Results Of Geant4 Simulations Research Articles

Shielding performance of multi-metal nanoparticle composites for diagnostic radiology: an MCNPX and Geant4 study.

Lead-free polymer composite shields are used in diagnostic radiology to protect patients from unnecessary radiation exposure. This study aimed to examine and introduce the radiation-shielding properties of single- and multi-metal nanoparticle (NP)-based composites containing Bi, W, and Sn using Geant4, MCNPX, and XCom for radiological applications. The mass attenuation coefficients and effective atomic numbers of single- and multi-metal NP-loaded polymer composites were calculated using the Geant4 and MCNPX simulation codes for X-ray energies of 20-140keV. The nano-sized fillers inside the polydimethylsiloxane (PDMS:C2H6SiO) matrix included W (K = 69.5keV), Bi (K = 90.5keV), and Sn (K = 29.20keV). For single-metal shields, one filler was used, while in multi-metal shields, two fillers were required. The MCNPX and Geant4 simulation results were compared with the XCom results. The multi-metal NP composites exhibited higher attenuation over a larger energy range owing to their attenuation windows. In addition, Bi2O3 + WO3 NPs showed a 39% higher attenuation at 100-140keV, and that of Bi2O3 + SnO2 NPs was higher at 40-60keV. Meanwhile, the WO3 + SnO2 NPs exhibited lower attenuation. The difference between the results obtained using Geant4 and XCom was less than 2%, because these codes have similar simulation structures. The results show that the shielding performance of the Bi2O3 + WO3 filler is better than that of the other single- and multi-metal fillers. In addition, it was found that the Geant4 code was more accurate for simulating radiation composites.

Monte Carlo GEANT4 Simulation Approach in Analyzing Radiation Shielding Parameter of Lombok Pumice

The linear attenuation coefficient (LAC), mean free path (MFP), half-value layer (HVL), and the radiation protection efficiency (RPE) parameters of Lombok pumice powder from 3 different regions (Ijobalit, Setangi beach, and Lingsar) have been analyzed. The radiation parameter analysis was carried out to determine the pumice that potential as a raw material of radiation shielding composite. The Monte Carlo simulation using the GEANT4 toolkit was applied to analyze those parameters using a gamma-ray transmission measurement for the photon energies of 57Co, 133Ba, 54Mn, 137Cs, 60Co, 65Zn, 22Na and 40K. The GEANT4 simulation results were compared to the XCOM theoretical calculation and show that the linear attenuation coefficient parameter has a good agreement with the XCOM results based on the determination coefficient of the correlation graph (R2 = 0.998) between those 2 approaches methods. Setangi beach pumice has a smaller LAC parameter than Ijobalit pumice and Lingsar pumice. The MFP and HVL parameter of the Setangi beach pumice indicate the absorption ability of gamma photons is low. In the low gamma energy 0.122 MeV, Ijobalit pumice and Lingsar pumice have more than 50 % RPE and are better used as a raw material of radiation shielding composite.
 HIGHLIGHTS
 
 New lead-free shielding materials of radiation becomes a critical concern in the investigation of raw shielding material
 GEANT4 Monte Carlo simulation and XCOM theoretical calculation was conducted to analyse the radiation LAC parameter
 Radiation parameters analysis of Lombok Pumice show that Ijobalit pumice and Lingsar pumice have more than 50 % RPE and are better used as a raw material of radiation shielding composite
 
 GRAPHICAL ABSTRACT

Simulation of the Particle Transport Behaviors in Nanoporous Matter

The transport behaviors of proton into nanoporous materials were investigated using different Monte Carlo simulation codes such as GEANT4, Deeper and SRIM. The results indicated that porous structure could enhance the proton scattering effects due to a higher specific surface area and more boundaries. The existence of voids can deepen and widen the proton distribution in the targets due to relatively lower apparent density. Thus, the incident protons would transport deeper and form a wider Bragg peak in the end of the range, as the target materials are in a higher porosity state and/or have a larger pore size. The existence of voids also causes the local inhomogeneity of proton/energy distribution in micro/nano scales. As compared, the commonly used SRIM code can only be used to estimate roughly the incident proton range in nanoporous materials, based on a homogeneous apparent density equivalence rule. Moreover, the estimated errors of the proton range tend to increase with the porosity. The Deeper code (designed for evaluation of radiation effects of nuclear materials) can be used to simulate the transport behaviors of protons or heavy ions in a real porous material with porosity smaller than 52.3% due to its modeling difficulty, while the GEANT4 code has shown advantages in that it is suitable and has been proven to simulate proton transportation in nanoporous materials with porosity in its full range of 0~100%. The GEANT4 simulation results are proved consistent with the experimental data, implying compatibility to deal with ion transportation into homogeneously nanoporous materials.

