NPD and NDT Experiments Christopher Crawford University of Kentucky 2008-07-01 NPD run at LANSCE...

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