The SPES production target first calculations using the FLUKA code

Abstract Monte Carlo simulations play a very important role in the prediction of the physical behavior during any kind of process, and irradiation as well. It can be helpful for the equivalent dose absorption rate or for the product spectra predictions, and is constantly improved with the rising calculation performances in modern computers. In this report we are going to introduce the aim of the SPES facility, and then we will focus on the FLUKA Monte Carlo code, a powerful tool that allows simulating the physical processes with the SPES beam and geometry. We will show that the results are close to the ones achieved with the MCMPX code, an improved software previously used by the SPES team.

Introduction

What’s FLUKA? General Monte Carlo tool for calculations of particle transport and interaction with matter; Distributed and documented on the official website http://www.fluka.org; Developed and maintained under INFN and CERN agreement; Has a wide range of applications.

FLUKA’s applications Cosmic ray's physic; Accelerator design (LHC systems); Particle physics: calorimetry, tracking and detector simulations etc. (ALICE, ICARUS); Neutrino physics (CNGS); Shielding design; Dosimetry and radioprotection; Space radiation (space related studies partially funded by NASA); Hadron therapy (treatment planning).

FLUKA collaborations CERN (Switzerland): M. Brugger, F. Cerutti, A. Ferrari, M. Mauri, G. Lukasik, S. Roesler, L. Sarchiapone, G. Smirnov, F. Sommerer, C. Theis, S. Trovati, H. Vinke, V. Vlachoudis SLAC (USA): A. Fassò Univ. of Siegen (Germany): J. Ranft INFN & Univ. Milano (Italy): G. Battistoni, F. Broggi, M. Campanella, P. Colleoni, E. Gadioli, S. Muraro, P.R. Sala INFN Frascati: M. Carboni, C. D’Ambrosio, A. Ferrari, A. Mostacci, V. Patera, M. Pelliccioni, R. Villari Univ. Roma II (Italy): M.C. Morone INFN & Univ. Bologna (Italy): A. Margiotta, M. Sioli DKFZ & HIT (Heidelberg, Germany): A. Mairani, K. Parodi Univ. of Houston (USA): A. Empl, L. Pinsky NASA-Houston (USA): K.T. Lee, T. Wilson, N. Zapp ARC Seibersdorf (Austria): S. Rollet Chalmers Univ. of Technology (Sweden): M. Lantz

FLUKA’s abilities Handles 60 different particles and Heavy Ions; Hadron-hadron and hadron-nucleus interactions up to 10000 TeV; Electromagnetic and μ interactions 1 keV - 10000 TeV; Nucleus-nucleus interactions 100 MeV/n to 10000 TeV/n; Charged particle transport – ionization energy loss; Neutron multi-group transport and interactions 0-19.6 MeV; Neutrino interactions; Transport in magnetic field; Combinatorial and Voxel geometry (“3D pixel”);

Flair graphic interface Advanced user interface for FLUKA by Vlachoudis et al., written in Python and Tkinter; Facilitates the editing of the input file, and the data merging; Downloadable from FLUKA website, but not part of FLUKA; Extremely useful for geometry view and debug; Uses Gnuplot to generate graphics; Gives the possibility of running processes in more cores (with different seeds); Runs under Linux

Different kind of plots Povray Gnuplot

SimpleGeo interactive solid modeler which allows for flexible and easy creation of the geometry models via drag & drop, as well as on-the-fly inspection Imports existing geometries for viewing Creating new geometries from scratch Export to various formats (FLUKA, MCNP,MCNPX)

Target – ion source SPES

FLUKA for SPES experiment Benchmarking of the code, results compared with a previously used program (MCMPX); 40 MeV proton beam with a 200 µA current hitting a target made of graphite and UC4;

Physics

Low energy neutrons in FLUKA Many particle are subject to point-wise dynamic; Neutrons below 20 MeV (19.6 MeV for the old library) are subject to multigroup algorithm Very used in low-energy transport codes; Based on the division of energy spectrum in a discrete number of energy groups; This range is continuously enriched and updated on the basis of many recent evaluations; Elastic and inelastic scattering simulated by group-to-group transfer probabilities (down-scattering matrix);

Multigroup algorithm logic In a material a certain kind of scattering probability between two groups is proportional to the matrix element aij, where i and j are the group indexes. Downscattering matrix σ: cross section µ: scattering angle N: chosen order of Legandre anisotropy P: Legandre polynomial function

Cross section library Available at many temperature for different materials (0, 87, 273 K); Hydrogen cross section available for three kind of binding: Free H2O CH2 Also photon scattering is treated with a multigroup scheme.

Library improvements Old library New library Up to 19.6 MeV 72 neutron groups, 1 thermal 260 neutron groups, 31 thermal 22 gamma groups 42 gamma groups 140 different materials/isotopes About 200 materials/isotopes at 0, 87 K and 296 K Self-shielding for Fe, Cu, Pb Self shielding for most isotopes Moreover, the point-wise library has been extended from few isotopes (H, 6Li, 10B, Ar, Xe and Cd) to all.

Residual nuclei scoring For many materials group-dependent information on the residual nuclei produced by low-energy neutron interactions isavailable in FLUKA library. This information can be used to score the residual nuclei after any fission/spallation reaction, and this feature has been useful for the work shown in this report for the UC4 fission production.

results

Power deposition

Power deposition

Power deposition Not centered beam (1cm from the center); Gaussian beam (σ=2.7mm); Good results, possible different developments.

