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Part II: nTOF_Simulations

Part II: nTOF_Simulations. Vasilis.Vlachoudis@cern.ch n_TOF Winter School 2004. BNV TOF-F09/012. Introduction Part I: FLUKA About Physics Models (hadron-nucleus) Electro Magnetic Fluka (EMF) Low Energy Neutrons Biasing Estimators Combinatorial Geometry Various.

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Part II: nTOF_Simulations

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  1. Part II: nTOF_Simulations Vasilis.Vlachoudis@cern.ch n_TOF Winter School 2004 BNV TOF-F09/012

  2. Introduction Part I: FLUKA About Physics Models (hadron-nucleus) Electro Magnetic Fluka (EMF) Low Energy Neutrons Biasing Estimators Combinatorial Geometry Various Part II: n_TOF Simulations Spallation Target Neutron Fluence Resolution Charged Particles & Gammas Activity Background Muon background TAC Detector Simulation Pulse Height on FIC Contents

  3. FLUKA coupled with: EAMC (Energy Amplifier) MCNP + MCNPX StarCD (Comp. Dynamics) ELSE3 (3D Spectral Element Code) ENSDF Decay Database Radioisotopes Evolution 3DS (Visualization & Animation) FLUKA + EAMC Spallation Target Design Target Optimization Fluence Resolution Activation Neutron Beam Profile Collimation System Reaction Rates Detectors Design FLUKA + MCNP Collimators Background Simulations for n_TOF [1/2]

  4. FLUKA Beam Related Charged Particle Contamination Prompt & Delayed Gammas Radioprotection Shielding FIC 241Am Pulse Height Background Muon Neutron background 3He detector response Proton background on TAC FLUKA + StarCD Thermodynamic behavior FLUKA + ELSE3 Target behavior: Stress & Sound Waves FLUKA + ENSDF DB Nuclei Decay Modes Delayed Photons FLUKA + 3DS Visualization Simulations for n_TOF [2/2]

  5. Geometry Simplified geometry Lead Block: Cylinder R=40cm, h=40cm Water layer: Cylinder R=40cm, h=5cm Beam Particle: Protons Momentum: 24 ± 0.0824 GeV/c Position: offset by 1.7cm (horizontal) Direction: towards Z Options No EMF Cutoffs Pions+/-, Protons 1 MeV Other 100 keV Neutrons 72 groups down to thermal Kill: Pizero, neutrino, anti-neutrino, electrons, photons 1 SPH1 2 3 p+ XYP4 XYP5 XYP3 ZCC2 y x z Lead Spallation Target Black Body Pb H2O

  6. 1 SPH1 2 3 p+ XYP4 XYP5 XYP3 ZCC2 y x z Lead Spallation Target Example [1/2]

  7. Lead Spallation Target Example [2/2] Electron Positron Neutrino A-v Photon Pizero pion+, pion-

  8. Problems USRBDX scores also the particles exiting transversely from the water layer (region 3) to the black hole. For the fluence at 200m we are interested only in the forward direction With the solid angle binning for angles the fluence at 200m changes, since weaverage thehalo+flat part Solutions To correct this one can add an extra region 4 made with vacuum in front of region 3 Use solid angle binning in USRBDX Score each neutron (position, direction, time) and propagate them to 200m. Then use only those falling inside a certain areaFLUKA Settings:Card: EXTRAWEIGHT to enable the call to fluscw.f, orCard: USERDUMP to enable the call to mgdraw.f Estimation of Fluence & Resolution Halo L=200m Neutron Fluence  80cm Flat

  9. Detector 200m Lead surface 0m Effective neutron path used in energy determination L Dl l Energy-Time Relation Moderation Flight The neutron velocity v is derived from the “effective neutron path” v=(l+L)/t with an uncertainty Dv =Dl/t Uncertainty

  10. Optimization Lead Spallation target Important Parameters: F ~ Fo /L2 DE/E ~ 2 Dl / L Figure of Merit For more info: CERN/INTC/2000-04

  11. Lead Target Design • Converters • To CAD • Convert FLUKA geometry to ACAD format with FlukaCAD http://home.cern.ch/vincke • Import in 3DS Max • To MCNP(X) with fluka2mcnp.r

  12. Collimation System Problem • The statistics of the simulation (10 CPU’s x 4 months) was not sufficient to have any real event with the capture collimation system (1.8cm @175m) Solution • For every particle with vz/v ≥ cos(1o) the direction was changed to scan a X-Y array of position in the target area • Each “new” particle was passing a survival test from the collimation + tube system

