• solid target
• beam line
• PET-cyclotron

The cyclotron is the best accelerator to produce radioisotopes for medical applications because of its energy and properties.
Sometimes, it is very important to have a very focused beam with specific intensity on a proper target. In these cases a beam transport line has to be installed at the exit port of the cyclotron in order to obtain a beam with small transverse dimension: for example this is required to produce PET (Positron Emission Tomography) radioisotopes, where for an efficient exploit of the expensive target the beam has to be very small and precisely positioned. For this purpose the medical cyclotron of the Bern's Hospital was equipped at one of the exit ports with a PET-Mini Beamline, consisting of two quadrupoles and two steering magnets. Before the installation inside the cyclotron bunker, the beam line was studied to find position and currents of the magnets providing the smallest spot and the best centrality with respect to a target.
In this thesis experimental measurements and simulations of the beam leaving the PET-Mini Beamline are reported. The beam profiles dependence on the current in the two quadrupoles and on their position along the transport line were studied in order to find the narrow and circular profiles of the beam.
After a short summary of the basic principles of PET imaging and of the role of the cyclotron in the production of PET-radionuclides, an overview of the Bern cyclotron laboratory and a detailed description of the PET-Mini Beamline is reported.
In particular the beam dynamic through the PET-Mini Beamline is described using the matrix notation. By means of the matrix formalism the dependence of the beam shape was simulated changing: a) the quadrupole currents; b) the magnet positions along the transport line; c) the cyclotron working time (i.e. less than an hour (cold machine) or greater than an hour (warm machine)). The results of these simulations were then compared with direct measurements of beam profiles changing currents and position of the PET-Mini Beamline magnets.
In fact UniBEam particle detector, developed at the LHEP of the Bern University and positioned along the beam path, allowed to derive the beam profile by measuring the flux density in different transverse positions of its fiber.
The beam profile was also measured by means of CDD sensors collecting photons emitted by a thin P47 phosphor layer coating an aluminium foil positioned at 45° along the beam path.
As a result of simulations and experimental measurements a strongly focused beam suitable for efficient radioisotope production has been obtained.