1. 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 ?

2. 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

3. 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 0 74Ge 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

4. 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

5. 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

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

7. Gamma-ray spectra after tracking (mgt) 1 MeV neutrons on 74Ge, no phdef 0 596 1208 74Ge 596 n = 6 n = 5 n = 4 n = 3 n = 2 n = 1 n = number of interaction points 596 bump

8. 596 keV n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 80 keV 1 MeV neutrons on 74Ge, no phdef

9. 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 = 2 - 6 Esecond n = 3 - 6

10. Criteria 2: θg – θc 15 596 keV gamma 1 MeV neutron n > 2 θg = θc θg from the position of the interaction points θc from Compton formula

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

12. Reduction in % 1 MeV Neutrons on 74Ge, Eth = 5keV, no phdef 596keV bump Eγ (keV) counts 23883557θg – θc or efirst or esec. 15752650θg – θc or efirst 662538efirst 11632341θg - θc 596 keV gamma bumppeak 596 keV total No conditions With conditions

13. 596 keV line with and without PHDEF 1 MeV Neutrons on 74Ge, Eth = 5keV 596 keV bump phdef phdef Eγ (keV) counts nophdef nophdef

14. Reduction in % 1 MeV Neutrons on 74Ge PHDEF, Eth = 5keV 596keV Eγ (keV) counts 123328θg – θc or efirst or esec. 113126θg – θc or efirst 165efirst 113126θg - θc 596 keV gamma peak + bump 596 keV total No conditions With conditions

15. Gamma-ray energy spectra after tracking (mgt) Neutrons on 74Ge, phdef 5 MeV 596 Eγ (keV) counts 3 MeV 2 MeV 1 MeV 596 608 1204 596 0 74Ge 596 608

16. 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

17. 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 keV Eγ (keV) counts No conditions With conditions

18. 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

19. Hittites 1650 - 1200 BC Ceremonial Standard Anakara U: A.Ataç, A. Kaşkaş, S. Akkoyun, M. Şenyiğit, T. Hüyük, O.Kara Uppsala U: J. Nyberg