A comparison between Geant4 simulation and experiment for time-of-flight measurement

A self-constructed Geant4 Monte Carlo simulation has been built to simulate time-of-flight (TOF) measurement for 236U accelerator mass spectrometry. Time resolution of the experiment in 9.4 and 2 µg cm−2 of carbon foil cases are 2.633 ns and 1.853 ns, respectively. The time resolution of Geant4 simulation in 9.4 and 2 µg cm−2 of carbon foil cases are 1.997 ns and 1.379 ns, respectively. The results show a good agreement between Geant4 simulation and experiment at two different thicknesses of carbon foil cases. The results of Geant4 simulation and experiment show this TOF detection system has ultrasensitivity in timing measurement.

Design of static and dynamic ridge filters for FLASH-IMPT: A simulation study.

This paper focused on the design and optimization of ridge filter-based intensity-modulated proton therapy (IMPT), and its potential applications for FLASH. Differing from the standard pencil beam scanning (PBS) mode, no energy/layer switching is required and total treatment time can be shortened. Unique dose-influence matrices were generated as a proton beam traverses through slabs of different thicknesses (i.e., modulation by different layers). To establish the references for comparison, conventional IMPT plans (single field) were created using a large-scale nonlinear solver. The spot weights from the reference IMPT plans were used as inputs for optimizing the design of ridge filters. Two designs were evaluated: model A (static) and model B (dynamic). The ridge filter designs were first verified (by GEANT4 simulation) in a water phantom and then in an H&N case. A direct comparison was made between the GEANT4 simulation results of two models and their respective references, with regard to plan quality, dose-averaged dose rate, and total treatment time. In both the water phantom and the H&N case, two models are able to modulate dose distributions with high conformity, showing no significant difference relative to the reference plans. Dose rate-volume histograms suggest that in order to achieve a dose rate of 40Gy/s over 90% PTV, the beam intensity needs to be 2.5×1011 protons/s for both models. For a fraction dose of 10Gy, the total treatment time (including both irradiation time and dead time) can be shortened by a factor of 4.9 (model A) and 6.5 (model B), relative to the reference plans. Two proposed designs (both static and dynamic) can be used for PBS-IMPT requiring no layer switching. They are promising candidates for FLASH-IMPT capable of reducing treatment time and achieving high dose rates while maintaining dose conformity simultaneously.

A method for converting microdosimetric spectra in diamond to tissue in proton therapy.

Diamond has been regarded as a promising microdosimeter in radiation protection and radiotherapy due to its excellent properties. However, as the diamond is not tissue equivalent, a conversion of the measured spectra in the diamond microdosimeter to the tissue site is needed. In this work, we intend to deduce a method for converting the microdosimetric spectra from diamond to tissue in the proton therapy application based on the Chapman-Kolmogorov equation and investigate the validity of this method in spectral conversion. The comparison of stopping power and energy deposition distribution of diamond and tissue shows that the conversion of the spectra in diamond to tissue can be performed by a simple scaling factor. Therefore, the equivalence of the energy deposition spectra in the diamond microdosimeter and a tissue site of the same size in the same radiation field was studied first to obtain the scaling factor. Then, the spectra conversion method was derived from the Chapman-Kolmogorov equation and the scaling factor. The Geant4 simulation was employed to settle this study. Theoretical and Geant4 simulation results indicate that the linear stopping power ratio of diamond to tissue is adequate to convert the microdosimetric spectra in diamond to tissue of identical dimension. The conversion results indicate that the energy deposition spectra converted from diamond to bone agree well with the spectra calculated by Geant4 along the Bragg curve. As for water, a good agreement of the converted and calculated spectra was found at the plateau of the Bragg curve and the distal part of the Bragg peak. At the proximal part of the Bragg peak, the converted and calculated spectrum is poorly coincident. The method of the energy deposition spectra conversion from the diamond microdosimeter to the tissue site of equal size shows relatively good results in most situations. But the deficiency was also found. Therefore, further investigation is needed to improve the reliability of this method.

Property investigation of the wedge-shaped CsI(Tl) crystals for a charged-particle telescope

Two types of wedge-shaped CsI(Tl) crystals were designed to be placed behind an annular double-sided silicon detector to identify light charged-particles with the ΔE−E method. The properties of the CsI(Tl) detectors with different shapes and sizes were investigated using an α source and a radioactive beam of 15C. The larger crystal was found to have better energy resolution, smaller light output non-uniformity, as well as better particle identification capability, and was finally adopted to form the ΔE-E telescope. The performance of the two types of CsI(Tl) crystals are interpreted based on Geant4 simulation results.

