simulations on “energy plus transmutation” setup, 1.5 gev

Simulations on “Energy plus

Transmutation” setup, 1.5 GeV

Mitja Majerle, V Wagner, A Krása, F Křížek

[email protected]

This document can be downloaded in form of report at :

http://ojs.ujf.cas.cz/~mitja/articles/ept.pdf

What was studied ? INFLUENCE OF

simplifications of the setup description different parts of the setup beam geometry inserted detectors reactions with protons intra-nuclear cascade model used in calculations

PARAMETERS OF THE SETUP the number of produced neutrons (spallation, fission, ..) k (criticality) heat production ...

Code, setup parameters

MCNPX 2.4.0 plots, photos of the setup will follow estimation of some parameters

(aluminum shielding, density of polyethylene, dimensions and material of holders, wooden plates, nuclear structure, ..)

position of detectors (input data !)

Control detectors for studying the setup

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

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

1E-07

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E+00

1E-10 1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04

Energy [MeV]

Nne

utro

ns

on the target

under Cd

outside box

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

Last winter V Wagner presented these spectra.

The spectra were taken inside the 1st and 3rd gap.

No influence on HE neutrons.1st gap, 3cm from axis

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E-10 1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04

without Cd

without box

whole_setup

3rd gap, 3 cm from axis

1E-07

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E-10 1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04

without Cd

without box

whole_setup

absorption done by 238U resonance capture

Comparison of HE part of spectra

0,85

0,9

0,95

1

1,05

1,1

1,15

0,1 1 10 100 1000

Neutron energy [MeV]

Ratio

w ith Cd/all

w ith box/all

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).

Without box. Detectors from top to

bottom. Asymmetry 5% =>

negligible wood influence. 0E+0

1E-5

2E-5

3E-5

4E-5

5E-5

-10 -5 0 5 10

Radial foil position [cm]

Pro

du

ctio

n r

ate

Au-198

Au-194

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):

Experiment

(Energy) Beam

integral [1013]

Beam integral on lead target [1013]

FWHM (vertical)

[cm]

FWHM (horizontal)

[cm]

Fraction of beam outside

Pb target [%]1)

Position (vertical)

[cm]

Position (horizontal)

[cm]

700 MeV 1.47(5) 1.04(8) 5.91(21) same < 27 -0.4(9) 0.2(2) 1 GeV 3.40(15) 3.25(14) 4.1(3) 2.5(3) < 6 0.2(2) 0.0(2)

1.5 GeV 1.14(6) 1.10(5) 3.7(5) 2.4(5) < 6 0.1(2) 0.3(2) 2.0 GeV 1.25(6) 1.07(10) 5.4(3) 3.8(3) <20 0.3(2) -1.4(2)

Beam profile

Simulations with 3mm, 3cm homogenous beams and with a beam with gaussian profile (FWMH=3cm).

Differences only for few percents.

Not important.-10

-8

-6

-4

-2

0

2

4

6

1 2 3 4 5 6 7 8 9 10

Foil and reaction number

beam

/3cm

-1 (i

n %

)

3mm/3cm-1

gauss/3cm-1

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 !

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10

Foil and reaction

Dis

pla

ced

bea

m/c

ente

r b

eam

-1 (

in %

)

3 mm

5 mm

8 mm

10 mm

Beam hits 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 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

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 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.

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

1E-10 1E-7 1E-4 1E-1 1E+2 1E+5

nothing

4mm polyeth foil

full poly

Intra-Nuclear Cascade models

In MCNPX are 3 models (above 150 MeV): Bertini CEM Isabel

The differences are up to 50% (standard, our detectors).

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10

Foil and reaction

mo

del

/ber

tin

i-1

(in

%)

cem

isabel

-40

-30

-20

-10

0

10

20

30

40

50

60

1 6

11

16

21

26

31

36

41

46

51

56

61

Foils and reactions of the Rez group

mo

del

/BE

RT

INI-

1 (i

n %

)

CEM/BERTINI-1

ISABEL/BERTINI-1

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=19.2% k was calculated also

by S.R. Hashemi-Nezhad - 22%.

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

Comparison with experiment

The Greek group measures the ratios of neutrons inside and outside the box.

Calculated results do not agree with experiment.

1E-07

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E+00

1E-10 1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04

Energy [MeV]

Nne

utro

ns

on the target

under Cd

outside box

Density of polyethylene ?

density 0.35kg/l

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

1E-10 1E-8 1E-6 1E-4 1E-2 1E+0 1E+2 1E+4

Energy [MeV]

Nn

eutr

on

s

on the target

under Cd

outside box

density 0.7 kg/l

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

1E-10 1E-8 1E-6 1E-4 1E-2 1E+0 1E+2 1E+4

Energy [MeV]

Nn

eutr

on

s

on the target

under Cd

outside box

Group from Poland

No comparison with experiment yet.

Cross-sections only for 2 reactions (+2 stable isotopes).

Y detectors at places :

Radial

1.00E-06

1.00E-05

1.00E-04

1 2 3 4 5

n,gamma

n,2n

The numbers on the drawings agree witch those in table 1.

1 3 4 52

1

23

45

67 8 9 10

11

Longitudinal

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1 2 3 4 5

n,gamma

n,2n

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

d)

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15Radial distance from the target axis R [cm]

exp

/sim

Au196 1.0 GeV Au196 1.5 GeV Au196 0.7 GeV

c)

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15Radial distance from the target axis R [cm]

exp

/sim


b)

0.0

0.5

1.0

1.5

2.0

2.5

-10 0 10 20 30 40 50Position along the target X [cm]

exp

/sim


a)

0.0

0.5

1.0

1.5

2.0

2.5

-10 0 10 20 30 40 50Position along the target X [cm]

exp

/sim


Comparison between experiment and simulations

194Au 196AuR

adia

l dis

trib

uti

onL

ongi

tudi

nal d

istr

ibu

tion

Longitunidal direction

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60

l [cm]

EX

P/C

EM

24Na

196Au

194Au

206Bi

58Co

6 MeV

8 MeV

11 MeV

23 MeV23 Mev

Radial direction

0

1

2

3

4

5

6

0 5 10 15

r [cm]

EX

P/C

EM

24Na

196Au

194Au

206Bi

58Co6 MeV

8 MeV

11 MeV

23 MeV 23 MeV

Experiment: Ep = 1.5 GeV

1.5 GeV -different shape of radial distribution for experiment and simulation

0.7 GeV, 1.0 GeV - the similar shape of radial distribution for experiment and simulation

Clear dependence on reaction energy threshold ↔ on the neutron energy

Longitudinal distribution – small differences, maybe done by not included protons

Radial distribution – big differences, description is worse for neutrons with higher energy

ratios normalized on first foil

Radial distribution 0.7 GeV

0.700.800.901.001.101.201.301.401.50

0 2 4 6 8 10 12

r [cm]

EX

P/S

IM 196Au

194Au

Radial distribution 1.0 GeV

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

0 2 4 6 8 10 12

r [cm]

EX

P/S

IM 196Au

194Au

Radial distribution for 0.7 GeV and 1.0 GeV

1) Very small differences of shape2) Maybe increase with energy?

Conclusions:

Very important: 1) To analyze 2 GeV experiment 2) To make 3 GeV experiment

0

0.2

0.4

0.6

0.8

1

1.2

0 500 1000 1500 2000

Beam energy [GeV]

EX

P/S

IM 196Au

194Au

Necessary systematic of experiments with different beam energy

Dependence of EXP/SIM ratios for firstradial foil on beam energy

simulations on “energy plus transmutation” setup, 1.5 gev

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