1. Neutron Phase Contrast Radiography Copyright, 1996 © Dale Carnegie & Associates, Inc.

2. Outline Who are we?Who are we? What is a Neutron?What is a Neutron? Where do we get neutrons?Where do we get neutrons? When do we get neutrons?When do we get neutrons? Why do we want neutrons?Why do we want neutrons? What are they good for?What are they good for? What is phase imaging?What is phase imaging? Why do we want to image with phase?Why do we want to image with phase? What is it good for?What is it good for?

3. Investigators and Support Brendan AllmanUniversity of Melbourne, AustraliaBrendan AllmanUniversity of Melbourne, Australia Phillip McMahonUniversity of Melbourne, AustraliaPhillip McMahonUniversity of Melbourne, Australia Keith NugentUniversity of Melbourne, AustraliaKeith NugentUniversity of Melbourne, Australia Muhammad ArifNIST Ionizing Radiation DivisionMuhammad ArifNIST Ionizing Radiation Division David L. JacobsonNIST Ionizing Radiation DivisionDavid L. JacobsonNIST Ionizing Radiation Division Samuel A. WernerUniversity of Missouri-Columbia/ NIST Ionizing Radiation DivisionSamuel A. WernerUniversity of Missouri-Columbia/ NIST Ionizing Radiation Division Work supported byWork supported by –United States Department of Commerce National Institute of Standards and TechnologyNational Institute of Standards and Technology –Ionizing Radiation Division –Center for Neutron Research –Australian Research Council –National Science Foundation Grant No. PHY-9603559

4. d u d The Neutron Weakly attenuated by many elements in the periodic table Strongly scattered by 1 H but not 2 H Strongly absorbed by several isotopes: 113 Cd, 6 Li, 3 He, 157 Gd Has refractive wave properties Magnetic moment of the neutron allows it to be used in studying magnetic properties of matter d u d  e n  p  e  d u u e  e Electrically neutral yet is composed of 3 charged quarks Neutron half life = 10 min. 14 sec

5. NIST Center for Neutron Research Located at the National Institute of Standards and Technology in Gaithersburg, MarylandLocated at the National Institute of Standards and Technology in Gaithersburg, Maryland The reactor achieved first criticality in 1967, began routine operation at 10 MW in 1969, and was increased in power to 20 MW in 1985.The reactor achieved first criticality in 1967, began routine operation at 10 MW in 1969, and was increased in power to 20 MW in 1985. Thermal neutron sourceThermal neutron source Cold neutron sourceCold neutron source More information at www.ncnr.nist.govMore information at www.ncnr.nist.gov Thermal Neutron Reactor Cold Neutron Guide Hall Cherry Trees

6. Thermal Neutron Source It is fueled with uranium, contained in 30 MTR type elements of unique split-core design with a 18 cm unfueled gap at the center plane.It is fueled with uranium, contained in 30 MTR type elements of unique split-core design with a 18 cm unfueled gap at the center plane. The reactor is cooled, moderated and reflected by D2O, producing a peak thermal flux at the reactor centerline of 4 x 10 14 neutrons/cm2/s at the rated power level of 20 megawatts.The reactor is cooled, moderated and reflected by D2O, producing a peak thermal flux at the reactor centerline of 4 x 10 14 neutrons/cm2/s at the rated power level of 20 megawatts. The reactor is operated on a seven week cycle, with approximately 38 continuous days at full power (20 MW) operation followed by 11 days for refueling and maintenance.The reactor is operated on a seven week cycle, with approximately 38 continuous days at full power (20 MW) operation followed by 11 days for refueling and maintenance. 100020003000400050000 Neutron Velocity (m/s) 5205080130 Neutron Energy (meV) 0

7. Cold Neutron Source Liquid hydrogen cold sorceLiquid hydrogen cold sorce Neutron Maxwell-Boltzman distribution now peaks at ~ 0.43 nm orNeutron Maxwell-Boltzman distribution now peaks at ~ 0.43 nm or Neutron guides coated with Ni-58 provide integrated fluence rates as much as 2x10 9 neutrons/cm 2 sNeutron guides coated with Ni-58 provide integrated fluence rates as much as 2x10 9 neutrons/cm 2 s 100020003000400050000 Neutron Velocity (m/s) 5205080130 Neutron Energy (meV) 0

8. Traditional Radiography (forget about waves) Contrast is due to attenuation of radiationContrast is due to attenuation of radiation Scattering density of material can be extractedScattering density of material can be extracted N - density of sample atoms per cm 3N - density of sample atoms per cm 3 I 0 - incident neutrons per second per cm 2I 0 - incident neutrons per second per cm 2  - neutron cross section in ~ 10 -24 cm 2  - neutron cross section in ~ 10 -24 cm 2 t - sample thicknesst - sample thickness Sample t

