: my supervisor, Professor Bob van Eijk, was working at NIKHEF (Nederlands Instituut voor Kern- en Hoge Energie Fysica) at the time, while teaching in Twente. The collaborations with Twente were all on a personal level.

Did you have a lot of contact with the people from CERN?

Yes, quite a lot. An Italian group, a group from Amsterdam and a group from CERN really worked side by side to develop the detector. It was a very close collaboration. This was one of the aspects I liked the most during the four years of my PHD: having the possibility work with other people from other countries and to travel, see other institutes and laboratories.

From a human point of view I was lucky for the people from CERN and NIKHEF were very interesting people. What I appreciated the most was that I was quite free to follow my own path. I started with a research project that was quite different, but I did not really believe in one of them and was completely free to devote all my energies on the other one. When I started on the TPC, with only one other person working on it at the beginning, it was a bit of a gamble. It could have been not productive at all, but still I was free to follow my interest.

It worked and we were all very happy.

But did you have moments of despair?

I certainly did, because it took is 1,5 years to get this device to work. We expected it to work, but it just didn’t. We tried and tried again, went about it in another way and we even talked about giving up. When we finally got it to work, we understood why it didn’t in the first place, which again added to our basic knowledge of the underlying physics.