Validation of Geant4 physics models for 56Fe ion beam in various media

Nuclear Instruments and Methods in Physics Research B 291 (2012) 7–11

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Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb

Validation of Geant4 physics models for

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Fe ion beam in various media

Summit Jalota, Ashavani Kumar ⇑ Department of Physics, National Institute of Technology, Kurukshetra 136 119, India

a r t i c l e

i n f o

Article history: Received 11 July 2012 Received in revised form 18 August 2012 Available online 21 September 2012 Keywords: Monte Carlo simulation Heavy-ion interaction Galactic cosmic rays Shielding

a b s t r a c t The depth-dose distribution of a 56Fe ion beam has been studied in water, polyethylene, nextel, kevlar and aluminum media. The dose reduction versus areal depth is also calculated for 56Fe ions in carbon, polyethylene and aluminum using the Monte Carlo simulation toolkit Geant4. This study presents the validation of physics models available in Geant4 by comparing the simulated results with the experimental data available in the literature. Simulations are performed using binary cascade (BIC), abrasion–ablation (AA) and quantum molecular dynamics (QMD) models; integrated into Geant4. Deviations from experimental results may be due to the selection of simple geometry. This paper also addresses the differences in the simulated results from various models. Ó 2012 Elsevier B.V. All rights reserved.

1. Introduction The interaction and propagation of highly-energetic, highlycharged (referred as HZE) particles are important in the study of astrophysics, space radiation protection and shielding design. Even though heavy ions of charge Z = 3–92 are far less abundant (1%) than protons (87%) in galactic cosmic rays (GCR), they are significant importance because of their high relative biological effectiveness (RBE) [1–4]. GCR, trapped particles, fragmentation products, recoil nuclei and neutrons cause the major health risk to astronauts, electronics and scientific equipment in a spacecraft [5–10]. The space radiation spectrum is a complex mixture of charged and uncharged particles with energies from few MeV/n to TeV/n [1]. The lower energy particles are easily stopped whereas particles with higher energies can penetrate deeply in shielding materials. The range of a 1 GeV A 56Fe ion beam in water, aluminum, nextel and kevlar is greater than 24 g/cm2. The primary incident particles undergo electromagnetic and nuclear interactions with these shielding materials. In an electromagnetic interaction, energy loss is due to transfer of electrons to the medium along the depth. In nuclear interactions, the incident particles undergo inelastic collisions with the atoms and molecules of the target. Due to this, incident particles are fragmented into various charged and uncharged particles. Usually, these fragments have a velocity the same as that of primaries [11]. These fragmentation reactions thus change the physical and biological effectiveness of radiation. Light hydrogenated materials, such as water and polyethylene are mostly used to study physical and biological effects of space radiation [12–15] ⇑ Corresponding author. Tel.: +91 1744 233548; fax: +91 1744 238050. E-mail addresses: [email protected] (S. Jalota), [email protected] (A. Kumar). 0168-583X/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2012.08.026

and liquid hydrogen is the second best shielding material against GCR [1]. A better protection from meteoroids and debris in low earth orbits could be provided by composite materials such as nextel and kevlar [6]. The depth dose profiles for 12C ion beam in water and polyethylene media were explained by Lechner et al. [16] on the basis of the G4QMDReaction model. Pshenichnov et al. [17] described the depth-dose distribution of heavy-ion, 56Fe, in water using the binary cascade and abrasion models with and without using multifragmentation processes. Also, Silvestri et al. [18] used the Geant4 Radiation Analysis for Space (GRAS) tool to study interactions of 56 Fe ions. In a previous study [19], we incorporated four models (stated here as the G4code): standard electromagnetic physics, binary cascade, Fermi break-up and statistical multi-fragmentation models to define the Bragg peak for a 12C ion beam in polyethylene more precisely. In the present study, we have analyzed the validity of the G4code [19], abrasion–ablation and QMD models for heavy ions; 56Fe, in water, polyethylene, nextel, kevlar and aluminum media by plotting dose profiles. Comparison of the dose reduction for a 56Fe ion beam in carbon, polyethylene and aluminum using Geant4 with experimental results is also presented. A brief description of all these models is provided in Section 2. The experimental data is derived from Refs. [6,7,20,21]. 2. Methodology 2.1. Dosimetry The present validation study focuses on the simulation of depth-dose profiles of a 56Fe ion beam in water, polyethylene, aluminum, nextel, kevlar and dose-reduction in carbon, aluminum and polyethylene media using in-built Geant4 physics models.

