Geant4 Version Research Articles

Status of the parallelized JUNO simulation software

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment. It consists of a central detector, a water pool and a tracker placed on top. The central detector, which is used for neutrino detection, consists of a 20 kt liquid scintillator target and about 18,000 20-inch photomultiplier tubes (PMTs) to detect scintillation photons. Simulation software is an important part of the JUNO offline software. To speed up the simulation, a parallelized simulation framework has been developed based on the SNiPER framework and Geant4 version 10. The SNiPER task components are in charge of the event loop, which can run in sequential mode, Intel TBB mode and other modes. Based on SNiPER, the simulation framework and its underlying parallel libraries have been decoupled. However, parallelized simulation of correlated events is a challenge. In order to keep the correct event order, a component called global buffer is developed in SNiPER. In this paper, an overview of the parallelized JUNO simulation framework is presented. The global buffer is used in the parallelized event correlation simulation. An event generator produces events with timestamps in sequential mode. These events are put into the global buffer and processed by the detector simulation algorithms in different tasks. After simulation, the events are saved into ROOT files with a ROOT I/O service running in a dedicated thread. Finally, the software performance is presented.

On the accuracy and efficiency of condensed history transport in magnetic fields in GEANT4

The purpose of this work was to investigate the accuracy and efficiency of electron transport in GEANT4 with and without a magnetic field present. Fano cavity simulations were performed in GEANT4 version 10.02 and 10.04.p01 using two multiple scattering (MSC) algorithms for two slab and one pseudo-ion chamber geometries. An iterative approach was used to optimize the transport parameters to obtain agreement with theory. Similar to previous works, the step lengths had to be severely restricted to obtain agreement with theory when using the Urban MSC model in GEANT4 v10.02. Using the Goudsmit–Saunderson MSC model with the UseSafetyPlus MSC step limitation in GEANT4 v10.04.p01 limited the maximum discrepancy from theory to 0.5%. Minor adjustments to the transport parameters were needed to obtain agreement within 0.16% of theory for all simulation configurations without a magnetic field present. The maximum deviation from theory was within 2% for all simulation configurations in the presence of a magnetic field except for two setups that exhibited discrepancies of up to 10.8%. This anomalous behavior was mitigated by forcing single scattering within the detector gas volume. Further adjustments to the transport parameters resulted in agreement with theory at the 0.21% level. Agreement with theory in the absence of a magnetic field can be obtained without significantly restricting the step size if the Goudsmit–Saunderson MSC model is used with the UseSafetyPlus MSC step limitation in GEANT4 v10.04.p01. The large discrepancies from theory observed for two simulation setups with a magnetic field present were attributed to an issue with energy loss sampling over a step when strict magnetic field transport parameters are used. This problem can be corrected by forcing single scattering within the detector gas volume; however, more work is needed to identify the cause of this anomalous behavior. This work has shown that GEANT4 can perform accurate electron transport with and without a magnetic field present without applying significant step-size reductions.

Direct measurement of neutrons induced in lead by cosmic muons at a shallow underground site

Neutron production in lead by cosmic muons has been studied with a Gadolinium doped liquid scintillator detector. The detector was installed next to the Muon-Induced Neutron Indirect Detection EXperiment (MINIDEX), permanently located in the Tübingen shallow underground laboratory where the mean muon energy is approximately 7 GeV. The MINIDEX plastic scintillators were used to tag muons; the neutrons were detected through neutron capture and neutron-induced nuclear recoil signals in the liquid scintillator detector. Results on the rates of observed neutron captures and nuclear recoils are presented and compared to predictions from GEANT4-9.6 and GEANT4-10.3. The predicted rates are significantly too low for both versions of GEANT4. For neutron capture events, the observation exceeds the predictions by factors of 1.65 ± 0.02 (stat.) ± 0.07 (syst.) and 2.58 ± 0.03 (stat.) ± 0.11 (syst.) for GEANT4-9.6 and GEANT4-10.3, respectively. For neutron nuclear recoil events, which require neutron energies above approximately 5 MeV, the factors are even larger, 2.22 ± 0.05 (stat.) ± 0.25 (syst.) and 3.76 ± 0.09 (stat.) ± 0.41 (syst.), respectively. Also presented is the first statistically significant measurement of the spectrum of neutrons induced by cosmic muons in lead between 5 and 40 MeV. It was obtained by unfolding the nuclear recoil spectrum. The observed neutron spectrum is harder than predicted by GEANT4. An investigation of the distribution of the time difference between muon tags and nuclear recoil signals confirms the validity of the unfolding procedure and shows that GEANT4 cannot properly describe the time distribution of nuclear recoil events. In general, the description of the data is worse for GEANT4-10.3 than for GEANT4-9.6.