9. B Be Li D20D20 H2OH2O Cross-Section Densities

10. Computer Collimating guide Neutron beam Lens to magnify or minify image to fit on CCD chip Light tight box Thermal electric cooler Axis of rotation Mirror CCD chip Rotary table Neutron to light converter Setup for Traditional Radiography/Tomography Neutron beam (shown in red) is incident on object.Neutron beam (shown in red) is incident on object. Converter screen (shown in green) 6 Li embeded in ZnS(Cu) absorbs neutrons and produces a charge particle, which induces the ZnS to scintillate.Converter screen (shown in green) 6 Li embeded in ZnS(Cu) absorbs neutrons and produces a charge particle, which induces the ZnS to scintillate. Lens focuses the scintillation light on a CCD chip.Lens focuses the scintillation light on a CCD chip. CCD chip views the beam from a 45° mirror. This prevents radiation from destroying the CCD.CCD chip views the beam from a 45° mirror. This prevents radiation from destroying the CCD. Image collected by CCD is downloaded to a computer for further processingImage collected by CCD is downloaded to a computer for further processing

11. All Slice Reconstructions 3D Reconstruction Tomography Radiographs Slice Reconstruction

12. Applications Determination of hydrogen distribution in materials.Determination of hydrogen distribution in materials. Study of structural defects in materials.Study of structural defects in materials. Coking determination in gas turbine engine nozzles.Coking determination in gas turbine engine nozzles. Investigation of hydrogen distribution in polymer electrolyte fuel cells.Investigation of hydrogen distribution in polymer electrolyte fuel cells. Study of lithium ion conductor motion in lithium batteries.Study of lithium ion conductor motion in lithium batteries. Visualization of porosity of oil containing shale.Visualization of porosity of oil containing shale. Determination of time dependent migration of hydrocarbons in rocks.Determination of time dependent migration of hydrocarbons in rocks. Study of hydrocarbons under pressure.Study of hydrocarbons under pressure. Nondestructive evaluation of archeological specimens.Nondestructive evaluation of archeological specimens. Visualization of liquid metal flow.Visualization of liquid metal flow. Examination of solar cell arrays.Examination of solar cell arrays. Contraband detection and identification in sealed containers.Contraband detection and identification in sealed containers. Visualization the motion of water in plants.Visualization the motion of water in plants.

13. Recent Interest in Phase Contrast Within the last ten years CCD image detection technology has made it feasible to easily image the scattered radiation from various objects. Inexpensive high speed computers have given way to sophisticated processing of images. Image resolution with x-rays can be as much as 50 nm Neutron image resolution 100  m, but may be improved to as low as 10  m.

14. The neutron as a wave Neutrons are massive particles with a wavelength given by the DeBroglie relation:Neutrons are massive particles with a wavelength given by the DeBroglie relation: Typical wavelengths for thermal neutrons are 0.1 nm to 0.3 nm.Typical wavelengths for thermal neutrons are 0.1 nm to 0.3 nm. This range is similar to most crystal lattice spacings.This range is similar to most crystal lattice spacings. Wavelengths for Cold neutrons are 0.2 nm to 1.0 nm.Wavelengths for Cold neutrons are 0.2 nm to 1.0 nm. These longer wavelengths allow studies at as much as 50 nm length scales.These longer wavelengths allow studies at as much as 50 nm length scales.  h mv Thermal Neutrons 0.1-0.3 nm Cold Neutrons 0.2-1.0 nm 

15. 0.43 nm Cold Neutrons 0.18 nm Thermal Neutrons 0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.4 Wavelength (nm) 82219.15.13.32.31.71.31.00.820.670.570.480.42 Energy (meV) >bullet speeds< Neutron fluence rate (n/cm 2 s) speed of sound 400020001320990790660570500440400360330300280 Velocity (m/s) MeV neutrons from reactor Neutron Flux Distribution

16. Neutron Refractive Index Neutrons have a DeBroglie wavelengthNeutrons have a DeBroglie wavelength Wavelength ranges:Wavelength ranges: –Thermal (0.1nm - 0.3nm) –Cold (0.2nm - 1.5 nm) Index of RefractionIndex of Refraction Index of refraction range for (1-n):Index of refraction range for (1-n): –Thermal (10 -6 - 10 -5 ) –Cold (10 -5 - 10 -4 ) Note that for visible light n ranges from 1-3Note that for visible light n ranges from 1-3 speed in medium  n speed in vacuum 11 22 Snell’s law n 1 sin  1 =n 2 sin  2 n 1 ~1 n 2 <1

