1 / 43

Steven W. Yates

Research at UKAL: Lessons Learned and New Adventures www.pa.uky.edu/accelerator/. Steven W. Yates. E**. E**. . Excited Nucleus. . E*. E*. gs. gs. gs. Inelastic Neutron Scattering. inelastically scattered neutron. Incident Neutron. Target Nucleus. Cooled Nucleus.

chaka
Télécharger la présentation

Steven W. Yates

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Research at UKAL: Lessons Learned and New Adventures www.pa.uky.edu/accelerator/ Steven W. Yates

  2. E** E**  Excited Nucleus  E* E* gs gs gs Inelastic Neutron Scattering inelastically scattered neutron Incident Neutron Target Nucleus Cooled Nucleus (n,n') reaction

  3. 2H or 3H gas n  Neutron Production 3H(p,n)3He Q = -1 MeV2H(d,n)3He Q = 3 MeV Neutron Energies (Accelerator Voltage: 1.5 – 7.0 MV) 3H(p,n) 0.5 < En < 6 MeV2H(d,n) 4.5 < En < 10 MeV Target Pulsed p or d beam from VdG accelerator

  4. Beam  γ (n,n') singles

  5. (n,n')Singles Measurements scattering sample Beam gas cell BGO HPGe

  6. (n,n')Singles Measurements scattering sample Beam Gas Handling System gas cell

  7. 94Zr (n,n) Compton suppressed TOF Gating

  8. 94Zr(n,n) Angular Distribution W() = 1 + a2 P2(cos ) + a4P4(cos ) Comparison with statistical model calculations (CINDY) → multipole mixing ratio ()and spins

  9. v  Detector Doppler-Shift Attenuation Method  E() = E (1 + v/c cos ) The nucleus is recoiling into a viscous medium. v  v(t) = F(t)vmax E() = E (1 + F() v/c cos )

  10. Level Lifetimes: Doppler-Shift Attenuation Method (DSAM) • Scattered neutron causes the nucleus to recoil. • Emitted γrays experience a Doppler shift. • Level lifetimes in the femtosecond region can be determined. τ = 7.6(9) fs τ = 76(7) fs T. Belgya, G. Molnár, and S.W. Yates, Nucl. Phys. A607, 43 (1996). E.E. Peters et al., Phys. Rev. C 88, 024317 (2013). 180° 0° γ γ

  11. Calculated curve Completely Doppler- shifted Not Doppler- shifted F()exp  DSAM τ = 76(7) fs K.B. Winterbon, Nucl. Phys. A246, 293 (1975). T. Belgya, G. Molnár, and S. W. Yates, Nucl. Phys. A607, 43 (1996).

  12. Scattering Sample HPGe HPGe HPGe HPGe Lithium Carbonate Loaded Paraffin Paraffin-Filled Shielding Gas Cell Beam  Kentucky Gamma-ray Spectrometer KEGS

  13. KEGS Beam gas cell

  14. “Monoenergetic” Neutron Production  Scattering Sample 3H(p,n)3He n Gas cell with Mo foil window Diagnostic MCNPX calculations of neutron production in gas cell

  15. Inelastic Neutron Scattering with Accelerator-Produced Neutrons  No Coulomb barrier/variable neutron energies  Excellent energy resolution ( rays detected)  Nonselective, but limited by angular momentum • Lifetimes by Doppler-shift attenuation method (DSAM) • T. Belgya, G. Molnár, and S.W. Yates, Nucl. Phys. A607, 43 (1996) • E.E. Peters et al., Phys. Rev. C 88, 024317 (2013).  Gamma-gamma coincidence measurements • C.A. McGrath et al., Nucl. Instrum. Meth. A421, 458 (1999) • E. Elhami et al., Phys. Rev. C 78, 064303 (2008)  Limited to stable nuclei  Large amounts of enriched isotopes required

