Principles of Neutron Imaging

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1 Wir schaffen Wissen heute für morgen Manuel Morgano Neutron Imaging & Activation Group, Paul Scherrer Institut, Switzerland Principles of Neutron Imaging PSI, 8. Oktober 2015

2 1. Absorption-based imaging Topics 2. How to attenuate a neutron beam: absorption vs. scattering (in brief) 3. Geometrical principles: L/D 4. Neutron collimation and exposure time 5. Main differences between x-ray and neutron imaging 6. Neutron imaging domain: big objects, hydrogen 7. Neutron conversion to light 8. Thermal and cold neutrons: pros and cons 9. A taste of more advanced neutron imaging techniques

3 What is neutron imaging Problem: You have an object

4 What is neutron imaging Problem: You have an object

5 What is neutron imaging Problem: You have an object You want to know what s inside this object (even the composition)

6 What is neutron imaging Problem: You have an object You want to know what s inside this object (even the composition) You also want to know how much of it is inside

7 What is neutron imaging Problem: You have an object You want to know what s inside this object (even the composition) You also want to know how much of it is inside And for some reasons you want to use neutrons (we ll see why later)

8 Solution: What is neutron imaging

9 What is neutron imaging Solution: Get yourself one of these:

10 What is neutron imaging Solution: Or one of these:

11 What is neutron imaging Moderate and transport the resulting neutrons See presentations from E. Lehmann and M. Strobl about this

12 What is neutron imaging Measure! Source Collimation Object Detector

13 What is neutron imaging Measure! Source Collimation Object Detector It s a little bit more complex than this

14 Attenuation-based imaging Problem: I 0 I=?

15 Attenuation-based imaging 1 st : let s divide the bulk into thin (differential) slices I 0 I=?

16 Attenuation-based imaging Let s consider one slab at a time (we ll sum the effect of each of them eventually) I 0 I=I 0 +di

17 Attenuation-based imaging In reality, a slab is made of discrete attenuators separated by vacuum I 0 I=I 0 +di

18 Attenuation-based imaging In reality, a slab is made of discrete attenuators separated by vacuum I 0 I=I 0 +di The area of each attenuator is called the (microscopic) cross section

19 Attenuation-based imaging If we have N absorber per unit volume and the slab has a thickness of dx I 0 I=I 0 +di we can express

20 Attenuation-based imaging We can solve the equation and integrate over the thickness t:

21 Attenuation-based imaging We can solve the equation and integrate over the thickness t: Beer-Lambert law

22 Attenuation-based imaging We can solve the equation and integrate over the thickness t: Beer-Lambert law For several absorbers

23 Attenuation-based imaging,,,, With C the line, of length t, in front of pixel (i,j)

24 Attenuation-based imaging

25 Attenuation-based imaging

26 Attenuation-based imaging

27 Attenuation-based imaging From this to quantification of the amount of material

28 Attenuation-based imaging A number of assumptions have been made: 1. The absorbers are independent on each other

29 Attenuation-based imaging A number of assumptions have been made: 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other

30 Attenuation-based imaging A number of assumptions have been made: 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic

31 Attenuation-based imaging A number of assumptions have been made: 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel

32 Attenuation-based imaging A number of assumptions have been made: 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material)

33 Attenuation-based imaging A number of assumptions have been made: 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present

34 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons:

35 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons: True for most applications

36 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons: True for most applications True for most elements

37 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons: True for most applications True for most elements The equation needs to be modified:

38 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons: True for most applications True for most elements The equation needs to be modified: Also beam hardening

39 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons: True for most applications True for most elements The equation needs to be modified: (Almost) true for imaging

40 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons: True for most applications True for most elements The equation needs to be modified: (Almost) true for imaging True for most elements

Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3.

The absorbers are not influenced by the radiation (i.e. no fission in the material) 6.

41 Attenuation-based imaging 1. The absorbers are independent on each other 2. The absorbers are diluted e.g. they do not shadow each other from one slab to the other 3. The attenuation does not depend on the wavelength or the beam is monochromatic 4. The beam is somewhat parallel 5. The absorbers are not influenced by the radiation (i.e. no fission in the material) 6. No scattering is present For (thermal and cold) neutrons: True for most applications True for most elements The equation needs to be modified: (Almost) true for imaging True for most elements Plain wrong for most elements

42 Absorption vs. Scattering Normalized absorption cross section Normalized scattering cross section

43 Absorption vs. Scattering Normalized absorption cross section Normalized scattering cross section See presentation of R. Harti about this