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These materials are commonly used for shielding purposes in space applications. To compare with the experimental results available in literature, the present validation study of a 56Fe ion beam of energies 968–1087 A MeV was considered. The target of a three dimensional box was employed as a phantom material having uniform density. These materials are used in simulation work in terms of their fractional mass as (1) water [16] (q = 0.997 g/cm3): 66.67% hydrogen, 33.33% oxygen; (2) polyethylene (q = 0.97 g/cm3): 33.33% carbon, 66.67% hydrogen; (3) kevlar (q = 1.44 g/cm3): 71% carbon, 13% oxygen, 12% nitrogen, 4% hydrogen; (4) nextel (q = 2.7 g/cm3): 52% oxygen, 33% aluminum, 11% silicon, 4% boron [6]. The target area (200  200 mm2) facing the beam was kept perpendicular along the direction of the incident beam. In all cases, the axis along the direction of the ion beam is kept larger than its range to obtain a fragmentation tail beyond the Bragg peak. A mono-energetic beam is utilized in the present simulation work. A moderate number of ions is selected for good statistical results. 2.2. Code description All the calculations and estimations were performed using the simulation toolkit: Geant4 (version 9.4) [22,23]. Geant4 consists of experimental, parameterized and theory driven models. In the present simulation study, a user-defined physics list is partially customized for simulation. The brief introduction of the processes and models used are provided. The present study aimed at achieving results from the G4code, G4WilsonAbrasionModel and G4QMDReaction models for a 56Fe ion beam and their comparison with experimental results.

In the first step, nucleons in the overlapping zone of the incident projectile and target nuclei are abraded, resulting in the formation of a hot zone named a ‘‘fireball’’. In this process, outer nucleons called ‘‘spectators’’ are also affected. In the second step, the remaining projectile and target fragments as well as fireball are de-excited with the evaporation of nucleons and light clusters. The fragments from the projectile move in the direction of the incident projectile with a velocity greater than or equal to that of the incident projectile. The target fragments have velocities much smaller than that of the projectile velocity. Fragments from the fireball have a velocity in the range between target and projectile fragments. In Geant4, the Abrasion model is available as G4WilsonAbrasionModel [26]. It is a simplified model for the study of nuclear interactions. This model is less detailed and the accuracy in calculation of the nuclear residue volumes and their excitation energies is small in comparison to the BIC and QMD models. By default, the Ablation process is not activated; it is activated by passing the Boolean value ‘true’ into the member function ‘‘SetUseAblation(G4bool)’’. This model also uses the inbuilt de-excited and more detailed models such as the evaporation, Fermi breakup and statistical multi-fragmentation models. The inbuilt G4WilsonAbrasionModel uses G4StatMF (statistical multi-fragmentation) to describe the multi-fragment breakup of excited residual nuclei at excitation energies more than 5 MeV/n and G4FermiBreakUp (Fermi break-up) to describe the fragmentation of highly excited light nuclei with Z 6 6 and A 6 12.