  16. Current and Future ResearchDirections at UKAL • Fast neutron physics • Nuclear shell structure and shape transitions • Nuclear level lifetime determinations with the Doppler-shift attenuation method • Nuclear structure relevant to double-β decay • Precision fast neutron reaction cross sections • Corporate and homeland security applications • Neutron detector development (with collaborators) • www.pa.uky.edu/accelerator/

  17. Current and Future ResearchDirections at UKAL • Fast neutron physics • Nuclear shell structure and shape transitions • Nuclear level lifetime determinations with the Doppler-shift attenuation method • Nuclear structure relevant to double-β decay • Precision fast neutron reaction cross sections • Corporate and homeland security applications • Neutron detector development (with collaborators) • www.pa.uky.edu/accelerator/

  18. 2νββ0νββ? 136Pr Is the neutrino its own antiparticle? What is the mass of the neutrino? BE 136Te 136I b- EC 136La 136Ce b- 136Cs 136Ba 136Xe EC b- 52 53 54 55 56 57 58 59 Z

  19. EXO-200: 200 kg of Xe (l) • 80.6% enriched in 136Xe • (remaining 19.4% is 134Xe) • Q-value: 2457.83 ± 0.37 keV Counts 1000 2000 E(keV) Pictures from R. Neilson TIPP 2011 and http://www-project.slac.stanford.edu/exo/ M. Auger et al., PRL 109, 032505 (2012)

  20. EXO Resolution 228Th 2615 keV FWHM ≈ 100 keV M. Auger et al., PRL 109, 032505 (2012)

  21. Neutron Backgrounds from Radioactive Decay Fig. 1. Neutron energy spectrum from U and Th traces in rock as calculated with modified SOURCES. Contributions from 60 ppb U (filled squares and lower curve), 300 ppb Th (open circles and middle curve) and the sum of the two (filled circles and upper curve) are shown. M.J. Carson et al., Astroparticle Phys. 21, 667 (2004).

  22. Neutron Backgrounds from Cosmic-ray Muons Fig. 7. Energy spectra of muon-induced neutrons at various boundaries: (a) filled circles––neutrons at the salt/cavern boundary, open circles––neutrons after the lead shielding; (b) filled circles––neutrons at the salt/cavern boundary (the same as in (a)), open circles––neutrons after the lead and hydrocarbon shielding. M.J. Carson et al., Astroparticle Phys. 21, 667 (2004).

  23. UKAL Experiments • Inelastic neutron scattering • Monoenergetic neutrons via 3H(p,n)3He • Allows determination of : • Level scheme • Transition multipolarities • Multipole mixing ratios • Level lifetimes • Transition probabilities • Solid XeF2 samples of 130Xe, 132Xe, 134Xe, 136Xe • Highly enriched, solid targets not used previously XeF2 in Teflon vial

  24. New Level: 2485 keV 2485 0.20 0.48 0.32 1614 847 134Xe

  25. New Level: 2485 keV 871 1638 2485

  26. 2485-keV Transition bg Q-value: 2458 keV σ Measurement

  27. Other New Levels 2502 2440 1655 1593 847 847

  28. Current and Future ResearchDirections at UKAL • Fast neutron physics • Nuclear shell structure and shape transitions • Nuclear level lifetime determinations with the Doppler-shift attenuation method • Nuclear structure relevant to double-β decay • Precision fast neutron reaction cross sections • Corporate and homeland security applications • Neutron detector development (with collaborators) • www.pa.uky.edu/accelerator/

  29. Applied Science with Monoenergetic Pulsed Neutrons from the University of Kentucky Accelerator Laboratory S. F. Hicks University of Dallas, Irving, TX J. R. Vanhoy US Naval Academy, Annapolis, MD M. T. McEllistrem and S. W. Yates University of Kentucky, Lexington, KY

  30. Part of the Advanced Fuel Cycle Initiative (AFCI) to develop safe, clean, and affordable energy sources Goals of Gen IV: Safer Sustainable Economical Physically Secure http://www.gen-4.org/Technology/evolution.htm • Critical need for high-precision and accurate elastic and inelastic neutron scattering data on materials important for fission reactor technology • Critical need for trained individuals (NEUP initiative)

  31. One of the Six Generation IV Nuclear Energy Systems Inelastic Neutron Scattering Fe* <http://nuclearpowertraining.tpub.com/h1019v1/css/h1019v1_69.htm.> Energy Loss Mechanism “A Technology Roadmap for Generation IV Nuclear Energy Systems,” Generation IV International Forum, December 2002. Neutron elastic and inelastic scattering cross sections are needed from structural materials such as Fe and coolants such as Na.