44 Absorption vs. Scattering Normalized absorption cross section Normalized scattering cross section

45 Absorption vs. Scattering Normalized absorption cross section Normalized scattering cross section

46 How to solve this problem: Absorption vs. Scattering

47 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult

48 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier Neutrons Sample Detector Assume 4 π scatterer (red)

49 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier Neutrons Sample Detector Assume 4 π scatterer (red)

50 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier Neutrons Sample Detector Assume 4 π scatterer (red)

51 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier Neutrons Sample Detector Assume 4 π scatterer (red)

52 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier Neutrons Sample Detector Assume 4 π scatterer (red) The pixel-wise solid angle quickly becomes small

53 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier Detector Sample Neutrons Assume 4 π scatterer (red) The pixel-wise solid angle quickly becomes small The cross talk quickly tapers off

54 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier 3. Measure far away from the detector Detector Neutrons Sample

55 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier 3. Measure far away from the detector Detector Neutrons Sample

56 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier 3. Measure far away from the detector 4. Use scattering rejection MCP Detector Neutrons Sample

57 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier 3. Measure far away from the detector 4. Use scattering rejection 5. Modelling tools and simulations for ex-post correction See presentation of P. Vontobel about this

58 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier 3. Measure far away from the detector 4. Use scattering rejection 5. Modelling tools and simulations for ex-post correction 6. Measure it! (Neutron Grating Interferometry) See presentation of B. Betz about this

59 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier 3. Measure far away from the detector 4. Use scattering rejection 5. Modelling tools and simulations for ex-post correction 6. Measure it! (Neutron Grating Interferometry)

60 Absorption vs. Scattering How to solve this problem: 1. Accept it: quantification of highly scattering elements through imaging is difficult 2. Flat samples are easier 3. Measure far away from the detector 4. Use scattering rejection 5. Modelling tools and simulations for ex-post correction 6. Measure it! (Neutron Grating Interferometry) Seems the easiest! Let s do that!

61 Depends on what you want to end up with: Geometric principles

62 Geometric principles Depends on what you want to end up with: This

63 Geometric principles Depends on what you want to end up with: This or this

64 Geometric principles The reason is: the neutron beam is never parallel

65 Geometric principles The reason is: the neutron beam is never parallel

66 Geometric principles The reason is: the neutron beam is never parallel l d d = = L D l L D

67 Geometric principles

68 Geometric principles The reason is: the neutron beam is never parallel l d d = = L D l L D

69 Geometric principles The reason is: the neutron beam is never parallel Minimize this! l d d = = L D l L D

70 Geometric principles The reason is: the neutron beam is never parallel Minimize this! l d d = = L D l L D Minimize these!

71 Geometric principles The reason is: the neutron beam is never parallel Minimize this! l d d = = L D l L D Minimize these! Maximize this!

72 Geometric principles Minimize this! d = l L D Minimize these! Maximize this!

73 Geometric principles Minimize this! d = l L D Minimize these! Maximize this! Minimizing l is your first choice!

74 Geometric principles Minimize this! d = l L D Minimize these! Maximize this! Minimizing l is your first choice! but it only gets you so far

75 Geometric principles Minimize this! d = l L D Minimize these! Maximize this! Minimizing l is your first choice! Maximize L: The source is a 4π emitter: flux tapers off as R -2

76 Geometric principles Minimize this! d = l L D Minimize these! Maximize this! Minimizing l is your first choice! Maximize L: The source is a 4π emitter: flux tapers off as R -2 Data acquisition time extended

77 Geometric principles Minimize this! d = l L D Minimize these! Maximize this! Minimizing l is your first choice! Maximize L: The source is a 4π emitter: flux tapers off as R -2 Data acquisition time extended Minimize D: Less neutrons will arrive at the sample

78 Geometric principles Minimize this! d = l L D Minimize these! Maximize this! Minimizing l is your first choice! Maximize L: The source is a 4π emitter: flux tapers off as R -2 Data acquisition time extended Minimize D: Less neutrons will arrive at the sample Data acquisition time extended

79 Neutron collimation and exposure time A compromise has to be found for the optimal L/D-resolution-data taking time:

80 Neutron collimation and exposure time A compromise has to be found for the optimal L/D-resolution-data taking time:

81 Why are we so concerned about the flux? Neutrons vs. X-rays

82 Neutrons vs. X-rays Why are we so concerned about the flux? TOMCAT beamline at PSI 10 %! "# $

83 Neutrons vs. X-rays Why are we so concerned about the flux? TOMCAT beamline at PSI ANTARES beamline at TUM 10 %! "# $ 10& % '! "# $

