Nuclear interactions of few MeV neutrons in Argon 40
Mary Tsagri
25th March 2009
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My work:
 Identify most important reactions in key materials as:
Ar, Xe, Ne, N2, CO2, CF4, …
 Model the energy deposition of neutrons in gas chambers &
Validate with existing benchmark and test beam data
(using Geant4 & Fluka).
 Simulate secondary particles (gammas, electrons) produced by
neutron interactions (using Garfield).
 Create simulation of neutrons in gas detectors, coupling Geant4
with Garfield signal generation.
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Motivation:
Study the impact of the neutron background in LHC detector environment
• Reconstruct neutron reactions in large volume gaseous detectors
 e.g. LHC gaseous detectors
• Cross section with detector sensitive material quite large
 a first survey for Argon gas
• Monte Carlo simulation of deposited energy:
 spots
 tracks
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Neutron Interactions:
 Elastic Scattering: (n,n)
 Inelastic Scattering: (n,nγ)
 Absorption / Radiative Capture: (n,γ)
 Transmutation: (n,alpha), (n,p) , (n,d), (n,t), (n,3He),
(n,n alpha), (n,n p), …
 Neutron - Producing Reactions: (n,2n), (n,3n), …
 Fission: (n,f)
 Beta Decay: n  p + e- + ve Spallation
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Interactions:
Cross section depends on:
- Kinetic energy Tn
- Nuclear structure
http://www.uio.no/studier/emner/matnat/fys/FYS-KJM4710/v07/undervisningsmateriale/Neutrons_07.pdf
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ENDF/B-VII.0 / JEFF3.1 / JENDL3.3
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1 MeV neutrons in 1m3 argon gas
Elastic Scattering
108 incident neutrons
Physics List: QGSP_BERT_HP
argon: ~1,78 mg/cm3
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1 MeV neutrons in 1m3 argon gas
Radiative Capture
108 incident neutrons
Physics List: QGSP_BERT_HP
argon: ~1,78 mg/cm3
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Neutrons in 1m3 argon gas
Radiative Capture
Incident En 1 MeV
Incident En 2 MeV
108 incident neutrons
Physics List: QGSP_BERT_HP
argon: ~1,78 mg/cm3
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1 MeV neutrons in 1m3 argon gas
All n-interactions
108 incident neutrons
Physics List: QGSP_BERT_HP
argon: ~1,78 mg/cm3
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Photoelectric
Effect
Nuclear Pair
Production
Compton
Scattering
electron Pair
Production
http://physics.nist.gov/cgi-bin/Xcom/xcom3_1
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The Photoelectric Effect: (Low energies below few 100 keV)
Orbital e-
nucleus
K-shell
vacancy
ephotoe-
from K-shell
Kα
X-Ray fluorecence radiation
hvf = BEK -BEL
Incident photon hvi
http://images.google.ch/imgres?imgurl=http://www.thermo.com/eThermo/CMA/Images/Various/151Image_15772.gif&imgrefurl=http://www.thermo.com/com/cda/technology/detail/0,2165,13655,00.ht
ml&usg=__1NVSpT6TVtlCGTpfurDHeFN5lEM=&h=276&w=539&sz=6&hl=de&start=186&um=1&tbnid=pLXCTE36z0HlQM:&tbnh=68&tbnw=132&prev=/images%3Fq%3Dphotoelectric%2Bprocess%26nd
sp%3D21%26hl%3Dde%26sa%3DN%26start%3D168%26um%3D1
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The PairProduction Reaction: (High energies > MeV)
http://en.wikipedia.org/wiki/Pair_production
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The Compton Effect: (Mid-energy phenomena above 10 keV)
http://ida1.physik.uni-siegen.de/praktikum/compt_e.pdf
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Compton Edge:
E is the incident photon energy
E' is the outgoing photon energy, which escapes the detector
me is the e- mass
c is the speed of light
θ is the angle of deflection for the photon
Gamma-spectrum of a radioactive Am-Be-source.
http://en.wikipedia.org/wiki/Compton_edge
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1.45 MeV gammas in 1m3 argon gas
108 incident neutrons
Physics List: Standard EM
argon: ~1.78 mg/cm3
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1.45 MeV gammas in 1m3 germanium
108 incident neutrons
Physics List: Standard EM
Germanium: ~5.3 g/cm3
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