Nuclear production from the target

Bertini + Orn production plot

Bertini + Ral production plot

Comparison with MCMPX

Comparison with MCMPX

Comparison with MCMPX

Neutron yield

Dose and activity scoring Important for radioprotection part; Decays may be activated in FLUKA, and the equivalent dose may be recorded at different times; It’s possible to make a map of the bunker with the target and the equivalent dose rate in each region; Dose sampled at 1 and 2 meters from the target at different irradiation and cooling times; 3 phases: Irradiation (14 days); Cooling (14 days); Storage.

Dose and activity scoring

Results in Fluka Irradiation Step Activity [Bq] Dose at 1m Dose at 2m 1 day 3.53E+13 2.08E+00 6.11E-01 4 days 3.85E+13 2.18E+00 6.40E-01 7 days 3.97E+13 2.21E+00 6.49E-01 14 days 4.09E+13 2.25E+00 6.60E-01 Cooling Step Activity [Bq] Dose at 1m Dose at 2m 1 second 3.87E+13 2.08E+00 6.16E-01 1 day 5.66E+12 1.71E-01 5.02E-02 3 days 3.23E+12 9.64E-02 2.84E-02 14 days 1.01E+12 3.50E-02 1.04E-02

Results in MCMPX Irradiation Step Activity [Bq] Dose at 1m Dose at 2m 1 day 1.50E+13 1.77E+00 4.43E-01 4 days 1.70E+13 1.92E+00 4.79E-01 7 days 1.80E+13 1.94E+00 4.86E-01 14 days 2.00E+13 2.09E+00 5.22E-01 Not too good, but the fission rate (9.23E12 fissions/sec) is close to the MCMPX one (8E12 fissions/sec) Cooling Step Activity [Bq] Dose at 1m Dose at 2m 1 second 2.00E+13 2.08E+00 5.19E-01 1 day 3.33E+12 1.95E-01 4.88E-02 3 days 1.78E+12 1.10E-01 2.75E-02 14 days 6.67E+11 4.12E-02 1.03E-02

Dose scoring inside the box After the 14 days of cooling the target is put into a lead and iron box; Is not possible to change the geometry during the virtual time of the simulation; Different strategy has to be adopted in order to prevent the activation of the box.

Geometry of the after-cooling simulation Box Low-energy neutron proof layer Air Target

Results

Results Problems due to: Geometry of the sampling; Time elapsed Dose at 1 m [Sv/h] Dose at 2 m Dose at 2m (MCMPX) 30 days 9,41∙10-4 3,85∙10-4 2,75∙10-4 90 days 1,57∙10-4 6,42∙10-5 5,98∙10-5 10 years 2,67∙10-7 9,78∙10-8 4,25∙10-7 100 years 2,56∙10-8 8,65∙10-9 7,24∙10-8 Problems due to: Geometry of the sampling; Low statistics (50 000 events)

Boris tube Important in order to transmit data from the chamber to the outside; External width: 330 mm Iron width: 10 mm PEHD diameter: 315 mm

Boris tube Positive results, no detectable scoring outside the chamber through the tubes;

Neither any neutron outside

Conclusions Strong points: User friendly program; Many application in physics; Results benchmarked in: Dose scoring; Nuclear production; Fission rate; Power deposition

Conclusions Weak points: Further developments: Overrated activity; Tricky when the geometry of the problem has to change; Further developments: Benchmark with GEANT4; Improved experiment with the box, and with other methods to “record” the activity of the target after 14 days of radiation; FLUKA on GRID;

Thanks

Some examples of program usage Appendix Some examples of program usage

Installing FLUKA Decompress the main folder; Make sure to have a FORTRAN compiler; Set the environment variable FLUPRO (path of the folder) and FLUFOR (name of the compiler); Run the makefile inside the folder; Create a startup bash script to include the FLUKA directory in the program path of Bash; Every detail is in the readme file; Flair is even easier, DEB packages.

Example of a run rfluka –N0 –M1 exp1 Calls the script Input file (no extension) Calls the script Previous and last cycle of the simulation

Example of an input file * ..+....1....+....2....+....3....+....4....+....5....+....6....+....7... TITLE FLUKA Course Exercise * DEFAULTS NEW-DEFA * beam definition BEAM -3.5 -0.8 -1.7 PROTON BEAMPOS -0.1 * Geometry * -------- * use names everywhere and free format for geometry (conventional format) GEOBEGIN COMBNAME 0 0 Cylindrical Target * Bodies * ------ * Blackhole to include geometry SPH BLK 0.0 0.0 0.0 10000.0 * Void sphere SPH VOID 0.0 0.0 0.0 1000.0 * Cylindrical target: RCC TARG 0.0 0.0 0.0 0.0 0.0 10. 5. END * * Regions * ------- * Blackhole BLKHOLE 5 +BLK -VOID * Void VOID 5 +VOID -TARG * Target TARGET 5 +TARG END GEOEND * Assign materials * ---------------- ASSIGNMA BLCKHOLE BLKHOLE ASSIGNMA VACUUM VOID ASSIGNMA LEAD TARGET RANDOMIZ 1.0 START 10.0 0.0 STOP

Flair first screenshot

Input with Flair All the cards organized per category