Geant4 Monte Carlo Simulation Research Articles

Electron spectrometry with Silicon drift detectors: a GEANT4 based method for detector response reconstruction

Precision electron spectrometry in the keV range has always been considered a challenging task. The reconstruction of the original electron energy from the detected signal is not trivial because multiple effects modify the kinetic energy of the electron along its path. If not correctly accounted for, these effects can spoil and bias the reconstructed energy with a dramatic reduction of accuracy and precision. In this paper we address one of the most critical aspects of electron spectrometry: the generally unknown effect of the detector entrance window. We show that, with a MonteCarlo-based approach, we are able to build a model of the entrance window accurate enough to reduce the negative effects due to its existence. We adopt for this purpose Silicon Drift Detectors that, thought primarily used for X-ray spectrometry, appear a promising device for electron spectrometry. The technique we discuss exploits characterization and validation measurements performed with electron beams from a Scanning Electron Microscope, later reconstructed with a GEANT4 MonteCarlo simulation.

Radioiodine (131-I) treatment for Graves’ disease: Geant4 Monte Carlo simulation for patient personalized dose estimation

Radioiodine (131-I) treatment for Graves’ disease: Geant4 Monte Carlo simulation for patient personalized dose estimation

Development of a Fast-Spectrum Self-Powered Neutron Detector for Molten Salt Experiments in the Versatile Test Reactor

The self-powered neutron detector (SPND) is a widely used flux monitor in thermal nuclear reactors. Although this is a mature technology, the current state of the art is tuned for a thermal neutron spectrum, so many of the devices currently in use lack sensitivity to fast neutrons. Because current in SPNDs is produced through nuclear reactions with the neutron flux inside a reactor, sensitivity in SPNDs is determined by the neutron cross section of the neutron-sensitive portion of the detector, termed the emitter. This neutron cross section drops by orders of magnitude between thermal and fast neutron energies for many emitters in currently used SPNDs, with a corresponding drop in current from the detector. This paper discusses efforts to develop a fast-spectrum self-powered neutron detector (FS-SPND) that is sensitive to neutrons with energies ranging from 0.025 eV up to 1 MeV. An in-depth analysis of Evaluated Nuclear Data File (ENDF)/B-VII.1 neutron-capture cross sections was performed, and four new materials were identified that are suitable emitter candidates for use in measuring fast neutrons. All four materials are stable mid-shell nuclei in the region between doubly magic132Sn and208Pb. Each candidate was simulated with the Geant4 Monte Carlo simulation toolkit to optimize overall detector efficiency.

Influence of preparation process on the transparency of CsI microcolumns in the structured CsI scintillation screen based on oxidized silicon micropore array template

The structured CsI scintillation screens based on oxidized silicon micropore array templates can maintain high spatial resolution in X-ray imaging while increasing their thickness. However, the detection efficiency of the screens is not only related to their thickness, but also related to the transparency of the CsI scintillation microcolumns in the screens, because it affects the output of the scintillation light. In this work, the hexagonal array arranged structured CsI scintillation screens based on oxidized silicon micropore templates with pore pitch about 4.3μm and diameter about 3.0μm were fabricated by vacuum melting and pressure injection method. In order to improve the transparency of the CsI microcolumns, the effects of filling temperature and pressure on the morphology, crystallinity, X-ray excited optical luminescence (XEOL) and transparency of the CsI scintillation microcolumns were studied after a preliminary research on TG-DSC, melt viscosity and bulk preparation of CsI material. The results show that with the increase of filling temperature, the cracks and microbubbles in the filled CsI microcolumns become less or even disappear under the filling pressure of 6 MPa, and the crystallinity of the microcolumns becomes better. Meanwhile, the intensity of the XEOL becomes stronger. The light attenuation coefficients of the CsI scintillation microcolumns prepared at different filling temperature were derived by Geant4 Monte Carlo simulation toolkit according to the results of XEOL. The light attenuation coefficient decreases significantly as the filling temperature increases. When the filling temperature reaches 660 °C, the light attenuation coefficient of the CsI microcolumns has dropped below 0.002μm−1. Such a low light attenuation coefficient is completely suitable for X-ray imaging of the structured high-resolution CsI scintillation screens based on oxidized silicon micropore array templates that have been developed.

