secondary particles produced by 1.5 gev proton beams

SECONDARY PARTICLES PRODUCED BY 1.5 GEV PROTON BEAMS INCIDENT ON LEAD-BISMUTH EUTECTIC TARGET OF C-ADS

Hongli Wu University of Science and Technology of China

Hefei, Anhui, China

Xiangqi Wang University of Science and Technology of China

Hefei, Anhui, China

Jingyu Tang University of Science and Technology of China

Institute of High Energy Physics, CAS ,Beijing, China

Yuanjie Bi China Institute of Atomic Energy

Beijing,China

Weimin Li University of Science and Technology of China

Hefei, Anhui, China

Lei Shang University of Science and Technology of China

Hefei, Anhui, China

ABSTRACT The double differential neutron yield generated by high

energy proton beam bombarding on the targets of Tungsten, Lead and the Lead-Bismuth Eutectic (LBE) have been investigated based on FLUKA (Version 2011.2.8). Some FLUKA results have been checked with MCNPX and experimental data. Secondary neutron angular spectra are studied for cylinder and slab targets. The results show that the shape of the spectra are almost independent of angular bins while the yields in lateral and backward directions show a significant decrease as a results of the self-shielding effect in the slab target. The angular spectra of the photon and proton are also presented. The work is important for the shielding design of the target and the accelerator system. INTRODUCTION

Accelerator-Driven System has been widely investigated for transmuting Minor Actinides (MAs) and High-Level radioactive Waste (HLW) such as Long-Life Fission Products (LLFPs). China ADS (C-ADS) consists of a high-intensity proton accelerator with energy of 1.5GeV, a subcritical core, and a spallation target of liquid Lead-Bismuth Eutectic (LBE). The transmuter is driven by spallation neutrons produced by proton beam bombarding the target . In the past few decades,

comprehensive studies of secondary particles produced by proton and heavy ion beams on thick targets have been carried out both experimentally and theoretically [1-4, 11]. The spectra of high energy secondary neutrons are one of the most important factors in designing the ADS shielding system. Furthermore, the secondary neutrons in the backward direction can cause radiation damage of magnets of the High Energy Beam Transport (HEBT) line of C-ADS, which one has to try to avoid in designing the system. The layout sketch of devices of C-ADS HEBT is shown in Fig.1 [13]. HEBT probably includes several sections: a straight horizontal section starting from the linac exit, a horizontal bending section, a horizontal transport section starting from the hurling magnet, a vertical bending section and a vertical section.

Besides, a complete knowledge of secondary neutron distribution should be extremely useful for the arrangement and design of the collimator located in front of the proton beam window (PBW).

In this paper, we will make a detailed analysis of secondary particles distribution at the end of transport line of C-ADS by employing the latest version of FLUKA Monte-Carlo program (version 2011.2).

Proceedings of the 2012 20th International Conference on Nuclear Engineering collocated with the

ASME 2012 Power Conference ICONE20-POWER2012

July 30 - August 3, 2012, Anaheim, California, USA

ICONE20-POWER2012-55280

1 Copyright © 2012 by ASME

Fig.1 The layout sketch of C-ADS HEBT starting from the exit of

hurling magnet, the red elements represent quadrupoles

FLUKA can simulate the interaction and transportation of about 60 different particle species, including photons and electrons with energies from 1 keV to thousands of TeV, neutrinos and muons of any energies, hadrons of energies up to 20 TeV, all the corresponding antiparticles, neutrons down to thermal energies and heavy ions.

In FLUKA, neutrons are treated in different hadronic interaction models, depending on the initial energy of the primary particle. The high energy neutrons (>5 GeV) are treated in the Glauber-Gribov formalism that couples Glauber multiple scattering to a Dual Parton Model description of

hadron-nucleon interactions. Neutrons with lower energies are described in the Pre Equilibrium Approach to Nuclear Thermalization (PEANUT) [5]. Transport of neutrons with energies lower than 20 MeV is performed in FLUKA by a multi-group (260 or 72 neutron energy group) algorithm. The multi-group technique, widely used in low-energy neutron transport programs, consists in dividing the energy range of interest in a given number of intervals ("energy groups"). In this case, elastic and inelastic reactions are simulated not as exclusive processes, but by group-to-group transfer probabilities forming the so-called downscattering matrix. The scattering transfer probabilities from each group g to any group g' are calculated by a Legendre polynomial expansion truncated at the (N+1)th term as shown in the following equation [6]:

)'()(4

12),'(0

ggPigg isi

N

is →

+=→ ∑

=

σμπ

μσ (1)

Where 'Ω⋅Ω=μ is the scattering angle and N is the chosen

Legendre order of anisotropy. Photonuclear interaction and nuclear interaction generated

by ions can also be simulated by FLUKA [7]. Charged particles transportation are described by the multiple scattering algorithm based on the Moliere's theory of Coulomb scattering. The energy loss from bremsstrahlung and pair production is determined according to the Bethe-Bloch theory. More detailed description of nuclear models in FLUKA can be found in Ref.[6,8,9].

