Neutron Gamma Discrimination in Agata Ay ş e Ataç Possibility of discriminating neutrons and gammas by tracking Identify the neutron interaction points in Agata detectors Find a ‘pattern’ for neutron interactions Aim: Reducing the background in the γ – ray spectra Agata as a neuton detector ?

Cross-sections for the n + nat Ge 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 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 Ge 010 Number of neutrons 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) Second step: 1 – 5 MeV neutrons on natGe Eth = 5 keV Mn, Mγ = 1

Number of interaction points in Ge after tracking 596 keV gamma 1 MeV neutron 596 keV gamma n n'n'n'n' Counts Number of interaction points

Recoil Energy elastic scattering of 1- 5 MeV neutrons on Ge isotopes JENDL Ge recoil energy Erec (keV) counts 1 MeV 2 MeV 3 MeV 4 MeV 5 MeV

Recoil Energy inelastic scattering of 1- 5 MeV neutrons on natGe 1 MeV counts 2 MeV 3 MeV 4 MeV 5 MeV no phdefphdef

Gamma-ray spectra after tracking (mgt) 1 MeV neutrons on 74Ge, no phdef Ge 596 n = 6 n = 5 n = 4 n = 3 n = 2 n = 1 n = number of interaction points 596 bump

596 keV n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 80 keV 1 MeV neutrons on 74Ge, no phdef

Criteria 1: Energy of the first and second interaction points Neutrons and gammas on 74Ge 1 MeV neutron 596 keV gamma 1 MeV neutron 596 keV gamma Energy (keV) counts Efirst n = Esecond n = 3 - 6

Criteria 2: θg – θc keV gamma 1 MeV neutron n > 2 θg = θc θg from the position of the interaction points θc from Compton formula

θg - θc n>1 n = 2 n = 3 n = 4 n = 5 n = 6

Reduction in % 1 MeV Neutrons on 74Ge, Eth = 5keV, no phdef 596keV bump Eγ (keV) counts θg – θc or efirst or esec θg – θc or efirst efirst θg - θc 596 keV gamma bumppeak 596 keV total No conditions With conditions

596 keV line with and without PHDEF 1 MeV Neutrons on 74Ge, Eth = 5keV 596 keV bump phdef phdef Eγ (keV) counts nophdef nophdef

Reduction in % 1 MeV Neutrons on 74Ge PHDEF, Eth = 5keV 596keV Eγ (keV) counts θg – θc or efirst or esec θg – θc or efirst 165efirst θg - θc 596 keV gamma peak + bump 596 keV total No conditions With conditions

Gamma-ray energy spectra after tracking (mgt) Neutrons on 74Ge, phdef 5 MeV 596 Eγ (keV) counts 3 MeV 2 MeV 1 MeV Ge

Gamma-ray energy spectrum after tracking (mgt) Flat distribution on 1 –5 MeV neutrons on natGe, phdef 010 Neutron energy (MeV) Number of neutrons 596 keV, 74Ge 608 keV, 74Ge 834 keV, 72Ge Eγ (keV) counts 1039 keV, 70Ge

Gamma-ray energy spectrum after tracking (mgt) Flat distribution on 1 –5 MeV neutrons on natGe, phdef θg – θc or efirst or esec θg – θc or efirst efirst θg - θc 1 MeV gamma bumppeak 834 keV total 834 keV Eγ (keV) counts No conditions With 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, BaF 2 and plastic detectors for TOF of the neutrons. Conclusion and Future Plans

Hittites BC Ceremonial Standard Anakara U: A.Ataç, A. Kaşkaş, S. Akkoyun, M. Şenyiğit, T. Hüyük, O.Kara Uppsala U: J. Nyberg