2.2.1. G4code The G4code consists of set of four models: standard electromagnetic physics, binary cascade, statistical multi-fragmentation and Fermi breakup models. The standard electromagnetic physics model is used to describe the energy loss due to ionization and multiscattering processes. This model is valid for all hadrons with energy ranging from 250 keV to 1 PeV. Inelastic interaction of primary and secondary particles with protons and nuclei of the target is described by the binary cascade model. The statistical multifragmentation model explains the multi-fragment breakup of highly excited nuclei having excitation energy greater than 3 MeV/n. The decay of cold and excited fragments with A < 16 is described by the Fermi breakup model. A detailed description of all these models is provided in Ref. [19] and references therein. 2.2.2. Abrasion–ablation model Violent nuclear spallation reactions occur at several hundreds of MeV. At these energies, peripheral collisions are the most frequently occurring nuclear reactions. These reactions result in fragmentation of both target as well as projectile nuclei. This is explained by the two-step abrasion–ablation model [24,25] as shown in Fig. 1. In peripheral collisions, the incident beam particle may lose one or several nucleons along the penetration depth.

Fig. 1. Abrasion–ablation model according to Serber et al. [25]. Image is adapted from Gunzert-Marx et al. [24].

Fig. 2. Calculated depth-dose distribution for a 56Fe ion beam at (a) 1087 A MeV and (b) 969.8 A MeV energies in water by Geant4 and compared with the experimental data from Refs. [20,21].

S. Jalota, A. Kumar / Nuclear Instruments and Methods in Physics Research B 291 (2012) 7–11

Fig. 3. Calculated normalized dose for from Ref. [6].

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Fe ion beam at 968 A MeV in (a) polyethylene, (b) Nextel, (c) Kevlar and (d) Aluminum and compared with the experimental data

2.2.3. Quantum molecular dynamics (QMD) model The interaction of particles with matter undergoes both dynamics and statistical effects. In the QMD model, dynamical considerations are taken into account to study the nuclear interactions and simulate the quantum effects and Pauli-blocking. QMD is a quantum mechanical extension of the classical molecular dynamics model. The particle–particle correlations are studied by considering individual collisions. Each nucleon state is represented by Gaussian wave packet of width L as [27]:

# ð~ r  h~ ri ðtÞiÞ2 i ~ ~ h p wi ð~ r; tÞ ¼ exp  ðtÞi r þ i h 4L ð2pLÞ3=4 1

"

where h~ r i ðtÞi and h~ pi ðtÞi represents the position and momentum of the ith nucleon at a given time t. The total wave function is obtained by the product of single particle wave functions wi. The properties of nuclear matter and nuclei are described by the Hamiltonian H [27]:

H¼

n X hp2 i i

I¼1

2M

9

þ V nucl þ V s þ V p

where Vnucl, VS and VP are the nuclear, surface and Pauli potentials, respectively. The detailed description is provided in Ref. [27,28] and references therein. In Geant4, the QMD model is available as G4QMDReaction, based on the Jaeri Quantum Molecular Dynamics (JQMD) code [27,29]. It was re-engineered and included in Geant4 version 9.1. Before this version, JQMD is used through interfaces [16]. G4QMDReaction is valid for generic ions, 2H, 3H, 3He and 4He for energy

P50 MeV/n and reaction cross sections data sets are activated for inelastic collisions. The term ‘generic ion’ represents all ions except 1H, 2H, 3H, 3He and 4He. The QMD model takes more time as compared to te binary cascade and abrasion–ablation models in performing all calculations. 3. Results and discussion Nuclear interactions with matter lead to a decrease in peak height with increase in buildup of low Z fragments and results in long tail beyond the peak. As the energy of the incident ion beam increases, the peak height decreases. These trends are systematically explained in our previous study [19] in a polyethylene medium. The fragmentation reactions result in disintegration of projectiles into N lighter components. The total ionization energy loss is proportional to the square of the nuclear charge as [17]:

ðZ 1 þ Z 2 þ . . . þ Z N Þ2 > Z 21 þ Z 22 þ . . . þ Z 2N The G4code [19] well describes the propagation and transportation of a 12C ion beam in a polyethylene medium. The MCHIT model [17] describes the propagation of light and heavy ions in tissue-like media using binary cascade and abrasion models. Lechner et al. [16] have shown the validity of the QMD reaction model by studying the interaction and propagation of a 12C beam in water and polyethylene media. G4ExcitationHandler class has been used to study the breakup of excited nuclei during de-excitation mechanism. G4Evaporation, G4FermiBreakUp and G4StatMF models have been passed to

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Fig. 4. Calculated dose-reduction per unit areal density as a function of material depth for a 56Fe ion beam at 1 A GeV energy in (a) carbon, (b) aluminum and (c) polyethylene using Geant4, compared with experimental data [7].

G4ExcitationHandler class through public methods. By default, multi-fragmentation is switched off in binary cascade and abrasion model. Multi-fragmentation is turned on through the G4ExcitationHandler class. In the present study, the depth-dose distribution of a 56Fe ion beam in water at 969.8 and 1087 A MeV and in polyethylene, nextel, kevlar and aluminum at 968 A MeV is simulated using the G4code, QMD reaction and abrasion–ablation models with and without multi-fragmentation and results are presented in Figs. 2 and 3. Simulated results are compared with the experimental data available [6,20,21]. The energy spread of the beam was assumed to be zero asa mono-energetic narrow pencil beam was selected for the simulation work. Also dose reduction for 56 Fe ion beam at 1 A GeV is calculated in carbon, aluminum and polyethylene media. Simulated results are compared with the experimental data available in the literature [7]. To the best of our knowledge, no Geant4 based study for validation of these models has been performed. 3.1. Bragg peak of a

56

Fe ion beam

The depth-dose profile as linear energy deposition per beam particle (MeV/mm) versus penetration depth (mm) are plotted for 56Fe ions in water at energies 969.8 and 1087 A MeV are presented in Fig. 2(a) and (b). Simulated results are compared with the experimental results [20,21]. It can be observed from Fig. 2. that the calculations performed with the G4code (using standard electromagnetic physics, binary cascade, Fermi breakup and statistical multi-fragmentation models) and QMD reaction models overestimate, while the abrasion–ablation model without multi-

fragmentation underestimates the linear energy deposition for a 56 Fe ion beam in water. Only the abrasion–ablation model with multi-fragmentation agrees well with the experimental data before the Bragg peak. The depth-dose profiles, as normalized dose versus depth (g/ cm2), are plotted for a 56Fe ion beam at 968 A MeV in polyethylene, nextel, kevlar and aluminum in Fig. 3. Simulated results are compared with the experimentally measured results of Lobascio et al. [6]. From Fig. 3(a), it is concluded that the G4code and QMD reaction model overestimate the dose-distribution, while simulation performed with the abrasion–ablation model without multi-fragmentation underestimates the dose-deposition before the Bragg peak. The abrasion–ablation model with multi-fragmentation nearly explains the dose-deposition before the Bragg peak whereas the QMD reaction model explains the dose-distribution after the Bragg peak. In Fig. 3(b) and (c), the QMD reaction model overestimates whereas the abrasion–ablation model with and without multi-fragmentation underestimates the depth-dose distribution. The G4code closely explains the depth-dose distribution of a 56Fe ion beam in kevlar and nextel. In Fig. 3(d), the G4code and abrasion–ablation (with and without multifragmentation) models underestimate the dose-distribution, while the QMD reaction model almost explains the dose-distribution for a 56Fe ion beam in aluminum. 3.2. Dose reduction Dose reduction for 56Fe ions per unit areal density dDn (cm2/g) in carbon, aluminum and polyethylene is calculated as [18]:

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dDn ¼

dosei 1  dose 1

depthi

where dosei is calculated at the depthi and dose1 is the dose calculated at the initial position. Experimental results are derived from Ref. [7]. From Fig. 4(a) and (b), one can conclude that the QMD reaction model underestimates whereas abrasion–ablation model with and without multi-fragmentation overestimates the dose reduction. The G4code nearly explains the dose reduction of a 56Fe ion beam in carbon and aluminum. In Fig. 4(c), the QMD, G4code and abrasion–ablation models with multi-fragmentation underestimate, whereas the abrasion–ablation model without multi-fragmentation closely explains the dose reduction for 1 A GeV 56Fe ion beam in polyethylene. 4. Conclusions The depth-dose distribution of a 56Fe ion beam in water, polyethylene, nextel, kevlar and aluminum are plotted by incorporating different models; integrated into Geant4. The dose reduction per unit areal density versus depth for 56Fe ions is also plotted in carbon, aluminum and polyethylene by incorporating the same models. Validation checks are performed by comparing the simulation results with the experimental data available in the literature. The abrasion model has no restrictions on the colliding particles and thus provides better agreement with experimentally measured depth-dose distribution data for 56Fe ions at high energy. In the case of dose-reduction, the G4code consisting of standard electromagnetic, binary cascade, statistical multi-fragmentation and Fermi breakup models provides better agreement with experimental data except for polyethylene. The present comparative study demonstrates the necessity of improving the models for better description of nucleus-nucleus interactions for heavy ions. Acknowledgments This research work was supported by Director, National Institute of Technology, Kurukshetra, India for providing the facilities in physics department. Dr. Kumar is also thankful to the Department of Science & Technology, SERC division for financial assistance under the Research & Development project No. SR/S2/HEP10/2009. The scientific discussions with Marco Durante, C. Zeitlin and Michael F. Moyers are gratefully acknowledged. References [1] M. Durante, F.A. Cucinotta, Physical basis of radiation protection in space travel, Rev. Mod. Phys. 83 (2011) 1245–1281. [2] P. Scampoli, M. Durante, G. Grossi, L. Manti, M. Pugliese, G. Gialanella, Fragmentation studies of relativistic iron ions using plastic nuclear track detectors, Adv. Space Res. 35 (2005) 230–235. [3] J. Miller, Recent measurements for hadrontherapy and space radiation: nuclear physics, Phys. Med. 17 (Suppl. 1) (2001). [4] P.M. O’Neill, Badhwar-O’Neill, Galactic cosmic ray flux model-revised, IEEE Trans. Nucl. Sci. 57 (2010) 3148–3153.