Development of a position-sensitive fast scintillator (LaBr3(Ce)) detector setup for gamma-ray imaging application

We have characterized a Cerium doped Lanthanum Bromide (LaBr3(Ce) ) crystal coupled with the position-sensitive photo-multiplier system for the gamma-ray imaging application. One can use this detector set-up for the scanning of high purity germanium detectors for pulse shape analysis in gamma-ray spectroscopy experiments and the image formation of an object by Compton back-scattering . The sensor has been tested for energy, timing and position information of the gamma-rays interacting within the detector crystal. The GEANT4 simulation results are consistent with the experimental results. We have reconstructed the image of irradiation spots in different positions throughout the detector crystal. Position resolution is found to be around 3.5 mm with the 2 mm collimated gamma-rays. The 2-d image of hexagonal Bismuth Germanate (BGO) crystal and a cylindrical LaBr3(Ce) crystal have been reconstructed in coincidence technique. The performance of the detector for imaging application has been investigated by coincidence technique in GEANT4 simulation and compared with the experimental data. We have reconstructed the 2-d images of objects with various geometrical shapes by Compton back-scattered events of the gamma-rays. This position-sensitive detector can be used as an absorber of a Compton camera for the image reconstruction of an extended radioactive source. One can also use this kind of set-up as in radiation imaging and many other applications where the energy and source position of the gamma-ray is the main interest.

Neutron yields of Be-9(p,xn) reactions and beam characterization for accelerator-based boron neutron capture therapy facility using MCNP6, PHITS, and GEANT4 simulation results

Neutron yields from 9Be(p,xn) reactions with a 2-cm thick beryllium target bombarded by proton beams of 5, 6, 7, 8, 9, and 10 MeV were investigated. Neutron beam characteristics through a pilot design of beam shaping assembly were calculated by using MCNP6, PHITS, and GEANT4. The neutron yield with a 10 MeV beam by MCNP6 was 7.7 times larger than values by the other codes, but close to the experimental data. The neutron spectrum and directionality were different among the codes. These differences could stem from different cross-section libraries and models used in the codes. The epithermal flux at the beam irradiation port by MCNP6 was 1.4 × 109 cm−2 s−1 for a proton current of 8 mA hitting the target. The ratio of thermal and epithermal flux was less than 0.01 and the forward directionality was 0.78. However, we suggest a new criterion regarding a ratio of fast and epithermal flux.

Characterization of the efficiency of a cubic NaI detector with rectangular cavity for axially positioned sources

Scintillation NaI(Tl) crystals are typically utilized at room temperature for detection of energetic photons in high energy and nuclear physics research, non-destructive analysis of materials testing, safeguards, verification of nuclear treaty, geological exploration and therapeutic imaging. The present work provides a new geometry for the source-to-detector combination. A special order cubic detector with rectangular cavity was used. The mathematical expressions of the path-lengths traveled by the incident photon as well as the geometrical solid angle were derived. The detector efficiency was determined for an axially positioned standard point-like gamma-ray source using the analytical efficiency transfer technique. Geant4 Monte Carlo simulation code was also used to predict the detector response under the calibration geometry. The analytical efficiency transfer and Geant4 simulation results were compared with those obtained experimentally and a good agreement between them was shown.

B2O3–BaCO3–Li2O3 glass system doped with Co3O4: Structure, optical, and radiation shielding properties

A novel glass system with nominal composition of (50B2O3+ 20BaCO3+ 30Li2O3+ xCo3O4: 0 ≤ x ≤ 0.5 mol%) has been synthesized using solid state reaction method. Non-crystallinity nature, structure, optical, γ-ray and neutron shielding characterizations of the produced glass samples were investigated. X-ray diffraction patterns for all glasses confirmed their amorphous nature. Density and molar volume were calculated. UV–Vis measurements were in the range of 190–1100 nm wavelength. The band gaps of optical energy in direct transition (EGapD), and in indirect transition (EGapI) as well as Urbach's energy (Eu) were calculated. Steepness parameter was found to be 0.099 for BBLC0.0 glass and 0.026 for BBLC0.5 glass. Mass attenuation coefficient (μ/ρ), as a basic parameter for gamma-ray shielding studies, was generated in the photon energy range of 0.015–15 MeV using GEANT4 Monte Carlo simulation for each prepared glass. The results of GEANT4 simulation were compared with those calculated by WinXcom program, and a good agreement was observed. All other parameters that can describe the gamma-ray shielding properties like mean free path (MFP), effective electron density (Neff), half value layer (HVL), and effective atomic number (Zeff) were calculated and discussed in detail. Additionally, neutron shielding features were estimated by determining the removal cross section for each prepared glass and compared with the common neutron shielding materials. Results revealed that the prepared glasses can be used as effective radiation shielding materials against gamma rays and neutrons.

