The n_TOF neutron flux and resolution function by GEANT4 simulations

The n_TOF neutron flux and resolution function by GEANT4 simulations

CERN, 25 – 27 February 2015

Sergio Lo Meo1,2, Cristian Massimi2,3,Nicola Colonna4, Federica Mingrone2,3, Gianni Vannini2,3

1 ENEA Research Centre of Bologna (Italy)2 INFN Section of Bologna (Italy)3 Physics and Astronomy Dept. Alma Mater Studiorum – University of Bologna (Italy)4 INFN Section of Bari (Italy)

Outline

• Introduction• Spallation Target• G4 Physics List• Results• Conclusion

Introduction

This work had several motivations:

- curiosity-driven, to check if Geant4 is able to reliably simulate the spallation process and the neutron production/transport in a large energy range;

- need-driven, to develop new tools and competence on simulations of the n_TOF facility, in particular for work related to EAR2 (analysis of the flux and resolution function);

- accuracy-driven, to double-check present simulations, now available only by FLUKA (two is always better than one!!!);

Fluka Spallation Target Setup

G4 Spallation Target Setup

Scoring Plane EAR1

Scoring Plane EAR2

Spallation Target

Physics List

FTFP: The Fritiof [1][2] model is used in Geant4 for simulation of the following interactions: hadron-nucleus at Plab > 3 - 4 GeV/c, nucleus-nucleus at Plab > 2 - 3 GeV/c/nucleon, antibaryon-nucleus at all energies, and antinucleus-nucleus.

INCLXX: we have used the Liège Intranuclear Cascade model INCL++ [3] [4] that is suitable for the simulation of any system where spallation reactions or light-ion-induced reactions play a dominant role. INCL++ is used for reactions induced by nucleons with Plab < 3 GeV/c HP: the NeutronHP model at low energy to simulate all reactions induced by neutrons using evaluated data libraries (G4NDL)

In Geant4 10.01 version (December 2014) we have used:FTFP_INCLXX_HP Physics List

For De-excitation we have not used the default (G4ExcitationHandler) model of INCL++ but ABLA [5] model that was recognized as one of the best de-excitation model by the IAEA Benchmark of Spallation Models [6]

Physics List

[1] B.Andersson et al. Nucl. Phys. B281 289 (1987) 427[2] B.Nilsson-Almquist, E.Stenlund, Comp. Phys. Comm. 43 387 (1987).[3] A. Boudard et al., Phys. Rev. C87 (2013) 014606.[4] D. Mancusi et al., Phys. Rev. C90 (2014) 054602.[5] A. Keli´c, M. V. Ricciardi and K.-H. Schmidt, Joint ICTP-IAEA Advanced Workshop on Model Codes for Spallation Reactions, Report INDC(NDC)-0530 (2008) 181.[6] Benchmark of Spallation Models, organized by the IAEA. Web site: http://www-nds.iaea.org/spallations[7] S. Lo Meo, D. Mancusi, C. Massimi, G. Vannini, A. Ventura “Fission induced by nucleons at intermediateenergies” Nuclear Physics A 993 (2015) 43 - 67

The choice of INCL++ and ABLA is also due to previous use that led the n_TOF group of Bologna, along with one of the developers of INCL++ (D. Mancusi) , to publish a work [7] that describes the calculation of cross sections of fission of some actinides and pre-actinides with incident nucleon energies from 100 MeV to 1 GeV

Neutron Tracking Cut modified as follow:G4NeutronTrackingCut *nCut = new G4NeutronTrackingCut(verboseLevel);nCut->SetTimeLimit(4000000.*ns);

All electromagnetic interactions (except Atomic De-excitation) are included as the decays of particles (except Radioactive Decay).

ResultsScoring plane at target: events with θ < 2°, propagated to EAR1

ResultsScoring plane at target: events with θ < 2°, propagated to EAR1

ResultsAbsolute value: G4 simulation 35% higher

Change Average reduction

1st collimator shifted 1 m 2%

1st collimator: Radius reduction 5 mm (R = 5.5 cm 5.0 cm)

7%

2nd collimator shifted 1 m 2%

2nd collimator: Radius reduction1 mm (R = 0.9 cm 0.8 cm)

28%Resampling 10% uncertainty on absolute value

ResultsSimulation arbitrarily scaled

ResultsSimulation arbitrarily scaled

Resultsλ = vtmod

Propagated to EAR1

Resultsλ = vtmod

Propagated to EAR1

Energy interval

FLUKAMEAN (cm) - R.M.S (cm)

GEANT4MEAN (cm) - R.M.S (cm)

1-10 eV 14.1 16.1 11.8 (15.3) 6.9 (12.0)

10-100 eV 14.8 17.3 12.3 (14.3) 9.0 (12.3)

100-1000 eV 16.2 18.0 14.9 (16.2) 10.0 (14.8)

1-10 keV 20.4 21.9 17.5 (21.0) 13.6 (18.5)

10-100 keV 31.9 32.2 29.0 (35.3) 25.0 (31.5)

100-1000 keV 51.6 38.3 51.4 (56.4) 37.1 (38.7)

ResultsNumerical Resolution function

TEST using 197Au data from 2012

ResultsNumerical Resolution function

TEST using Fe and 238U data from 2011 measurement campaign

ResultsNumerical Resolution function

Conclusion

- Geant4 seems to reproduce n_TOF flux further tests are foreseen;

- Geant4 seems to reproduce neutron moderation time inside neutron-producing target Effect due to the propagation on the Lambda values can be investigated;

- The result can improve the accuracy of the resolution function.

Sergio Lo Meo - [email protected] Massimi - [email protected]

www.unibo.it

Flux Vs target rings

Flux Vs target rings

EAR 2Simulation arbitrarily scaledEAR2

EAR 2λ = vtmod

Propagated to EAR2

EAR2 – Resolution functionn+238UEAR2

EAR2 – Resolution functionn+238UEAR2

EAR 1 – 10B content 1.28% 1.38% B

Resampling

protons

target 1st collimatorR = 5.5 cm 2nd collimator

R = 0.9 cmneutrons

135.75 m 2.0 m

177.55 m

2.85 m

EAR1

1st collimatorR = 5.5 cm

2nd collimatorR = 0.9 cm

~ 5x106 protons 1 neutron

1/2 week CPUs = 106 protons !!!

θ

θ < 2°

Resampling

protons

target neutrons

EAR1

1st collimatorR = 5.5 cm

1st collimatorR = 5.5 cm

2nd collimatorR = 0.9 cm

2nd collimatorR = 0.9 cm

Θ’ < 0.128°

40 cm

Al3.6 cm H2O grigliata

1.4 cm

58 cm Pb

Pb 1 cm

1 cm

5 cm

5 cm

70cm

Z

H2O0.3 cm

40cm

H2O0.7 cm

Al0.3 cm

15 cm

5.4 cm

H2O1 cm

Al0.4 cm

10 cm

3.5 cm

Al0.3 cm

Acqua Borata4.0cm

Al0.7 cm

Al (griglia)1.5 cm

60cm

9.45cm

1.1 cm

1.5cm

Sergio Lo Meo - [email protected] Massimi - [email protected]

www.unibo.it