Institute of Physics EURISOL-DS-Task5-TN-06-02
Monte-Carlo code validation on accelerator shielding experiments
A. Plukis, A. Žukauskaite, R. Plukiene Internal report 2006-01-31
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BENCHMARK EXPERIMENTS ON NEUTRON AND PHOTON ATTENUATION For the assessment of suitability of Monte-Carlo codes for the accelerator shielding purposes within the EURISOL DS project, the experimental data from SINBAD database [1] have been used. For this purpose two the most suited experiments were chosen and analyzed. As there is lack of photon shielding data for high energy hadron accelerators, AVF cyclotron data (Research Center of Nuclear Physics, Osaka University) for 65 MeV energy protons (P65 experiment) [2] have been used. For neutron shielding the most appropriate was high-energy (up to 800 MeV) neutron data from Heavy Ion Medical Accelerator of Chiba (HIMAC experiments) [3]. DESCRIPTION OF SIMULATIONS All calculations are done with the MCNPX [4] multi-particle transport code, using LA150 [5] and ENDF-VI [6] cross-section libraries and Bertini intra-nuclear cascade model for high energies. For the particle flux spectra, neutron and photon transport has been taken into account. Several different setups were modeled for benchmarking P65 and HIMAC (Self-TOF and NE213 detectors) experiments.
Fig. 1. Calculation geometry used with the MCNPX code: a) Self-TOF detector; b) NE213 detector.
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Concrete collimator with iron lining Concrete or Fe shielding
50 cm
Concrete collimator with iron lining
10 - 40 cm
Fig 2. Calculation geometry as modeled with the MCNPX code in P65.
1. Photon shielding simulations (P65): First, the 65 MeV proton beam was modeled at the distance of 380 cm from the shielding plates. In brief, protons from the source were interacting with a 1.0 cm-thick (stopping length) copper target. Neutrons and photons angular distributions were calculated near the copper target and used as a secondary source in calculations afterwards. Secondary particles then pass through a 7.5 cm-diameter x 50 cm-long ironlined concrete collimator towards the iron or concrete shield (transverse dimensions 40 cm x 40 cm, and width from 10 cm to 40 cm). The calculation geometry for comparison with the experimental results is shown in Figure 2. For photon flux calculations, statistics up to 109 particles was used. The following atomic densities of shielding materials were employed (atoms/cm3): Concrete shield composition Hydrogen 1.70E+22 Oxygen 4.26E+22 Sodium 7.44E+20 Magnesium 3.77E+20 Aluminum 2.29E+21 Silicon 1.25E+22 Calcium 3.50E+21 Iron 4.44E+20 Iron shield composition Iron (nat. composition) 8.48E+22 2. Neutron shielding simulations (HIMAC): The source neutron spectrum was taken from [3]. The calculation geometry for comparison with the results of Self-TOF and NE213 scintillator detectors is shown in Figure 1. We note that the room wall and other surrounding equipments were not considered in the simulation. Self-TOF detector was placed 509 cm from the source. For the NE213 detector, neutron flux was calculated at position (A) – 233 cm from the source and at position (B) – at the distance of 503 cm from the source.
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For neutron flux calculations, statistics up to 107 particles was used. RESULTS Photon and neutron flux in concrete and iron shielding was calculated and compared with experiments; the results are shown in Figs. 3, 4, 5, 6 and 7. Table 1. Comparisons of relative photon flux (variable thickness versus no material, i.e. shielding with 0 cm thickness) in P65 between experimental results and calculations with MCNPX. Concrete Iron 20 cm/0 cm 50 cm/0 cm 20 cm/0 cm Experiment 0.194 1.194 0.014 MCNPX 0.210 1.210 0.069
1E-9
-2
-1
-1
Photon flux [cm MeV proton ]
1E-8
1E-10 Experiment, 0cm Experiment, 20cm Experiment, 50cm MCNPX, 0cm
1E-11
MCNPX, 20cm MCNPX, 50cm
2
4
6
8
10
Photon energy [MeV] Fig. 3. Photon spectra calculated with MCNPX and experimentally measured behind concrete shield (thickness 20 and 50 cm) in P65 benchmark.
