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Generationof quasi-monochromatic

soft x-rays usinga table-top electron accelerator

Alexander Lobko

Institute for Nuclear Problems Belarus State University

July 2009 X Intl Gomel HEP School

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Light sources

http://www.lightsources.org/cms/?pid=1000166

NanoscienceLife sciences

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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 photo-emission spectroscopy (XPS), Auger spectroscopy.

Problems:Complex materials Magnetic materials

Environmental scienceCatalysis

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 scienceSoft 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

ConcernRadiation-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 forMedical Imaging

• mammography - 17-21 keV;

• radiography of chest,

extremities and head - 40-50 keV;

• abdomen and pelvis

radiography - 50-70 keV;

• digital angiography - ~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

The Physics of Medical Imaging / S. Webb (Ed.), Bristol: Hilger, 1978.

2 2 21(1 )exp( ) /( ( ) )N k R t x x

xt

1

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

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Comparison of some x-ray generation processes at accelerators

Type of radiation Yield,

photon/e

Е,

MeV

BR 1.2*(-8) 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) 50

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

V. Baryshevsky, I. Feranchuk, A. Ulyanenkov Parametric X–ray Radiation in Crystals: Theory, Experiment and Applications // Springer, 2006, 176 p.

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0, 0, , , , , , , , , , ,...nPXRB s

NNF eQ g L T X

k k

2

2( ) 1 1

2pn

1 cos 0vn k

sinnB

B

cn

d

Condition for the Cherenkov radiation emission

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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

Rensselaer Polytechnic Institute, NY, USA

Nihon University, Japan

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Racetrack microtron 70 MeV

http://nuclphys.sinp.msu.ru/nuc_techn/el_ac/index.html

2.2*1.8*0.9 м3

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PXR at MIRROCLE

Photon Production Laboratory Japan

www.photon-production.co.jp

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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

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Evaluations of 33 keV PXR emissionfrom 20 MeV electrons

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.

Si, L=0,01 cm

0,0E+00

5,0E-05

1,0E-04

1,5E-04

2,0E-04

2,5E-04

3,0E-04

3,5E-04

4,0E-04

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

Polar angle, rad

Ang

ular

den

sity

, pho

tons

/(e- s

rad)

111

220

400

Dia 20 cm at 1.5 m~7·10-2 rad

Quantum Yield:(111) - 3·10-6 /e-

(220) – 4.5·10-7 /e-

(400) – 1.4·10-7 /e-

In some cases account of CB interference is needed

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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 toL0=L/cos(55 arc degrees)=0,0141 cm

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Optimal PXR crystal target - wedgeTo 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

Azimuth angle, rad

1

2

31 – plane target symmetric geometry2 – plane target asymmetric geometry3 – wedge target asymmetric geometry

Ang

ular

den

sity

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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 = ~210-6 ph/e-;

• Intensity of diffracted BR = ~510-6 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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ConclusionsPXR radiation mechanism and table-top

accelerator can provide flux needed for contemporary soft x-ray applications in high-quality 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 targetsTarget heatingPXR angular distributionX-ray harmonics filteringApplication of x-ray opticsTargets made of photonic crystals – way to T-rays

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MinskYa. Kolas Sq.

1967

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Many thanks for your attention