Monte Carlo Study of 3D Stray Radiation during Interventional Procedures

In interventional medical procedures, other than the highly important issue of optimizing image quality and patient exposure using the primary beam, there remains a continuing need for the study of staff exposure from the scattered radiation. Herein, investigation is made of the 3D stray-radiation distribution, the simulation being made of a realistic interventional scenario through use of the Monte Carlo code Geant4 (version 10.3). The simulation is conducted based on the high definition reference Korean-man (HDRK-man) computational phantom and a GE Infinia 3/8” C-arm machine, focusing on the effect of variation of kVp and field of view (FoV) on the scattered particles’ spatial distribution. With direct measurement of the absorbed dose remaining challenging, not least in respect of the organs at risk, we computed the scatter fractions, defined as the ratio of the air kerma free-in-air to the entrance surface air kerma (ESAK), which are both easily quantifiable. Scatter fraction distributions were simulated for X-ray tube outputs (and half-value layers, HVL) of 60 kVp (2.3 mm Al), 80 kVp (3.2 mm Al) and 120 kVp (4.3 mm Al) and FoV of 15, 20, 25 and 30 cm. The distributions are obtained for different height levels, corresponding to the lens of the eye, and the lung and prostate, all radiosensitive organs. Investigations are made for eight likely locations around the patient. At fixed FoV results reveal an inverse relationship between ESAK and kVp, also that change in kVp from 60 to 80 has a greater effect than from 80 to 120. For change in FoV at fixed kVp, the scatter fraction remains constant. The particular staff locations are found to be optimal in seeking mitigation of dose. Moreover, the combined usage of numerical human model and Monte Carlo simulation can be considered as an added value to the radiation safety research field, especially to the interventional radiology staff and to the patient.

Compton camera study for high efficiency SPECT and benchmark with Anger system

Single photon emission computed tomography (SPECT) is at present one of the major techniques for non-invasive diagnostics in nuclear medicine. The clinical routine is mostly based on collimated cameras, originally proposed by Hal Anger. Due to the presence of mechanical collimation, detection efficiency and energy acceptance are limited and fixed by the system’s geometrical features. In order to overcome these limitations, the application of Compton cameras for SPECT has been investigated for several years.In this study we compare a commercial SPECT-Anger device, the General Electric HealthCare Infinia system with a High Energy General Purpose (HEGP) collimator, and the Compton camera prototype under development by the French collaboration CLaRyS, through Monte Carlo simulations (GATE—GEANT4 Application for Tomographic Emission—version 7.1 and GEANT4 version 9.6, respectively). Given the possible introduction of new radio-emitters at higher energies intrinsically allowed by the Compton camera detection principle, the two detectors are exposed to point-like sources at increasing primary gamma energies, from actual isotopes already suggested for nuclear medicine applications. The Compton camera prototype is first characterized for SPECT application by studying the main parameters affecting its imaging performance: detector energy resolution and random coincidence rate. The two detector performances are then compared in terms of radial event distribution, detection efficiency and final image, obtained by gamma transmission analysis for the Anger system, and with an iterative List Mode-Maximum Likelihood Expectation Maximization (LM-MLEM) algorithm for the Compton reconstruction.The results show for the Compton camera a detection efficiency increased by a factor larger than an order of magnitude with respect to the Anger camera, associated with an enhanced spatial resolution for energies beyond 500 keV. We discuss the advantages of Compton camera application for SPECT if compared to present commercial Anger systems, with particular focus on dose delivered to the patient, examination time, and spatial uncertainties.

