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Simulations on “Energy plus Transmutation” setup, 1.5 GeV. Mitja Majerle The document about simulations of EPT setup can be downloaded in form of report at : Outline. Cluster of computers (linux) MCNPX 2.4.0

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simulations on energy plus transmutation setup 1 5 gev

Simulations on “Energy plus Transmutation”setup, 1.5 GeV

Mitja Majerle

The document about simulations of EPT setup can be downloaded in form of report at :

  • Cluster of computers (linux)
  • MCNPX 2.4.0
  • First tests with PVM (in Třešt)
  • Simulations of PHASOTRON experiment (presented in Pavia, Avignon)
  • Simulations of ENERGY PLUS TRANSMUTATION setup (Dubna, Jaipur)
  • 1 server (the slowest machine)
  • Hosts boot through DHCP, filesystem through NFS – extendable to many hosts
  • Connections through SSH
  • PVM (Parallel Virtual Machine)
  • PVM works also on li1 and li2.

Parallel processing

  • The use of parallel processing (PVM) speeds up our calculations significantly.
  • A very powerful tool – where to use it ?


simulations how what we calculate
Simulations, how/what we calculate
  • MCNPX code v. 2.4.0 (on Linux, parallel computing)
  • Input :
    • setup geometry
    • starting conditions
  • Output 1:
    • neutron distribution
  • Cross-section libraries (Au, Al - ENDF; Bi - experimental; Iodine - ?)
  • Output 2:
    • masses of produced elements or B-values
influence of the setup parts
Influence of the setup parts

No walls

  • Concrete walls :
    • Neutrons are moderated and reflected back


energy transmutation
    • simplifications of the setup description
    • different parts of the setup
  • SYSTEMATIC ERROR (not accurately known exp. conditions)
    • beam geometry
    • reactions with protons
    • inserted detectors
    • intra-nuclear cascade model used in calculations
    • the number of produced neutrons (spallation, fission, ..)
    • k (criticality)
control detectors for studying the setup
Control detectors for studying the setup

- with (n,g) we study LE neutrons (flat part) – odd numbers

-(n,4n) threshold is 23 MeV – even numbers

the influence of setup parts
The influence of setup parts
  • We cannot remove some things from the setup and measure.
  • Simulations help us understand what would happen if we did that.
the simplifications of the blanket
The simplifications of the blanket
  • No influence on high energy neutrons (even numbers)
  • Box has no influence on HE neutrons !
  • Box blurs differences.
  • 40%, 10%
polyethylene cd layer
Polyethylene, Cd layer
  • The spectra were taken inside the 1st and 3rd gap.
  • No influence on HE neutrons.

absorption done by238U

resonance capture

aluminum and iron holders upper iron plate
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
The wooden plate
  • Wooden plate under the target(1+2cm,0.5kg/l).
  • Without box.
  • Detectors from top to bottom.
  • Asymmetry 5% => negligible wood influence.
systematic error
Systematic error
  • Systematic error may be done, because we can/did not measure all the experimental conditions.
  • Simulations give us the estimation of the error.
  • In simulations we vary experimental conditions in limits of the accuracy with which we measured them.
beam parameters 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
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 displacement
  • Beam displaced for 3,5,8, and 10 mm.
  • Differences between results up to tens of %Displacement must be measured as accurately as possible !
the influence of protons
The influence of protons
  • Activation detectors could also be activated by 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
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 has no influence on detectors in other gaps.
  • Only 0.1 mm thick golden strap is an obstacle for thermal neutrons : it can reduce the production rates of reactions with thermal neutrons inside the same gap for 20%.
the influence of plastic foils for detectors on neutron field
The influence of plastic foils for detectors on neutron field
  • The 4mm and 8mmpolyethylene 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
Intra-Nuclear Cascade models
  • In MCNPX are 3 models (above 150 MeV):
    • Bertini
    • CEM
    • Isabel
  • The differences are up to 50% (standard, our detectors).
neutrons per proton criticality
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 was calculated also by S.R. Hashemi-Nezhad - 22%.

If we add polyethylene wall at the back, k stays the same.

Neutrons per proton, criticality,..
neutrons per proton with beam energy
Neutrons per proton with beam energy
  • Neutrons per 1 proton and per 1 MeV in the beam
  • Box adds ca. 5 neutrons
  • Saturation
  • Peak at 1500 MeV
comparison with the experiment
Comparison with the experiment
  • The Greek group measures the ratios of neutrons inside and outside the box.
  • Calculated results do not agree with experiment.
  • Possible reason...
group from e
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



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

Cleardependenceon 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


  • 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