Radiation protection study for a reloading operation of cobalt 60 sources in the Moroccan ionisation station using the GEANT4 Monte-Carlo simulation code

The operation of reloading the irradiators is considered among the tasks requiring high radiation protection monitoring, to protect the intervening manipulators, the public and the environment. Morocco is among the countries that have a cobalt irradiator, installed at the National Institute of Agricultural Research (NIAR) of Tangier, to carry out research in the field of agronomy. In the beginning, the irradiator used low doses of activity for the study of products only, for treatment of high doses. The NIAR carried out a reload to increase the activity. To perform this, a temporary pool was installed inside the irradiation room to handle the sources safely. A radiation protection study is necessary to ensure the safe operation. This operation requires a height level of exposure. To ovoid the exposer risk, it is proposed to use the Monte Carlo method thanks to its reliability in the dosimetric calculation. This article presents a radiation protection study of the Moroccan irradiator reloading operation using the GEANT4 Monte-Carlo Simulation Code.

Low-energy electromagnetic processes affecting free-falling test-mass charging for LISA and future space interferometers

Galactic cosmic rays and solar energetic particles charge gold-platinum, free-falling test masses (TMs) on board interferometers for the detection of gravitational waves in space. The charging process induces spurious forces on the test masses that affect the sensitivity of these instruments mainly below 10−3 Hz. Geant4 and FLUKA Monte Carlo simulations were carried out to study the TM charging process on board the LISA Pathfinder mission that remained into orbit around the Sun–Earth Lagrange point L1 between 2016 and 2017. While a good agreement was observed between simulations and measurements of the TMs net charging, the shot noise associated with charging fluctuations of both positive and negative particles resulted 3–4 times higher that predicted. The origin of this mismatch was attributed to the propagation of electrons and photons only above 100 eV in the simulations. In this paper, low-energy electromagnetic processes to be included in the future Monte Carlo simulations for LISA and LISA-like space interferometers TM charging are considered. It is found that electrons and photons below 100 eV give a contribution to the effective charging comparable to that of the whole sample of particles above this energy. In particular, for incident protons ionization contributes twice with respect to low energy kinetic emission and electron backscattering. The other processes are found to play a negligible role. For heavy nuclei only sputtering must be considered.

Surface Ionizing Dose for Space Applications Estimated With Low Energy Spectra Going Down to Hundreds of Electronvolt

The contribution of low-energy particles down to ~200 eV to the dose deposited on the very near surface of materials subject to the space environment is investigated by means of GEANT4 Monte Carlo simulations. The contribution to the dose, of the low-energy parts of Global Radiation Earth ENvironment (GREEN) spectra (200 eV-40 keV for electrons, 200 eV-100 keV for protons), is compared with calculations performed with AE8/AP8. Both geostationary earth orbit (GEO) and low earth orbit (LEO) SPOT like orbits are studied. The dose depth profiles are estimated for silicon material. The impact on the dose calculation of different transport models is also investigated. Below 1 keV, the relevance of continuous processes is analyzed for electrons by comparison with a discrete model [GEANT4/microelectronic (MICROELEC)]. This analysis is also performed for protons below 10 keV.

Assessment of metallic nanoparticles as radioenhancers in gastric cancer therapy by Geant4 simulation and local effect model