Table 1 Beam energies and target geometry Proton energy (GeV) Material Thickness (cm) Size (cm) Density (g/cm3)

0.35 Lead slab 12.5 6×6 11.35 0.25 Tungsten slab 5 20×20 19.3

Lead-Bismuth Eutectic slab 20 60×60 10.58 1.5

Lead-Bismuth Eutectic cylinder 20 15 (radius) 10.58

In present simulation, double differential distribution of neutrons and protons in energy and solid angle are recorded at spherical surfaces 10 m distant from the center of the target. Geometry and material of the targets considered in present study are listed in Table 1 and the basic properties of lead-Bismuth Eutectic used in calculation are shown in Table 2. The statistical uncertainties of present simulations are all reduced to a few percent.

Table 2 Properties of Lead-Bismuth Eutectic Characteristic Value

Thermal neutron absorption cross-section 0.11 Neutron scattering cross-section /barn 6.9 Volume change upon solidification /% 0 Melting point /℃ 125 Boiling point /℃ 1670 Density liquid /g/cm3 10.58

FLUKA-MCNPX CROSS-CHECK AND EXPERIMENTAL CHECK OF FLUKA

In order to validate the FLUKA results, we compared the calculated results obtained by both FLUKA and MCNPX programs in the same case of 0.25GeV proton beam bombarding the Tungsten slab target. The double differential yield

Ω⋅ddEdφ from FLUKA simulation is generally given in unit of cm-2GeV-1Sr-1 per incident primary particle. The yield can also be rewritten in the form of EE φ⋅ , where

dEdE φφ = . The spectra represented by EE φ⋅ is more intuitive since it can describe the major features of the spectra, such as the average energies and the peak value of the spectra. A good agreement in neutron spectra obtained between the two programs can be seen in Fig.2. Obviously, both codes give the consistent distributions for forward neutrons ( °−° 100 ) and for backward neutrons ( °−° 18090 ).


Fig.2. Calculated double differential yield of neutrons in the forward (0o-10 o) and backward (90o-180 o)

Furthermore, the neutron yield at 0-degree generated by a proton beam of 0.35 GeV impinges on a lead slab target of 12.5 thickness has been measured in the experiment performed at RCNP of Osaka University [8]. Fig.3 shows the comparison between the experimental data and the simulation results given by FLUKA and MCNPX (with the LA150N evaluated neutron data library and Bertini model). The neutron yields in our calculation are in the range 0 degree - 3 degree. The agreement between the calculated and measured yield is impressive within the uncertainties below 100 MeV and 20 MeV for FLUKA and MCNPX, respectively. Above 100 MeV (FLUKA) and 20MeV (MCNPX), the calculation yield is underestimated resulting from the strong self-shielding in target nucleus and the underestimation of neutron-production cross-section at small angles.

As can be seen in Fig.3, the results of FLUKA are slightly closer to the experimental data than those of MCNPX in this situation, especially for high energy neutrons. Compared with MCNPX, FLUKA can give more appropriate estimate for proton distribution at large angles [10, 12]. SECONDARY PARTICLE DOSTRIBUTION INDUCED BY 1.5 GEV PROTON IMPINGING ON THE LBE TARGET OF C-ADS

In this paper, we focus on investigating the angular distribution of secondary particles produced by 1.5 GeV proton pencil beam incident on the LBE target of C-ADS. The

calculated neutron spectra in the angular bins0o-10o, 40o-50 o and 90o-180o for both cylinder and slab targets are shown in Fig.4.

Fig.3 Measured and calculated differential neutron spectra for the Pb target bombarded by 0.35GeV protons.

Fig.4 Neutron spectra in the forward (0o-10 o ), lateral (40 o -50 o ) and backward (90 o -180 o ) direction produced by proton beam impinging on the cylinder target and the slab target.

For both targets, no major difference have been found among three angular bins in terms of the spectrum shapes except for the high energy peaks in the forward °−° 100 direction. This can be explained by the fact that the high-energy secondary


particles are mainly from the direct (cascade) process and thus peaked in the forward direction whereas the low-energy ones are mainly from the indirect (evaporation) process and emit nearly isotropically. For slab target, larger difference in neutron yields between the lateral °−° 5040 and the backward ( °−° 18090 ) directions can be found than that for the cylinder target. This large difference may be due to the self-shielding effect in the slab target. Compared with the neutron yield in the forward direction, the yield of back-scattered neutrons decrease by a factor of 1.2 (2) for cylinder (slab) target. Our calculation shows that this suppression factor can be as large as 2.5 for slab target with thickness of 30 cm. Nevertheless, for the cylinder target with thickness larger than 20 cm, the yield of back-scattered neutrons will rapidly increase, which makes it difficult in designing the collimator and the effective shielding of the accelerator system.