84 Neutrons vs. X-rays Why are we so concerned about the flux? TOMCAT beamline at PSI ANTARES beamline at TUM 10 %! "# $ 10& % '! "# $

85 Neutrons vs. X-rays Why are we so concerned about the flux? TOMCAT beamline at PSI ANTARES beamline at TUM 10 %! "# $ 10& % '! "# $ That s one of the main differences between x-ray and neutron imaging

86 Neutrons vs. X-rays Why are we so concerned about the flux? TOMCAT beamline at PSI ANTARES beamline at TUM 10 %! "# $ 10& % '! "# $ practical That s one of the main differences between x-ray and neutron imaging

87 Neutrons vs. X-rays X-rays: Interacting with the electron shell Neutrons: Interacting with the nucleus

88 Neutrons vs. X-rays X-rays: Interacting with the electron shell Neutrons: Interacting with the nucleus

89 Neutrons vs. X-rays X-rays: Interacting with the electron shell Neutrons: Interacting with the nucleus

90 Neutrons vs. X-rays X-rays: Interacting with the electron shell Neutrons: Interacting with the nucleus Already this creates a clear domain for neutron imaging!

91 Neutrons vs. X-rays X-rays: Interacting with the electron shell Neutrons: Interacting with the nucleus Photo X-rays Neutrons Already this creates a clear niche for neutron imaging!

92 Neutrons vs. X-rays X-rays: Interacting with the electron shell Neutrons: Interacting with the nucleus Photo X-rays Neutrons See presentation of C. Grünzweig about this Already this creates a clear niche for neutron imaging!

93 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed Neutrons: Interacting with the nucleus Massive / variable speed

94 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed Neutrons: Interacting with the nucleus Massive / variable speed See presentation of S. Peetermans about this

95 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed No magnetic moment Neutrons: Interacting with the nucleus Massive / variable speed Inherent magnetic moment

96 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed No magnetic moment Neutrons: Interacting with the nucleus Massive / variable speed Inherent magnetic moment See presentation of N. Kardjilov about this

97 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed No magnetic moment Point-like source Neutrons: Interacting with the nucleus Massive / variable speed Inherent magnetic moment Extended source

98 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed No magnetic moment Point-like source Ionizing Neutrons: Interacting with the nucleus Massive / variable speed Inherent magnetic moment Extended source Non-ionizing (directly)

99 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed No magnetic moment Point-like source Ionizing Neutrons: Interacting with the nucleus Massive / variable speed Inherent magnetic moment Extended source Non-ionizing (directly) This has an influence on the way you convert neutrons into visible light

100 Neutrons vs. X-rays X-rays: Interacting with the electron shell Massless / Fixed speed No magnetic moment Point-like source Ionizing Neutrons: Interacting with the nucleus Massive / variable speed Inherent magnetic moment Extended source Non-ionizing (directly) This has an influence on the way you convert neutrons into visible light (even though you can avoid going through visible light altogether i.e. MCP based detectors)

101 Neutron conversion to light Absorption cross section Scattering cross section H He Li Be B C N O Mg Al Si S Ca Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge Zr Mo Tc Ag Cd In Sn Eu Gd Tb Dy W Os Ir Pt Au Hg Pb Bi Th U

102 Neutron conversion to light Absorption cross section Scattering cross section H He Li Be B C N O Mg Al Si S Ca Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge Zr Mo Tc Ag Cd In Sn Eu Gd Tb Dy W Os Ir Pt Au Hg Pb Bi Th U

103 Neutron conversion to light 940 b 3 H (2.73 MeV) n 6 Li α (2.05 MeV) 259 kb e - ( kev) n 157 Gd 157 Gd 3840 b 7 Li (94%: 840 kev) ( 6%: 1.02keV) n 10 B α (94%: 1.47 MeV) ( 6%: 1.78 MeV)

104 Neutron conversion to light 940 b 3 H (2.73 MeV) n 6 Li α (2.05 MeV) 259 kb e - ( kev) n 157 Gd 157 Gd Ionizing! 3840 b 7 Li (94%: 840 kev) ( 6%: 1.02keV) n 10 B α (94%: 1.47 MeV) ( 6%: 1.78 MeV)

105 Neutron conversion to light ZnS:Ag or ZnS:Cu Gd 2 O 2 S:Tb Slide from B. Walfort, WCNR-10, Grindelwald (CH) (2014)

106 Neutron conversion to light ZnS:Ag or ZnS:Cu Gd 2 O 2 S:Tb Photosensitivity of CCD Slide from B. Walfort, WCNR-10, Grindelwald (CH) (2014)

