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Precision Measurements of the (n,2n  ) Reaction Cross Sections on Actinides

Precision Measurements of the (n,2n  ) Reaction Cross Sections on Actinides. Goal: Improve partial cross section data of actinide nuclei for the Stockpile Stewardship Program Emphasis : The 239 Pu(n,2n  ) cross section

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Precision Measurements of the (n,2n  ) Reaction Cross Sections on Actinides

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  1. Precision Measurements of the (n,2n) Reaction Cross Sections on Actinides Goal: Improve partial cross section data of actinide nuclei for the Stockpile Stewardship Program Emphasis :The 239Pu(n,2n) cross section Technique: High-resolution -ray spectroscopy measurements: • in beam with pulsed and monoenergetic neutron beam • off-line with DC neutron beam Modeling: Hauser-Feshbach theory (GNASH, EMPIRE) TUNL and Duke Univ.

  2. TUNL and In-beam Measurements Deuterium gas cell Id =2mA beam pick-off 7.8 atm DENIS Shielded Neutron Source Area Neutron production • D(d,n) neutron source • n = 3x104 n /(cm2 sec) • Tunable from 4 – 18 MeV • Pulsed at 2.5 MHz TUNL and Duke Univ.

  3. TUNL and In-beam Measurements DENIS Shielded Neutron Source Area TUNL and Duke Univ.

  4. Neutron Collimator and Beam Profile Shielded Neutron Source Area Neutron profile scan d=215 cm d=427 cm d n Scanning conditions step: 0.3 cm in  and direction 75 cm TUNL and Duke Univ.

  5. NNSA Setup at TUNL • 4 Clovers + BGO • 2 Planars + BGO • 10 keV < E < 10 MeV • 200 < lab < 1600 • array = 1.4%@E = 1.33 MeV n-beam Capabilities • - coincidence measurements • Angular distribution measurements • Lifetimes (by Doppler method) • Excellent tool for precision neutron induced cross section measurements in the fast energy region (4  En 18 MeV) TUNL and Duke Univ.

  6. Neutron Induced Cross Section on 235U En = 10 MeV, Beam time = 87 h 234U TUNL and Duke Univ.

  7. First Results from 238U(n,n)238Uat TUNL Egamma Transition TUNL OakRidge1) LANL2) (keV) (mb) (mb) (mb) 635.2 1- --> 2+ 83 (4) 76(7) 67(2) 687.0 3- --> 2+ 86 (4) 80(7) 106(2) 885.5 (1-) --> 2+ 63 (4) 56(7) 79(2) 905.5 2- --> 2+ 34 (3) 33(5) 40(2) 957.3 3+ --> 4+ 50 (3) 45(5) 65(2) 1060.3 2+  0+ 95 (4) Partial Cross Sections at En = 6 MeV 93(11) 116(3) D.K. Olsen, et al., ORNL report TM-6832 1979. N. Fotiades et al., PRC 69 (2004) 024601. A. Hutcheson et al. NIMB (2007) in press. TUNL and Duke Univ.

  8. Motivation for the 241Am(n,2n) Reaction Cross Section Measurements Improved 241Am(n,2n) cross sections are needed for: • Nuclear forensics ΔA(240Am/241Am) • Analogous to P (238Pu/239Pu) • Sensitive to high-energy neutrons • Advance Fuel Cycle / new fast reactors • Important in transmutation studies Goal: 5-10% measurement from threshold (6.7 MeV) to 14.5 MeV TUNL and Duke Univ.

  9. 241Am(n,2n)240Am Measurements • (n,2n) data for 241Am around 14 MeV • Energy dependence near 14 MeV • No data below ~13 MeV • Different evaluation TUNL and Duke Univ.

  10. 241Am(n,2n)240Am Measurements • (n,2n) data for 241Am around 14 MeV • Energy dependence near 14 MeV • No data below ~13 MeV • Different evaluations • The recent data shows very high (n,2n) CS at En11MeV Phys. Rev. C 73, 067601 (2006) Need to extend the 241Am(n,2n)240Am cross section to lower energies TUNL and Duke Univ.

