Vertical orbit excursion Fixed Field Accelerators (vFFAs) feature highly nonlinear magnetic fields and strong transverse motion coupling. The detailed study of their Dynamic Aperture (DA) requires computation codes allowing long-term tracking and advanced analysis tools to take the transverse motion linear and nonlinear coupling into account. This coupling completely transforms the beam dynamics compared to a linear uncoupled motion, and an explicit definition of the DA is needed to characterize the performance and limitations of these lattices. A complete study of the DA in the 4D phase space in highly nonlinear and strongly coupled machines must give a measure of the stability domain but also means to assess the operating performance in the physical coupled space. This work presents a complete set of methods to perform such detailed analysis. These methods were explored and compared to compute and characterize the DA of an example vFFA lattice. The whole procedure can be further applied to evaluate DA using realistic models of the magnetic fields, including fringe fields and errors.

In the framework of the LHC Injector Upgrade project, a new internal dump for the CERN Proton Synchrotron (PS) ring has been designed, installed, and successfully commissioned. This device is designed to move rapidly into the beam and stop charged particles over several thousand turns to provide protection to PS hardware against beam -induced damage. Due to its design, the internal dump absorbs only a fraction of the secondary particles shower produced by the beam particles that impinge on it. The performance of the dump should ensure efficient use throughout the PS energy range, i.e. from injection at 2 GeV (kinetic energy) to flat top at 26 GeV (total energy). This paper presents comprehensive numerical simulations that combine advanced beam dynamics and beam -matter interaction codes to analyse the behaviour of stopped or scattered particles. Based on the impacts computed by multi -turn beam dynamics simulations, detailed shower simulations with FLUKA were performed to assess the impact of the radiation field on downstream equipment, with a particular emphasis on the dose measured by Beam Loss Monitors. The results of these numerical simulations are compared with the data collected during the routine operation of the PS and its internal dump.

Particle tracking codes such as MAD-X or TRANSPORT commonly use a matrix formalism to propagate beams through magnetic elements as it simplifies the analysis of particle behavior, facilitates beam optimization and component design, and enables accurate particle accelerator simulations. However, these codes are inefficient when tracking many particles or accounting for energy degradation along the beamline. To overcome these limitations, we introduce Georges, a Python library used in the field of particle accelerators for medical applications comprising two modules: Manzoni and Fermi. Manzoni is an efficient particle tracking code that can track many particles while calculating beam losses and energy degradation using the Fermi–Eyges formalism implemented in the Fermi module. In this paper, we present the implementation details of Georges, which includes a verification conducted against other software tools such as MAD-X and BDSIM, along with a documentation on computational time.

Proton therapy systems are used worldwide for patient treatment and fundamental research. The generation of secondary particles when the beam interacts with the beamline elements is a well known issue. In particular, the energy degrader is the dominant source of secondary radiation. This poses new challenges for the concrete shielding of compact systems and beamline elements activation computation. We use a novel methodology to seamlessly simulate all the processes relevant to the activation evaluation. A realistic model of the system is developed using Beam Delivery Simulation (BDSIM), a Geant4-based particle tracking code that allows a single model to simulate primary and secondary particle tracking and all particle-matter interactions. The secondary particle fluxes extracted from the simulations are provided as input to FISPACT-II to compute the activation by solving the rate equations. This approach is applied to the Ion Beam Applications (IBA) Proteus ® ONE (P1) system and the shielding of the proton therapy research centre of Charleroi, Belgium. Proton loss distributions are used to model the production of secondary neutrals inside the accelerator structure. Two models for the distribution of proton losses are compared for the computation of the clearance index at specific locations of the design. Results show that the variation in the accelerator loss models can be characterised as a systematic error.

Proton therapy systems produce large fluxes of energetic secondary particles when tailoring the beam energy and transverse profile to the specificities of each irradiation plan. A Low Activation Concrete (LAC) mix is foreseen for parts of the shielding of the Ion Beam Applications (IBA) Proteus® One (P1) compact system at the ProtherWal proton therapy centre in Charleroi, Belgium, to limit the long-term activation of the concrete shielding. To experimentally monitor the long-term activation and validate the beneficial impact of the LAC mix, a setup of four removable cores to be placed at critical locations in the cyclotron vault is optimised. We report on the experimental and simulation monitoring setup design. Our validated BDSIM/FISPACT-II methodology combines particle tracking and Monte-Carlo particle-matter interactions simulations using Beam Delivery Simulation (BDSIM) and the computation of the activation using FISPACT-II. We show that the evaluation of the short-term activation of the cores is essential to the measurement analysis. We detail a hybrid workflow based on numerical simulations that uses logging data of the workloads of the clinical and research beam production and experimental measurements to evaluate and monitor the short- and long-term activation at any point during the centre lifetime and decommissioning period. The activation of the cores using a realistic foreseen irradiation pattern is studied, allowing for the characterisation of the measurement process and radiation protection considerations related to the measurement campaign. The final experimental setup and the supporting online simulation tools are discussed in detail.

