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Imaging chambers in
medicine, biology and
astrophysics
• F.A.F. Fraga
• LIP - Coimbra, CFRM and Departamento de Física
da Universidade de Coimbra, 3004-516 Coimbra,
Portugal
Outline
•
•
•
•
Imaging gas scintillators
The GEM - an active scintillator
CCDs
Apllications
– Quality control
– Imaging chamber
• Alpha tracking
• Neutrons
– Radiography
– Therapeutic beam monitoring
• Other projects
– Neutron spectrometer
– Thermal neutron imaging
– Pollarimeter
• Conclusions
Introduction
• 2D imaging detectors
• Advantages of optical readout
– Electronics decoupled from detection media
– Insensitive to electronic noise or RF pickup signals
– Real multi hit capability with true pixel readouts complex events
– Large areas without dead spaces - optical systems
(lenses, mirrors, fibers and tapers)
New developments in optical imaging detectors, A. Breskin, NIM
A498(1989)457c-468c
Gaseous avalanche chambers with
optical readout
• 2D gas scintillators with optical
readout by PMs or intensified
CCDs
• Initially used with wires and pure
gases
– Xe, Kr, Ar and He with the
addition of N2 - UVscintillation,
innefficient and expensive optics,
optical wavelenght shifters
• Improvements
– continuous amplifying structures
(PPAC, grids)
– gas mixtures scintillating at >
250 nm
The gas proportional scintillation chamber, A.J.P. Policarpo, Space Sci. Instr. 3(1977)77
A few examples
• High pressure xenon (up to 20 bar) waveshifter fibers
– A. Parsons, B. Sadoulet, S. Weiss, T. Edberg, J. Wilkerson, IEEE TNS
36(1989)931-935
• Multistep, low pressure and high gas gain (light gap ~ 9 mm, light yield
up to 3 ph./el.)
– A. Breskin, R. Chechik and D. Sauvage NIM A286(1990)251-256
• PPACs at atmospheric preassure light gap ~ 1.5 mm, TEA, TMAE,
Penning effect, higher light to charge ratio
– G. Charpak, W. Dominik, J.P. Fabre, J. Gaudaen, F. Sauli and M. Suzuki,
NIM A269(1988)142-148
– V. Peskov, G. Charpak, W. Dominik and F. Sauli NIM A227(1989)547-556
• TPC with optical readout (multistep, low pressure TEA)
– U. Titt, A. Breskin, R. Chechik, V. Dangendorf , H. Schmidt-Böcking and H.
Schuhmacher, NIM A416 (1998)85
• Optical imaging with capillary plate, argon-TMA and intensified CCD.
– T. Masuda, H. Sakurai, Y. Inoue, S. Gunji and K. Asamura, IEEE TNS
49(2002)553-558
• Some limiting features
• Low number of emitted photons
– image intensifiers - expensive, degrade image resolution, limited
size
• Large scintillation gaps
– degrade position resolution, diffusion, optical depth of field
• Technically complicated and expensive
– low pressure, high temperature, capillary plates
Luminiscence in microstrips
• 1993 A. Oed and P. Geltenbort
reported high luminosity from
pure gas mixtures
• 1998 We used scintillation to
perform quality control of
microstrips
– CCD with Ar2% Xe
Microstrip operation in noble gases: an active scintillator, P. Geltenbort and A.
Oed, Proceedings of the Workshop on Progress in Gaseous Microstrip
Proportional Chambers, Grenoble, 21-23 June 1993
Towards a method for quality control of microstructures for gaseous detectors
based on scintillation light, F.A.F. Fraga, M.M. Fraga, R. Ferreira Marques, J.R.