  11. Activation Measurements at TUNL DENIS Neutron TOF area Preparation room Activation parameters Irradiation setup • n = 1x108 n /(cm2 sec) • ~ 1mg 241Am targets • 3 monitor foils (Al, Ni, Au) • n-flux monitoring: 3 neutron detectors (00,  100) TUNL and Duke Univ.

  12. Activation Measurements at TUNL DENIS Neutron TOF area High Res. Gamma Spec. • 60% HPGe detectors • Genie 2000 spec. system Low-background counting system Highly enriched 241Am TUNL and Duke Univ.

  13. TUNL and Activation Measurements DENIS Neutron TOF area Low-background counting system Irradiation setup TUNL and Duke Univ.

  14. 240Am 99.6(11)% 987.8 keV 888.8 3+; 1030.6, T1/2 = 1.32 ns 25.1(4)% 73.2(10)% 4+; 141.8 2+; 42.9 0+; 0.0 keV 240Pu 241Am(n,2n)240Am Measurements • Activation technique:  count 240Am activity after irradiation of 241Am trick: attenuate the low-energy g-rays (59.5 keV) coming from 241Am target using 3 mm Pb • Irradiated target with mono-energetic neutrons produced by D(d,n) reaction TUNL En= 7.6 - 14.5 MeV / fn ~ 107–108 n/cm2-s • ~1 mg/cm2241Am target / 1 cm dia. sandwich targets on Pt backing • Measure neutron fluence using a set of witness foils mounted before & after target 197Au(n,2n)196Au (t1/2 = 6.2 d), T= 8.1 MeV 27Al(n,)24Na (t1/2 = 15 hr), T= 3.2 MeV 58Ni(n,p)58Co (t1/2 = 71 d), T= 0 MeV 58Ni(n,2n)57Ni (t1/2 = 36 hr), T= 12.4 MeV TUNL and Duke Univ.

  15. High-Resolution Gamma Ray Spectra Plastic ring Foil 8 Foil 9 Plastic ring 4 4 4 4 0.5 mil Pt 0.5 mil Pt 513 mg/cm2 241Am 519 mg/cm2 241Am • Fabrication of 241Am target(LANL and LLNL) • 3 stippled targets (Evelyn Bond/LANL) • 6 electroplated targets after additional chemical purification (Mark Stoyer/LLNL) • ~ 2% statistical uncertainties • Improved -spectra from the electroplated targets  Need for nuclear radiochemists TUNL and Duke Univ.

  16. First Results on 241Am(n,2n)240Am Reaction Cross Section TUNL and Duke Univ.

  17. First Results on 241Am(n,2n)240Am Reaction Cross Section TUNL and Duke Univ.

  18. First Results on 241Am(n,2n)240Am Reaction Cross Section A. Tonchev et al. PRC in preparation. TUNL and Duke Univ.

  19. Summary • Morethan 160 new parities measured in nuclei: 40Ar, 88Sr, 92Zr, 96Mo,112,124Sn, 138Ba, 140Ce, 172,174,176Yb, 164,162Dy, 207Pb. • Complete cross section measurements of the 241Am(n,2n)240Am reaction. • Preliminary data from TUNL support the recent statistical prediction from LANL (2005 Kawano) • Intense, pulsed, monoenergetic TUNL neutron source provides powerful capabilities for Science-Based Stockpile Stewardship and Nuclear Science.  Strong TUNL-LANL-LLNL Collaboration Effort TUNL and Duke Univ.

  20. Participants* Livermore J.A. Becker D. Dashdorj* J. Kenneally R.A. Macri D. Shaughnessy M.A Stoyer Ch.Y. Wu TUNLke: Duke: A.S. Crowell B. Fallin C.R. Howell A. Hutchison A.P. Tonchev W. Tornow Univ. of N. Carolina: H.J. Karwowski C.T. Angell N. Carolina State: J.H. Kelley D. Dashdorj* NC A&T: R. S. Pedroni Los Alamos E. Bond J. FitzPatrick R.S. Rundberg A. Slemmons D.J. Vieira J.B. Wilhelmy *(n,2n) measurements supported by the NNSA Stewardship Science Academic Alliance and by DOE/NNSA LANL & LLNL TUNL and Duke Univ.