Next-generation proton therapy centres couple treatment and research programs, leading to higher beam currents and longer irradiation times than in clinical conditions. Large fluxes of energetic secondary particles are produced and long- and short-term radioactive nuclides are generated in the concrete shielding of the cyclotron vault. While the overall long-term activation of the centre is well known from the shielding design activation studies, the short-term activation peaks are still of importance when radiation protection studies are involved. The centre shielding design was validated using the BDSIM/FISPACT-II methodology combining particle tracking and Monte Carlo particle-matter interactions simulations using Beam Delivery Simulation (BDSIM) and the computation of the activation using FISPACT-II. We establish, as the next stage of our methodology, the simulation of the decay radiation of the activated concrete shielding and the accurate scoring of the related radiation protection quantities. A single BDSIM simulation per radioactive nuclide is performed based on the nuclide concentration obtained from the prior FISPACT-II activation computations at the start of a given cooling period. The evolution of the radiation protection quantities is obtained by scaling the results with the nuclides activity obtained at later times from fast FISPACT-II computations. We show the evolution of the ambient dose equivalent in the centre vault when considering regular concrete and Low Activation Concrete (LAC) as shielding material to demonstrate the efficiency of LAC mix in mitigating the shielding activation.

The study of beam dynamics in accelerators featuring main magnets with complex geometries such as Fixed Field Accelerators (FFAs) requires simulation codes allowing step-by-step particle tracking in complex magnetic fields, such as the Zgoubi ray-tracing code. To facilitate the use of Zgoubi and to allow readily processing the resulting tracking data, we developed a modern Python 3 interface, Zgoubidoo, using Zgoubi in the backend. In this work, the key features of Zgoubidoo are illustrated by detailing the main steps to obtain a non-scaling FFA accelerator from a scaling design. The results obtained are in excellent agreement with prior results, including the tune computation and orbit shifts. These results are enhanced by Zgoubidoo beam dynamics analysis and visualization tools, including the placement of lattice elements in a global coordinate system and the computation of linear step-by-step optics. The validation of Zgoubidoo on conventional scaling and non-scaling FFA designs paves the way for future uses in innovative FFA design studies.

Arc-therapy and flash therapy are promising proton therapy treatment modalities as they enable further sparing of the healthy tissues surrounding the tumor site. They impose strong constraints on the beam delivery system and rotating gantry structure, in particular in providing high dose rate and fast energy scanning. Fixed-field achromatic transport lattices potentially satisfy both constraints in allowing instant energy modulation and sufficient transmission efficiency while providing a compact footprint. The presented design study uses fixed-field magnets with spiral edges respecting the FFA scaling law. The cell structure and the layout are studied in simulation and integrated in a compact gantry. Results and further optimizations are discussed.

Proton therapy is a well established treatment method for ocular cancerous diseases. General-purpose multi-room systems which comprise eye-treatment beamlines must be thoroughly optimized to achieve the performances of fully dedicated systems in terms of depth-dose distal fall-off, lateral penumbra, and dose rate. For eye-treatment beamlines, the dose rate is one of the most critical clinical performances, as it directly defines the delivery time of a given treatment session. This delivery time must be kept as low as possible to reduce uncertainties due to undesired patient movement. We propose an alternative design of the Ion Beam Applications (IBA) Proteus Plus (P+) eye treatment beamline, which combines a beam-stopping device with the already existing scattering features of the beamline. The design is modelled with Beam Delivery SIMulation (BDSIM), a Geant4-based particle tracking and beam-matter interactions Monte-Carlo code, to demonstrate that it increases the maximum achievable dose rate by up to a factor 3 compared to the baseline configuration. An in-depth study of the system is performed and the resulting dosimetric properties are discussed in detail.

