1. Monte Carlo methods in spallation experiments Defense of the phD thesis Mitja Majerle “Phasotron” and “Energy Plus Transmutation” setups (schematic drawings)

2. Status of issue Accelerator Driven System research Accelerator Driven System research Experiments with simplified ADS Experiments with simplified ADS Studies of the spallation reaction (thin targets) Studies of the spallation reaction (thin targets) Improving computer codes, cross-section libraries Improving computer codes, cross-section libraries JINR experiments JINR experiments Cross-section measurements on 660 MeV protons Cross-section measurements on 660 MeV protons Thin target experiments (Yurevich et al.) Thin target experiments (Yurevich et al.) Different setups with thick lead target Different setups with thick lead target Distribution of produced neutrons Distribution of produced neutrons Transmutation properties of neutron field Transmutation properties of neutron field

3. Overview The main aim: The main aim: Studies of JINR experiments with computer codes - simulations Spectroscopy Spectroscopy Phasotron experiment Phasotron experiment EPT setup EPT setup

4. Simulations Event by event simulation on nuclear scale Event by event simulation on nuclear scale Sampling of many events to get quantities on macroscopic scale Sampling of many events to get quantities on macroscopic scale Used codes Used codes MCNPX MCNPX FLUKA FLUKA Resources: Resources: CESNET Meta Centrum CESNET Meta Centrum 64 processors on OJS (MPI and PBS) 64 processors on OJS (MPI and PBS)

5. Gamma spectroscopy MCNPX and FLUKA simulations of the HPGe detectors –  P,  T MCNPX and FLUKA simulations of the HPGe detectors –  P,  T Exp/sim ~ ±10% (  P ), 30% (  T ) Exp/sim ~ ±10% (  P ), 30% (  T )

6.  P  T Inaccurate placement of samples (sim.): Inaccurate placement of samples (sim.): 1 mm (at 2.4 cm) ~ 4% 1 mm (at 2.4 cm) ~ 4% 1 mm (at 4.1 cm) ~ 3% 1 mm (at 4.1 cm) ~ 3% 1 mm (at 6.5 cm) ~ 2% 1 mm (at 6.5 cm) ~ 2% Activity of the samples ~2% Activity of the samples ~2%  intensity ~ 1%  intensity ~ 1%  peak fit ~ 1-3%  peak fit ~ 1-3% Together ~ 5-10% ! Together ~ 5-10% ! Only few useful calibration isotopes: Only few useful calibration isotopes: One gamma line Background subtraction Accuracy of the fit ~ 15% Accuracy of the fit ~ 15%  T important only in COI corrections, which are max. 10%  T important only in COI corrections, which are max. 10% COI accuracy 15%x10%=1.5% is below  P accuracy COI accuracy 15%x10%=1.5% is below  P accuracy

7. Geometrical correction Dimensions and position of the source foil is modified Dimensions and position of the source foil is modified Simulated  P are compared Simulated  P are compared Differences up to 5% - experimentally verified Differences up to 5% - experimentally verified

8. Cascade coefficients FLUKA subroutine source.f was modified, decay of radioisotopes with more photons/history was programmed FLUKA subroutine source.f was modified, decay of radioisotopes with more photons/history was programmed Obtained spectra compared with one photon/history simulation Obtained spectra compared with one photon/history simulation The angular correlation between photons was also studied The angular correlation between photons was also studied Conclusion: analytical methods which we use to calculate COI are sufficient Conclusion: analytical methods which we use to calculate COI are sufficient 60 Co decay

9. Neutron detection problems Spectra of produced particles at spallation (not only neutrons are produced) Cross-sections for n,  and n,xn reactions (and corresponding reactions with other particles which produce the same radioisotope)

10. Influence of other particles These are typical numbers at our experiments (1 GeV deuterons were directed to 50 cm lead in this simulation): These are typical numbers at our experiments (1 GeV deuterons were directed to 50 cm lead in this simulation): eg. 197 Au(n,6n) 192 Au eg. 197 Au(n,6n) 192 Au 20% of 192 Au produced by protons 20% of 192 Au produced by protons 5% by deuterons, 5% by deuterons, <1% by pions and photons. <1% by pions and photons. Contributions from other particles should always be considered at spallation experiments ! Contributions from other particles should always be considered at spallation experiments ! Exception (n,  ) sensible only to low energy neutrons. Exception (n,  ) sensible only to low energy neutrons.

