The ( n , a ) Reaction in the s-Process B ranching Point 59 Ni

1. The (n,a) Reaction in the s-Process Branching Point 59Ni Analysis Group Meeting 28. November 2012 Christina Weiss

2. The (n,a) Reaction in the s-Process Branching Point 59Ni Introduction • The Diamond Mosaic-Detector • 59Ni Sample • Setup at n_TOF • Simulation • Preliminary Results • Conclusions

3. The (n,a) Reaction in the s-Process Branching Point 59Ni The Diamond Mosaic-Detector1) • 8 sCVD + 1 DOI diamond diodes: • Thickness: 150 mm • Electrodes: 200 nm Al (in addition: 500 um sCVD diamond diode and Si diode for background measurements) Materials: • Diodes: C, Si, B, P • Electrodes: Al, Au, Pt, C • Glued and bonded to PCB structure: Materials: • PCB: epoxy resin, Cu, Au, Ni • Bonding: Staystick thermoplastic (?), Al • Sample fixed on the PCB structure: => 1.85 mm maximum distance between sample and detector 1) Sponsored by CIVIDEC Instrumentation GmbH

4. The (n,a) Reaction in the s-Process Branching Point 59Ni 59Ni Sample • Radioactive Isotope 59Ni: • Decay via e—capture and b+, with t1/2 = 76.000 y • Decay radiation: X-rays (Emax = 7.7 keV), Auger e- (Emax= 6keV), b+ (Emax= 25 keV) • 2 samples from ORNL (used in the 70ies) were available, d = 1.5 cm: Sample specifications1): • (180 ± 5) mg metallic Ni: 95% 59Ni => 516 kBq • thickness = 102 nm • (205 ± 5)mg LiF: 95% 6Li • thickness = 394 nm • electro-plated on 25 mm Pt foil Compromise: • Focus on 59Ni(n,a) reaction for • Neutron fluenceand cross-section measurement in parallel 1) Notebook of Yuri Gledenov, copy from P. Koehler

5. The (n,a) Reaction in the s-Process Branching Point 59Ni Setup at n_TOF • Dedicated electronics1): • 180 ns shaping amplifiers • 8 mV/fC • SNR: 14/fC • Measurement under vacuum: • pmin = 5*10-6 mbar • 59Ni run 15.10. – 9.11.2012: • Sample out • Ptbacking • 59Ni + 6Li sample • Beam off • Calibration with 4-a source Protons in total: 1.57 * 1018 Spectroscopic amplifiers Neutrons Vacuum Chamber 1) Sponsored by CIVIDEC Instrumentation GmbH

6. The (n,a) Reaction in the s-Process Branching Point 59Ni Simulation – Expected Spectra • FLUKA Simulation with sample specifications • Primary particles (see Table) emitted isotropically in 2p

7. The (n,a) Reaction in the s-Process Branching Point 59Ni Amplitude over Neutron Energy • Included in Analysis: • En < 50 keV • TOF pulses • Dedicated threshold per diode • Online calibration Ni a Li t Li a

8. The (n,a) Reaction in the s-Process Branching Point 59Ni • Neutron Energy Spectrum without Amplitude cuts - Background • Different materials can be seen in the background spectra => Resonances can be used to calibrate TOF-Energy conversion • Pt resonances clearly visible in Dummy and Ni runs • Au resonance clearly visible in all spectra • Pt backing seems to enhance detection efficiency of in-beam g-rays

9. The (n,a) Reaction in the s-Process Branching Point 59Ni Amplitude Spectra - Resolution Neutron Fluence Measurement Cross section measurement

10. The (n,a) Reaction in the s-Process Branching Point 59Ni Neutron Fluence • Measured via 6Li(n,a)t reaction => Anisotropy at higher energies => Low neutron energy region (up to 100 eV) for fluence measurement • Fluence in total = 46% of n_TOF Flux1) (DOI not in evaluation) • Check of the alignment: Diamond mosaic detector as seen from the neutrons, values given as % of total n_TOF flux: 1) nTOFFluence2010Borated_Evaluation100bpd_5August2011_27keVlimit.root

11. The (n,a) Reaction in the s-Process Branching Point 59Ni • Reaction Yield for 59Ni • Resonance at 203 eV is clearly visible in the experimental data • Background-subtraction not clean yet • 46% of n_TOF neutron fluence in yield calculation P R E L I M I N A R Y

12. The (n,a) Reaction in the s-Process Branching Point 59Ni • Gain Drift of the Diodes • Sudden positive gain shift in DIAM2 during run 15480 • Small negative gain shift in 5 out of 8 diodes at the end of the Ni measurement (=> HV Inversion) • Online-check for the gain drift via triton peak

13. The (n,a) Reaction in the s-Process Branching Point 59Ni Amplitude Spectra - Resolution High amplitude background?!

14. The (n,a) Reaction in the s-Process Branching Point 59Ni Amplitude over Neutron Energy High amplitude background?! Ni a Li t Li a

15. The (n,a) Reaction in the s-Process Branching Point 59Ni • Conclusionsresp. To Do Conclusions: • Stable, high-resolution spectroscopic cross-section measurement with focus on 59Ni(n,a) cross-section (choice of sample) • Detector is suited for “high Q-value” (n,a) cross-section measurements To Do: • Analyze data with refined ‘dst to ROOT’ – routine & DOI data • Calibrate TOF-Energy conversion • Implement a maximum amplitude threshold for the Ni-a • Revise error propagation • Improve background subtraction • Clarify origin of high-amplitude background in low neutron-energy region • Make corrections for tails of distributions • Compare with existing data • Resonance analysis

16. Acknowledgements J. Andrzejewski, E. Berthoumieux, C. Chery, E. Chiaveri, G. Ehrlich-Joop, D. Grenier, E. Griesmayer, C. Guerrero, B. Hallgren,F. Käppeler, P. Koehler, I. McGill, A. Mongelluzzo, H. Pernegger, J. Perkowski, M. Pomorski, P. Riedler, L. Tassan-Got, A. Tsinganis The n_TOF Collaboration, CIVIDEC Instrumentation GmbH