Download Generation of Hard Quasimonochromatic Radiation Using a Table

Alexander Lobko
Generation
of quasi-monochromatic
soft x-rays using
a table-top electron accelerator
Institute for Nuclear Problems
Belarus State University
July 2009
X Intl Gomel HEP School
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Light sources
Nanoscience
Life sciences
http://www.lightsources.org/cms/?pid=1000166
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Typical size of contemporary
synchrotron
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Budget of the SOLEIL synchrotron
Construction
• Investment…………….235 M€
• Operation………………..64 M€
• Salaries………………….150 M€
Total………………………….449 M€
Yearly………………………...53 M€
www.synchrotron-soleil.fr
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Why do we need
(quasi)-monochromatic
soft x-rays?
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Soft X-Ray Spectroscopy
Methods: Soft x-ray absorption spectroscopy (XAS),
near-edge x-ray absorption fine structure (NEXAFS)
spectroscopy, soft x-ray emission spectroscopy (SXES),
resonant inelastic x-ray scattering (RIXS), x-ray
magnetic circular dichroism (XMCD), x-ray photoemission spectroscopy (XPS), Auger spectroscopy.
Problems:
Complex materials
Magnetic materials
Environmental science
Catalysis
The photon energy tunability and its brilliance
for some above listed applications are
essential.
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Soft X-Ray Scattering
Methods: Soft x-ray emission spectroscopy (SXES), inelastic
x-ray scattering (IXS), resonant x-ray inelastic scattering
(RIXS), speckle patterns, small-angle x-ray scattering (SAXS).
Problems:
Strongly correlated materials
Magnetic materials
Environmental science
Catalysis
The tunability of radiation and its brilliance for
some above listed applications are essential.
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Soft X-Ray Imaging
Methods: Soft x-ray imaging, photoelectron emission
microscopy (PEEM), scanning transmission x-ray microscopy
(STXM), full-field microscopy, x-ray diffraction imaging (XDI),
x-ray tomography, computer-aided tomography (CAT).
Problems:
Cell biology
Nano-magnetism
Environmental science
Soft matter, polymers
The tunability of radiation is absolutely essential
for the creation of contrast mechanisms.
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Applications to the life sciences
• Potential to form high spatial resolution
images in hydrated bio-material
• Ability to identify atomic elements by the
coincidence between photon energy and
atomic resonances of the constituents of
organic materials
Concern
Radiation-induced damage: photon energy
deposited per unit mass (dose) can cause
observable changes in structure
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Soft x-ray water window
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Micro-beam radiotherapy
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Indirect radiation therapy
www.mpsd.de/irt
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Monochromatic X ray medical imaging
By narrowing x-ray spectrum inside of the range required
for a specific medical imaging application, a patient’s
radiation-induced damage may be significantly reduced.
It has been evaluated that x-ray examinations performed
with quasi mono-energetic x-rays (even 15-20%) will deliver
a dose to the patient that will be up to 70% less than dose
deposited by a conventional x-ray system [P. Baldelli [et al] //
Phys. Med. Biol. 49 (2004) 4135].
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Optimal X-Ray Energies for
Medical Imaging
• mammography
• radiography of chest,
extremities and head
• abdomen and pelvis
radiography
• digital angiography
- 17-21 keV;
- 40-50 keV;
- 50-70 keV;
- ~33 keV.
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How much monochromatic
soft x-ray photons we need?
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Evaluation of X-Ray Flow
for Medical Imaging
1
x
t
2
N  k (1  R)exp(1t ) /( ( x) x )
2
2
The Physics of Medical Imaging / S. Webb (Ed.), Bristol: Hilger, 1978.
2
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What do we need for
high-quality in vivo imaging?
Number of x-ray quanta needed to visualize
1.0 mm3 of biological tissue at 1% contrast is
~3x107 photons/mm2.
This evaluation made for film registration.
In case of digital detection 4×104 photons per ~0.4
mm2 detector pixel are required. It leads to the
flux of
~106 photons/mm2.
Due to heart beat and breathing, above photon
flux must be provided within ~1/100 s.
Photons must penetrate considerable field of vision.
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What do we exactly need for
high-quality in vivo imaging?
We need, for example,
3x107 mm-2 * 100x100 mm2 / 10-2 s =
~3x1013 (1012) photons/s
with tunable x-ray energy in 10-70 keV range
Mono-chromaticity could be of ~10-2 for a
patient’s dose reduction
Radiation background should be low
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Spectral brilliance of x-ray sources
There is large gap between properties
of common and high energy
accelerator-based x-ray sources 19
Comparison of some x-ray generation
processes at accelerators
BR
Yield,
photon/e
1.2*(-8)
Е,
MeV
500
CBR
1.7*(-7)
0.2
SR
1.2*(-5)
3 *(+3)
TR
1.0*(-9)
125
RR
1.6*(-7)
50
PXR
1.3*(-5)
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Type of radiation
V.G. Baryshevsky, I.D. Feranchuk // NIM 228 (1985) 490
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Compact x-ray source based on
Compton back scattering
http://www.lynceantech.com/sci_tech_cls.html
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Parametric x-rays
 p2
n( )  1  2  1
2
1  vn k   cos  0


Condition for the Cherenkov
radiation emission
n
B
 cn

k  k 
d sin  B
2


 Nn
 N PXR
 F  eQ,  , g0, , B , s , L, T , ,  , X 0 ,
,... 