11. (n,  ) – neutron absorption in activation foils We need ca. 1 g of detector material, eg. 2x2x0.005 cm 3 Au We need ca. 1 g of detector material, eg. 2x2x0.005 cm 3 Au Absorption of LE neutrons in such only 50  m foil is significant – experimentally verified Absorption of LE neutrons in such only 50  m foil is significant – experimentally verified (n,  ) ~ 1000 barns (n,  ) ~ 1000 barns (n,xn) ~ parts of barn

12. Bare, lead target

13. Phasotron experiment Simple, lead target (diameter 10 cm, length 0.5 m) Simple, lead target (diameter 10 cm, length 0.5 m) Intensive protons 660 MeV, 10 min Intensive protons 660 MeV, 10 min Activation detectors (Al, Au, Bi, Cu) Activation detectors (Al, Au, Bi, Cu) Iodine samples ( 129 I) Iodine samples ( 129 I)

14. Experimental data, Au

15. Simulated neutron spectrum MCNPX

16. Exp/sim comparisons (Al, Au) MCNPX - INCL4/ABLA MCNPX – CEM03 FLUKA

17. Systematic uncertainties Simulations with changed parameters are compared Simulations with changed parameters are compared Beam parameters (3 mm ~ 15% uncertainty) Beam parameters (3 mm ~ 15% uncertainty) Detector displacement (1 mm ~ <5%) Detector displacement (1 mm ~ <5%) Iodine samples – not precise placement, unknown sample details Iodine samples – not precise placement, unknown sample details The experimental results are The experimental results are 15-20% accurate 15-20% accurate

18. Energy Plus Transmutation

19. SABRINA plot from MCNPX input file, provided by J. Šolc.

20. Simulation analysis Influence of setup parts Influence of setup parts iron and detectors have negligible influence iron and detectors have negligible influence polyethylene box (next slide) polyethylene box (next slide) Systematic uncertainties – displacements: Systematic uncertainties – displacements: incident beam : 3mm = 15-20% uncertainty incident beam : 3mm = 15-20% uncertainty detectors displacement: 5mm = 20% detectors displacement: 5mm = 20% The calculations apply only to threshold activation detectors. The calculations apply only to threshold activation detectors.

21. Polyethylene box – biological shielding Neutron spectra inside box Neutron spectra emitted to environment

22. Neutron production, k eff At 1.5 GeV experiment, 50 neutrons were produced per proton At 1.5 GeV experiment, 50 neutrons were produced per proton Maximum production (proton -1 GeV -1 ) in 1- 1.5 GeV range Maximum production (proton -1 GeV -1 ) in 1- 1.5 GeV range k eff =0.202 k eff =0.202 flooded with water k eff rises to 0.41 (and heavy water 0.26) flooded with water k eff rises to 0.41 (and heavy water 0.26) Total neutron production with the EPT setup.

23. Conclusion Spectrometry Spectrometry Systematic uncertainties 5-10% Systematic uncertainties 5-10% Corrections under control Corrections under control Phasotron experiment Phasotron experiment Experimental analysis Experimental analysis (spatial distribution of neutrons, iodine transmutation properties) Good agreement with MC codes Good agreement with MC codes Systematic uncertainties 15-20% Systematic uncertainties 15-20% EPT EPT Precise study of systematical uncertainties (30%) Precise study of systematical uncertainties (30%) and setup parameters