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NPD  and NDT  Experiments

NPD  and NDT  Experiments. Christopher Crawford University of Kentucky 2008-07-01. NPD  run at LANSCE preparations for SNS run feasibility test of NDT . Madison. Spencer. HWI experimental program. C.-P. Liu , LA-UR-07-0737, Mar 2007. Existing measurements.

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NPD  and NDT  Experiments

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  1. NPD and NDT Experiments Christopher Crawford University of Kentucky 2008-07-01 • NPD run at LANSCE • preparations for SNS run • feasibility test of NDT Madison Spencer

  2. HWI experimental program C.-P. Liu, LA-UR-07-0737, Mar 2007

  3. Existing measurements Polarized proton scattering asymmetries Light nuclei gamma transitions (circular polarized gammas) p-p and nuclei Nuclear anapole moment (from laser spectroscopy) Anapole

  4. Existing measurements Medium with circular birefringence Spin rotation Linear Polarization ? Circular components p-p and nuclei Anapole Neutron spin rotation Spin rot/Ag

  5. The NPDGamma Collaboration Alracon1, S. Balascuta1, L. Barron-Palos2, S. Baeßler3, J.D. Bowman4, R.D. Carlini5, W.C. Chen6, T.E. Chupp7, C. Crawford8, M. Dabaghyan9, A. Danagoulian10, M. Dawkins11, N. Fomin12, S.J. Freedman13, T.R. Gentile6, M.T. Gericke14 R.C. Gillis11, G.F. Greene4,12, F. W. Hersman9, T. Ino15, G.L. Jones16, B. Lauss17, W. Lee18, M. Leuschner11, W. Losowski11, R. Mahurin12, Y. Masuda15, J. Mei11, G.S. Mitchell19, S. Muto15, H. Nann11, S. Page14, S.I. Penttila4, D. Ramsay14,20, A. Salas Bacci10, S. Santra21, P.-N. Seo22, E. Sharapov23, M. Sharma7, T. Smith24, W.M. Snow11, W.S. Wilburn10 V. Yuan10 1Arizona State University 2Universidad Nacional Autonoma de Mexico 3University of Virginia 4Oak Ridge National Laboratory 5Thomas Jefferson National Laboratory 6National Institute of Standards and Technology 7Univeristy of Michigan, Ann Arbor 8University of Kentucky 9University of New Hampshire 10Los Alamos National Laboratory 11Indiana University 12University of Tennessee 13University of California at Berkeley 14University of Manitoba, Canada 15High Energy Accelerator Research Organization (KEK), Japan 16Hamilton College 17Paul Scherrer Institute, Switzerland 18Spallation Neutron Source 19University of California at Davis 20TRIUMF, Canada 21Bhabha Atomic Research Center, India 22Duke University 23Joint Institute of Nuclear Research, Dubna, Russia 24University of Dayton

  6. Overview of NPD experiment

  7. Overview of NPDG experiment

  8. Pulsed neutron beam ~6x108 cold neutrons per 20 Hz pulse at the end of the 20 m supermirror guide (largest pulsed neutron flux)

  9. The peak moderator brightness at 3.3 meV is 1.25 x 108 n/s/sr/cm2/meV/mA. The pulsed neutron source allows us to know the neutron time of flight. The installed beam chopper allows us to select a range of neutron energies. The ability to select only part of the neutron spectrum is an important tool and determines the ability to effectively polarize, spin-flip and capture the neutrons as well as take beam-off data when it is closed. LANSCE Flight Path 12 Beam Line Seo P.N., et al., Nucl. Instr. and Meth. Accepted 2003

  10. Beam stability

  11. 3He neutron polarizer p + n + n n n p p p • n + 3He  3H + p cross section is highly spin-dependentJ=0 = 5333 b /0J=1¼ 0 • 10 G holding field determines the polarization angle rG < 1 mG/cm to avoid Stern-Gerlach steering P3 = 57 % Steps to polarize neutrons: Optically pump Rb vaporwith circular polarized laser Polarize 3He atoms viaspin-exchange collisions Polarize 3He nuclei viathe hyperfine interaction Polarize neutrons by spin-dependent transmission