Gastric cancer ranks as one of the most common and poor prognosis human malignancies. We investigated the radioenhancer effects of gold, silver, platinum, bismuth, iron oxide, titanium oxide and germanium nanoparticles on simulated gastric adenocarcinoma cells, irradiated with 6 MV X-rays in presence of 0.05 µM, 0.25 µM and 0.5 µM homogeneous distributed metal nanoparticles throughout the cell, including the nucleus, cytoplasm and extracellular matrix using Geant4 Monte Carlo simulation along with LEM radiobiological model. The survival reduction coefficient was obtained 0.5 for light nanoparticles including 0.5 μM titanium oxide, iron oxide and germanium and also 0.3–0.1 for heavy nanoparticles including 0.5 μM gold, silver, bismuth and platinum. Nanoparticle-mediated Enhancement Ratio for 0.5 μM internuclear Gold, Silver, Bismuth, Germanium, Platinum, Iron oxide and Titanium oxide nanoparticles was calculated to 0.10, 0.27, 0.26, 0.47, 0.09, 0.50, and 0.58, respectively. Radiosensitization by NPs may enhance therapeutic efficacy of gastric adenocarcinoma.

New measurements of cross sections and S-factors for $$d(p,\gamma )^{3}\text{He}$$ reaction at BBN energies

This communication is a summary of our measurements of cross sections and astrophysical S-factors for radiative proton capture on deuteron. The measurements are a part of a new program to study light-ion induced nuclear capture and inelastic scattering reactions relevant to nucleosynthesis and astrophysics. We are primarily interested in the capture reactions relevant to primordial or Big Bang Nucleosynthesis (BBN). Section 1 provides a brief and general overview of nuclear astrophysics and the primary experimental challenges in the measurements of cross sections and S-factors for reactions relevant to nuclear astrophysics. The next section discusses the significance of the $$d(p,\gamma )^{3}\text{He}$$ reaction in context of BBN and the need for generating a more precise data in the relevant energy window. The subsequent section is devoted to the experiment and results of measurements of cross sections and astrophysical S-factors for the $$d(p,\gamma )^{3}\text{He}$$ reaction at three new BBN energies. One salient features of the measurements is the use of large volume LaBr $$_{3}$$ :Ce scintillation detector for measurement of the capture $$\gamma $$ -rays. To the best of our knowledge, capture $$\gamma $$ -rays for this reaction had so far been measured with NaI(Tl) or HPGe detectors only. The detection efficiency of the detector has been measured experimentally for different monochromatic $$\gamma $$ -ray energies. In addition, realistic GEANT4 Monte Carlo simulations have been carried out to generate the response of the detector for $$\gamma $$ -ray energies of interest. The measured cross section and astrophysical S(E)-factor for the three incident proton energies are found to be in agreement with the overall trend of the global data set for the BBN region, reported in the literature. The measured S-factors are also found to be in agreement with recent microscopic calculations of Marcucci et al. (2016).

Development of SiO2 based doped with LiF, Cr2O3, CoO4 and B2O3 glasses for gamma and fast neutron shielding

Abstract In this study, the fast neutron and gamma-ray absorption capacities of the new glasses have been investigated, which are obtained by doping CoO,CdWO4,Bi2O3, Cr2O3, ZnO, LiF,B2O3 and PbO compounds to SiO2 based glasses. GEANT4 and FLUKA Monte Carlo simulation codes have been used in the planning of the samples. The glasses were produced using a well-known melt-quenching technique. The effective neutron removal cross-sections, mean free paths, half-value layer, and transmission numbers of the fabricated glasses have been calculated through both GEANT4 and FLUKA Monte Carlo simulation codes. Experimental neutron absorbed dose measurements have been carried out. It was found that GS4 glass has the best neutron protection capacity among the produced glasses. In addition to neutron shielding properties, the gamma-ray attenuation capacities, were calculated using newly developed Phy-X/PSD software. The gamma-ray shielding properties of GS1 and GS2 are found to be equivalent to Pb-based glass.

Design and performance study of a gas-Cherenkov detector with an off-axis parabolic reflector for inertial confinement fusion experiments

In this work, the gas-Cherenkov detector with an off-axis parabolic reflector (OprGCD) is designed using the Geant4 Monte Carlo simulation toolkit, which is helpful to improve the collection efficiency of Cherenkov photons. The method to study the performance of OprGCD based on femtosecond laser-wakefield-accelerated electron beams is presented. Cherenkov signals with high signal-to-noise ratio were obtained, and the measured Cherenkov signals changing with the CO2 pressure were consistent well with the simulation results. The design and study of this OprGCD system lay the foundation for the application of fusion gamma diagnostics system in large laser facilities of China.