The treatment protocols of cancerous ocular diseases with proton therapy are well established, and dedicated eye-treatment systems can produce the clinical beam properties that meet the peculiar features required by eye-treatment modalities. However, for general-purpose multiroom systems comprising eye-treatment beamlines and nozzles, the design and commissioning procedures must be optimized to achieve the performances of fully dedicated systems in terms of depth-dose distal falloff, lateral penumbra, and dose rate. This paper presents a realistic start-to-end beam transport and particle-matter interactions model of the ion beam applications Proteus (R) Plus (P+) single-scattering eye-treatment room with Beam Delivery SIMulation (BDSIM) using Geant4. The model is used to establish optimization patterns in terms of beam optics to achieve a smaller depth-dose distal falloff than the design baseline while maintaining a nominal dose rate and lateral flatness of the dose deposition profile. An alternative design is proposed to increase the dose rate further by up to a factor 3, allowing for delivering a complete hypofractionated treatment session under 60 s. It uses a beam-stopping device to complement the existing scattering features of the nozzle. An in-depth study of the system is performed using BDSIM and the numerical simulations are discussed in detail.

In X‐ray excited photoelectron emission (XPS), the shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface. It is also influenced by intrinsic excitations due to the sudden creation of the static core hole. In order to approximately determine the primary excitation spectrum of the considered transition corrected for both extrinsic and intrinsic excitations, we developed in a previous work [E. Gnacadja, N. Pauly, S. Tougaard, Surf. Interface Anal. 52 (2020) 413] a universal analytical expression for the energy loss cross section including extrinsic and intrinsic excitations. We apply the present universal cross section to test to what extent these primary excitations spectra can be used for XPS quantification based on peak area ratios. The procedure is applied to the study of three sets of polycrystalline alloys (Cu0.75Au0.25, Cu0.50Au0.50, and Cu0.25Au0.75) and to three metal oxides (HfO2, ZrO2, and Cu2O). We show that although the individual peaks are very different from those obtained with the classical universal Tougaard cross section, the determined quantitative compositions are equivalent (but not better). This implies that the relative contribution from intrinsic excitations is roughly the same for all peaks for a given sample and they therefore cancel out when peak area ratios are considered.

Due to the advancement of proton therapy for cancer treatment, there has been a worldwide increase in the construction of treatment facilities. Therapy centres are often coupled with clinical, biological or material-science research programs. Research activities require proton beams at energies spanning an extensive range with higher beam currents and longer irradiation times than clinical conditions. Additionally, next-generation proton therapy systems are evolving towards more compact designs. In addition to the increased centres’ workloads, reducing the system in size produces a more significant number of secondary particles per unit volume and time. Therefore, the activation level of materials constituting those future proton therapy centres is expected to be higher, increasing the ambient dose and the amount of radioactive waste collected at the end of a centre’s lifetime. These operating conditions pose new challenges for the shielding design and the reduction of the concrete activation. To tackle them, we propose a novel approach to seamlessly simulate all the processes relevant for the evaluation of the concrete shielding activation using, as an illustration, the Ion Beam Applications Proteus $$^\circledR $$ One system. A realistic model of the system is developed using Beam Delivery Simulation (BDSIM), a Geant4-based particle tracking code. It allows a single model to simulate primary and secondary particle tracking in the beamline, its surroundings, and all particle-matter interactions. The code system and library database FISPACT-II allows the computation of the shielding activation by solving the rate equations using ENDF-compliant group library data for nuclear reactions, particle-induced or spontaneous fission yields, and radioactive decay. As input, FISPACT-II is provided with the secondary particle fluences scored using the BDSIM Monte Carlo simulations. This approach is applied to the proton therapy research centre of Charleroi, Belgium. Results compare the evolution of the clearance level and the long-lived nuclide concentrations throughout the facility lifetime when using regular concrete or the newly developed Low Activation Concrete (LAC). A comparison with the initial shielding dimensioning has been performed for all the shielding walls to validate the methodology and highlight the clear benefits of integrating LAC inserts in the shielding design. The effectiveness of coupling BDSIM and FISPACT-II gives a glimpse of the possibility of a complete activation study following the actual workloads of the centre, allowing a better assessment of the shielding activation level at any time of the facility lifespan.