  12. Neutron Beam Monitors • 3He ion chambers • measure transmissionthrough 3He polarizer

  13. Neutron Polarization

  14. RF Spin Rotator holding field sn BRF • essential to reduce instrumental systematics • spin sequence:   cancels drift to 2nd order • danger: must isolate fields from detector • false asymmetries: additive & multiplicave • works by the same principle as NMR • RF field resonant with Larmor frequency rotates spin • time dependent amplitude tuned to all energies • compact, no static field gradients

  15. 16L liquid para-hydrogen target p p para-H2 • 30 cm long  1 interaction length • 99.97% para  1% depolarization • pressurized to reduce bubbles • SAFETY !! E = 15 meV p p ortho-H2 ortho 15 meV para  (b) capture En (meV)

  16. Ortho-Para Conversion Cycle

  17. O/P Equilibrium Fraction

  18. Neutron Intensity on Target

  19. CsI(Tl) Detector Array • 4 rings of 12 detectors each • 15 x 15 x 15 cm3 each • VPD’s insensitive to B field • detection efficiency: 95% • current-mode operation • 5 x 107 gammas/pulse • counting statistics limited • optimized for asymmetry

  20. Asymmetry Analysis yield (det,spin) P.C. asym background asym P.V. asym geometry factor raw, beam, inst asym RFSF eff. neutron pol. target depol.

  21. Systematic Uncertainties Statistical and Systematic Errors Systematics, e.g: • activation of materials, • e.g. cryostat windows • Stern-Gerlach steering • in magnetic field gradients • L-R asymmetries leaking into • U-D angular distribution • (np elastic, Mott-Schwinger...) • scattering of circularly polarized • gammas from magnetized iron • (cave walls, floor...) •  estimated and expected to be • negligible (expt. design) A stat. err. (proposal) systematics slide courtesy Mike Snow

  22. Left-Right Asymmetries • Parity conserving: • Three processes lead to LR-asymmetry • P.C. asymmetry • Csoto, Gibson, and Payne, PRC 56, 631 (1997) • elastic scattering • beam steered by analyzing power of LH2 • eg. 12C used in p,n polarimetry at higher energies • P-wave contribution vanishes as k3 at low energy • Mott-Schwinger scattering • interaction of neutron spin with Coulomb field of nucleus • electromagnetic spin-orbit interaction • analyzing power: 10-7 at 45 deg 0.23 x 10-8 2 x 10-8 ~ 10-8 at 2 MeV

  23. Detector position scans detector target UP-DOWN LEFT-RIGHT 5 mm resolution ~ 1 deg

  24. Engineering Runs calibration asymmetry Cl A=(-21.01.6)x10-6

  25. Production run of NPD at LANSCE 2006 NPD ran in 2006 at LANSCE for about 3 months collecting 4-5 Tb of data . The apparatus was well commissioned, except for the LH2 target which was approved just before the cycle. The target accommodated over 700 h of good -asymmetry data. mean proton current 89 A or 3.4£107/pulse over 4£106 pulses at 20 Hz

  26. Preliminary Hydrogen Results:

  27. Preliminary Hydrogen Results: Total statistical error: Total systematic error: a (very) conservative 10% mostly due to pol.

  28. Preliminary Hydrogen Results:

  29. Spallation Neutron Source (SNS) Oak Ridge National Laboratory, Tennessee

  30. Spallation Neutron Source (SNS) • spallation sources: LANL, SNS • pulsed -> TOF -> energy • LH2 moderator: cold neutrons • thermal equilibrium in ~30 interactions