Upgrades for the CMS simulation

We report the current status of the full simulation application developed by the CMS experiment. For LHC run-II, CMS is using Geant4 10.0p02 built in sequential mode. About 16 billion events were produced for run-II analysis during 2015-2016. A new method to handle pileup events has been developed and is now used for regular processing of simulation events. We plan to use Geant4 10.2p02 for 2017 production. In this work, we present CPU and memory performance of the CMS full simulation for different configurations and Geant4 versions considered during our testing. We also discuss technical aspects of the migration to Geant4 10.2 and a new premixing scheme for the simulation of pileup.

Abstract ID: 22 Validation of Geant4 fragmentation for heavy ion therapy

C-12 ion therapy has had growing interest in recent years for its excellent dose conformity. However at therapeutic energies, which can be as high as 400 MeV/u, carbon ions produce secondary fragments. For an incident 400 MeV/u C-12 ion beam, ∼70% of the beam will undergo fragmentation before the Bragg Peak. The dosimetric and radiobiological impact of these fragments must be accurately characterised, as it can result in increasing the risk of secondary cancer for the patient as well as altering the relative biological effectiveness. This work investigates the accuracy of three different nuclear fragmentation models available in the Monte Carlo Toolkit Geant4, the Binary Intranuclear Cascade (BIC), the Quantum Molecular Dynamics (QMD) and the Liege Intranuclear Cascade (INCL++). The models were benchmarked against experimental data for a pristine 400 MeV/u C-12 beam incident upon a water phantom [1] , including fragment yield, angular and energy distribution. Geant4 version 10.2p2 was used. For fragment yields the three alternative models (QMD, BIC and INCL++) agreed between ∼5 and 35% with experimental measurements, the QMD using the “Frag” option gave the best agreement for lighter ions but had reduced agreement for heavier ions. For angular distributions INCL++ was seen to provide the best agreement among the models for all elements with the exception of Hydrogen. BIC and QMD showed to produce broader distributions compared to experiment. BIC and QMD performed similar to one another for kinetic energy distributions while INCL++ suffered from producing softer energy distributions compared to the other models and experiment. This set of tests were repeated with successive public releases of Geant4 to check that the accuracy of the physics models did not change over time.

The simulation library of the Belle II software system

SuperKEKB, the next generation B factory, has been constructed in Japan as an upgrade of KEKB. This brand new e+ e- collider is expected to deliver a very large data set for the Belle II experiment, which will be 50 times larger than the previous Belle sample. Both the triggered physics event rate and the background event rate will be increased by at least 10 times than the previous ones, and will create a challenging data taking environment for the Belle II detector. The software system of the Belle II experiment is designed to execute this ambitious plan. A full detector simulation library, which is a part of the Belle II software system, is created based on Geant4 and has been tested thoroughly. Recently the library has been upgraded with Geant4 version 10.1. The library is behaving as expected and it is utilized actively in producing Monte Carlo data sets for various studies. In this paper, we will explain the structure of the simulation library and the various interfaces to other packages including geometry and beam background simulation.

Validation of Physics Models of Geant4 using Data from CMS Experiment

CMS has tuned its simulation program and has chosen a specific physics model of GEANT4 by comparing the simulation results with dedicated test beam experiments. CMS continues to validate the physics models inside GEANT4 using the test beam data as well as collision data. Several physics lists (collection of physics models) inside the most recent version of GEANT4 provide good agreement of the energy response, resolution of pions and protons. The validation results from these studies are used to make the choice of physics list and GEANT4 version for the CMS experiment.