  13. Neutron Fluence For more info: CERN/INTC/2000-004

  14. Resolution • The resolution experiences a peak + a tail due to the peculiarity of the moderation process of the lead + water moderator target • Dl was represented with 2 ways: (i) as the sigma obtained by a fit on the peak of a small energy interval (20 bpd), (ii) as the RMS of the l distribution over the same energy interval

  15. Using the same input as for the neutron fluence, but enabling the EMF transport Score all the particles exiting the front face of the lead target (USRBDX) With an offline program correct the distributions with the on-flight decays of the particles, ignoring the change in the trajectory Charged Particles and Photons Fluxes of charged and neutral particles as a function of their momentum. Prompt photons distribution at 200 m.

  16. Lead Target Activation • Score residual nuclei with the RESNUCLEi card for all the regions. It is good to slice the lead target into smaller regions or layers. • Do time evolution of the residual nuclei with the usrsuwev.f program • Second simulation, using a custom made source routine source.f that generates random delayed gamma events based on the activity of the residual nuclei Activation of the exit face of the target Delayed photon distribution from the exit face of the target.

  17. Temperature Map • Score energy deposition per cm3 with USRBIN in a 3D mesh • Convert the Energy to Temperature solving for the Tmax Temperature map for one pulse of 7 1012 pr

  18. Sound Waves Calculation • FLUKA coupled with ELSE3 • Rapid energy deposition  Adiabatic heat up • Thermal expansion is immediate and not balanced inside the material  Stress & waves are generated • 15% of elastic vibrations go to water • Displacement 1mm/m2 produce up to 75 dB noise

  19. Background Features 50 larger than simulations Three time components 400 ns “flash” 20 ms – fast neutrons > 16 ms – thermal neutrons Position depended Strong Left-Right asymmetry Strong ionization signal TLD’s scored a signal probably muons Not sample related Possible Sources Elements in the neutron Tube Collimators Escape line Insufficient concrete shielding in the exp. area Charged particles deflected from the magnet High energy neutron leaking from the target area Negative muon capture … Background Problem June 2001 For more info: CERN/INTC 2001-038

  20. n_TOF Tunnel Geometry The tunnel geometry was generated with a special C program, creating an extruded object from the cross section of the tunnel and the tunnel path

  21. Background from NEL and Collimator • Creation of a source.f that samples from the neutron fluence spectrum (and also the other particles), with direction pointing the specific object under investigation (collimator or NEL) • Score with USRBIN, USRTRACK the neutron fluence in the experimental area Neutron Background from the Neutron Escape Line Neutron background from the last Collimator

  22. Minimum Mass Calculation • Use the pseudo particleRAY • Generate a source.f routine, scanning from all possible positions from Z=7m to all possible positions at Z=185m • The RAY pseudo particle travels in a straight line and writes in a file all the positions of the regions and material density it crosses. • Plot from all the scanned tracks the one track which “sees” less mass Experimental Area Lead Target Area Revealed paths with minimum mass of 1.4 kg/cm2 2 GeV/c energy losses for Minimum Ionizing Particles

  23. Muon Fluence Simulation • Performed a full simulation starting with the protons hitting the lead target • Minimum mass simulations showed that only minimum ionizing particles with P>2GeV/c can arrive at the experimental area. So we used of high threshold of 100 MeV (PART-THRES) • Set the importance biasing: usimbs.f,BIASING • Bias the pions to decays every 1 m. LAM-BIAS • Bias the neutrino direction of the pion decay, so the muon to go towards the direction of the experimental area LAM-BIAS, udcdrl.f • Tag on each particle that enters in the experimental area, scoring also the position of decay and the inelastic reaction that generated the parent particle. Routines stupr.f, fluscw.f

  24. Muon Fluence Results: • Muon fluence at the experimental area of 10-100 m/cm2/pulse @ 185 m • Strong Asymmetry Right - Left almost a factor of 100 Muon Fluence entering the experimental area Muon Fluence and position  of the inelastic reaction that generated the parent of the muon,  decay position of the parent of the muon

  25. Neutron Fluence in EAR We reconstructed these plots from the TAG information that was associating each particle that entered in the experimental area. Neutron Fluence in the experimental area divided into the various sources Neutron Fluence in the experimental area for a some time windows

