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Detection of relativistic neutrons by BaF2 scintillators

Simulation on MCNPX

Nuclear Physics InstituteDoctor V. Wagner

Mitja Majerle

Antonin Krasa

Ondrej Svoboda

Ludovic BATTISTA

Description of the beam

sdef erg 600 dir 1 vec 0. 0. 1. x=d1 y=d2 z=-3.95 par n ccc=2

si1 h -10 10

sp1 d 0 1

si2 h -10 10

sp2 d 0 1

OR

sdef erg 600 dir 1 vec 0. 0. 1. rad d1 pos 0.0 0.0 -3.95 par n ccc=20

si1 h 0 3.5

sp1 -21 1

TALLY Selection

- F6 :Energy deposition over a cell (in MeV/g)

secondary particles are not taken into account.

- *F8 : energy deposition created in a detector (in MeV)

not a spectra

- F8 : Energy distribution of pulses, created in a detector by radiation (in pulses)

Take into account secondary particles.

25 cm

Determination of the amount of neutron passing through the detector without depositing energyσ =

σ = 77,8 %

Determination of the amount of neutron passing through the detector without depositing energy

tally type 1 number of neutrons crossing a surface 4.

energy e11 0 499.999999 500

0.0000E+00 0.00000E+00 0.0000 1.0000E-06 0.00000E+00 0.0000 4.9900E+02 4.13000E-02 0.0561 5.0000E+02 0.00000E+00 0.0000 5.0000E+02 1.00000E+00

tally type 1 number of neutrons crossing a surface 6.

energy e21 0 499.999999 500

0.0000E+00 0.00000E+00 0.0000 1.0000E-06 0.00000E+00 0.0000 4.9900E+02 1.66600E-01 0.0360 5.0000E+02 1.25400E-01 0.0264 5.0000E+02 2.79500E-01 0.0161

BaF2 Cylinder view : pz=3

σ ≈ 30 %

Set up view : py=0

Determination of the amount of neutron passing through the detector without depositing energy

F1 : current integrated over a surface (in particles)

tally type 1 particle(s): neutron surface 31 energy e1 0 399.999999 400

0.0000E+00 0.00000E+00 0.0000 4.0000E+02 2.31560E-01 0.0130 4.0000E+02 1.00000E+00 0.0000

tally type 1 particle(s): neutron surface 311 energy e11 0 399.999999 400

0.0000E+00 0.00000E+00 0.0000 4.0000E+02 4.20900E-01 0.0079 4.0000E+02 3.02080E-01 0.0068

Setup view : py=0

σ≈30 %

Energy Deposition on Central Module

Shape of beam 400 MeV nps=5e5

SHAPE OBTAINED BY F8 TALLY IS ACCEPTED

Problem of Normalization ?

tally type 8 particle(s): neutron surface 311 energy e11 0 1e-6 400

0.0000E+00 0.00000E+00 0.0000 1.0000E-06 2.95440E-01 0.0069 4.0000E+02 6.93760E-01 0.0030

F8

tally type 1 particle(s): neutron surface 311 energy e11 0 399.999999 400

0.0000E+00 0.00000E+00 0.0000 4.0000E+02 4.20900E-01 0.0079 4.0000E+02 3.02080E-01 0.0068

F1

F8 tally DOES take into account particle passing through without depositing energy

Fig. 5 : ε=f(EKIN,LTHR)

Neutron efficiency of the BaF2 cluster detector for various values of the electronic threshold LTHR as a function of EKIN

Script : beam for (i=200, i<=1500, i=i+50)

Code : F8:n,e,p,h,/ 1

E8: 0 1e-6 9 25 45 90 1500

Fig. 6 : ε=f(LTHR,EKIN)

Neutron efficiency of the BaF2 cluster detector for various incident neutron kinetic energies EKINas a function of LTHR

Script : beam for (i=200, i<=1500, i=i+50)

Code : F8:n,e,p,h,/ 1

E8: 0 1e-6 9 25 45 90 1500

Graph 20 : Exponential Regression of Fig. 6 for 23 different beams:

Exponential Regression

Exponential Regression of Fig. 6 for 23 different beams

Fig. 4 : δ=f(EKIN)

Pulse height spectra measured with the BaF2 cluster detector for neutrons with kinetic energies EKIN =200, 300, 400, 800 MeV

Script :

beam for i in 200 300 400 800

Code : F8:n,e,p,h,/ 1

E8: 0 1e-6 80i 800

Shape of beam 400 MeV nps=5e4 -->

PHYS:N J 100 3J -1

beam 600 MeV

Fig 4

In output file : warning. f8 tally unreliable since neutron transport nonanalog

manual extension

Coincidence counting of capture multiplicities and moments requires analog capture: CUT:N 2J

0 0. Calculations must be totally analog, with no variance reduction. Fission multiplicity also is

required: PHYS:N J 100 3J –1. An FT8 CAP tally in an input file automatically will set analog

capture, fission multiplicity, and exit with error messages if variance reduction is used. The

capture multiplicities and moments are stored in 80 cosine bins, which are printed out with the

F8 tally. A much more readable table of capture multiplicities and moments is given in Print

Table 118. The captures and moments can be compared with Print Table 117, which has the

spontaneous-fission source and induced-fission summaries of fission neutrons and moments

(Section 3.3.3).

Dealing with 2ndary particles

BaF2 detector

Delimitation of free path

BaF2 detector 3x bigger

Neutron beam 800 MeV

Neutron beam 800 MeV

Fig 7 :pulse height spectra observed in (a) central module (b) the all cluster

Central hits selected by the condition that the maximum signal occurs in the central module

Fig 7 : 200 MeV

(a) central module (b) the whole cluster

(a) central module (b) the whole cluster

(a) central module (b) the whole cluster

(a) central module (b) the whole cluster

Conclusions

- MCNPX cannot describe “maximum signal occurs in the central module”
- MCNPX code is designed for integral quantities determination , doesn’t take into account dead time of detector.

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