  21. Participants TUNL and Duke Univ.

  22. Extra Viewgraphs TUNL and Duke Univ.

  23. 240Am Gamma-ray Signature - 889 keV line is partially contaminated by a weak 241Am line, but the 988 keV line is clean - Measured 2000-3000 g-events after a 1-2 day irradiation and 1day count time - Measured 11 energies in March, Nov., Dec. 2006 runs TUNL and Duke Univ.

  24. Completed Experiments Time Reaction Energies [MeV] May 2003 238U(n,2n )237U 6, 10 Aug 2004 238U(n,2n )237U 8, 10, 14 Feb 2005 90Zr(n,n' )90Zr 6 Feb 2005 89Yb(n,n' )89Yb 6 Feb 2005 112Sn(n,n' )112Sn 6.5, 7.5, 8.0 Feb 2005 124Sn(n,n' )124Sn 6.5, 7.5, 8.0 May 2005 235U(n,n' )235U 5 Jun 2005 235U(n,2n' )234U 12 Jun 2005 natHf(n,xn' ) 12 Jun 2005 16O(n,n' )16O 7 Jun 2005 12C(n,n' )12C 7 Dec 2005 235U(n,2n' )234U 12 Time Reaction En [MeV] Time Reaction Energies [MeV] Jan 2006 235U(n,2n' )234U 10, 8 Jan 2006 181Ta(n,2n' )180Ta 14.5 Feb 2006 140Ce(n,2n' )139Ce 14.5 Mar 2006 94Zr(n,n' ) 5.0 Mar 2006 241Am(n,2n) 8-14 Jun 2006 natCu, natPb(n,n‘ ) 8,12 Oct 2006 235,238U(n, 2n ) 10 Nov 2006 241Am(n,2n) 8-16 Dec 2006 241Am(n,2n) 8-16 Dec 2006 235U(n, 2ng) 12 Jan 2007 235U(n,2ng) 8 Feb 2007 235U(n,2ng) 10 Time Reaction En [MeV] • Total amount of used beam time: 120 days • Collaborators from 2 National Labs and 3 Universities • www.tunl.duke.edu/groups/nnsa TUNL and Duke Univ.

  25. Neutron Monitors n-monitors / BCI n-flux fluctuation Tact = 12.5 h TUNL and Duke Univ.

  26. NRF Spectra on 138Ba En = 8.5 MeV 8434 keV 1- 1- 8074 2+ 2+ E2 0+ 138Ba E = 8.50.08 MeV Primary transitions to the 2+ states 2+ 2639 2218 1436 Branching ratio (1- 2+)  3% ! TUNL and Duke Univ.

  27. Decay Scheme of Am Isotopes TUNL and Duke Univ.

  28. Absolute Flux Measurements at HIS Compton Scattered Setup Compton Scattered Spectra TUNL and Duke Univ.

  29. NNSA Synergistic Activities at TUNL NNSA (n,xn) activity: low-energy introduction to nuclear experimental techniques for the Research Experience for Undergraduates (REU) program at TUNL • Average 8-10 REU students every summer • For the past three years one or two has been involved in the TUNL NNSA project • Diversification of the NNSA setup for basic research: • nuclear structure • nuclear astrophysics • neutrino and dark matter • Synergistic activities at TUNL TUNL and Duke Univ.

  30. Beam Correlated Measurements TUNL pulsed n-beam U Start Stop G n-beam G-BG ~2ns ON / 400ns Off TUNL and Duke Univ.

  31. Laser Compton Backscattering E2 UNDULATOR E1 TUNL and Duke Univ.

  32. Laser Compton Backscattering E2 E1 UNDULATOR P TUNL and Duke Univ. CAARI 2004

  33. Laser Compton Backscattering E1 UNDULATOR P E2 TUNL and Duke Univ. CAARI 2004

  34. Laser Compton Backscattering E1 E2 UNDULATOR γ P TUNL and Duke Univ. CAARI 2004

  35. Laser Compton Backscattering E2 E1 UNDULATOR P TUNL and Duke Univ. CAARI 2004

  36. TUNL and Duke Univ.

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