 

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V. Baryshevsky, I. Feranchuk, A. Ulyanenkov Parametric X–ray Radiation in
Crystals: Theory, Experiment and Applications // Springer, 2006, 176 p.
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Motivation to use PXR
• it is quasi-monochromatic x-rays
• x-rays energy can be tuned smoothly by
single crystal target rotation
• it is well directed and polarized x-rays
• x-rays energy does not depend on energy of
incident electrons
• radiation angle can be as large as
180 arc degrees - it means, one may work at
virtually low background
• Optimal target thickness – 10-50 µm of light
crystal material (diamond, silicone, graphite,
LiF, quartz, etc) – weak multiple scattering
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PXR practical applications
Nihon University, Japan
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Rensselaer Polytechnic Institute, NY, USA
Racetrack microtron 70 MeV
2.2*1.8*0.9 м3
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http://nuclphys.sinp.msu.ru/nuc_techn/el_ac/index.html
PXR at MIRROCLE
Photon Production Laboratory Japan
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www.photon-production.co.jp
Table-top storage ring MIRRORCLE-20
Electron energy – 20 MeV
Average current – about units of Ampere
Due to strong multiple scattering only very
thin (up to some tens microns) x-ray
production targets can be used to prevent
beam destruction
Number of BR photons from such thin target
will be much lower than come from massive
anode of a conventional x-ray tube 27
Evaluations of 33 keV PXR emission
from 20 MeV electrons
Si, L=0,01 cm
Dia 20 cm at 1.5 m
~7·10-2 rad
4,0E-04
Quantum Yield:
(111) - 3·10-6 /e(220) – 4.5·10-7 /e(400) – 1.4·10-7 /e-
111
3,0E-04
220
-
Angular density, photons/(e srad)
3,5E-04
400
2,5E-04
2,0E-04
1,5E-04
1,0E-04
5,0E-05
0,0E+00
0,0E+00
1,0E-02
2,0E-02
3,0E-02
4,0E-02
5,0E-02
6,0E-02
7,0E-02
8,0E-02
9,0E-02
1,0E-01
In some cases
account of CB
interference is
needed
Polar angle, rad
Ee = 20 MeV, Si target of L=0.01 cm thickness, 33 KeV x-rays,
symmetrical Laue case for (111), (220), and (400). Angles
between electron velocity direction and direction to diffraction
reflex are ~6.9, 11.2, and 15.9 degrees, respectively.
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Asymmetric case
Angle between electron velocity and
input plane normal is equal 55 arc
degrees, angle between output plane
normal and outgoing radiation is equal
35 arc degrees.
Plane thickness was chosen equal to
0,00811 сm to provide electron path in
crystal equal to
L0=L/cos(55 arc degrees)=0,0141 cm
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Optimal PXR crystal target - wedge
To calculate optimal asymmetric
geometries and wedge
configurations – dynamical theory
required
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Angular distributions in symmetric and
asymmetric cases plus 30 degree wedge
Angular density
3
1 – plane target symmetric
geometry
2 – plane target asymmetric
geometry
3 – wedge target asymmetric
geometry
2
1
Azimuth angle, rad
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Soft PXR intensity at M-20
•
•
•
•
•
•
•
•
•
Target Si (111) wedge shaped;
Bragg angle = 45 arc degrees; EPXR = 2.8 keV;
Absorption length 3.57 µm;
Geometry – Symmetric Laue;
Wedge thickness 0.01 cm;
Wedge angle - 30 degrees;
Energy resolution (integration) /= 10-3;
Intensity of PXR+diffracted TR = ~210-6 ph/e-;
Intensity of diffracted BR = ~510-6 ph/e-.
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Wedge targets prototypes
At a moment wedge-shaped
targets available of Si (111)
and (100) base planes with
length 3 through 24 mm (step
3 mm) and maximal thickness
450 or 350 mkm.
Angle of the wedge and its
material can be customized.
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PXR reflex integral intensity at M-20
Depending on the beam fraction we can
apply for PXR generation, in the ideal
integral flux may be as high as
10-5 ph/e * 1019 e/s.
It means 1014 s-1 X ray photons
of 10-3 monocromaticity
with tunable energy
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M-20 beam shape
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Conclusions
PXR radiation mechanism and table-top
accelerator can provide flux needed for
contemporary soft x-ray applications in highquality medical imaging and lowered dose radiation
therapy.
Problems to be considered:
Commissioning of the real beam shape as income
for more exact evaluations and production of
specific targets
Target heating
PXR angular distribution
X-ray harmonics filtering
Application of x-ray optics
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Targets made of photonic crystals – way to T-rays
Minsk
Ya. Kolas Sq.
1967
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Many thanks for your attention
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