17. Unlike the refractive powers of glass for visible light, neutron refractive powers are very weak.Unlike the refractive powers of glass for visible light, neutron refractive powers are very weak. Light refractive indices vary from 1-3.Light refractive indices vary from 1-3. Neutron refractive indices are typically less than 1 and differ from 1 by parts in 10 5 or 10 6.Neutron refractive indices are typically less than 1 and differ from 1 by parts in 10 5 or 10 6. This low refractive power owes to the rather high energy or short wavelength of the neutron.This low refractive power owes to the rather high energy or short wavelength of the neutron. Much longer wavelength neutrons, called very cold neutrons, are currently difficult to produce in large enough quantities to be useful for imaging.Much longer wavelength neutrons, called very cold neutrons, are currently difficult to produce in large enough quantities to be useful for imaging. Refractive Power of Neutrons

18. Attenuation v.s. Phase Contrast Amplitude objects are objects that attenuate the intensity or amplitude of the wave front like the motor seen previously.Amplitude objects are objects that attenuate the intensity or amplitude of the wave front like the motor seen previously. Are transparent objects invisible?Are transparent objects invisible? Not quite, actually they distort a wavefront that passes through them redistributing intensity downstream of the object.Not quite, actually they distort a wavefront that passes through them redistributing intensity downstream of the object. This is called phase objectThis is called phase object Therefore transparent phase objects can be rendered visible.Therefore transparent phase objects can be rendered visible.

19.  (r,t) = A r e -i(kr-  t) Wave amplitude decreases as 1/r |  (r,t) | 2 = A2A2 r2r2 Energy propagates perpendicular to the wavefront and decreases as 1/r 2 Energy redirected by lens Example: Lens redistribution of intensity

20. Cold neutron beam polychromatic or monochromaticCold neutron beam polychromatic or monochromatic Point source that produces a very coherent image (here 0.4mm dia.)Point source that produces a very coherent image (here 0.4mm dia.) Sample placed downstream about 2 meters awaySample placed downstream about 2 meters away Image planes are:Image planes are: –position 1) directly behind the sample –position 2) downstream about 2 meters away Sample Horizontal scale 1 m Contact image Phase contrast image Cold neutron beam Neutrons from point source (0.4 mm dia) 2d detector position 1 2d detector position 2 Typical Phase Contrast Setup

21. 400  m Pinhole Apperture 1.8 m Contact Image Polychromatic Neutrons Phase Contrast of a Lead Slug 1.8 m Phase Contrast Image

22. 1.8 m Contact Image 1.8 m Phase Contrast Image 400  m Pinhole Apperture Monochromatic Neutrons Neutron are monochromaticNeutron are monochromatic Pinhole aperture is 0.4 mm in diameterPinhole aperture is 0.4 mm in diameter Details of delicate organ structure is visible to phase contrastDetails of delicate organ structure is visible to phase contrast Phase Contrast of a Wasp

23. Reconstructed Neutron Optical Density of Lead Slug

24. Reconstructed Phase of Lead Sinker

25. Turbine Blade Phase Image

26. Why do it? Low attenuation contrast.Low attenuation contrast. Smaller radiation dose.Smaller radiation dose.

27. Neutron Interferometer and Optics Facility

28. Coherence Beam characteristicsBeam characteristics –High transverse coherence –High intensity BeamsBeams

29. Conclusion Thermal and cold neutrons have short wavelengths, which results in very low refractive powers in matter. In spite of this fact coherent wave scattering can be utilized as an image contrast mechanism.Thermal and cold neutrons have short wavelengths, which results in very low refractive powers in matter. In spite of this fact coherent wave scattering can be utilized as an image contrast mechanism. Beams with suitable coherence require small pinhole apertures resulting in very low neutron flux. We need more flux.Beams with suitable coherence require small pinhole apertures resulting in very low neutron flux. We need more flux. Real time imaging capabilities allow for study of time dependent phenomenonReal time imaging capabilities allow for study of time dependent phenomenon Beam lines designed specifically for this application would be able to optimize flux. We need better resolution.Beam lines designed specifically for this application would be able to optimize flux. We need better resolution. Dedicated higher flux beam lines are available at NIST and will be developed in the near future.Dedicated higher flux beam lines are available at NIST and will be developed in the near future. Neutron detector technology improvements (more, faster, better):Neutron detector technology improvements (more, faster, better): –Higher flux detectors 10 6 neutrons / cm 2 / s –Near real time image capture –Higher resolution ~ 10  m might be possible