Evaluation of GATE/Geant4 multiple Coulomb scattering algorithms for a 160 MeV proton beam

Abstract Purpose To systematically evaluate simulated characteristic multiple Coulomb scattering (MCS) angles with GATE/Geant4 against experimental data for 158.6 MeV proton beams. Methods The open source toolkit GATE alongside Geant4 in release 9.5 patch 02, 9.6 patch 03, 10.0 patch 02, 10.1, and 10.2 patch 02 were used to simulate a 158.6 MeV collimated monoenergetic proton beam impinging on a scattering disc of various materials and thicknesses: in total 144 different set-ups were investigated per Geant4 release and compared to measured data. Data was read out into a phase space providing information of individual particle momentum. For analysis a one dimensional Gaussian was fit to the beam profile and the multiple Coulomb scattering angles were calculated using the ROOT toolkit. Results The agreement between simulated and experimental data was found to be dependent on the Geant4 release. On average an agreement of - 1.1 % with a standard deviation of 3.4 % was reached with Geant4 release 10.2. Increased differences were found for very thick targets close to the particle range and for older Geant4 versions employing the previous electromagnetic model, Urban MCS. Conclusion Multiple Coulomb scattering algorithms implemented in the latest Geant4 releases and in particular Geant4.10.2 showed a very satisfactory agreement with measured data for applications in proton pencil beam scanning.

Geant4 Standard and Low Energy electromagnetic libraries

Geant4 is a Monte Carlo toolkit well established for large scale simulations for high energy physics, medicine, space science and other applications. Electromagnetic (EM) physics libraries are key components of these simulations. In this work we describe the Standard and Low Energy EM libraries available in Geant4 version 10.3 including descriptions of new models and interfaces relevant for dark matter searches and limits of applicability for these models.

Quantitative Test of the Evolution of Geant4 Electron Backscattering Simulation

Evolutions of Geant4 code have affected the simulation of electron backscattering with respect to previously published results. Their effects are quantified by analyzing the compatibility of the simulated electron backscattering fraction with a large collection of experimental data for a wide set of physics configuration options available in Geant4. Special emphasis is placed on two electron scattering implementations first released in Geant4 version 10.2: the Goudsmit-Saunderson multiple scattering model and a single Coulomb scattering model based on Mott cross section calculation. The new Goudsmit-Saunderson multiple scattering model appears to perform equally or less accurately than the model implemented in previous Geant4 versions, depending on the electron energy. The new Coulomb scattering model was flawed from a physics point of view, but computationally fast in Geant4 version 10.2; the physics correction released in Geant4 version 10.2p01 severely degrades its computational performance. Evolutions in the Geant4 geometry domain have addressed physics problems observed in electron backscattering simulation in previous publications.

Hadron shower decomposition in the highly granular CALICE analogue hadron calorimeter

The spatial development of hadronic showers in the CALICE scintillator-steel analogue hadron calorimeter is studied using test beam data collected at CERN and FNAL for single positive pions and protons with initial momenta in the range of 10–80 GeV/c. Both longitudinal and radial development of hadron showers are parametrised with two-component functions. The parametrisation is fit to test beam data and simulations using the QGSP_BERT and FTFP_BERT physics lists from GEANT4 version 9.6. The parameters extracted from data and simulated samples are compared for the two types of hadrons. The response to pions and the ratio of the non-electromagnetic to the electromagnetic calorimeter response, h/e, are estimated using the extrapolation and decomposition of the longitudinal profiles.

