Post on 25-Feb-2016
description
Neutron Gamma Discrimination in Agata
Possibility of discriminating neutrons and gammas Possibility of discriminating neutrons and gammas by trackingby tracking
Identify the neutron interaction points in Agata detectorsIdentify the neutron interaction points in Agata detectors
Find a ‘pattern’ for neutron interactionsFind a ‘pattern’ for neutron interactions
AimAim: Reducing the background in the : Reducing the background in the γ – ray spectraγ – ray spectra
Agata as a neuton detectorAgata as a neuton detector ? ?
NIM A, in print
A.Ataç, A. Kaşkaş, S. Akkoyun, M. Şenyiğit, A.Ataç, A. Kaşkaş, S. Akkoyun, M. Şenyiğit,
T. Hüyük, O.Kara T. Hüyük, O.Kara and and J. NybergJ. Nyberg
Cross-sections for the n + natGe reaction ● elastic scattering natGe (n,n) ● inelastic scattering natGe (n,n´γ)
J. Ljungvall, J. Nyberg, NIM A550 (2005)379
J. Ljungvall, J. Nyberg, NIM A546 (2005)553
Inelastic scatteringInelastic scattering
Method1) Simulations Geant4 with AGATA geometry J. Allison et al. NIM A506(2003)250. E. Farnea, D. Bazzacco LNL Anual Report 2003, p.158.
J. Ljungvall, J. Nyberg, NIM A546 (2005)553. Geant4 correction, pulse-height defect (PHDEF)2) Tracking MGT code, D. Bazzacco
----------------------------------------------------1208
596
074Ge
00 1010N
umbe
r of
N
umbe
r of
ne
utro
nsne
utro
ns
First step: 1 MeV neutrons on 74Ge (with and without PHDEF)
596 keV from the center of Agata
Methods: • small energy deposition produced by neutrons
• direction of the gammas
• Figure of Merit (FM) values
Neutron Energy (MeV)Neutron Energy (MeV)
Second step: 1 – 5 MeV neutrons on natGe
MnMn = 6 = 6, M, Mγ = 1γ = 100
EEth th = 5 keV= 5 keV, trigger threshold = 50 keV, trigger threshold = 50 keV
Recoil Energyinelastic scattering of 1- 5 MeV neutrons on natGe
1 MeV
coun
ts
2 MeV
3 MeV
4 MeV
5 MeV
no phdef phdef
596 keV596 keVn = 1
n = 2
n = 3
n = 4
n = 5
n = 665 keV
1 MeV neutrons on 74Ge, no phdef
Tracking –mgt
• clustering
• FM values
Method 1: Energy of the first and second interaction pointsNeutrons and gammas on 74Ge
1 MeV neutron1 MeV neutron
596 keV gamma596 keV gamma
1 MeV neutron1 MeV neutron
596 keV gamma596 keV gamma
Energy (keV)Energy (keV)
coun
tsco
unts
EfirstEfirst
n = 2 - 6n = 2 - 6
EsecondEsecond
n = 3 - 6n = 3 - 6
Method 2: θg – θc
1515
596 keV gamma596 keV gamma
1 MeV 1 MeV neutronneutron
n > 2n > 2
n > 2n > 2
θg = θc
θg from the position of the interaction points
θc from Compton formula
Method 3: Figure of Merit (FM)
Reduction in %1 MeV Neutrons on 74Ge, Eth = 5keV, no phdef
totalpeak at
596 keV
bump596 keV gamma
efirst 40 6 63 6θg - θc 46 26 65 11FM 44 28 55 5efirst or
FM 58 32 77 11
efirst or θg – θc or FM or esec.
69 47 92 22
II
GatesII
Gates I
596 keV line with and without PHDEF 1 MeV Neutrons on 74Ge, Eth = 5keV
596 keV596 keV
bumpbump
phdefphdef
EEγ (keV)γ (keV)
coun
tsco
unts
nophdefnophdef
Gamma-ray energy spectra after tracking (mgt)Neutrons on 74Ge, phdef
5 MeV596
Eγ (keV)
coun
ts
3 MeV
2 MeV
1 MeV
596
596
596
608
608
608
1204
596
074Ge
596596
608608
Gamma-ray energy spectrum after tracking (mgt)Flat distribution on 1 –5 MeV neutrons on natGe, phdef
834 keV834 keV
EEγ (keV)γ (keV)
countscountsNo No gatesgates
With With gatesgates
totalpeak at
596 keV
bump596 keV gamma
efirst 11 1 38 6θg - θc 36 25 51 11FM 36 23 45 4efirst or
FM 40 23 58 5
efirst or θg – θc or FM or esec.
51 39 76 14
Gates I
Gates II
The neutron rejection methods were tested on a case where 6 neutrons with energies between 1 to 5 MeV were emitted in coincidence with a cascade of 10 rays.
RPTB = PTB / PTB(after neutron rejection)
Gates I
Gates II
Rε = ε / ε (after neutron rejection)
At Eγ = 1MeV, PTB is ratio is increased by a factor of 2.4
and the ε is reduced by a factor of 1.25 for gates II.
We identified the γ-rays produced by neuton inelastic scattering on Ge isotopes by checking its direction, FM value and by the small energy it deposits in the detector.
The neutron rejection methods were also tested on a case where 6 neutrons with energies between 1 to 5 MeV were emitted in coincidence with a cascade of 10 rays. As a result, at a gamma-ray energy of 1 MeV, the suggested gate set increases the PTB value by a factor of 2.4, whereas the photopeak efficiency is reduced by a factor of 1.25.
• En > 5 MeV is being studied. For Giant Resonance studies• An experiment with AGATA detectors by using a 252Cf source and
BaF2 detector for TOF selection of neutrons. Menekşe’s talk
Conclusion and Future Plans
Number of interaction points in Ge after tracking
596 keV gamma596 keV gamma
1 MeV neutron1 MeV neutron
596 keV gamma
nn
nn''
596 keV gamma
Cou
nts
Number of interaction points
Gamma-ray energy spectrum after tracking (mgt)Flat distribution on 1 –5 MeV neutrons on natGe, phdef
00 1010 Neutron energy (MeV)Neutron energy (MeV)
Num
ber
of
Num
ber
of
neut
rons
neut
rons
596 keV, 74Ge596 keV, 74Ge
608 keV, 74Ge608 keV, 74Ge
834 keV, 72Ge834 keV, 72Ge
EEγ (keV)γ (keV)
coun
tsco
unts
1039 keV, 70Ge1039 keV, 70Ge
Hittites 1650 - 1200 BCCeremonial StandardCeremonial Standard
AAnakara nakara U: A.Ataç, A. Kaşkaş, S. U: A.Ataç, A. Kaşkaş, S. Akkoyun, M. Şenyiğit, T. Hüyük, Akkoyun, M. Şenyiğit, T. Hüyük,
O.Kara O.Kara
UUppsala ppsala U: J. Nyberg U: J. Nyberg