Gonçalo, E. Antunes, C. Bueno and A.J.P.L Policarpo
The GEM should be a good
candidate for a gas scintillator
See http://gdd.web.cern.ch/GDD/
F.Sauli. NIMA386(1997)351
Electric field simulation
GEM 80/70
GEM 60/50
GEM 45/35
60
50
E (kV/cm)
40
30
20
10
0
-100
-50
0
50
100
z (micron)
• Magnitude of the electric field along the center of the GEM
channel for equal measured gain in GEMs of different metal
hole size
• Thin gap, high gain, no blurring
Study of luminiscence of GEMs
X-ray
Vd
Drift Grid
Ed
5mm
GEM1
Et
2mm
GEM2
Induction Grid
• Both charge
and light
signals were
digitized
Ei
2mm
PMT
P.A
Camberra 2005
P.A
Camberra 2006
Digitizer
Tektronix
TDS 7104
V1
V2
V3
V4
Typical light signal shape using He40%CF4
• The light
signal
risetime at
the
preamplifier
output is
39ns
Average rise time of the light and charge
signals versus induction field, Ei
80
Double GEM, He+40%CF 4 (1bar),
Ed=0.5kV/cm, Et=2kV/cm,
Effective Gain ~3.1x10
60
Charge
Light
Rise Time (ns)
• 55Fe
• Ed=0.5kV/cm
• Et= Ei =
2kV/cm
• double GEM
gain ~ 3.1x103.
3
40
20
0
0
1
2
3
Ei (kV/cm)
4
5
Energy resolution
250
Double GEM, He+40%CF4 -1bar
Ed=0.5kV/cm, Et=Ei=2kV/cm, Effective Gain ~ 9x104
55
200
Fe (5.9keV)
Charge (R~20%)
Light (R~20%)
#Counts
150
100
50
0
0
100
200
Channel
300
400
CCD characteristics
•
•
•
•
•
CCD camera: QUANTIX 1400
(PHOTOMETRICS)
Number of pixels 1317 x 1035 (6.8 x 6.8
mm pixels)
Read noise (1 MP/s) 18 e RMS
Dark current 0.03 e/p/s (-25ºC, Peltier
cooled)
Binning - 2x2 up to 7x7
– less position resolution but lower
noise!
Nikon 50mm f1.8 photographic lens with
C mount adapter
Qunatum efficiency (%)
•
60
50
40
30
20
10
0
300
400
500
600
700
800
900
1000
Wavelength (nm)
•
Quantum efficiency of
the Quantix 1400 camera
versus wavelengh
1100
What is a CCD?
• Pixel type silicon light sensitive
detector
• High quantum efficiency - up to 90% but no gain
• Integrating type device - exposure
time from ms to minutes
• Limited range
• Low noise - cooling can be needed
• Pixel sizes up to 30 x 30 m
• High number of pixels up to 4000 x
4000
• Analog-digital serial readout - slow
Why using CCDs for the readout
of radiation detectors?
• High resolution - up to
4000x4000 pixels
• Large area detection using lenses
or mirrors
• Can be placed away of detection
media
• Cheap cost
• Electrical noise free
• Simple interface with computers
CCD readout of GEM
scintillation
GEM
Radiation
source
Glass window
-Vdrift
Front electrode
Minimum focusing distance~30cm
Back electrode
First images of GEM
scintillation
• Scintillation image of a GEM
foil. The holes of the GEM
are seen as emitting dots in
the small zone which is
shown magnified
• Ar-2%Xe
Gas study and optimization
Quality control
light/current (a.u.)
100
50
0
250
Ar(1)
Ar(3)
Ar(2)
Ar2.5%Co2
Ar5%CO2
Ar5%CO2
Ar10%CO2
Ar10%CO2
Ar10%CO2
300
350
400
450
Vgem
•Increasing the CO2 amount lowers the light emission
•A small amount of quencher enhances stability of
light emission
•Ar-5%CO2 was found to be the optimum mixture for
q.c.
•Light yield ~ 0.03 photons/secondary electron
Quality control
– scintillation is sensitive to
electric field configuration
– checks GEMs gain uniformity
– identification of local defects
– finds optically unseen deffects
a)
b)
GEM characteristics
• Electrical field can have higher values than in PPACs
• Cascaded GEMs
– Micro-Pattern Gaseous Detectors, by F. Sauli and A. Sharma, Ann.