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[5] J. Sabol, P.S. Weng, Introduction to Radiation Protection Dosimetry, World Scientific Publishing Co., Singapore, 1995. [6] C. Lobascio et al., Accelerator-based tests of radiation shielding properties of materials used in human space infrastructures, Health Phys. 94 (2008) 242– 247. [7] C. Zeitlin, S.B. Guetersloh, L.H. Heilbronn, J. Miller, Measurements of materials shielding properties with 1 GeV/nuc 56Fe, Nucl. Instrum. Methods B 252 (2006) 308–318. [8] S. Guetersloh, C. Zeitlin, L. Heilbronn, J. Miller, T. Komiyama, A. Fukumura, Y. Iwata, T. Murakami, M. Bhattacharya, Polyethylene as a radiation shielding standard in simulated cosmic-ray environments, Nucl. Instrum. Methods B 252 (2006) 319–332. [9] F.A. Cucinotta, M. Durante, Cancer risk from exposure to galactic cosmic rays: implications for space exploration by human beings, Lancet Oncol. 7 (2006) 431–435. [10] M. Durante, Biological dosimetry in astronauts, La Riv. del Nuovo Cimento 19 (1996) 1–44. [11] C. Zeitlin, L. Heilbronn, J. Miller, S.E. Rademacher, T. Borak, T.R. Carter, K.A. Frankel, W. Schimmerling, C.E. Stronach, Heavy fragment production cross sections from 1.05 GeV/nucleon 56Fe in C, Al, Cu, Pb, and CH2 targets, Phys. Rev. C 56 (1997) 388–397. [12] I. Schall et al., Charge-changing nuclear reactions of relativistic light-ion beams (5 6 Z 6 10) passing through thick absorbers, Nucl. Instrum. Methods B 117 (1996) 221–234. [13] F. Flesch, S.E. Hirzebruch, G. Hüntrup, H. Röcher, T. Streibel, E. Winkel, W. Heinrich, Fragmentation cross section measurements of iron projectiles using CR-39 plastic nuclear track detectors, Radiat. Meas. 31 (1999) 533–536. [14] G.D. Badhwar, W. Atwell, F.F. Badavi, T.C. Yang, T.F. Cleghorn, Space radiation absorbed dose distribution in a human phantom, Radiat. Res. 157 (2002) 76– 91. [15] D. Zhou, E. Semones, R. Gaza, S. Johnson, N. Zapp, K. Lee, T. George, Radiation measured during ISS-Expedition 13 with different dosimeters, Adv. Space Res. 43 (2009) 1212–1219. [16] A. Lechner, V.N. Ivanchenko, J. Knobloch, Validation of recent Geant4 physics models for application in carbon ion therapy, Nucl. Intrum. Methods B 268 (2010) 2343–2354. [17] I. Pshenichnov, A. Botvina, I. Mishustin, W. Greiner, Nuclear fragmentation reactions in extended media studied with Geant4 toolkit, Nucl. Instrum. Methods B 268 (2010) 604–615. [18] M. Silvestri, E. Tracino, M. Briccarello, M. Belluco, R. Destefanis, C. Lobascio, M. Durante, G. Santin, R.D. Schrimpf, Impact of spacecraft-shell composition on 1 GeV/nucleon 56Fe ion-fragmentation and dose reduction, IEEE Trans. Nucl. Sci. 58 (2011) 3126–3133. [19] A. Kumar, S. Jalota, R. Gupta, Simulation of depth-dose distributions for various ions in polyethylene medium, Adv. Space Res. 49 (2012) 1691–1697. [20] M.R. James, G.W. McKinney, J.S. Hendricks, M. Moyers, Recent enhancements in MCNPX: heavy-ion transport and the LAQGSM physics model, Nucl. Instrum. Methods A 562 (2006) 819–822. [21] C. Zetilin, L. Heilbronn, J. Miller, Detailed characterization of the 1087 MeV/ nucleon Iron-56 beam used for radiobiology at the alternation gradient synchrotron, Radiat. Res. 149 (1998) 560–569. [22] S. Agostinelli et al., Geant4- a simulation toolkit, Nucl. Instrum. Methods A 506 (2003) 250–303. [23] J. Allison et al., Geant4 developments and applications, IEEE Trans. Nucl. Sci. 53 (2006) 270–278. [24] K. Gunzert-Marx, H. Iwase, D. Schardt, R.S. Simon, Secondary beam fragments produced by 200 MeVu-1 12C ions in water and their dose contributions in carbon ion radiotherapy, New J. Phys. 10 (2008) 1–21 (075003). [25] R. Serber, Nuclear reactions at high energies, Phys. Rev. 72 (1947) 1114–1115. [26] Geant4 (version 9.4) Physics reference manual. Website: , 2010. [27] K. Nitta, S. Chiba, T. Maruyama, T. Maruyama, H. Takada, T. Fukahori, Y. Nakahara, A. Iwamoto, Analysis of the (N, N0 ) reactions by quantum molecular dynamics plus statistical decay, Phys. Rev. C 52 (1995) 2620–2635. [28] S. Chikazumi, T. Maruyama, K. Niita, A. Iwamoto, QMD simulation of expanding nuclear matter, Phys. Lett. B 476 (2000) 273–278. [29] K. Niita, T. Maruyama, Y. Nara, S. Chiba, A. Iwamoto, Development of JQMD (Jaeri Quantum Molecular Dynamics) code, Nippon Genshiryoku Kenkyujo JAERI, Data, Code, 1999.