Comparison of MC Geant4 simulation with the measurements of gamma photons produced by neutrons

In this work, we have focused on results of measurements of the hydrogen line 2223 keV and compared them with the results of Geant4 simulations. The paraffin containing hydrogen was irradiated by neutrons produced by the weak AmBe source. Produced gammas were measured with the germanium detector. The experimental setup was placed inside a carbon chamber which provided the shielding from the external neutrons. The measurements were performed for different amounts of paraffin. The processes playing a role in the description of our measurements are transport and moderation of neutrons, production of gamma rays in neutron-hydrogen interactions, transport and detection of gamma rays. It has been shown that the correctly carried out Monte Carlo simulations reproduced the measured values of the intensity of the observed gamma line 2223 keV from the neutron capture on hydrogen. The absorption of gamma rays is also described correctly. This has been shown in comparing the measurements of gamma line 322 keV from [Formula: see text]Pb with the simulations.

GEANT4 simulations of small cosmic ray detection modules based on scintillators and WLS bars

This paper describes the results of GEANT4 simulations for a prototype of detection module designed as a basic element of a low-cost, reconfigurable, modular mini-array for detection of cosmic rays. The basic layout of each individual module is based on a 400 cm2 scintillator tile, optically coupled to a Wavelength Shifter (WLS) bar and a Silicon Photomultiplier (SiPM) for light collection and readout. The array will include about 50 modules in its final stage, to be employed in various geometrical configurations. GEANT4 simulations of the transport of optical photons inside the detector are here reported, with the aim of estimating the key parameters contributing to the photon collection efficiency and compare different solutions.

Benchmarking Geant4 for Simulating Galactic Cosmic Ray Interactions Within Planetary Bodies

Galactic cosmic rays undergo complex nuclear interactions with nuclei within planetary bodies that have little to no atmosphere. Radiation transport simulations are a key tool used in understanding the neutron and gamma ray albedo coming from these interactions and tracing these signals back to geochemical composition of the target. We study the validity of the code Geant4 for simulating such interactions by comparing simulation results to data from the Apollo 17 Lunar Neutron Probe Experiment. Different assumptions regarding the physics are explored to demonstrate how these impact the Geant4 simulation results. In general, all of the Geant4 results overpredict the data; however, certain physics lists perform better than others. In addition, we show that results from the radiation transport code MCNP6 are similar to those obtained using Geant4.

Position and depth of interaction measurements using silicon photostrip detectors and CsI(Tl) crystal

The photoelectric absorption of gamma rays in silicon occurs with such low probability that scintillation material is employed in the photostrip detector. We fabricate single-sided photostrip sensors which are sensitive to visible light. Two photodetectors in a photon counting mode are optically coupled with the scintillator with a sandwich structure. The photostrip sensors have 128 strips, a 200μm strip pitch and a size of 3.8×2.8cm2. Sensor signals are read by a 128-channel VA1TA3 readout chip. A CsI(Tl) crystal is then optically combined to measure both of depths of interaction (DOI) and 2-D images, while the position of the LED are varied. We also performed a simulation of gamma ray irradiation at different locations inside the scintillator using the GEANT4 Monte Carlo simulation tool. We measured the 2-D position of incoming light with two photostrip sensors, and also measured the DOI and 2-D position of scintillating light by placing a scintillator between the photostrip sensors. The DOI measurement results and the GEANT4 simulation results were compared.

Preliminary assessment of the ATHENA/WFI non-X-ray background

We present a preliminary assessment of the non-X-ray background for the WFI on board ATHENA conducted at IAAT in the context of the collaborative background and radiation damage working group activities. Our main result is that in the baseline configuration originally assumed for the camera the requirement on the level of non-X-ray background could not be met. In light of the results of Geant4 simulations we propose and discuss a possible optimization of the camera design and pinpoint some open issues to be addressed in the next phase of investigation. One of these concerns the possible contribution to the non-X-ray background from soft protons and ions funneled to the focal plane through the optics. This is not quantified at this stage, here we just briefly report on our ongoing activities aimed at validating the mechanisms of proton scattering at grazing incidence.