GEANT4 simulation of cyclotron radioisotope production in a solid target

The use of radioisotopes in nuclear medicine is essential for diagnosing and treating cancer. The optimization of their production is a key factor in maximizing the production yield and minimizing the associated costs. An efficient approach to this problem is the use of Monte Carlo simulations prior to experimentation. By predicting isotopes yields, one can study the isotope of interest expected activity for different energy ranges. One can also study the target contamination with other radioisotopes, especially undesired radioisotopes of the wanted chemical element which are difficult to separate from the irradiated target and might result in increasing the dose when delivering the radiopharmaceutical product to the patient.The aim of this work is to build and validate a Monte Carlo simulation platform using the GEANT4 toolkit to model the solid target system of the South Australian Health and Medical Research Institute (SAHMRI) GE Healthcare PETtrace cyclotron. It includes a GEANT4 Graphical User Interface (GUI) where the user can modify simulation parameters such as the energy, shape and current of the proton beam, the target geometry and material, the foil geometry and material and the time of irradiation.The paper describes the simulation and presents a comparison of simulated and experimental/theoretical yields for various nuclear reactions on an enriched nickel 64 target using the GEANT4 physics model QGSP_BIC_AllHP, a model recently developed to evaluate with high precision the interaction of protons with energies below 200MeV available in Geant4 version 10.1. The simulation yield of the 64Ni(p,n)64Cu reaction was found to be 7.67±0.074 mCi·μA−1 for a target energy range of 9–12MeV. Szelecsenyi et al. (1993) gives a theoretical yield of 6.71mCi·μA−1 and an experimental yield of 6.38mCi·μA−1. The 64Ni(p,n)64Cu cross section obtained with the simulation was also verified against the yield predicted from the nuclear database TENDL and compared to experimental yield obtained from literature.

Assessment of Geant4 Prompt-Gamma Emission Yields in the Context of Proton Therapy Monitoring.

Monte Carlo tools have been long used to assist the research and development of solutions for proton therapy monitoring. The present work focuses on the prompt-gamma emission yields by comparing experimental data with the outcomes of the current version of Geant4 using all applicable proton inelastic models. For the case in study and using the binary cascade model, it was found that Geant4 overestimates the prompt-gamma emission yields by 40.2 ± 0.3%, even though it predicts the prompt-gamma profile length of the experimental profile accurately. In addition, the default implementations of all proton inelastic models show an overestimation in the number of prompt gammas emitted. Finally, a set of built-in options and physically sound Geant4 source code changes have been tested in order to try to improve the discrepancy observed. A satisfactory agreement was found when using the QMD model with a wave packet width equal to 1.3 fm2.

Progress in Geant4 Electromagnetic Physics Modelling and Validation

In this work we report on recent improvements in the electromagnetic (EM) physics models of Geant4 and new validations of EM physics. Improvements have been made in models of the photoelectric effect, Compton scattering, gamma conversion to electron and muon pairs, fluctuations of energy loss, multiple scattering, synchrotron radiation, and high energy positron annihilation. The results of these developments are included in the new Geant4 version 10.1 and in patches to previous versions 9.6 and 10.0 that are planned to be used for production for run-2 at LHC. The Geant4 validation suite for EM physics has been extended and new validation results are shown in this work. In particular, the effect of gamma-nuclear interactions on EM shower shape at LHC energies is discussed.

Geant4 VMC 3.0

Virtual Monte Carlo (VMC) [1] provides an abstract interface into Monte Carlo transport codes. A user VMC based application, independent from the specific Monte Carlo codes, can be then run with any of the supported simulation programs. Developed by the ALICE Offline Project and further included in ROOT [2], the interface and implementations have reached stability during the last decade and have become a foundation for other detector simulation frameworks, the FAIR facility experiments framework being among the first and largest.Geant4 VMC [3], which provides the implementation of the VMC interface for Geant4 [4], is in continuous maintenance and development, driven by the evolution of Geant4 on one side and requirements from users on the other side. Besides the implementation of the VMC interface, Geant4 VMC also provides a set of examples that demonstrate the use of VMC to new users and also serve for testing purposes. Since major release 2.0, it includes the G4Root navigator package, which implements an interface that allows one to run a Geant4 simulation using a ROOT geometry.The release of Geant4 version 10.00 with the integration of multithreading processing has triggered the development of the next major version of Geant4 VMC (version 3.0), which was released in November 2014. A beta version, available for user testing since March, has helped its consolidation and improvement. We will review the new capabilities introduced in this major version, in particular the integration of multithreading into the VMC design, its impact on the Geant4 VMC and G4Root packages, and the introduction of a new package, MTRoot, providing utility functions for ROOT parallel output in independent files with necessary additions for thread-safety. Migration of user applications to multithreading that preserves the ease of use of VMC will be also discussed. We will also report on the introduction of a new CMake [5] based build system, the migration to ROOT major release 6 and the improvement of the testing suites.

