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
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C.-P. Liu, LA-UR-07-0737, Mar 2007
p-p and nuclei
Existing measurements
Anapole
Nuclear anapole moment(from laser spectroscopy)
Light nuclei gamma transitions(circular polarized gammas)
Polarized proton scattering asymmetries
p-p and nuclei
Existing measurements
Spin rot/A Anapole
Circular components
Medium withcircular birefringence
Linear Polarization
?
Spin rotation
Neutron spin rotation
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 University2Universidad Nacional Autonoma de Mexico
3University of Virginia 4Oak Ridge National Laboratory
5Thomas Jefferson National Laboratory6National Institute of Standards and Technology
7Univeristy of Michigan, Ann Arbor8University of Kentucky
9University of New Hampshire10Los Alamos National Laboratory
11Indiana University12University of Tennessee
13University of California at Berkeley14University of Manitoba, Canada
15High Energy Accelerator Research Organization (KEK), Japan16Hamilton College
17Paul Scherrer Institute, Switzerland 18Spallation Neutron Source
19University of California at Davis20TRIUMF, Canada
21Bhabha Atomic Research Center, India22Duke University
23Joint Institute of Nuclear Research, Dubna, Russia24University of Dayton
Overview of NPD experiment
Overview of NPDG experiment
Pulsed neutron beam
~6x108 cold neutrons per 20 Hz pulse at the end of
the 20 m supermirror guide(largest pulsed neutron flux)
LANSCE Flight Path 12 Beam LineLANSCE Flight Path 12 Beam LineThe peak moderator brightness at 3.3 meV is 1.25 x 10The peak moderator brightness at 3.3 meV is 1.25 x 1088 n/s/sr/cm n/s/sr/cm22/meV/mA./meV/mA.
The pulsed neutron source allows us to The pulsed neutron source allows us to know the neutron time of flightknow the neutron time of flight..
The installed beam chopper allows us to select a range of neutron energies.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 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 and determines the ability to effectively polarize, spin-flip and capture the
neutrons as well as take beam-off data when it is closed.neutrons as well as take beam-off data when it is closed.
Seo P.N., et al., Nucl. Instr. and Meth. Accepted 2003
Beam stability
3He neutron polarizer• n + 3He 3H + p cross section is highly spin-dependent
J=0 = 5333 b /0
J=1 ¼ 0
• 10 G holding field determines the polarization anglerG < 1 mG/cm to avoid Stern-Gerlach steering
Steps to polarize neutrons:
1. Optically pump Rb vaporwith circular polarized laser
2. Polarize 3He atoms viaspin-exchange collisions
3. Polarize 3He nuclei viathe hyperfine interaction
4. Polarize neutrons by spin-dependent transmission
nn + nnpp
ppnnpp
nn +pp
P3 = 57 %
Neutron Beam Monitors • 3He ion chambers• measure transmission
through 3He polarizer
Neutron Polarization
RF Spin Rotator
– 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
holding field
sn
BRF
16L liquid para-hydrogen target
15 m
eV
ortho
para
capture
En (meV)
(b
)
• 30 cm long 1 interaction length• 99.97% para 1% depolarization• pressurized to reduce bubbles• SAFETY !!
pp pp
para-H2
pp pp
ortho-H2
E = 15 meV
Ortho-Para Conversion Cycle
O/P Equilibrium Fraction
Neutron Intensity on Target
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
Asymmetry Analysisyield (det,spin)
P.C. asym
background asym
geometry factor
P.V. asym
RFSF eff. neutron pol. target depol.
raw, beam, inst asym
• 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)
Systematics, e.g:
A
stat. err.
systematics
(proposal)
Statistical and Systematic Errors
Systematic Uncertainties
slide courtesy Mike Snow
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
Detector position scans
5 mm resolution ~ 1 deg
target
detector
UP-DOWN LEFT-RIGHT
Engineering Runs
Cl
calibration asymmetry
A= (-21.01.6)x10-6
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
Preliminary Hydrogen Results:Preliminary Hydrogen Results:
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Preliminary Hydrogen Results:Preliminary Hydrogen Results:
( ) ( ) 7,
7, 100.29.1101.21.1 −− ×±−=×±−= LRUD AA γγ
Total statistical error:Total statistical error:
Total systematic error: a (very) conservative 10% mostly Total systematic error: a (very) conservative 10% mostly due to pol.due to pol.
Preliminary Hydrogen Results:Preliminary Hydrogen Results:
Spallation Neutron Source (SNS)Oak Ridge National Laboratory, Tennessee
Spallation Neutron Source (SNS)
• spallation sources: LANL, SNS– pulsed -> TOF -> energy
• LH2 moderator: cold neutrons– thermal equilibrium in ~30 interactions
0
500
1000
1500
2000
2500
3000
3500
4000
2006-2 2007-1 2007-2 2008-1 2008-2 2009-1 2009-2 2010-1 2010-2 2011-1
Date
MW*Hours/half-year
Planned Power Ramp-up of SNS Operations
LANSCE:- 100 A- 800 MeV- 3000h/half-year=> 80 MWh/half-year
Better experiment
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.
• Thinner aluminum 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.
The NPDGamma Experiment at FnPB
Supermirror polarizer
FNPB guide
CsI Detector Array
Liquid H2 Target
H2 Vent Line
Beam Stop
Magnetic Field Coils
H2 Manifold Enclosure
Spin Flipper
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
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
Neutron beam chopper design: opening angles
Beam Polarization
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
Design of supermirror polarizer• McStas optimization of polarizer for NPDGamma
as a function of (bender length, bend radius, #channels)• 96% polarization, 30% transmission ) 2.6£1010 n/s• 4x improvement in P2N
Background in -detector indicates that detector requires more in beam related -shielding
Beam
Ring 1 Ring 2Ring 3
Ring 4
40%
22%
17% 20%
• Gain in the figure of merit at the SNS:Gain in the figure of merit at the SNS:– 12.0 x brighter at the end of the SNS 12.0 x brighter at the end of the SNS
guideguide– 4.1 x gain by new SM polarizer4.1 x gain by new SM polarizer– 6.5 x longer running time 6.5 x longer running time – + Higher duty factor at SNS+ Higher duty factor at SNS
A ~ 1×10A ~ 1×10-8-8 in 10 in 1077 s at the SNS s at the SNS
• Installation: currently underwayInstallation: currently underway• Commissioning: early Commissioning: early 20092009
Sensitivity of NPDGamma to ASensitivity of NPDGamma to A at SNS at SNS
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
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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
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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
Neutron Depolarization in D2O
• 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
B-field
3He cell 3He cell
Comptonpolarimeter
Comptonpolarimeter
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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
Existing Measurements