Initial development of goCMC: a GPU-oriented fast cross-platform Monte Carlo engine for carbon ion therapy

Monte Carlo (MC) simulation is considered as the most accurate method for calculation of absorbed dose and fundamental physics quantities related to biological effects in carbon ion therapy. To improve its computational efficiency, we have developed a GPU-oriented fast MC package named goCMC, for carbon therapy. goCMC simulates particle transport in voxelized geometry with kinetic energy up to 450 MeV u−1. Class II condensed history simulation scheme with a continuous slowing down approximation was employed. Energy straggling and multiple scattering were modeled. δ-electrons were terminated with their energy locally deposited. Four types of nuclear interactions were implemented in goCMC, i.e. carbon–hydrogen, carbon–carbon, carbon–oxygen and carbon–calcium inelastic collisions. Total cross section data from Geant4 were used. Secondary particles produced in these interactions were sampled according to particle yield with energy and directional distribution data derived from Geant4 simulation results. Secondary charged particles were transported following the condensed history scheme, whereas secondary neutral particles were ignored. goCMC was developed under OpenCL framework and is executable on different platforms, e.g. GPU and multi-core CPU. We have validated goCMC with Geant4 in cases with different beam energy and phantoms including four homogeneous phantoms, one heterogeneous half-slab phantom, and one patient case. For each case carbon ions were simulated, such that in the region with dose greater than 10% of maximum dose, the mean relative statistical uncertainty was less than 1%. Good agreements for dose distributions and range estimations between goCMC and Geant4 were observed. 3D gamma passing rates with 1%/1 mm criterion were over 90% within 10% isodose line except in two extreme cases, and those with 2%/1 mm criterion were all over 96%. Efficiency and code portability were tested with different GPUs and CPUs. Depending on the beam energy and voxel size, the computation time to simulate carbons was 9.9–125 s, 2.5–50 s and 60–612 s on an AMD Radeon GPU card, an NVidia GeForce GTX 1080 GPU card and an Intel Xeon E5-2640 CPU, respectively. The combined accuracy, efficiency and portability make goCMC attractive for research and clinical applications in carbon ion therapy.

Modeling of radio emission from a particle cascade in a magnetic field and its experimental validation

The SLAC T-510 experiment was designed to compare controlled laboratory measurements of radio emission of particle showers to predictions using particle-level simulations, which are relied upon in ultra-high-energy cosmic-ray air shower detection. Established formalisms for the simulation of radio emission physics, the "endpoint" formalism and the "ZHS" formalism, lead to results which can be explained by a superposition of magnetically induced transverse current radiation and charge-excess radiation due to the Askaryan effect. Here, we present the results of Geant4 simulations for the SLAC T-510 experiment, taking into account the details of the experimental setup (beam energy, target geometry and material, magnetic field configuration, and refraction effects) and their comparison to measured data with respect to e.g. signal polarisation, linearity with magnetic field, and angular distribution. We find that the microscopic calculations reproduce the measurements within uncertainties and describe the data well.

A Monte Carlo Library Least Square approach in the Neutron Inelastic-scattering and Thermal-capture Analysis (NISTA) process in bulk coal samples

A new Monte-Carlo Library Least Square (MCLLS) approach for treating non-linear radiation analysis problem in Neutron Inelastic-scattering and Thermal-capture Analysis (NISTA) was developed. 14MeV neutrons were produced by a neutron generator via the H(H2,n)He43 reaction. The prompt gamma ray spectra from bulk samples of seven different materials were measured by a Bismuth Germanate (BGO) gamma detection system. Polyethylene was used as neutron moderator along with iron and lead as neutron and gamma ray shielding, respectively. The gamma detection system was equipped with a list mode data acquisition system which streams spectroscopy data directly to the computer, event-by-event. A GEANT4 simulation toolkit was used for generating the single-element libraries of all the elements of interest. These libraries were then used in a Linear Library Least Square (LLLS) approach with an unknown experimental sample spectrum to fit it with the calculated elemental libraries. GEANT4 simulation results were also used for the selection of the neutron shielding material.

Energy correction for the BGO calorimeter of DAMPE using an electron beam**Supported by the Chinese 973 Program (2010CB833002), the Strategic Priority Research Program on Space Science of the Chinese Academy of Science (XDA04040202-4) and 100 Talents Program of CAS

The DArk Matter Particle Explorer is an orbital indirect dark matter search experiment which measures the spectra of photons, electrons and positrons originating from deep space. The electromagnetic calorimeter (ECAL), made of bismuth germinate (BGO), is one of the key sub-detectors of DAMPE, and is designed for energy measurement with a large dynamic range from 5 GeV to 10 TeV. In this paper, methods for energy correction are discussed, in order to reconstruct the primary energy of the incident electrons. Different methods are chosen for the appropriate energy ranges. The correction results of Geant4 simulation and beam test data (at CERN) are presented.