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1E-8
-1
-1
Photon flux [cm MeV proton ]
1E-7
-2
1E-9
1E-10 Experiment, 0cm Experiment, 20cm MCNPX, 0cm MCNPX, 20cm
1E-11 2
4
6
8
10
Photon energy [MeV] Fig. 4. Comparison of photon spectra calculated with MCNPX and experimentally measured behind the iron shield (thickness of 0 cm and 20 cm) in P65 model.
0.01
1E-4
-1
-1
Neutron flux [sr MeV ion ]
1E-3
-1
1E-5 1E-6 1E-7
-1
MCNPX, 20cm, x10
-2
MCNPX, 40cm, x10
-3
1E-8
MCNPX, 60cm, x10
-1
Experiment, 20cm, x10
-2
Experiment, 40cm, x10
1E-9 10
-3
Experiment, 60cm, x10
100
1000
Neutron energy [MeV] Fig. 5. Comparison of neutron spectra calculated with MCNPX and experimentally measured using the NE213 detector immediately after shield (position A) as a function of the different thickness of iron shield.
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1E-4
-1
-1
Neutron flux [sr MeV ion ]
1E-3
-1
1E-5
1E-6
1E-7
1E-8
-1
MCNPX, 20cm, x10 -2 MCNPX, 40cm, x10 -3 MCNPX, 60cm, x10 -1 Experiment, 20cm, x10 -2 Experiment, 40cm, x10 -3 Experiment, 60cm, x10
10
100
1000
Neutron energy [MeV] Fig. 6. Comparison of neutron spectra calculated with MCNPX and experimentally measured using the NE213 detector far from shield (position B) as a function of the different thickness of iron shield. 0.1 0.01
-1
1E-4
-1
Neutron flux [sr MeV ion ]
1E-3
1E-5
-1
1E-6 1E-7 1E-8 1E-9 1E-10 1E-11
MCNPX, 0cm MCNPX, 20cm, x10-1 MCNPX, 40cm, x10-2 MCNPX, 60cm, x10-3 MCNPX, 80cm, x10-4
Experiment, 0cm Experiment, 20cm, x10-1 Experiment, 40cm, x10-2 Experiment, 60cm, x10-3 Experiment, 80cm, x10-4
1E-12
Neutron energy [MeV] Fig. 7. Comparison of the high energy neutron spectra calculated with MCNPX and experimentally measured using the Self-TOF detector as a function of the different thickness of iron shield.
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CONCLUSIONS In order to assess the suitability of the MCNPX Monte-Carlo code for the accelerator shielding purposes within the EURISOL DS project, the experimental data from SINBAD database has been benchmarked. We concluded that the 1-10 MeV energy photon transport in concrete shielding can be adequately modeled using MCNPX. On the other hand, the photon flux in iron calculated with MCNPX is significantly higher than the corresponding experimental data. The shielding of high energy (20-800 MeV) neutrons in iron is modeled sufficiently well with MCNPX. Best agreement is obtained for higher energy >100 MeV neutrons. The results obtained can serve as the MCNPX code validation for accelerator and target shielding calculations within the EURISOL DS project. REFERENCES 1. 2. 3.
4. 5. 6.
SINBAD - an International Database for Integral Shielding Experiments http://www.nea.fr/html/science/shielding/sinbad/sinbadis.htm H. Nakashima et al., Benchmark Problems for Intermediate and High Energy Accelerator Shielding, JAERI 94-012 (Sept.1994). T. Kurosawa, N. Nakao,T. Nakamura, Y. Uwamino,T. Shibata, A. Fukumura and K. Murakami, "Measurements of Secondary Neutrons Produced from Thick Targets Bombarded by High-Energy Helium and Carbon Ions" Nucl. Sci. Eng. 132, 30 (1999). MCNPX- Monte Carlo N-Particle Transport Code System for Multiparticle and High Energy Applications http://mcnpx.lanl.gov/. M.B. Chadwick, P.G. Young, R.E. MacFarlane, P. Moller, G.M. Hale, R.C. Little, A.J. Koning, and S. Chiba, “LA150 Documentation of Cross Sections, Heating, and Damage", Los Alamos National Laboratory report LA-UR-99-1222 (1999). J. S. Hendricks, S. C. Frankle, and J. D. Court, "ENDF/B-VI Data for MCNP," Los Alamos National Laboratory report LA-12891 (1994).
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