Study on the Dose Enhancement of Gold Nanoparticles When Exposed to Clinical Electron, Proton, and Alpha Particle Beams by Means of Geant4.

Background:Various factors effecting deposited energy and dose enhancement ratio (DER) in the simplified model of cell caused by the interaction of a cluster of gold nanoparticles (GNPs) with electron beams were assessed, and the results were compared with other sources through Geant4 Monte Carlo simulation toolkit.Method:The effect of added GNPs on the DNA strand breaks level, irradiated to electron, proton, and alpha beams, is assessed.Results:Presence of GNPs in the cell makes DER value more pronounced for low-energy photons rather than electron beam. Moreover, the results of DER values did not show any significant increase in absorbed dose in the presence of GNP for proton and alpha beam. Moreover, the results of DNA break with GNPs for proton and alpha beam were negligible. It is demonstrated that as the sizes of the GNPs increase, the DER is enlarged until a certain size for 40 keV photons, while there is no striking change for 50 keV electron beam when the size of the GNPs changes. The results indicate that although energy deposited in the cell for electron beam is more than low-energy photon, DER values are low compared to photon.Conclusion:Larger GNPs do not show any preference over smaller ones when irradiated through electron beams. It is proved that GNPs do not significantly increase single-strand breaks (SSBs) and double-strand breaks during electron irradiation, while there exists a direct relationship between SSB and energy.

Microdosimetric measurements of a monoenergetic and modulated Bragg Peaks of 62MeV therapeutic proton beam with a synthetic single crystal diamond microdosimeter.

The purpose of this study was to investigate for the first time the performance of a synthetic single crystal diamond detector for the microdosimetric characterization of clinical 62MeV ocular therapy proton beams. A novel diamond microdosimeter with a well-defined sensitive volume was fabricated and tested with a monoenergetic and spread-out Bragg peak (SOBP) of the CATANA therapeutic proton beam in Catania, Italy. The whole sensitive volume of the detector has an active planar-sectional area of 100µm×100µm and a thickness of approximately 6.3 um. Microdosimetric measurements were performed at several water equivalent depths, corresponding to positions of clinical relevance. From the measured spectra, microdosimetric quantities such as the frequency mean lineal energy ( ), dose mean lineal energy ( ) as well as microdosimetric relative biological effectiveness (RBEµ ) values were derived for each depth along both a pristine Bragg curve and SOBP. Finally, Geant4 Monte Carlo simulations were performed modeling the detector geometry and CATANA beamline in order to calculate the average linear energy transfer (LET) values in the diamond active layer and water. The microdosimetric spectra acquired by the diamond microdosimeter show different shapes as a function of the water equivalent depths. No spectral distortion, due to pile-up events and polarization effects, was observed. The experimental spectra have a very low detection threshold due to the electronic noise during the irradiation of about 1keV/μm. The and values were in agreement with expected trends, showing a sharp increase in mean lineal energy at the distal edge of the Bragg peak. In addition, a good agreement between the mean lineal energy values and the calculated average LET ones was also observed. Finally, the RBE values evaluated with the diamond microdosimeter were in excellent agreement with those obtained with a mini tissue equivalent proportional counter as well as with radiobiological measurements in the same proton beam field. The microdosimetric performance of the tested synthetic single crystal diamond microdosimeter clearly indicates its suitability for quality assurance in clinical proton therapy beam.

Gamma and conversion electron spectroscopy using GABRIELA

GABRIELA (Gamma Alpha Beta Recoil Investigations with the Electromagnetic Analyzer) is a detection system installed at the focal plane of the SHELS (Separator for Heavy Elements Spectroscopy) recoil separator for gamma and internal conversion electron spectroscopy of heavy and superheavy nuclei. GABRIELA has recently been upgraded. The characteristics of the new setup are presented using the Geant4 Monte Carlo simulation toolkit and validated against experimental results. The impact of summing on the gamma-ray and electron detection efficiencies is discussed.