GEANT4 calculations of neutron dose in radiation protection using a homogeneous phantom and a Chinese hybrid male phantom.

The purpose of this study is to verify the feasibility of applying GEANT4 (version 10.01) in neutron dose calculations in radiation protection by comparing the calculation results with MCNP5. The depth dose distributions are investigated in a homogeneous phantom, and the fluence-to-dose conversion coefficients are calculated for different organs in the Chinese hybrid male phantom for neutrons with energy ranging from 1 × 10(-9) to 10 MeV. By comparing the simulation results between GEANT4 and MCNP5, it is shown that using the high-precision (HP) neutron physics list, GEANT4 produces the closest simulation results to MCNP5. However, differences could be observed when the neutron energy is lower than 1 × 10(-6) MeV. Activating the thermal scattering with an S matrix correction in GEANT4 with HP and MCNP5 in thermal energy range can reduce the difference between these two codes.

Monte Carlo simulation and parameterized treatment on the effect of nuclear elastic scattering in high-energy proton radiography**Supported by NSAF (11176001) and Science and Technology Developing Foundation of China Academy of Engineering Physics (2012A0202006)

A version of Geant4 has been developed to treat high-energy proton radiography. This article presents the results of calculations simulating the effects of nuclear elastic scattering for various test step wedges. Comparisons with experimental data are also presented. The traditional expressions of the transmission should be correct if the angle distribution of the scattering is Gaussian multiple Coulomb scattering. The mean free path (which depends on the collimator angle) and the radiation length are treated as empirical parameters, according to transmission as a function of thickness obtained by simulations. The results can be used in density reconstruction, which depends on the transmission expressions.

SU‐E‐T‐521: Investigation of the Uncertainties Involved in Secondary Neutron/gamma Production in Geant4/MCNP6 Monte Carlo Codes for Proton Therapy Application

Purpose:A major concern in proton therapy is the production of secondary neutrons causing secondary cancers, especially in young adults and children. Most utilized Monte Carlo codes in proton therapy are Geant4 and MCNP. However, the default versions of Geant4 and MCNP6 do not have suitable cross sections or physical models to properly handle secondary particle production in proton energy ranges used for therapy. In this study, default versions of Geant4 and MCNP6 were modified to better handle production of secondaries by adding the TENDL‐2012 cross‐section library.Methods:In‐water proton depth‐dose was measured at the “The Svedberg Laboratory” in Uppsala (Sweden). The proton beam was mono‐energetic with mean energy of 178.25±0.2 MeV. The measurement set‐up was simulated by Geant4 version 10.00 (default and modified version) and MCNP6. Proton depth‐dose, primary and secondary particle fluence and neutron equivalent dose were calculated. In case of Geant4, the secondary particle fluence was filtered by all the physics processes to identify the main process responsible for the difference between the default and modified version.Results:The proton depth‐dose curves and primary proton fluence show a good agreement between both Geant4 versions and MCNP6. With respect to the modified version, default Geant4 underestimates the production of secondary neutrons while overestimates that of gammas. The “ProtonInElastic” process was identified as the main responsible process for the difference between the two versions. MCNP6 shows higher neutron production and lower gamma production than both Geant4 versions.Conclusion:Despite the good agreement on the proton depth dose curve and primary proton fluence, there is a significant discrepancy on secondary neutron production between MCNP6 and both versions of Geant4. Further studies are thus in order to find the possible cause of this discrepancy or more accurate cross‐sections/models to handle the nuclear interactions of protons with energy ranges used for therapy.NSERC‐CRSNG’ CREATE Medical Physics Research Training Network compute calcul CANADA; McGill University health center research institute the fast foundation; LM acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering; Research Council Grant number 432290