Rev.Nucl.Part.Sci 49(1999)341
• High gain up to 4 stages, gain up to 105 - 106
– J. Va´vra, A. Sharma, NIM A Vienna 2001
– A. Breskin, PSD6
• Free from ion feedback
– Study of ion feedback in multi-GEM structures, A. Bondar, A.
Buzulutskov, L. Shekhtman, A. Vasiljev, 2002, submitted to NIM A
• Photon screening, free from photon feedback
– R. Chechik et al. NIMA419(1998)423
• Large areas (~30 x 30cm)
– Gem detectors for COMPASS, by B. Ketzer, S. Bachmann, M.
Capeáns, M. Deutel, J. Friedrich, S. Kappler, I. Konorov, A. Placci, K.
Reisinger, L. Ropelewski, L. Shekhtman, F. Sauli. IEEEE NSS Lyon,
2000..
• No need to collect the electrons on the induction electrode avoiding
breakdown in the last stage
Tracking chamber
• Sensitive volume ~250
cm3
• Track lenghts up to 8cm
• Cascaded standard
double GEM (10x10cm)
30 cm
Tracking chamber views
Data on Ar CF4 gain and relative
luminosity
EC=0; Ar 5%CO2 shown for comparison
1000
30
Light Yield (a.u./e)
Gain
Ar+5%CO2
100
Ar+5%CO2
Ar+5%CF4
Ar+80%CF4
100%CF4
10
25
Ar+5%CF4
20
Ar+80%CF4
100%CF4
15
10
5
0
300
350
400
450
Vgem (Volt)
500
550
600
300
350
400
450
500
550
600
Vgem (Volt)
• Ar CF4 has greater light emission than Ar CO2
• Good light emission for higher percentage of quencher
• Ar-5% CF4 light yield 0.57 photon/secondary electron (>400 nm)
•
Performance of a tracking device based on the GEM scintillation, F. A.
F. Fraga, S. T. G. Fetal, L. M. S. Margato, R. Ferreira Marques and A. J.
P. L. Policarpo, Presented at the IEEE 2000 NSS
3
0,7
Ar + 5% CF4
0,6
2
G=40
0,5
Inorm (a.u.)
0
3
500
2
Ar + 10% CF4
1
550
600
650
700
750
800
850
Nph/e-
1
0,4
0,3
5% CF4
10% CF4
67% CF4
0,2
0,1
G=90
1
0
3
10
Gain
500
550
600
650
700
750
800
850
Nº of photons emitted, between
400 and 1000 nm, per secondary
1
G=40
electron, as a function of the
0
effective gain, in Ar-CF4 mixtures.
500
550
600
650
700
750
800
850
 (nm)
(Measurements performed with
Visible and NIR emission spectra of Ar- the photodiode).
CF4 mixtures, normalized to the light
intensity at 620 nm.
2
Ar + 67% CF4
The GEM scintillation in He-CF4, Ar-CF4, Ar-TEA and Xe-TEA mixtures, M. M.
Fraga, F. A. F. Fraga, S. T. G. Fetal, L. M. S. Margato, R. Ferreira Marques and
A. J. P. L. Policarpo, presented at Beaune 2002 conference, submitted to NIM A
Images of alpha tracks taken using the
tracking chamber with Ar -5%CF4
•
• VGEM1=VGEM2=400V
(Gain~140), ET=5.45KV/cm,
EC=5.86KV/cm,
Texp.=10ms.
(a,b)VGEM1=VGEM2=400V
(Gain~140), ET=5.45KV/cm,
EC=5.86KV/cm, CCD Binning
4x4, Texp.=10ms; (c,d)
VGEM1=VGEM2=430V
(Gain~300), ET=5.45KV/cm,
EC=0, CCD Binning 7x7,
T=10ms.