  31. Planned Power Ramp-up of SNS Operations LANSCE: - 100 A - 800 MeV - 3000h/half-year => 80 MWh/half-year

  32. NPD at the FnPB – major changes • Curved beamline – less  background • New polarizer - supermirror bender • figure of merit 3-4 times of FOM of the 3He spin filter. • Improved target illumination - beam spot on target up to 8” in diameter. • Thinneraluminum windows in the cryostat • Reduction in material thickness in beam by a factor of 2 • Reduced backgrounds - improved absorption of scattered neutrons. • Experiment better modeled with MCNP. • Modified LH2 target will not affect target performance or safety. • 60 Hz pulses – DAQ and spin flipper. (20 Hz at LANSCE) • New spin flipper to accommodate larger beam diameter. • New beam monitors - only one between polarizer and target. • Better guide field - more homogeneous. Better experiment

  33. The NPDGamma Experiment at FnPB Supermirror polarizer CsI Detector Array Liquid H2 Target H2 Vent Line H2 Manifold Enclosure Spin Flipper FNPB guide Magnetic Field Coils Beam Stop

  34. Magnetic and radiological shielding • integrated shielding: • 9”-18” concrete walls • 0.25”–0.75” 1010 steel • open design for LH2 safety,access to experiment • external field B < 50 mG • shield npd from B-field of other experiments • flux return for uniform magnetic field:Stern-Gerlach steering

  35. Magnetic Field • B-field gradients must be < 10 mG/cm • prevent Stern-Gerlach steering of neutrons • prevent depolarization of 3He in spin filter • B-field modeled in OPERA3D (S. Balascuta) • Flux return / shieldingon ceiling,floor,sides • extra coil neededto compensatehigher ceilingflux return

  36. Neutron beam chopper design: opening angles

  37. Beam Polarization

  38. New supermirror polarizer • two methods of neutron polarization • spin-dependent n-3He absorption cross section • magnetized SM coating selectively absorbs 1 spin state • supermirror polarizer • spin-dependent reflection from magnetized supermirror coating • high polarization possible • requirements:at least 1 reflectionpreserve phase space

  39. Design of supermirror polarizer • McStas optimization of polarizer for NPDGammaas a function of (bender length, bend radius, #channels) • 96% polarization, 30% transmission ) 2.6£1010 n/s • 4x improvement in P2N

  40. Background in -detector indicates that detector requires more in beam related -shielding Ring 1 Ring 2 Ring 3 Beam Ring 4 22% 40% 17% 20%

  41. Sensitivity of NPDGamma to A at SNS • Gain in the figure of merit at the SNS: • 12.0 x brighter at the end of the SNS guide • 4.1 x gain by new SM polarizer • 6.5 x longer running time • + Higher duty factor at SNS • A ~ 1×10-8 in 107 s at the SNS • Installation: currently underway • Commissioning: early 2009

  42. NDT vs NPD • capture cross section • H = .3326 b, D = .000519 b • neutron polarization • para-hydrogen: no depolarization • D2O: spin-flip scattering • expected asymmetry • 20 times larger than NPDGamma • previous measurement (ILL) • goal: measure A = 4£10-7 at the SNS

  43. NDT Target Design • need extremely low background • conflicting D2 safety requirement: thick vacuum chamber • must shield gammas from all windows • D2O ice needs cooled from outside shielding • target thickness optimization: 13 cm

  44. NDT Detectors • will use the NPD detectors • possibly run in counting mode to discriminate background • 200 kHz * 107 s * 48 detectors = 1014 events or A Pn = 10-7 ~1 s decay time in CsI crystals • will test counting rates and energy resolution at LANSCE July 2008

  45. Neutron Depolarization in D2O B-field Compton polarimeter 3He cell 3He cell Compton polarimeter • Compton Polarimetry test run at LANSCE, July 2008 • DePauw U., Indiana U., U. Kentucky, U.N.A. Mexico, Michigan U., Hamilton C., NIST, ORNL, LANL

  46. Summary • NPD successful run at LANSCE • will achieve A=1£10-8 at the SNS • theory in good shape: will determine f or t • NDT a possible follow-up experiment at the SNS • test run at LANCE to demonstrate feasibility • need modern calculation of sensitivity to couplings • both experiments are applicable to ChPT low-energy limit

  47. Existing Measurements

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