Particle Accelerators and Detectors for medical Applications

Research on particle accelerators and detectors is centred on the versatile 18-MeV cyclotron facility, which is used in different research lines, from radioisotope production for radiopharmacy, to radiation hardness studies. We have developed a method to reduce the beam current, from the factory-defined range of current (10-150-uA), down to the pA range. We have conceived and realised an innovative beam monitoring detector (UniBEaM) to measure on-line the horizontal and vertical profiles by means of scintillating fibres passed through the beam. An innovative apparatus to measure on-line the transverse beam emittance using 4 UniBEaM detectors was built and tested.

We have recently developed a novel active irradiation system to enhance the production of radioisotopes using medical cyclotrons, named Automatic Focusing System (AFS).

Research on beam monitoring techniques has led to the design and construction of two beam monitors, the Pi2 (capable of 2D reconstruction of the beam) and the Pi3 (where the monitoring is extended to the third dimension). 

The use of doped silica scintillating fibres for the detection of radiation is at the basis of the UniBEaM and of an innovative detector for FLASH radiation therapy that we are developing in the framework of the PROOF project.


The AFS system

The Automatic Focusing System (AFS) allows for enhancement of the irradiation performance of the Bern cyclotron for the production of radioisotopes using solid targets. The apparatus is based on a compact focusing and steering magnet system, followed by a two-dimensional beam monitoring detector and a specific software that drives the magnets for improved focusing. The system automatically reacts to perturbations, ensuring that the beam is optimally focused on the target. Its compactness guarantees its employability in limited-space facilities, such as medical cyclotrons.

The first prototype was built and tested using the BTL and showed that the production yield can be enhanced up to a factor of 20. The AFS was then installed directly in the cyclotron bunker and further developments are ongoing.


The Pi2 beam monitor

Pi2 is a two-dimensional non-destructive beam monitor, entirely realised by the LHEP medical group. It is based on a thin aluminium foil coated with P47 scintillating material that can be remotely inserted in and extracted from the beam. The scintillating light is read out by a CCD camera located outside of the vacuum chamber. It measures the transverse position, shape and intensity of the beam, and can be used in numerous applications, such as radiation hardness and radioisotope production studies.

Pi2 beam monitoring detector operation scheme
Scheme of operation of the Pi2 beam monitoring detector.


The Pi3 beam monitor

Based on Pi2, Pi3 is a three-dimensional non-destructive beam monitor that has been conceived, realised and tested in Bern. Based on a thin aluminium foil coated with P47 scintillating material and equipped with a miniaturised CCD camera, this detector moves along the beam axis and allows for a 3D reconstruction of the beam envelope. Differently from its predecessor, whose camera is located in air and collects light through a transparent window, the Pi3 beam monitor is like an endoscopic camera that operates in vacuum.  

This general-purpose instrument is suitable for any ion accelerator facility and can be operated inside magnetic fields to study focusing and defocusing properties of the beam. 

The beam as seen by the Pi3 detector. The camera and the scintillating foil are moving in vacuum along the beam. The beam, during the video, gets shrunk by the focusing magnets. Scattered protons hitting the camera appear as flashing dots and traces.
3d reconstruction of beam envelope obtained using Pi3 beam monitor
The 3D reconstruction of the beam envelope, obtained using the Pi3 beam monitor.

The External Fiber Monitor

The External Fiber Monitor (EFM) is a novel beam monitoring detector based on Ce-doped silica optical fibres designed to track particle beam position and current, particularly for  medical  applications. Unlike traditional methods, which require intercepting the beam and  working within a vacuum environment, the EFM operates externally, making it an innovative, robust  and versatile tool for monitoring particle beams.

At the Bern Medical cyclotron, an experiment was performed in which the EFM was used to monitor a 150 nA beam of 18 MeV protons directed into a beam dump. The EFM demonstrated its capability to measure relative beam current and displacement in X and Y directions through real-time Radiation-Induced Emission (RIE) measurements, providing a highly effective and non-invasive method for monitoring particle beams with excellent linearity and potential for further applications. Further developments are ongoing aimed at monitoring currents in the range 10-100 uA, typical of medical radioisotope production.


Photo of experimental setup in the BTL, showing the UniBeam used for position monitoring, and the collar on which four scintillator fibers are mounted surrounding the beam dumo
Photo of experimental setup in the BTL, showing the UniBeam used for position monitoring, and the collar on which four scintillator fibers are mounted surrounding the beam dump


Selected publications

P. D. Häffner, C. Belver-Aguilar, S. Braccini, P. Casolaro, G. Dellepiane, P. Scampoli, An Active Irradiation System with Automatic Beam Positioning and Focusing for a Medical Cyclotron, Appl. Sci. 2021, 11(6), 2452;

C. Belver-Aguilar, S. Braccini, T.S. Carzaniga, A. Gsponer, P. Häffner, G. Molinari, P. Scampoli, M. Schmid, Development of novel non-destructive 2D and 3D beam monitoring detectors at the Bern medical Cyclotron, IBIC 2020;

C. Belver-Aguilar, S. Braccini, T. S. Carzaniga, A. Gsponer, P. D. Häffner, P. Scampoli, M. Schmid, A Novel Three-Dimensional Non-Destructive Beam-Monitoring Detector, Appl. Sci. 2020, 10(22), 8217;