In hadron therapy beamlines, passive elements are used to reduce the beam energy or to shape its transverse profile and frequently complement the magnetic transport channel elements. In particular, cyclotron-based facilities feature energy degraders to tailor the energy to the treatment value. As such, the numerical modeling of hadron therapy beamlines is crucially reliant on the accuracy of the available beam–matter interaction models to simulate the beam properties at levels suitable for clinical applications. While integrated Monte Carlo codes reach these accuracy levels, ultra-fast numerical codes are essential for beam commissioning controls applications or fast iterative optimization of new designs. To that end, we propose a novel effective model to compute the beam–matter interactions in a hybrid fashion, using tabulated range tables, the semi-analytical Fermi–Eyges approximation, and fits extracted from Monte Carlo data. In this work, we detail the method and benchmark each step with Geant4 simulations. Finally, we validate its accuracy with beam-based measurements from a proton therapy facility using our Python-language implementation which is shown to provide computation time of the order of milliseconds. The results are discussed in detail.

Beam Delivery Simulation (BDSIM) is a program based on Geant4 that creates 3D radiation transport models of accelerators from a simple optical description in a vastly reduced time frame with great flexibility. It also uses ROOT and CLHEP to create a single simulation model that can accurately track all particle species in an accelerator to predict and understand beam losses, secondary radiation, dosimetric quantities and their origin. BDSIM provides a library of scalable generic geometry for a variety of applications. Our Python package, Pyg4ometry, allows rapid preparation and conversion of geometries for BDSIM and other radiation transport simulations including FLUKA. We present a broad overview of BDSIM developments related to a variety of experiments at several facilities. We present a model of the forward experiment FASER at the LHC, CERN where the geometry is composited from multiple sources using Pyg4ometry. The analysis of particle history is presented as well as production mechanisms. We also present the application of recently introduced laser interactions in Geant4 to Compton photons from a laserwire diagnostic at the ATF2.

Hadron therapy centres are evolving towards reducedfootprint layouts, often featuring a single treatment room. The evaluation of beam properties, radiation protection quantities, and concrete shielding activation via numerical simulations poses new challenges that can be tackled using the numerical beam transport and Monte-Carlo code Beam Delivery Simulation (BDSIM), allowing a seamless simulation of the dynamics as a whole. Specific developments have been carried out in BDSIM to advance its efficiency toward such applications, and a detailed 4D Monte-Carlo scoring mechanism has been implemented. It produces tallies such as the spatial-energy differential fluence in arbitrary scoring meshes. The feature makes use of the generic boost::histogram library and allows an event-by-event serialisation and storage in the ROOT data format. The pyg4ometry library is extended to improve the visualisation of critical features such as the complex geometries of BDSIM models, the beam tracks, and the scored quantities. Data are converted from Geant4 and ROOT to a 3D visualisation using the VTK framework. These features are applied to a complete IBA Proteus One model.

The high importance of X‐ray photoelectron spectroscopy (XPS) in surface analysis is well established. In XPS, the shape of the measured peaks is affected by two classes of energy loss: extrinsic losses because of the transport of photoelectrons in the matter and intrinsic losses because of the sudden creation of the static core hole. In order to perform a quantitative, comprehensive determination of the zero‐energy loss spectrum, a systematic and physically meaningful background subtraction method must be used. In this paper, we propose a universal analytical expression to model the energy loss cross section of the emitted photoelectrons for transition metals and their oxides. The proposed expression is a generalization of the well‐known Tougaard's universal inelastic scattering cross section to also account for the intrinsic losses. We demonstrate the use of this to determine the primary excitation spectra of several transition metals and their oxides, and we compare the results with a more accurate calculation based on the dielectric response model for XPS.

Hadron therapy installations are evolving towards more compact systems that require higher-quality beams for advanced treatment modalities such as proton flash and arc therapy. Therefore the accurate modelling of present and next-generation systems poses new challenges where the simulations require both magnetic beam transport and particle-matter interactions. We present a novel approach to building simulations of beam delivery systems at a level suitable for clinical applications while seamlessly providing the computation of quantities relevant for beam dose deposition, radiation protection assessment, and shielding activation determination. A realistic model of the Ion Beam Applications (IBA) Proteus® One system is developed using Beam Delivery Simulation (BDSIM), based on Geant4, that uniquely allows simulation using a single model. Its validation against measured data is discussed in detail. The first results of self-consistent simulations for beam delivery and equivalent ambient dose are presented. The results show that our approach successfully models the complex interactions between the beam transport and its interactions with the system for relevant clinical scenarios at an acceptable computational cost.

A detailed model of the IBA Proteus One compact gantry system has been created with BDSIM (Beam Delivery Simulation) that has been validated against experimental data. Results regarding activation studies have been obtained for the first time using seamless simulations of the transport of protons in the beamline and their interactions with the environment. The activation of the concrete shielding of the system is estimated after a period of 20 years of operation. These main results are presented and discussed in detail.