Development of novel instrumentation for proton beam characterisation and monitoring for medical and other applications
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BORIS DOI
Abstract
This thesis presents the development, implementation, and evaluation of novel beam-diagnostic instrumentation for 18 MeV proton beams at the Bern Medical Cyclotron (BMC) Laboratory of the University of Bern. The BMC, an IBA Cyclone 18/18 HC cyclotron, serves both routine radiopharmaceutical production and a diverse research programme enabled by a dedicated Beam Transfer Line (BTL). The wide range of beam configurations and irradiation scenarios encountered in this dual-use environment motivates the development of novel diagnostic tools that are accurate, radiation-tolerant, and practical under realistic operational constraints.
Three main areas of beam diagnostics are addressed. First, the stacked foil method for proton beam energy determination is extended into a Bayesian inference framework, providing not only a best estimate of the beam energy but also a rigorous, traceable uncertainty budget. The method is validated at both the nominal 18 MeV energy and at reduced energies around 8 MeV, where conventional approaches become challenging. Complementary time-of-flight measurements confirm the cyclotron RF time structure in the extracted beam, opening a route towards timing-based energy diagnostics. An independent, simulation-supported energy cross-check using activation data from a radiation-hardness campaign further corroborates the results.
Second, beam profile, position, and intensity monitoring are addressed through the development of the Chromoscope, a radiation-hard upgrade of the Pi2 camera-based beam profiler that was previously developed by our group. The Chromoscope replaces the original powdered scintillator screen with a mechanically robust Chromox (Al$_2$O$_3$:Cr$_2$O$_3$) ceramic and relocates the camera electronics away from the radiation zone via a flexible optical fiber bundle. Dedicated radiation-hardness studies demonstrate stable scintillation response of the Chromox screen up to fluences representative of one year of routine operation at the BMC, and negligible degradation of the fiber bundle's spatial resolution and transmission. In parallel, a secondary electron monitor (SEM) is developed and qualified for non-destructive, relative beam-intensity monitoring across the wide dynamic range of the BTL.
Third, non-destructive secondary-radiation monitoring is investigated using the External Fiber Monitor (EFM) and its upgraded version, the External Cube Monitor (ECM), which employs high-light-yield GAGG:Ce inorganic scintillator cubes. The ECM is tested parasitically on existing beamline components at both the BMC and TRIUMF (Vancouver, Canada), demonstrating its capability as an attach-and-monitor intensity sensor. Furthermore, the feasibility of pulse shape discrimination (PSD) with GAGG:Ce is established, achieving clear separation of alpha and gamma events -- a first step towards selective particle identification in mixed secondary-radiation fields, with potential applications e.g. in radioisotope production monitoring.
The commissioning of a solid target beamline, including the development of a remotely controllable motorised bellow system and the optimisation of the respective cyclotron extraction parameters, is documented in the appendix.
Taken together, these developments provide a complementary diagnostic toolkit tailored to the operational realities of a medical cyclotron research facility, addressing beam energy, profile, intensity, and secondary-radiation monitoring with an emphasis on robustness, radiation tolerance, and practical deployability.
Three main areas of beam diagnostics are addressed. First, the stacked foil method for proton beam energy determination is extended into a Bayesian inference framework, providing not only a best estimate of the beam energy but also a rigorous, traceable uncertainty budget. The method is validated at both the nominal 18 MeV energy and at reduced energies around 8 MeV, where conventional approaches become challenging. Complementary time-of-flight measurements confirm the cyclotron RF time structure in the extracted beam, opening a route towards timing-based energy diagnostics. An independent, simulation-supported energy cross-check using activation data from a radiation-hardness campaign further corroborates the results.
Second, beam profile, position, and intensity monitoring are addressed through the development of the Chromoscope, a radiation-hard upgrade of the Pi2 camera-based beam profiler that was previously developed by our group. The Chromoscope replaces the original powdered scintillator screen with a mechanically robust Chromox (Al$_2$O$_3$:Cr$_2$O$_3$) ceramic and relocates the camera electronics away from the radiation zone via a flexible optical fiber bundle. Dedicated radiation-hardness studies demonstrate stable scintillation response of the Chromox screen up to fluences representative of one year of routine operation at the BMC, and negligible degradation of the fiber bundle's spatial resolution and transmission. In parallel, a secondary electron monitor (SEM) is developed and qualified for non-destructive, relative beam-intensity monitoring across the wide dynamic range of the BTL.
Third, non-destructive secondary-radiation monitoring is investigated using the External Fiber Monitor (EFM) and its upgraded version, the External Cube Monitor (ECM), which employs high-light-yield GAGG:Ce inorganic scintillator cubes. The ECM is tested parasitically on existing beamline components at both the BMC and TRIUMF (Vancouver, Canada), demonstrating its capability as an attach-and-monitor intensity sensor. Furthermore, the feasibility of pulse shape discrimination (PSD) with GAGG:Ce is established, achieving clear separation of alpha and gamma events -- a first step towards selective particle identification in mixed secondary-radiation fields, with potential applications e.g. in radioisotope production monitoring.
The commissioning of a solid target beamline, including the development of a remotely controllable motorised bellow system and the optimisation of the respective cyclotron extraction parameters, is documented in the appendix.
Taken together, these developments provide a complementary diagnostic toolkit tailored to the operational realities of a medical cyclotron research facility, addressing beam energy, profile, intensity, and secondary-radiation monitoring with an emphasis on robustness, radiation tolerance, and practical deployability.
Date of Publication
2026
Year of graduation
2026
Theses Type
dissertation
Keyword(s)
Beam Monitoring
•
Scintillation Detection
•
Radiation Hardness
•
Medical Cyclotron
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Proton Beam Instrumentation
•
Pulse-Shape Discrimination
Language(s)
en
Author(s)
Faculty/Graduate School
Access(Rights)
open.access
Primary OA Publication
true