  32. Forward monitor Long counter Beam line Neutron detector > 2-meter deep scattering pit Copper shielding Gas cell (n,n') TOF

  33. 3H(p,n) Q= -0.76 MeV 2H(d,n) Q= 3.3 MeV 3H(d,n) Q= 17.6 MeV Tungsten wedge Neutron detector Beam line Gas cell Na sample Typical adjustment of wedge with cell and sample

  34. Neutron Detection: Main • Flight paths to about 4 m can be used for neutron scattering. Angles between 30 and 145 degrees are accessible with the Na and Fe samples. • Neutrons are detected by a deuterated benzene liquid scintillation detector (1x5.5). • Pulse Shape Discrimination Understanding background generation in TOF spectra

  35. Inelastic Cross Sections --Two Techniques (n,n') (n,n'γ) Inelastic cross sections to a given final state can be measured directly via (n,n’) or derived from g-ray excitation functions. Angular distributions of (n,n’) provide the best information on the reaction mechanism. Gamma-ray measurements provide the best information on the partition of reaction strength. 23Na

  36. EXPERIMENTAL DATA EVALUATIONS

  37. Current and Future ResearchDirections at UKAL • Fast neutron physics • Nuclear shell structure and shape transitions • Nuclear level lifetime determinations with the Doppler-shift attenuation method • Nuclear structure relevant to double-β decay • Precision fast neutron reaction cross sections • Corporate and homeland security applications • Neutron detector development (with collaborators) • www.pa.uky.edu/accelerator/

  38. SCINTILLATOR Development • Multi-radiation detectors • CLYC: Cs2LiYCl6 • CNYC: Cs2NaYCl6 • CLLC: Cs2LiLaCl6 • CLLB: Cs2LiLaBr6 http://www.rmdinc.com/ Measured detector response for En = 0.5 - 22 MeV ~7 scintillators in 36 hours. Glodo-IEEETransNuclSci.60.864.2012

  39. Detector Design & Characterization DEuteratedSCintillator Array for Neutron Tagging @ TRIUMF • Neutron Detectors • Efficiency(En) • Pulse Shape Discrimination • Amplitude Distribution n n D g e scintillator fluid C6D6 Different recoiling ions excite the atomic/molecular structure differently, and exhibit different characteristic decay times. http://atguelph.uoguelph.ca/2011/11/guelph-physicist-leads-project-at-triumf-lab/ http://www.physics.uoguelph.ca/Nucweb/tigress.html

  40. https://www.facebook.com/photo.php?fbid=645033412191460&set=pb.114964088531731.-2207520000.1373380138.&type=3&theaterhttps://www.facebook.com/photo.php?fbid=645033412191460&set=pb.114964088531731.-2207520000.1373380138.&type=3&theater TIGRESS g-ray detector array http://atguelph.uoguelph.ca/2011/11/guelph-physicist-leads-project-at-triumf-lab/ DESCANT neutron detector array http://www.physics.uoguelph.ca/Nucweb/tigress.html

  41. Our Colleagues University of Dallas U.S. Naval Academy University of Guelph University of Wisconsin at Lacrosse Georgia Institute of Technology University of Notre Dame Radiation Monitoring Devices University of Cologne HIgSat TUNL Yale University Technical University Darmstadt University of the West of Scotland University of the Western Cape (South Africa) iThemba Labs TRIUMF ANU

More Related