Neutron Gamma Discrimination in AgataAyAyşşe Atae Ataçç

Possibility of discriminating neutrons and gammas by trackingPossibility of discriminating neutrons and gammas by 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 ? ?

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

Method

1) 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

um

ber

of

Nu

mb

er o

f n

eutr

ons

neu

tron

s

First step: 1 MeV neutrons on 74Ge (with and without PHDEF)

596 keV from the center of Agata

Criteria: • small energy deposition produced by neutrons

• direction of the gammas

Neutron Energy (MeV)Neutron Energy (MeV)

Second step: 1 – 5 MeV neutrons on natGe

EEth th = 5 keV= 5 keV

Mn, MMn, Mγ = 1γ = 1

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

Recoil Energyelastic scattering of 1- 5 MeV neutrons on Ge isotopes

JENDLJENDL

Ge recoil energy Ge recoil energy Erec (keV)Erec (keV)

cou

nts

cou

nts

1 MeV

2 MeV

3 MeV

4 MeV

5 MeV

Recoil Energyinelastic scattering of 1- 5 MeV neutrons on natGe

1 MeV

cou

nts

2 MeV

3 MeV

4 MeV

5 MeV

no phdef phdef

Gamma-ray spectra after tracking (mgt)1 MeV neutrons on 74Ge, no phdef

00

596596

12081208

74Ge74Ge

596 596

n = 6n = 6

n = 5n = 5

n = 4n = 4

n = 3n = 3

n = 2n = 2

n = 1n = 1

n = number of interaction points n = number of interaction points

596596

bumpbump

596 keV596 keVn = 1

n = 2

n = 3

n = 4

n = 5

n = 680 keV

1 MeV neutrons on 74Ge, no phdef

Criteria 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)

cou

nts

cou

nts

EfirstEfirst

n = 2 - 6n = 2 - 6

EsecondEsecond

n = 3 - 6n = 3 - 6

Criteria 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

θg - θc

n>1n>1

n = 2n = 2

n = 3n = 3

n = 4n = 4

n = 5n = 5

n = 6n = 6

Reduction in %1 MeV Neutrons on 74Ge, Eth = 5keV, no phdef

596keV

bumpbump

EEγ (keV)γ (keV)

cou

nts

cou

nts

23883557θg – θc or efirst or esec.

15752650θg – θc or efirst

662538efirst

11632341 θg - θc

596 keV gamma

bumppeak

596 keV

total

No conditionsNo conditions

With conditionsWith conditions

596 keV line with and without PHDEF 1 MeV Neutrons on 74Ge, Eth = 5keV

596 keV596 keV

bumpbump

phdefphdef

EEγ (keV)γ (keV)

cou

nts

cou

nts

nophdefnophdef

Reduction in % 1 MeV Neutrons on 74GePHDEF, Eth = 5keV

596keV

EEγ (keV)γ (keV)

cou

nts

cou

nts

123328θg – θc or efirst or esec.

113126θg – θc or efirst

165efirst

113126θg - θc

596 keV gamma

peak + bump

596 keV

total

No conditionsNo conditions

With conditionsWith conditions

Gamma-ray energy spectra after tracking (mgt)Neutrons on 74Ge, phdef

5 MeV

596

Eγ (keV)

cou

nts

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

00 1010 Neutron energy (MeV)Neutron energy (MeV)

Nu

mb

er o

f N

um

ber

of

neu

tron

sn

eutr

ons

596 keV, 74Ge596 keV, 74Ge

608 keV, 74Ge608 keV, 74Ge

834 keV, 72Ge834 keV, 72Ge

EEγ (keV)γ (keV)

cou

nts

cou

nts

1039 keV, 70Ge1039 keV, 70Ge

Gamma-ray energy spectrum after tracking (mgt)Flat distribution on 1 –5 MeV neutrons on natGe, phdef

14692838θg – θc or efirst or esec.

11562534θg – θc or efirst

137-10efirst

10512432θg - θc

1 MeV gamma

bumppeak

834 keV

total

834 keV834 keV

EEγ (keV)γ (keV)

coun

tscou

ntsNo conditionsNo conditions

With conditionsWith conditions

We identified the γ-rays produced by neuton inelastic scattering on Ge isotopes by checking its direction and by the small energy it deposits in the detector.

For En = 1-5 MeV, if the recoil energy is included in a cluster during tracking, we can eliminate 69% of the background with a loss of 14 % in good γ-rays from the target place.

• We may improve the results by doing the selection during the tracking!

• Mn > 1 should be studied.

• An experiment with AGATA detectors by using a 252Cf

source, BaF2 and plastic detectors for TOF of the neutrons.

Conclusion and Future Plans

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