In fact, a significant reduction of the neutron yield in the lateral direction induced by the self-shielding effect in the slab target can be seen in Fig.5 by comparing the neutron yields in the forward and the lateral directions between the cylinder target and the slab target. The self-shielding effect, however, almost does not influence the neutron spectra shapes. Fig.5 The neutron yields in the forward (0o-10 o) and lateral (70o-80 o)

directions for both cylinder and slab targets.

The photon yield and proton yield in the same three angular bins (forward, lateral and backward) are shown in Fig.6 and 7, respectively. The electron positron annihilation peak (0.511 MeV) and nuclear de-excitation peaks can be easily distinguished from the continuous background in Fig.6. The shapes of the photon spectra do not depend on the emission directions. As can be seen in Fig.7, both the yields and average energies of protons are rapidly decreasing functions of angles from the beam direction.

Fig.6 Photon spectra in the forward (0o-10 o), lateral (40o-50 o) and backward (90o-180 o) directions for the cylinder target

Fig.7 Proton spectra in the forward (0o-10 o), lateral (40o-50 o) and backward (90o-180 o) directions for the cylinder target.

CONCLUSION Secondary particle yields induced by the high energy proton

beam impinging on the Lead Bismuth Eutectic target have been studied in this paper. A simulation of the spectra for the neutrons, photons and protons emitted in the forward, lateral and backward directions is given. The results show that the shapes of neutron spectra are independent of emission directions except for the high energy peaks in the forward direction induced by cascade process. However, the geometry of the target has a great impact on the neutron yield. The self-shielding effect in the slab target leads to a significant decrease of the neutron yields in the lateral and backward directions. The shapes of photon spectra are independent of the emission directions, whereas the yields and average energies of protons sharply decease as the angles


from the beam direction increase. The simulation results, thus, give information about the source of secondary particles to be used in designing the collimator and shielding calculation for radiation protection of accelerator system.

ACKNOWLEDGMENTS The authors acknowledge Q.Wang from USTC and H.T.Jing from IHEP for their helpful discussions and suggestions.

References [1] S.Agosteo et al., Double differential spectra of secondary particles

from hadrons on tissue equivalent targets Radiation Protection Dosimetry (2008)1-13 doi:10.1093/rpd/ncn273.

[2] T.Nakamura, L. Heibronn, Overview of secondary particle production and transport by high-energy heavy ions, Nuclear Instruments and Methods in Physics Research A 562(2006)706-709.

[3] T.Kato, T.Kurosawa, Systematic analysis of neutron yields from thick targets bombarded by heavy ions and protons with moving source model, Nuclear Instruments and Methods in Physics Reasearch A 480(2002)571-590.

[4] T.Nakamura, L. Heibronn, Handbook on Secondary Particle Production and Transport by High-energy Heavy ions, World Scientific Publishing, 2006, ISBN981-256-558-2.

[5] B.A.S.Adam, E.Z.Buthelezi, Monte carlo simulation of the production of neutrons at LABS, Radiation Measurement 45(2010)1193-1196.

[6] A.Ferrari, P.R sala, A.Fasso, FLUKA User's manual Version 2011.2.8, November,2011.

[7] G.Battistoni, S.Muraro, P. R. Sala et al. The FLUKA code: description and benchmarking. In:M. Albrow, R. Raja(Eds.), Proc.

of the Hadronic Shower Simulation Workshop 2006, Fermilab 6-8 September 2006, AIP Conf. Proc. vol.896,2007,pp.31-49.

[8] F.Ballarini, G. Battistoni, Nuclear models in FLUKA: Present Capabilities, Open Problems, and Future Improvement, Proceeding of the International Congerence on Nuclear Data for science and Technology, ND2004, Santa Fe, NM, USA, 26 September-1 October 2004, SLAC-PUB-10813.

[9] A.Ferrari, P. R. Sala, "The Physics of High Energy Reactions," in Proseedings of the Workshop on Nuclear Reaction Data and Nuclear Reaction Physics, Design and Safety (World Scientific,1998), v.2,pp.424-532

[10] J.S.Hendricks, MCNPX model/table comparison, 2003, LA14030. [11] M.Brugger, A.Ferrari, S.Roesler, Validation of the FLUKA Monte

Carlo code for predicting induced radioactivity at high-energy accelerators, Nuclear Instruments and Methods in Physics Research A 562(2006)814-818.

[12] A.Ferrari, M.Ferrarini, Secondary particle yields from 400MeV/u carbon ion and 250MeV proton beams incident on thick targets, Nuclear Instruments and Methods in Physics Research B 269(2011)1474-1481.

[13] Huanli Luo, et. al.. Private communications: Feb. 12, 2012.


secondary particles produced by 1.5 gev proton beams

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