Fast Neutron Background study with Fast Neutron Background study with the ATLAS MDT chambers and the ATLAS MDT chambers and development of a simulation model development of a simulation model P.S. Savva 1 1 , , T. T. Alexopoulos Alexopoulos 1 1 , M. , M. Dris Dris 1 1 , E. , E.N. N. Gazis Gazis 1 1 , , P.S. Savva E. Katsoufis Katsoufis 1 , M. Kokkoris Kokkoris 1 , A. Lagoyannis A. Lagoyannis 2 , S. Maltezos Maltezos 1 , E. 1 , M. 1 , 2 , S. 1 , G. Tsipolitis Tsipolitis 1 1 G. 1 Physics Department, National Technical University of Athens, Physics Department, National Technical University of Athens, 1 Zografou, GR , GR- -15780 Athens, Greece 15780 Athens, Greece Zografou 2 Nuclear Physics Department, NCSR Nuclear Physics Department, NCSR “ “Demokritos Demokritos” ”, , Aghia Aghia Paraskevi Paraskevi, , 2 Athens, Greece Athens, Greece 13 April 2006, Ioannina Ioannina, HEP2006 , HEP2006- -EESFYE EESFYE 13 April 2006, 1 1
Why to study the Why to study the neutron sensitivity neutron sensitivity of a muon muon detector? detector? of a 2 2
� The The LHC LHC environment produces fluxes of environment produces fluxes of � photons and and neutrons neutrons in the in the ATLAS ATLAS muon muon photons spectrometer area which are comparable area which are comparable spectrometer � The The neutron neutron ionization charge deposition ionization charge deposition � can be hundreds of times larger larger than the than the can be hundreds of times charge deposition of a muon muon charge deposition of a � The increased charge per unit length of The increased charge per unit length of � the anode could cause aging aging to the detector to the detector the anode could cause electronics electronics 3 3
BIS BIS MDT MDT The expected The expected neutron fluence neutron fluence (kHz/cm 2 (kHz/cm 2 ) ) in the in the ATLAS Hall ATLAS Hall (ATLAS muon (ATLAS muon TDR, 1997) TDR, 1997) The energy spectrum The energy spectrum of the expected of the expected neutron background neutron background radiation in the Atlas radiation in the Atlas Hall (ATLAS Hall (ATLAS muon muon TDR, 1997) TDR, 1997) 4 4
� The ATLAS MDT sensitivity has been The ATLAS MDT sensitivity has been � studied to fast neutrons of energies: studied to fast neutrons of energies: 0.518- -10.00 10.00 MeV MeV 0.518 by the 7 Li(p,n) Li(p,n) 7 7 Be Be and a d(d,n) d(d,n) 3 3 He He by the 7 and a reactions at the TANDEM accelerator reactions at the TANDEM accelerator (Demokritos Demokritos) ) ( � A A simulation model using the � simulation model using the GEANT4 toolkit has been developed GEANT4 toolkit has been developed 5 5
The ATLAS Detector The ATLAS Detector 6 6
The ATLAS MDT The ATLAS MDT Detector Detector The ATLAS Muon Muon The ATLAS Spectrometer Spectrometer 7 7
The ATLAS MDT The ATLAS MDT Aluminum walls Aluminum walls Ar:CO 2 (93:7) Gas mixture Ar:CO 2 (93:7) Gas mixture W:Re (97:3) Anode Wire ( 3080V) W:Re (97:3) Anode Wire ( 3080V) 8 8
9 9
The neutron facility The neutron facility � It is a 5.5 MV Tandem Van It is a 5.5 MV Tandem Van der der Graaff Graaff accelerator accelerator � � Three neutron energy ranges can be produced by Three neutron energy ranges can be produced by � this facility, via three different nuclear reactions this facility, via three different nuclear reactions Neutron Energy Neutron Energy Proton/Deuteron Proton/ Deuteron Range Range Nuclear Reaction Energy Range Range Nuclear Reaction Energy (MeV MeV) ) ( (MeV MeV) ) ( 7 Li(p,n) Li(p,n) 7 7 Be Be 1,92 to 7,9 7 1,92 to 7,9 0,121 1 to 6, to 6,2 242 42 0,12 Η (d,n) (d,n) 3 He 0,8 to 8,4 8,4 3,9 to 11,5 to 11,5 2 Η 2 3 He 0,8 to 3,9 16,4 ,4 to 2 to 25 5, ,7 7 16 3 Η Η (d,n) (d,n) 4 4 He He 0,8 to 8,4 8,4 3 0,8 to 10 10
Background radiation in the experimental Background radiation in the experimental area and measures for its limitation area and measures for its limitation � Neutrons coming from neutron elastic and inelastic scatterings with the surrounding materials � Prompt photons coming from neutron inelastic scatterings with the surrounding materials A BF 3 Detector, sensitive only to neutrons, was used to monitor the neutron flux 11 11
