1. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 1 Report on Radiation Background Task Force Started in september 2000 Context: predicted radiation levels had increased since TP transport program FLUKA & GCALOR showed differences detector description not up-to-date, not evolved consistently Mandate: The taskforce was asked to look into both the geometry and material input, and the physics models and analysis methodologies used for evaluating the radiation background. It should analyze the levels predicted and their impact on ATLAS. It should evaluate the most critical areas, i.e. where small variations in physics, geometry and material have the strongest impact on the radiation levels. Geometry/Material descriptions should be “signed-off” by the systems as being in agreement with the planned detectors

2. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 2 Report on Radiation Task Force Progress Players:M.Bosman, I. Dawson, M. Huhtinen, P. Norton, M. Shupe, I. Štekl, W. Witzeling  V.Hedberg S.Pospisil, A.Nisati, S.Baranov + A.Morev Lines of work that were followed:  Update geometry and material  Understand effect on detectors Identify corresponding critical particle type/ energy range  Understand origin of various components of radiation background  Shielding optimization  Systematic studies of uncertainty related to Event generator Particle transport  Activation (see V.Hedberg talk)

3. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 3 Geometry / Material composition Revise: Beam pipe + vacuum equipment: according to drawings from LHC vacuum group ID: TRT, SCT, Pixel material Calo: all calorimeters revised + study of sensitivity to gap Muon: chamber dimension/material, barrel coils, endcap cryostats/coils Shielding: realist materials, chicanes, etc. Understand/implement the necessary level of detail Comment: a useful and necessary exercise... + some cross-checks done with DICE

4. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 4 Main background sources Dominant contribution = pp interactions (over beam gas, beam loss, cosmic) particles produced in intermediate p T diffractive and central collisions that hit in order of importance of the intensity of the “source” TAS collimator, FCAL shower max, Beam Pipe + Vacuum Equipment 11/10 1/100 But this this has to be weighted by the effectiveness of the shielding TAS well shielded by big JF FCAL auto-shielded  one of the largest contributor = beam pipe line source under the thin JT shield

5. FLUKA av16

8. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 8 Nature of neutral radiation background Neutron escaping shielding or calorimeter ~ 8 kHz/cm 2 >10 MeV 0.5 kHz/cm 2 (example of 2nd Frwd mid-eta) photons from capture (n,  or inelatic (n,n’  ~ 4 kHz/cm 2

9. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 9 Nature of charged radiation background protons from (n,p) ~ 12 Hz/cm 2 electrons from  photoelectric effect or Compton scattering ~ 58 Hz/cm 2

10. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 10 Nature of charged radiation background muons (in-flight decay of primary  /K and in shower) ~ 2.2 Hz/cm 2 decreased compared to TP by factor 2 to 8 (new K 0 transport) pions rates small (except in ID region) ~ 0.8 Hz/cm 2 decreased by factor 10 (new K 0 transport)

11. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 11 Effect of radiation background Muon system: Uncorrelated noise hits in chambers (pattern recognition, space-charge build-up, ageing) (1) Single plane counting rate = n*  n +  *   + ½(p +  +  + 0.25*e)  n ~ 10 -4 and   ~ 5  10-3 ; ½ for current vs fluence 0.25 to avoid double counting with  separate e not locally produced in chambers themselves Penetrating particles (couple of RPC/TGC in a station  contribute to fake trigger rate) (2) Penetrating particle rate = 0.1*  *   + ½(p +  +  + 0.25*e) 0.1*  *   rough estimator of  firing a couple of chamber Inner Fwrd(1)10% n 73%  6% p 5%  6% e (2) 30%  24% p 20%  26% e Middle Barrel(1)1% n 89%  2% p 1%  7% e (2) 45%  12% p 7%  36% e

12. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 12 Muon chambers efficiencies & fake trigger rate Discussed in the framework of the Task Force. -detailed G3 simulation of muon system set-up (S.Baranov) including magnetic field -understand relevant part of energy spectrum, understand effect of material, trigger logic, double-counting  -e, etc. -fold efficiency with energy spectrum & angular distribution -every region, case needs a detailed study for uncertainty on efficiencies to remain acceptable!! Ongoing …

13. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 13 Effect of radiation background Inner Detector: primary particles + albedo neutrons & accompanying  (occupancy) Electronics in all region: Dose (ionization) N on I onizing E nergy L oss (  neutrons>100 keV) x Energy dependent K-factor SEU (hard hadrons >10 MeV, mostly neutrons) USA15: Dose - penetrating component in 2 m concrete due to neutrons > 10 MeV  need understand uncertainty on many  particle types + energy range

14. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 14 Shielding optimization Mainly done with GCALOR by V.Hedberg and M.Shupe Important trends checked with FLUKA by I.Dawson reduce big JF shield to the necessary level optimize the regions with limited space: dense material + moderator + type of dopant + cladding -respective thickness – trade-off dense vs moderating see: http://atlasinfo.cern.ch/Atlas/TCOORD/Activities/CommonSys/Shielding/Activation/back/background.html + Vincent’s talk

15. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 15 Benchmarking of Shower Simulation packages  Most of radiation background predictions in Atlas done with FLUKA2001 and GEANT3-CALOR Both programs extensively benchmarked on many experimental data -share common “ancestry” via G3-FLUKA (hadrons>10 GeV) -different neutron and low-energy hadron transports -FLUKA new neutral kaon transport (GCALOR taken from Gheisha)  MARS completely independent program used extensively at Fermilab uses MNCP4 the most reliable neutron transport A set of comparisons have been performed (I.Dawson,..): see http://dawson.home.cern.ch/dawson/fluka/ 1.FLUKA2001-MARS(14.02) on cylindrical geometry 2.FLUKA2001-GCALOR on simplified ATLAS geometry Identical dimensions, material, min.bias events, etc… 3.FLUKA2001-GCALOR on detailed ATLAS geometry Identical min.bias events, similar but nor identical geometry & material more than 100 elements and mixtures)

16. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 16 Benchmarking of Shower Simulation packages CYLINDER SIMPLIFIED ATLAS GEOMETRY FLUKA2001-MARS FLUKA2001-GCALOR

18. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 18 Benchmarking of Shower Simulation packages Brief summary of comparison Fluka higher for almost all fluxes Neutron-Photons (+electrons) excellent agreement for Fe (20%) (benchmarking of Fe absorber by Ch.Fabjan et al. data vs FLUKA agree within 1.2) somewhat worse for Cu (<~2) (Atlas JT), all ratios < 2.5 (uncertainty associated to transport that had been considered so far) Protons / Muons: FLUKA/GCALOR <2 : FLUKA/MARS Protons < 3: Muons<5 Still detailed analysis to be completed (per energy range, etc..) !

19. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 19 Event Generator Up to Task Force time: 1500 events of DTUJET93 Now, use higher statistics sample of PHOJET1.12 (R.Engel) Dual Parton Model + aspects of QCD Neutron fluences decrease w.r.t. DUTJET by about 5 (10) % in the barrel (forward) region,  ’s somewhat less Study differences PHOJET/ PYTHIA6.2 ( “best” model for multiple interaction) Both models give acceptable fit to available experimental data For more info see ATL-COM-PHYS-2002-017 A.Moraes, I.Dawson et al.

20. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 20 Event Generator Phojet/Pythia Inner Detector <  1.1 Muon Barrel & Forward <  1.2 Except  in Muon forward <  1.5

21. Atlas Plenary, 27th of June 2002M.Bosman / IFAE-Barcelona for the Radiation Task Force 21 Conclusion Took much longer than initially thought! But quite a daunting task for a reduced number of people at <100% FTE ¡ Many thanks to the ones who have contributed ! Our main simulators M.Shupe & I.Dawson Acknowledge V.Hedberg contribution in Shielding & Activation Writing report (aim september, already 80 pages … ) + all tables/figures etc on Atlas official archiving system Slowing down activities – some isues to follow-up still like finalizing shielding optimization phi-dependent radiation levels simple comparison with magnetic field etc… complete understanding of muon chamber efficiencies