d,p γ as surrogate for neutron capture in inverse kinematics

1. William A. Peters d,pγas surrogate for neutron capture in inverse kinematics ANL

2. d B* C Surrogate method ANL Compound nucleus b A D a “Surrogate” reaction “Desired” reaction c different decay modes

3. Surrogate candidates • Fission vs. neutron capture • Recent capture/fission ratio work shows promise. • J. M. Allmond et al., Phys. Rev. C 79, 054610 (2009). • Short-lived isotopes • Important for stewardship and basic science. • Astro-physical reactions • Nuclear reactors and device modeling • Stockpile and waste storage ANL

4. Hauser-FeshbacH Weisskopf-ewing Limit Compound nucleus decay becomes independent of spin and parity. No sum over J,π! sacWE(E) = saCN(E) .Gc(E) ANL First factor can be calculated. Second factor is difficult.

5. Ratio method • Requires W-E limit of H-F. • Measure one reaction relative to another. • Reduces systematic uncertainties. • No need to measure singles rate. Assumes Np1/Np2 cancel ANL

6. Yb 171/173 setup • Targets: two isotopically enriched metallic foils of 171Yb (0.981 mg/cm2) and 173Yb (0.502 mg/cm2)‏ • 3 Si detectors for particle detection (STARS)‏: dE: 500 m, 48 rings, 16 sectors E1: 1000 m, 24 rings, 8 sectors E2: 1000 m, 16 rings, 16 sectors angular range covered: 44° to 73° • 6 Ge clover detectors to detect coincident -rays (LiBerACE)‏ 18.5 MeV deuteron beam from cyclotron ANL

7. Yb results ANL

8. Yb lessons learned • Not in W-E limit • Resolution not as good as n,γ • Try to selectively match neutron capture spin distribution • Singles rate might not cancel • Ratio seems consistent above 100 keV ANL

9. d,pγin Inverse kinematics • Needed for short lived isotopes (<100 days). • A reliable method and analysis could start an exciting new campaign of capture measurements. ANL

10. Beam direction View of (d,pγ) components Target manipulator High-rate diamond detector 8 Silicon (ORRUBA) detectors Cubic chamber 4 Germanium clovers -J. Cizewski ANL

11. ORRUBA + Gammasphere – chamber concept 214mm 28° 145mm Feed-throughs 175mm BGO -S. Pain

12. Current setup ANL Original design by Charles Reed, first used by Micah Johnson

13. 75Asd,pγ • 73As/74As = 1/2 σ74(n,2n)Фn (D.Vieira) • Isotope ratios measured after event • (n,2n) reactions most important • (n,γ) reactions can effect results ANL

14. Experimental details • Deuterated plastic target 400 μg/cm2 • 75As at 530 MeV • Tandem voltage near 24 MV • Beam rate was 10^7 pps • 1 week of beam time • Trigger on ORRUBA (proton) singles ANL

15. Decay from excited 76As Doppler corrected 6 keV FWHM ANL Partial level scheme (from ENDSF) of 76As used to identify successful (d,pγ) events. Quoted branching are from (n,γ) experiments. 511 165 Spectrum not Doppler corrected Gamma Spectrum (keV)

16. kinematics CD2 target Carbon target ANL

17. 76As Excitation Sn=7.33 MeV ANL

18. 75As lessons learned • Fusion on carbon dominates background • Resolution poor • Still need to gate on γ-rays • Will Gc(E) match n,γ? ANL

19. Open issues • Can n,γ CN be mimicked by surrogates? • Can d,pγ work in inverse kin? • Will another reaction work for rare isotopes? • Must we give up on ratio method if W-E not met? • Can we calculate spin mismatch of d,pγ-n,γ? • How to deal with deformed nuclei? Way Forward • Use n-rich beams. • Tag on d,p recoils. • Timing • Recoil separator • Pure target • Increase resolution and acceptance. ANL

20. d,pγ at atlas with gammasphere • Improved signal to noise for gammas. • Improved resolution with more space for ORRUBA. • Beam energy range better for d,pg. • More n-rich beams available. • Might work with less beam. ANL

21. My gratitude • Rutgers University. • J. Cizewski, R. Hatarik, P. O’Malley • University of Tennessee • K. L. Jones, K. Schmitt, R. Kapler, B. Moazen, A. Chae, S. Pittman • Louisiana State University • J.C. Blackmon • Tennessee Technological University • R.L. Kozub • LANL • D. Vieira, M Jandel, J.B. Wilhelmy • ORAU • C. Matei • LLNL • A. Becker, C. Y. Wu, J. Escher, F. Dietrich • ORNL • D.W. Bardayan, S.D. Pain, M.S. Smith, D. Stracener ANL

22. As campaign goals • Measure 75As d,pγfor benchmark. • Develop 73,74As beams at HRIBF. • Use benchmark for ratio measurements to radioactive As isotopes. Measured (n,γ) cross section (from NNDC) to compare to surrogate (d,pγ). ANL

23. γ-proton coincidences PRELIMINARY 511 keV 165 keV ANL Gamma energy (keV) Proton energy (a.u.)

24. Jp distributions considered d b c a calculating spin/parity PRELIMINARY -J. Escher ANL

25. C-Fusion evaporation EvapOR calculations show high energy protons come out at back angles from C-fusion. –J. Cizewski ANL

26. Confirmation Diamond beam-rate detector was tested for activation. Beta-gamma analysis confirmed 82Sr, 85Sr, and 83Rb. ANL

27. “Engagement ring” • Multi-crystal • 350 um thick • Gold plated • 1.0” diameter • 0.1 ns timing • 10^8 pps limit ANL

28. DRS • Preceded by large-bore quad • No need to tune past first set of slits • Install Silicon stack for id (need rate less than 10 kHz). • Will have more trouble with unreacted beam than C-fusion ANL

29. Ratio Method Known neutron capture cross sections for 171Yb and 173Yb from K. Wisshak et al., Phys Rev C 61, (2000) 065801. Using 4-2 transition ANL

30. J 6+ 4+ 2+ 0+ Account for mismatch • Intensity ratios of the 4+ 2+ and 6+ 4+ different for 171Yb (1/2-) and 173Yb (5/2-) • Calculated by DICEBOX • R. Hatarik • Subtract 6+ feeding of 4+ to get spin distribution closer to (n,) ANL