Neutron Gamma Discrimination in Agata 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 ? NIM A, in print A.Ataç, A. Kaşkaş, S. Akkoyun, M. Şenyiğit, T. Hüyük, O.Kara and J. Nyberg

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 Methods: small energy deposition produced by neutrons direction of the gammas Figure of Merit (FM) values Neutron Energy (MeV) Second step: 1 – 5 MeV neutrons on natGe Mn = 6, Mγ = 10 Eth = 5 keV, trigger threshold = 50 keV

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

596 keV n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 65 keV 1 MeV neutrons on 74Ge, no phdef Tracking –mgt clustering FM values

Method 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

Method 2: θg – θc keV gamma 1 MeV neutron n > 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 total peak at 596 keV bump 596 keV gamma efirst θg - θc FM efirst or FM efirst or θg – θc or FM or esec II GatesII Gates I

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

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 834 keV Eγ (keV) counts No gates With gates total peak at 596 keV bump 596 keV gamma efirst θg - θc FM efirst or FM efirst or θg – θc or FM or esec 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.

R PTB = PTB / PTB(after neutron rejection) Gates I Gates II R ε = 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 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 gamma 1 MeV neutron 596 keV gamma n n'n'n'n' Counts Number of interaction points

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

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