Simulations on “Energy plus Transmutation” setup, 1.5 GeV

1. Simulations on “Energy plus Transmutation” setup, 1.5 GeV Mitja Majerle majerle@ujf.cas.cz

2. What was studied ? • the influence of the simplifications of the setup description • the influence of the different parts of the setup to the results • the influence of the beam geometry • the influence of the inserted detectors • the influence of protons • the influence of the intra-nuclear cascade model used in calculations • parameters of the setup - the number of produced neutrons, produced in spallations, in fission, the influence of protons, k (criticality), heat production ...

3. Code, setup parameters • MCNPX 2.4.0 • plots of the setup will follow • estimation of some parameters (aluminum shielding, density of polyethylene, dimensions and material of holders, wooden plates, nuclear structure, ..) • detectors (input data !)

7. Control detectors for studying the setup - with (n,g) we study LE neutrons (flat part) -(n,4n) threshold is 23 MeV.

8. The simplifications of the blanket • No influence on high energy neutrons (even numbers in graphs) • Box has no influence on HE neutrons ! • With polyethylene lower influence • 40%, 10%

9. Polyethylene, Cd layer • Last winter V. Wagner presented these spectra. • The spectra were taken inside the 1st and 3rd gap. absorption done by238U resonance capture

10. Aluminum and iron holders, upper iron plate • Two simulations with and without Al, Fe components. The results do not differ outside the limits of statistical error (HE 3%, LE 10%) • The upper iron plate reduces the number of neutrons for 2%.

11. The wooden plate • Wooden plate under the target(1+2cm,0.5kg/l). • Detectors from top to bottom. • No box. • Asymmetry 5% => negligible wood influence.

12. Beam parameters influence • Beam profile is approximated with Gaussian distribution (good only near the beam center). • We must always count with beam displacement. • Experimentally determined beam profiles and displacement (V. Wagner using monitor and track detector data – for profile mainly I. Zhuk data):

13. Beam profile • Simulations with 3mm, 3cm homogenous beams and with a beam with gaussian profile (FWMH=3cm). • Differences only for few percents. • Not important.

14. Beam displacement • Beam displaced for 3,5,8, and 10 mm. • Differences between results up to 30% ! • Displacement must be measured as accurately as possible !

15. Beam hitting uranium • Badly focused beam also hits uranium blanket. • The influence of few percents of beam hitting uranium was not seen in simulations. • Gaussian distribution is not valid for the tails and in reality we don’t know how much big is this influence.

16. The influence of protons • Activation detectors could also be detected with protons. • Cross-sections for reactions with protons are not included in MCNPX. • Estimations from Phasotron experiment and neutron/proton ratio : in gaps, near the central axis ca. 10% of activation is due to protons.

17. The influence of detectors on neutron field • Metal plate on top reduces the number of neutrons only for 2%. Our detectors are much smaller. • Golden strap (2mm, 4mm) in the first gap did not influence detectors in other gaps. • Only 0.1 mm thick golden strap is an obstacle for thermal neutrons : it can reduce the number of thermal neutrons inside the same gap for 20%.

18. The influence of detectors on neutron field • The 4mm and 8mm polyethylene on which were placed the detectors for 1.5 GeV experiments had effect on LE neutrons. • Au in sandwich of 2 Bi foils => no influence.

19. Intra-Nuclear Cascade models • In MCNPX are 3 models (above energy 150 MeV): • Bertini • CEM • Isabel • The differences are up to 50% (our detectors).

20. Experimentally we cannot measure these. For 1.5 GeV experiment, neutron production : 29 in nuc. Interactions 8 in (n,xn) 14 prompt fission. Together 54 neutrons per 1 proton. Without box 49 neutrons, box reflects back 10% of them. KCODE calculations for criticality : k=19.2% k was calculated also by S.R. Hashemi-Nezhad - 22%. If we add polyethylene wall ath the back, k stays the same. Neutrons per proton, criticality,..

21. Comparison with experiment • The Greek group measures the ratios of neutrons inside and outside the box. • Calculated results do not agree with experiment.

22. Density of polyethylene ?

23. Group from Poland • No comparison with experiment yet. • Cross-sections only for 2 reactions (+2 stable isotopes). • Y detectors at places :

24. Group from Řež • 4 detector types • A lot of cross-section libraries • Trends in ratios experiment/simulation are seen • 3 GeV experiment would confirm these trends

25. Comparison between experiment and simulations 194Au 196Au Longitudinal distribution Radial distribution

26. 6 MeV 8 MeV 11 MeV 23 MeV 23 Mev 23 MeV 23 MeV 11 MeV 8 MeV 6 MeV Experiment: Ep = 1.5 GeV 0.7 GeV, 1.0 GeV - the similar shape of radial distribution for experiment and simulation 1.5 GeV-different shape of radial distribution for experiment and simulation Clear dependence on reaction energy threshold ↔ on the neutron energy ratios normalized on first foil Longitudinal distribution – small differences, maybe done by not included protons Radial distribution– big differences, description is worse for neutrons with higher energy

27. Radial distribution for 0.7 GeV and 1.0 GeV Conclusions: • Very small differences of shape • Maybe increase with energy? Necessary systematic of experiments with different beam energy Dependence of EXP/SIM ratios for first radial foil on beam energy Very important: 1) To analyze 2 GeV experiment 2) To make 3 GeV experiment