In order to prevent scattered neutrons from reaching the In order to prevent scattered neutrons from reaching the BF 3 detector, three conditions have been studied : BF 3 detector, three conditions have been studied : (a) Neutron beam hitting directly the BF 3 detector (b) A paraffin Collimator was placed in frond of the Gas Cell (c) Paraffin Blocks were placed on the floor Condition Direct Paraffin Paraffin Condition Direct Paraffin Paraffin hitting Collimator Collimator + hitting Collimator Collimator + Blocks Blocks BF 3 Counts 179114 108691 105767 BF 3 Counts 179114 108691 105767 A combination of the paraffin collimator and A combination of the paraffin collimator and the paraffin blocks on the floor minimizes the the paraffin blocks on the floor minimizes the scattered neutrons that reach the BF3 scattered neutrons that reach the BF3 detector detector 12 12
Gas Cell Gas Cell built in built in paraffin paraffin Paraffin Paraffin blocks blocks Collimator Collimator Paraffin Blocks Paraffin Blocks on the floor on the floor 13 13
The neutron flux versus the angle of emission was The neutron flux versus the angle of emission was also studied also studied Gas cell 70000 Paraffin collimator 60000 BF 3 counts 50000 40000 Angle of emission 30000 20000 -40 -20 0 20 40 Angle of emission (deg) BF 3 Detector 14 14
Prompt photons Study of two conditions: • collimator's exit open • collimator's exit closed collimator's exit open collimator's exit closed BF 3 counts 610537 139821 MDT counts 3557123 3103159 collimator's exit closed Many MDT counts are due to Limitation of emitted neutrons to 22,90% Prompt Photons Limitation of MDT counts only to 87,2% 15 15
So finally…. MDT completely BF3 built in Pb blocks Paraffin collimator Detector 16 16
Determination of the Determination of the MDT response MDT response to to 0.518 - - 10 10 MeV MeV 0.518 neutrons neutrons 17 17
E n = 0.518 to 4 MeV MeV ~> ~> E n = 0.518 to 4 Neutrons via the 7 7 Li(p,n) Li(p,n) 7 7 Be Be reaction reaction Neutrons via the � Threshold reaction with Q = -1,644 MeV � Neutron Energies between 0,12 and 6,24 MeV � The proton beam hits a F:Li (50:50) target � For E p ≥ 4 MeV ~> Lower energy neutrons from the 9 F(p,n) 10 Ne reaction 18 18
E n = 6 to 8 MeV MeV ~> ~> E n = 6 to 8 Η (d,n) (d,n) 3 He reaction 2 Η 3 He Neutrons from the 2 reaction Neutrons from the � Exothermic reaction with Q=3.269 Exothermic reaction with Q=3.269 � MeV MeV � Neutron energies between 3.9 and Neutron energies between 3.9 and � 11.5 MeV MeV 11.5 � A deuteron beam hits a gas cell A deuteron beam hits a gas cell � target, filled with deuterium gas target, filled with deuterium gas � The gas cell is 3.7 cm long and is The gas cell is 3.7 cm long and is � made of stainless steel made of stainless steel � The entrance window is 5 The entrance window is 5 μ μ m Mo foil m Mo foil � and the beam stops on a 1 mm Pt foil and the beam stops on a 1 mm Pt foil � The deuterium gas pressure can be The deuterium gas pressure can be � monitored and refilled electronically monitored and refilled electronically when the cell pressure falls below a when the cell pressure falls below a 19 19 Gas Cell preset level preset level
14000 10000 12000 # of events 1000 10000 # of events E n = 6 MeV 6 MeV E n = 8000 100 E n = 8 MeV 8 MeV E n = 6000 E n = 10 MeV 10 MeV E n = 4000 2004006008001000 1200 1400 1600 1800 2000 ADC channel 100000 2000 100000 90000 0 200 400 600 800 1000 1200 1400 1600 1800 2000 80000 10000 ADC channel dN / dE 70000 60000 E n = 3,5 MeV 1000 50000 dN / dE Neutron beam 40000 0 25 50 75100 125 150 175 200 225 250 30000 Activation Energy (keV) 20000 Neutron Beam, Pb 10000 Activation, Pb 0 0 25 50 75 100 125 150 175 200 225 250 Energy (keV) 20 20
5500 27 Mg Mg ~> decay through ~> decay through β β – – 27 ) + Ι 2 e (-x/ τ Ι = Ι 0 + Ι 1 e (-x/ τ ) 5000 1 2 emission emission 4500 Ι 0 = 1525 ± 13 Ε max Ε max = = 1765 1765 keV keV Ι 1 = 1655 ± 74 4000 # events τ 1 = 567 ± 0 3500 Ι 2 = 2534 ± 61 28 Al Al ~> decay through ~> decay through β β – – 28 τ 2 = 136 ± 6 3000 emission emission 2500 Ε max Ε max = = 2862 2862 keV keV 2000 1500 0 200 400 600 800 1000 1200 1400 1600 1800 Detection of the β - particle Time (s) by more than one drift tubes Counting rate drop when the 7 MeV neutron beam stops Curve fit: Possible problem on the muon track 27 Al (n,p) 27 Mg, τ = 567,48 s reconstruction 27 Al (n, γ ) 28 Al, τ = 134,48 s 21 21 efficiency
Electrons with energy Electrons with energy 1765 keV keV, coming from , coming from 1765 the 27 27 Mg decay Mg decay the Problem on the muon track reconstruction efficiency Electrons with energy Electrons with energy 2862 keV coming from coming from the 28 Al decay decay the 2 2 2 2
Development of a Development of a simulation model simulation model 23 23
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