Fast Neutron Background study with Fast Neutron Background study - - PowerPoint PPT Presentation

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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 P.S. Savva1

1,

, T.

• T. Alexopoulos

Alexopoulos1

1, M.

, M. Dris Dris1

1, E.

, E.N.

• N. Gazis

Gazis1

1,

, E.

• E. Katsoufis

Katsoufis1

1, M.

, M. Kokkoris Kokkoris1

1,

, A. Lagoyannis

• A. Lagoyannis2

2, S.

, S. Maltezos Maltezos1

1,

, G.

• G. Tsipolitis

Tsipolitis1

1

1 1Physics Department, National Technical University of Athens,

Physics Department, National Technical University of Athens, Zografou Zografou, GR , GR-

• 15780 Athens, Greece

15780 Athens, Greece

2 2 Nuclear Physics Department, NCSR

Nuclear Physics Department, NCSR “ “Demokritos Demokritos” ”, , Aghia Aghia Paraskevi Paraskevi, , Athens, Greece Athens, Greece 13 April 2006, 13 April 2006, Ioannina Ioannina, HEP2006 , HEP2006-

• EESFYE

EESFYE

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Why to study the Why to study the neutron sensitivity neutron sensitivity

• f a
• f a muon

muon detector? detector?

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• The

The LHC LHC environment produces fluxes of environment produces fluxes of photons photons and and neutrons neutrons in the in the ATLAS ATLAS muon muon spectrometer spectrometer area which are comparable area which are comparable

• The

The neutron neutron ionization charge deposition ionization charge deposition can be hundreds of times can be hundreds of times larger larger than the than the charge deposition of a charge deposition of a muon muon

• The increased charge per unit length of

The increased charge per unit length of the anode could cause the anode could cause aging aging to the detector to the detector electronics electronics

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BIS BIS MDT MDT The expected The expected neutron neutron fluence fluence (kHz/cm (kHz/cm2

2)

) in the in the ATLAS Hall ATLAS Hall (ATLAS (ATLAS muon muon TDR, 1997) TDR, 1997) The energy spectrum The energy spectrum

• f the expected
• f the expected

neutron background neutron background radiation in the Atlas radiation in the Atlas Hall Hall (ATLAS

(ATLAS muon muon TDR, 1997) TDR, 1997)

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• 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 0.518-

• 10.00

10.00 MeV MeV by the by the

7 7Li(p,n)

Li(p,n)7

7Be

Be and a and a d(d,n) d(d,n)3

3He

He reactions at the TANDEM accelerator reactions at the TANDEM accelerator ( (Demokritos Demokritos) )

• A

simulation model using the A simulation model using the GEANT4 toolkit has been developed GEANT4 toolkit has been developed

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The ATLAS Detector The ATLAS Detector

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The ATLAS The ATLAS Muon Muon Spectrometer Spectrometer The ATLAS MDT The ATLAS MDT Detector Detector

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The ATLAS MDT The ATLAS MDT Aluminum walls Aluminum walls Ar:CO Ar:CO2

2 (93:7) Gas mixture

(93:7) Gas mixture W:Re (97:3) Anode Wire ( 3080V) W:Re (97:3) Anode Wire ( 3080V)

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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 Nuclear Reaction Nuclear Reaction Proton/ Proton/Deuteron Deuteron Energy Energy Range Range ( (MeV MeV) ) Neutron Energy Neutron Energy Range Range ( (MeV MeV) )

7 7Li(p,n)

Li(p,n)7

7Be

Be

2 2Η

Η(d,n) (d,n)3

3He

He

3 3Η

Η(d,n) (d,n)4

4He

He 1,92 to 7,9 1,92 to 7,9 0,8 to 0,8 to 8,4 8,4 0,8 to 0,8 to 8,4 8,4 0,12 0,121 1 to 6, to 6,2 242 42 3,9 3,9 to 11,5 to 11,5 16 16,4 ,4 to 2 to 25 5, ,7 7

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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 BF3 Detector, sensitive only to neutrons, was used to monitor the neutron flux

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In order to prevent scattered neutrons from reaching the In order to prevent scattered neutrons from reaching the BF BF3

3 detector, three conditions have been studied :

detector, three conditions have been studied : (a) Neutron beam hitting directly the BF3 detector (b) A paraffin Collimator was placed in frond of the Gas Cell (c) Paraffin Blocks were placed on the floor Condition Condition Direct Direct hitting hitting Paraffin Paraffin Collimator Collimator Paraffin Paraffin Collimator + Collimator + Blocks Blocks BF BF3

3 Counts

Counts 179114 179114 108691 108691 105767 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

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Gas Cell Gas Cell built in built in paraffin paraffin blocks blocks Paraffin Paraffin Collimator Collimator Paraffin Blocks Paraffin Blocks

• n the floor
• n the floor

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The neutron flux versus the angle of emission was The neutron flux versus the angle of emission was also studied also studied

• 40
• 20

20 40 20000 30000 40000 50000 60000 70000

BF3 counts Angle of emission (deg)

Gas cell

BF3 Detector Angle of emission Paraffin collimator

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Prompt photons

Study of two conditions:

• collimator's exit open
• collimator's exit closed

collimator's exit open collimator's exit closed BF3 counts 610537 139821 MDT counts 3557123 3103159 collimator's exit closed Limitation of emitted neutrons to 22,90% Limitation of MDT counts only to 87,2%

Many MDT counts are due to

Prompt Photons

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So finally…. Paraffin collimator MDT completely built in Pb blocks BF3 Detector

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Determination of the Determination of the MDT response MDT response to to 0.518 0.518 -

• 10

10 MeV MeV neutrons neutrons

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Neutrons via the Neutrons via the 7

7Li(p,n)

Li(p,n)7

7Be

Be reaction reaction 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 Ep ≥ 4 MeV ~> Lower energy neutrons from the 9F(p,n)10Ne reaction

E En

n = 0.518 to 4

= 0.518 to 4 MeV MeV ~> ~>

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Neutrons from the Neutrons from the 2

2Η

Η(d,n) (d,n)3

3He

He reaction reaction

• 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 11.5 MeV MeV

• 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 μm 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 preset level preset level Gas Cell

E En

n = 6 to 8

= 6 to 8 MeV MeV ~> ~>

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En = 3,5 MeV

Neutron beam Activation Neutron Beam, Pb Activation, Pb

# of events

200 400 600 800 1000 1200 1400 1600 1800 2000 2000 4000 6000 8000 10000 12000 14000

ADC channel

2004006008001000 1200 1400 1600 1800 2000

100 1000 10000

# of events ADC channel

E En

n =

= 6 MeV 6 MeV

E En

n =

= 8 MeV 8 MeV E En

n =

= 10 MeV 10 MeV

dN / dE

25 50 75 100 125 150 175 200 225 250

10000 20000 30000 40000 50000 60000 70000 80000 90000 100000

Energy (keV)

0 25 50 75100 125 150 175 200 225 250

1000 10000 100000

Energy (keV)

dN / dE

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200 400 600 800 1000 1200 1400 1600 1800 1500 2000 2500 3000 3500 4000 4500 5000 5500

Time (s)

Ι = Ι0 + Ι1e(-x/τ

1 ) + Ι2e(-x/τ 2 )

Ι0 = 1525 ± 13 Ι1 = 1655 ± 74 τ1 = 567 ± 0 Ι2 = 2534 ± 61 τ2 = 136 ± 6

# events

Counting rate drop when the 7 MeV neutron beam stops

27Al (n,p) 27Mg, τ = 567,48 s 27Al (n,γ) 28Al, τ = 134,48 s

Curve fit:

27 27Mg

Mg ~> decay through ~> decay through β β –

–

emission emission Ε Εmax

max =

= 1765 1765 keV keV

28 28Al

Al ~> decay through ~> decay through β β –

–

emission emission Ε Εmax

max =

= 2862 2862 keV keV Detection of the β- particle by more than one drift tubes Possible problem on the muon track reconstruction efficiency

2 2 2 2 Electrons with energy Electrons with energy 1765 1765 keV keV, coming from , coming from the the 27

27Mg decay

Mg decay Electrons with energy Electrons with energy 2862 keV coming from coming from the the 28Al decay decay

Problem on the muon track reconstruction efficiency

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Development of a Development of a simulation model simulation model

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• Use of the

Use of the GEANT4 GEANT4 simulation toolkit simulation toolkit

• Good description of the geometry

Good description of the geometry

• Good description of neutron physics

Good description of neutron physics

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The geometry used for the simulation model and the The geometry used for the simulation model and the neutron beam hitting the neutron beam hitting the MDTs MDTs

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2 4 6 8 10 0,02 0,03 0,04 0,05 0,06 0,07

ε

Energy (MeV) Experiment Simulation

The experimental and the simulated results for the The experimental and the simulated results for the MDT response to 0.518 MDT response to 0.518 – – 10 10 MeV MeV neutrons neutrons

Good agreement between the experiment and the simulation

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The ratio of the simulated over the experimental MDT The ratio of the simulated over the experimental MDT response to response to 0.5 0.5 -

• 10

10 MeV MeV neutrons neutrons

2 4 6 8 10 0,4 0,6 0,8 1,0 1,2 1,4

Energy (MeV)

εsim/εex

p

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To summarize To summarize… …

• We determined the response of an array of

We determined the response of an array of ATLAS ATLAS-

• MDTs

MDTs exposed to neutron beams of exposed to neutron beams of energies 0.518 to 10 energies 0.518 to 10 MeV MeV. .

• We developed a simulation model of the

We developed a simulation model of the experiment, using the Geant4 toolkit. experiment, using the Geant4 toolkit.

• We found a very good agreement between

We found a very good agreement between the experimental and the simulating data. the experimental and the simulating data.

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To conclude To conclude… …

High energy neutrons ~> Creation of high background radiation consisting of: Photons coming from (n,γ) and (n,n’) reactions Possible damage to the MDT electronics Electrons coming from the 28Al and 27Mg decays Time correlated signals in more than one drift tubes ~> consequences to the muon track reconstruction efficiency Use of heavy materials for shielding ~> further photonic background creation due to (n,γ) and (n,n’) reactions