  26. The simulation results have clearly demonstrated the ineffectiveness of a possible wall close to the target area: 50% of parent pions are still in the tube at the exit of the target shielding 10% of muons/parent pions are still in the tube as far as 60 m from the target Therefore a suitable shielding should be located where the fraction of muons/pions in the pipe is minimal or just after the sweeping magnet 3 m of Iron will lower the muon energy by 3.5 GeV The 3m Iron Wall The 3 m long Iron wall

  27. Muon & Neutron Fluence Attenuation C6D6 raw data with various setups

  28. Fast Induction Counter (FIC) Gas: Ar (90%) CF4 (10%) Gas pressure: 720 mbar Electric field: 600 V/cm Gap pitch: 5 mm Electrode diameter: 12 cm Electrode thickness: 15 mm (Al) Deposit thickness: 125 mg/cm2 Backing thickness: 100 mm (Al) Window thickness: 125 mm (Kapton) Targets: Beam axis: 13 Normal to beam axis: 3 FIC0 – low activity isotopes FIC1 – sealed source for highly radioactive isotopes • CERN AB-ATB-EET group • JINR(Dubna) • IPPE (Obninsk)

  29. FIC1 FLUKA Simulation Geometry • Infinite Z Cylinder  12cm (ZCC) • Cut by 5 Z planes (XYP) Simulation • With the card EVENTBIN score on Z slices the energy deposition on event per event basis • Set a threshold to 1keV per nucleon for the heavy ions • Separate runs for alphas and for fission fragments a

  30. FIC1 Source routines Alphas • Energy = 5.49 MeV • Position sampled randomly on the 241Am layer r2 = Rnd(), f=Rnd() • Direction Isotropic over 2p Fission Fragments • Symmetric fission mass width taken from systematic of G.D.Adeev et al., Preprint INR 861/93 1993A1 = RndGauss(AMEAN,s)AMEAN = 140, s = 6.5A2 = A+1-A1-(NFISS=2)Zs(A)=A / (2+0.0156 A2/3)Z1=Zs(A1) + 0.5 × [Z-Zs(A1)-Zs(A2)]Z2=Z-Z1R=A1/AET= -13 A2/3 × [(1-R)2/3 + R2/3-1] + .6 × Z2 / A1/3 × [1-R5/3-(1-R)5/3](MeV)Smoothed by a gaussian 15%ET = ET / [ 1 + 0.084 * RndGauss() ]E1 = ET / [ 1 + A1/A2 ]E2 = ET – E1 FF Mass Distribution FF Energy Distribution

  31. Pulse Reconstruction [1/3] From Energy Deposition to Charge • The total electron charge to drift at any time is given by:where: v drift speed (12 cm/ms)dEn(z,t)=dEn(z+vt) Energy deposited per z-slice (EVENTBIN × Surface)Wf work function ( 25 eV/electron) Fission Fragment Energy Deposition

  32. Pulse Reconstruction [2/3] Current where t time of observation tRC RC=10ns

  33. Pulse Reconstruction [3/3] • As a last step we add randomly on a sufficiently large time frame • White noise (few %) • Current pulses from various alphas corresponding to the activity of 250 MBq of 241Am • Current pulses from the fission fragments from various events with a rate equal to what we will expect for TOF times En1MeV neutrons at n_TOF.

  34. Pulse Height Simulation of 241Am • Using a pulse fitting program, we reconstructed the pulse height of both Alphas and Fission fragments for neutron energies around 1MeV • Still good separation FF and a with 250 MBq 241Am target

  35. Bibliography Bibliography • FLUKA V2003 Manual • MCNPTM – A General Monte Carlo N-Particle TransportCode, LA-12625-M, UC705&UC700 Los Alamos 1997 • The Physics of High Energy Reactions,A.Ferrari and P.R.Sala, Proceedings of “Workshop on Nuclear Reaction Data and Nuclear Reactors Physics, Design and Safety” Triest, Italy 1996 • Neutron Physicsby K.H.Beckurts and K.Wirtz, Springer-Verlag 1964 • Radiation Detection and Measurementsby Glenn.K.Knoll, ISBN 0-471-07338-5 • A Third Monte Carlo SamplerC.J.Everett, E.D.Cashwell, LA-9721-MS, UC-32 1983 • Particle Data Bookhttp://pdg.bnl.gov • The Particle Detector Briefbook • by R.K.BOCK, at CERN, Geneva, and A.VASILESCU, at IFA, Bucuresti. • http://physics.web.cern.ch/Physics/ParticleDetector/BriefBook/ • The Data Analysis Briefbook • http://rkb.home.cern.ch/rkb/titleA.htmlsame authors

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