ï high resolution detector close to sample ï weak diffraction signal ï high efficiency detector needed ï. 30i80 keV Xirays ï. High Z scintillator ï. Divergent beam ï.
High efficiency detectors for micrometer resolution
U.L. Olsen1, S. Schmidt1, H.F. Poulsen1, J. Linnros2, X. Badel2, T. Martin3 and M. Di Michiel3
Present technology Detector
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Present technology Detector issues 5
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Structured scintillator Principle
Decoupling of scintillator thickness and resolution
Structured scintillator Simulation - Methodology 1
Rayleigh
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0.8 scattering
Thomson Compton
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Photons
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raytrace MCNPRadiative Loss
Electrons
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absorption
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2
500 0 0
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100
1000 1500 [nm]
2
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n cos θ 2 − n2 cos θ1 + 1 n1 cos θ1 + n2 cos θ 2
Q Q 2
2000
150 200 Width of Silicon dioxide
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sin θ1 n2 = sin θ 2 n1
1 R= 2
-1
10
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&
0
−3
10
50
66>&
1
Q
2500
250
300
Structured scintillator Simulation results 20
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& 15
µm 10
6. 8
5
5
1.5 µm •Increase in PSF at small pitch due to vanishing active area
Photons
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−2
Intensity cross section of structured (red) and planar (blue) scintillator hit by a pencil beam
Resolution versus Pitch
Single focal plane • High NA-lenses or direct CCD-coupling can be used, which increase photons efficiency
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Di Michiel 2005
0.01
FWHM [µm]
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Jung 2002 Koch 2000
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Design Principle Total internal reflection of secondary generated photons • Resolution given by pore pitch • Efficiency given by pore depth
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0
0.07
Resolution [µm]
Detector fabrication
Structured compared to regular scintillators. Both simulated performance and experimental point from literature has been included for regular scintillator.
Intensity [a.u.]
Aim
Effeciency
Structured Scintillator
• Structured scintillators with 4 µm pitch tested [3] • Structured scintillators with 1.4 µm and 1.0 µm fabricated
1500 0 −0.2 1000 −0.4 −0.6
500
Exitons
−0.8 0
0
500
1000
1500
2000
2500
Width [nm]
Field strength in ¼ pore from EM modelling
relative intensity @ 50keV: Sample S30: 1.000 LAG 25µm: 0.433 YAG 100µm: 0.541
Flow chart of interactions in MC simulation
3D detector Simultaneous near field detection at multiple sample distances •faster reconstruction of volume (3D) •post processing (super resolution [2]) Images from array of three 100µm CsI screens separated by 800 µm air.
Micrographs of plasma-etched pores with 1.4µm pitch
Tomographic image of 3µm slit with 4 µm scintillator
4
0
0
x 10
10
0 10
6 50
50
8
100
100
6
150
150
4
5
e
Conclusions
e8
• Structured scintillators represent a potential 15 increase in photons efficiency at the same resolution • PSF degradation due to fluorescence is negligible below 100keV • Resolution is given directly by pitch size • 3D detection is possible without crosstalk between layers
50
4 100 6
e
3 150
4
e
2 200 250 0
50
100
150
Test Image
200
200
2
250 0 250
0
1 50
100
150
200
Image of 3rd screen
250
200
0 250 0
2
e 50
100
150
200
Image of 3rd screen - log
250
Institutions:
Acknowledgements: We would like to acknowledge Erik Nonbøl (Risø - DTU) and Mats Hjelm (Midsweden University) for an introduction to the MCNP code and useful discussions. Support from the Danish national research Council, from the EU 6th Framework program "TotalCryst" and from the ID-15 at ESRF are also gratefully acknowledged.
1Center for Fundamental Research: Metal Structures in Four Dimensions, Materials Research Department, Risø National Laboratory, Technical University of Denmark 4000 Roskilde, Denmark. 2IMIT, Royal Institute of Technology, Electrum 229,16440 Kista, Sweden 3ESRF, 6 rue Jules Horowitz,38043 Grenoble Cedex, France
References: [1] U.L. Olsen, S. Schmidt & H.F. Poulsen, J. Synch. Rad. 2008, 15 (4) [2] S.C. Park, M.K. Park & M.G. Kang, Signal Processing M., IEEE, 2003, 20, 21-36 [3] U.L. Olsen et al, Nucl. Instr. Meth. A, 2007, 576, 52-55
High resolution detectors motivation )8 ; / 0 . - )' ' )8 - ' . .
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Acknowledgements
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