Assessment of radionuclide impurities in [18F]fluoromethylcholine ([18F]FMCH).

[18F]Fluoromethylcholine ([18F]FMCH) is a radiopharmaceutical used in positron emission tomography (PET) imaging for the study of prostate, breast, and brain tumors. It is usually synthesized in cyclotron facilities where 18F is produced by proton irradiation of [18O]H2O through 18O(p,n)18F reaction. Due to the activation of target materials, the bombardment causes unwanted radionuclidic impurities in [18O]H2O, that need to be removed during the radiopharmaceutical synthesis. Thus, the aim of this study is to quantify the radionuclide impurities in the 18F production process and in the synthesized [18F]FMCH, demonstrating the radionuclidic purity of this radiopharmaceutical. Long-lived radionuclide impurities were experimentally assessed using high-resolution gamma and liquid scintillation spectrometries, while short-lived impurities were monitored analyzing the decay curve of the irradiated [18O]H2O with an activity calibrator. As spectrometric radionuclide library, a Geant4 Monte Carlo simulation of the 18F-target assembly was previously performed. 3H, 52,54Mn, 56,57,58Co, 95m,96Tc, 109Cd, and 184Re were found in the irradiated [18O]H2O, but no radionuclide was found in the non-irradiated [18O]H2O neither in the final [18F]FMCH solution with an activity concentration greater than the minimum detectable activity concentration. A total impurity activity<6.2kBq was measured in the irradiated [18O]H2O, whereas a [18F]FMCH radionuclide purity>99.9999998% was estimated. Finally, the decay curve of the irradiated [18O]H2O revealed a very low maximum of 13N activity (<0.03% of 18F) even immediately after the end of bombardment. This study demonstrated the radionuclidic purity of [18F]FMCH according to the EU Pharmacopeia.

In-orbit background simulation study of SVOM/GRM

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a Chinese-French satellite dedicated to the observation and study of Gamma-Ray Bursts (GRBs) and other variable sources. Among the four scientific payloads onboard SVOM, the Gamma-Ray Monitor (GRM) is designed to detect GRBs in the 15 keV to 5 MeV energy range. The final performance of GRM can be affected by the space environment background during the flight. In this paper, the authors present the in-orbit background simulation results by using the GEANT4 Monte-Carlo simulation toolkit. Additionally, we studied the Earth occultation effect of the space background due to the anti-solar pointing strategy of SVOM. The total background count rate of each spectrometer of GRM fluctuates between about 840 counts/s and 1341 counts/s, and is dominated by the cosmic X-ray background. Finally, we discuss the emission lines of the background and their potential use for in-orbit calibration of GRM. Our simulation study results can help to understand the impact of the space radiation environment on GRM with the latest geometrical model and can be further compared and updated with the real in-orbit measurement in the future.

Design and performance prediction of large-area hybrid gamma imaging system (LAHGIS) for localization of low-level radioactive material

In the present study, a large-area hybrid gamma imaging system was designed by adopting coded aperture imaging on the basis of a large-area Compton camera to achieve high imaging performance throughout a broad energy range (100–2000 keV). The system consisting of a tungsten coded aperture mask and monolithic NaI(Tl) scintillation detectors was designed through a series of Geant4 Monte Carlo radiation transport simulations, in consideration of both imaging sensitivity and imaging resolution. Then, the performance of the system was predicted by Geant4 Monte Carlo simulations for point sources under various conditions. Our simulation results show that the system provides very high imaging sensitivity (i.e., low values for minimum detectable activity, MDA), thus allowing for imaging of low-activity sources at distances impossible with coded aperture imaging or Compton imaging alone. In addition, the imaging resolution of the system was found to be high (i.e., around 6°) over the broad energy range of 59.5–1330 keV.

