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Simulations on “Energy plus Transmutation” setup, 1.5 GeV. Mitja Majerle firstname.lastname@example.org. 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
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Simulations on “Energy plus Transmutation” setup, 1.5 GeV Mitja Majerle email@example.com
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 ...
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 !)
Control detectors for studying the setup - with (n,g) we study LE neutrons (flat part) -(n,4n) threshold is 23 MeV.
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%
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
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%.
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.
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):
Beam profile • Simulations with 3mm, 3cm homogenous beams and with a beam with gaussian profile (FWMH=3cm). • Differences only for few percents. • Not important.
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 !
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.
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.
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%.
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.
Intra-Nuclear Cascade models • In MCNPX are 3 models (above energy 150 MeV): • Bertini • CEM • Isabel • The differences are up to 50% (our detectors).
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,..
Comparison with experiment • The Greek group measures the ratios of neutrons inside and outside the box. • Calculated results do not agree with experiment.
Group from Poland • No comparison with experiment yet. • Cross-sections only for 2 reactions (+2 stable isotopes). • Y detectors at places :
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
Comparison between experiment and simulations 194Au 196Au Longitudinal distribution Radial distribution
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
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