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