Efficency of a HPGe extended range detector for determination of 7Be concentration in air filters

Using the GEANT4 Monte Carlo simulation software, the efficiency of the HPGe extended range detector of the Environmental Radiological Surveillance Laboratory of CIMAV was modeled. A 137Cs certified point source was employed to determine the experimental gamma efficiency in the desired geometry for the energy of 662 keV. The resulting value was compared with the theoretical efficiency obtained by the Monte Carlo simulation. The results of the simulation were consistent with the experimental one. The same method was applied to calculate the theoretical efficiency in the same detector for borosilicate filters in an extended geometry. The energy then was 477 keV, of the gamma quanta from 7Be, to determine its concentration in air. This efficiency value was applied for air sampling in the city of Chihuahua.

Molière maximum likelihood proton path estimation approximated by cubic Bézier curve for scatter corrected proton CT reconstruction

A maximum likelihood approach to the problem of calculating the proton paths inside the scanned object in proton computed tomography is presented. Molière theory is used for the first time to derive a physical model that describes proton multiple Coulomb scattering, avoiding the need for the Gaussian approximation currently used. To enable this, the proposed method approximates proton paths with cubic Bézier curves and subsequently maximizes the path likelihood through parametric optimization, based on the Molière model. Results from the Highland formula-based Gaussian approximation are also presented for comparison. The simplex method is utilized for optimisation. The scattering properties of the material(s) of the scanned object are taken into account by appropriately calculating the scattering parameters from the stopping power map that is calculated/updated at every iteration of the algebraic reconstruction process. Proton track length constraint imposed by the proton energy loss is accounted for. The method is also applied in the case that no exit angle data are measured. Geant4 Monte Carlo simulations were performed for model validation. Our results show that use of Molière probability density function for modelling the multiple Coulomb scattering presents a modest 2% accuracy improvement over the Gaussian approximation and most-likely-path method. Simulations of voxelized phantom showed no essential benefit from the inclusion of the material information into the optimization, while path optimization with energy constraint slightly increased path resolution in a bone/water interface phantom. Method error was found to depend on energy, proton track-length within the medium, and proportion of data filtering.

The effects of La2O3 addition on mechanical and nuclear shielding properties for zinc borate glasses using Monte Carlo simulation

Effects of La2O3 addition on the mechanical and nuclear shielding properties of zinc borate glasses with the form (55-x)ZnO-45B2O3-xLa2O3: x = 0, 2, 5, and 10 mol% labelled as LZB1-LZB4, respectively were investigated. Bond compression (BC) model and Geant4 simulation code were utilized to achieve these objectives. The value of the bulk modulus (KBC) decreased from 153.116 GPa for LZB1 glass sample to 136.662 GPa for LZB4 glass sample corresponding to an increment of La2O3 from 0 to 10 mol%. Longitudinal modulus (LBC) decreased from 280.729 GPa to 249.610 GPa and the Young's modulus (EBC) also decreased from 238.11 GPa to 211.03 GPa for LZB1 to LZB4 glasses. Poisson's ratio (σBC) increased from 0.240 to 0.243 with the increase of La3+ ions in the LZB-glasses. Hardness of LZB-glasses was decreased from 16.578 GPa to 14.572 Gpa. The nuclear radiation shielding properties of the LZBx glasses were explored by utilizing Geant4 Monte Carlo simulations and different theoretical approaches such as ESTAR and XCOM platforms. The obtained values of mass attenuation (MAC) increased in the glasses in the order: LZB1< LZB2 < LZB3 < LZB4. The maximum values of MAC obtained at energy of 15 keV were 39.157, 40.117, 41.356 and 43.019 cm2g-1 for LZB1, LZB2, LZB3, and LZB4 respectively. Calculated values of fast and thermal neutron macroscopic cross sections varied from 0.1143 to 0.1156 cm-1 and 1.9378 to 27,786 cm-1 as La2O3 varied from 0 to 10 mol% in the glasses. Also, the electron attenuation capacity of the LZBx glasses improved as La2O3 content increased. The observed promising properties of LZBx glasses is an indication that they can be useful for several applications including shielding against photons, electrons, and fast/thermal neutrons.