107 Neutron conversion to light ZnS:Ag or ZnS:Cu Gd 2 O 2 S:Tb Photosensitivity of CCD See presentation of P. Trtik about this Slide from B. Walfort, WCNR-10, Grindelwald (CH) (2014)

108 Neutron conversion to light How do you choose which absorber?

109 Neutron conversion to light How do you choose which absorber? Rule-of-thumb: thickness = spatial resolution (valid because these scintillators are powder)

110 Neutron conversion to light How do you choose which absorber? Rule-of-thumb: thickness = spatial resolution (valid because these scintillators are powder) 50um-LiF+ZnS 20um-Gadox 10um-Gadox 1mm

111 Neutron conversion to light How do you choose which absorber? Rule-of-thumb: thickness = spatial resolution (valid because these scintillators are powder) 50um-LiF+ZnS 20um-Gadox 10um-Gadox 1mm That s not the end of the story (of course)

112 Neutron conversion to light 940 b 3 H (2.73 MeV) n 6 Li α (2.05 MeV) 259 kb e - ( kev) n 157 Gd 157 Gd 3840 b 7 Li (94%: 840 kev) ( 6%: 1.02keV) n 10 B α (94%: 1.47 MeV) ( 6%: 1.78 MeV)

113 Neutron conversion to light 940 b 3 H (2.73 MeV) n 6 Li α (2.05 MeV) 259 kb e - ( kev) n 157 Gd 157 Gd 3840 b 7 Li (94%: 840 kev) ( 6%: 1.02keV) n 10 B α (94%: 1.47 MeV) ( 6%: 1.78 MeV)

114 Neutron conversion to light 940 b 3 H (2.73 MeV) n 6 Li α (2.05 MeV) 259 kb e - ( kev) The range of these particles is different! n 157 Gd 157 Gd 3840 b 7 Li (94%: 840 kev) ( 6%: 1.02keV) n 10 B α (94%: 1.47 MeV) ( 6%: 1.78 MeV)

115 Neutron conversion to light 940 b 3 H (2.73 MeV) n 6 Li α (2.05 MeV) 259 kb e - ( kev) n 157 Gd 157 Gd 3840 b 7 Li (94%: 840 kev) ( 6%: 1.02keV) n 10 B α (94%: 1.47 MeV) ( 6%: 1.78 MeV)

116 Neutron conversion to light

117 Neutron conversion to light Absorption probability Resolution Light yield

118 Neutron conversion to light Absorption probability You can only choose two Resolution Light yield

119 Neutron conversion to light

120 Thermal and cold neutrons Thermal neutrons Cold neutrons

121 Thermal and cold neutrons Thermal neutrons Cold neutrons

122 Thermal and cold neutrons Thermal neutrons Cold neutrons Wavelength

123 Thermal and cold neutrons Thermal neutrons Cold neutrons Wavelength Energy

124 Thermal and cold neutrons Thermal neutrons Cold neutrons Wavelength Energy Cross section

125 Thermal neutrons 35 Thermal and cold neutrons Cross section of 56Fe Cold neutrons Cross Section (barn) Wavelength Energy Cross section Wavelength (Angstrom)

126 Thermal and cold neutrons Thermal neutrons Cold neutrons Wavelength Energy Cross section Penetration length

127 Thermal and cold neutrons Thermal neutrons Cold neutrons Wavelength Energy Cross section Penetration length Sensitivity

128 Examples

129 Coffee

130 Engine running See presentation of P. Boillat about this

131 Buddha See presentation of D. Mannes about this

132 Army-knife See presentation of A. Kaestner about this

133 Fly

134 Thermal neutrons Cold neutrons Wavelength Energy Cross section Penetration length Sensitivity

135 Thermal neutrons Cold neutrons Wavelength Energy There s much more to that, Cross section see next talks! Penetration length Sensitivity

136 Other great stuff with neutrons λ 0 See presentations of S. Peetermans and M. Raventos about these

Atomic Physics. Chapter 6 X ray. Jinniu Hu 24/12/ /20/13

Atomic Physics. Chapter 6 X ray. Jinniu Hu 24/12/ /20/13 Atomic Physics Chapter 6 X ray 11/20/13 24/12/2018 Jinniu Hu 1!1 6.1 The discovery of X ray X-rays were discovered in 1895 by the German physicist Wilhelm Roentgen. He found that a beam of high-speed electrons