Bragg curves of 241Am alpha
particles
• Light callibration
using full tracks ~
180 detected
photons per
deposited keV
• light yield ~0.6
photons/secondary
electron
Projections of alpha tracks Ar-5%CF4
• Triple GEM, VGEM=450V, g=82, ED=1kV/cm, ET=3.4 kV/cm, b=7x7,
EC=0,
•
•
241Am
alpha particles energy = 5.48 Mev
Range of 241Am alpha particles in Ar = 3.42 cm
The length and
orientation of the
track can be
measured using
charge or PMT
signals
Perfomance of a Tracking Device Based on the GEM Scintillation", F.A.F. Fraga,
L.M.S. Margato, S. T. G. Fetal, R. Ferreira Marques and A.J.P.L Policarpo, IEEE
Trans. on Nucl. Sci. 49, NO.1, February 2002, pg.281- 284
3He
thermal neutron detectors
• Thermal neutron capture in 3He
• 3He + n  p + 3H + 770 keV
• proton range = 4.4 mm, triton range = 1.6mm (1bar CF4)
•
R.B. Knott, G.C. Smith, G. Watt, J.W. Boldemann, NIM
A392(1997)62
Data on charge gain and light emission in
CF4 pressures 400mbar, 1, 2 and 3 bar
0,4 bar (420 V)
2 bar (740 V)
1000
1 bar (560 V)
3 bar (740 V)
Gain
100
10
1
35
45
55
65
Hole diameter (micron)
75
• Gain saturates for smaller
holes at lower pressures as
reported in NIMA
419(1998)410
85
• 60 m hole GEMs have
higher light yield
Data on CF4 + He
CF4 pressure = 400mbar, He = 0.6 and 3.6 bar
GEM 140/80: He-CF4 (600/400 mbar)
GEM 140/60: He-CF4 (600/400 mbar)
GEM 140/45: He-CF4 (600/400 mbar)
10000
100
100
Gain
1000
Gain
1000
10
10
1
1
300
350
400
450
500
550
300
350
400
450
500
550
600
VGEM (V)
VGEM (V)
100%CF4
GEM 140/80: He-CF4 (0,6/0,4 bar)
GEM 140/60: He-CF4 (0,6/0,4 bar)
GEM 140/45: He-CF4 (0,6/0,4 bar)
1E-05
8E-06
Light Yield (a.u./e)
GEM 140/80: He-CF4 (3600/400 mbar)
GEM 140/60: He-CF4 (3600/400 mbar)
GEM 140/45: He-CF4 (3600/400 mbar)
10000
Photon yield 0.077
photons/secondary electron
at 1 bar He-60%CF4
6E-06
4E-06
2E-06
0E+00
300
350
400
450
VGEM (V)
500
550
600
Closed detector
• Clean GEM chamber- stainless
steel
– GEMs 5 x 5cm
– 50mm diameter transparent window
– carbon fiber window or aluminum cover
Details of the clean
GEM chamber
Images of proton and triton tracks
in 3He- 400 mbar CF4
•
•
•
•
•
•
•
•
•
Triple GEM camera
two 80 m, one 60 m metal
hole
absorbtion space 3 mm
ED (drift field) =1KV/cm,
ET (transfer field) = 3.25
kV/cm,
EC (collection field) = 0
VGEM1 =VGEM2 =350V.
Binning 7x7
AmBe source with
Polyethylene shielding
Images of proton and triton tracks
in 3He- 400 mbar CF4
• Projection of the light
intensity along the track
as measured by the CCD
CCD readout of GEM based neutron detectors, F.A.F. Fraga, L.M.S. Margato, S. T. G. Fetal,
M.M.F.R. Fraga, R. Ferreira Marques, A.J.P.L Policarpo, B. Guerard, A. Oed, G. Manzini and
T. van Vuure, Nucl. Instr. and Meth. In Physics Research A 478 (2002) 357
X-rays radiography
Car key (~5 cm) radiography
X-ray energy ~8keV
Xe-10%CO2 at 1bar
absobtion length ~3 mm
Plastic gearwheel ~1.5 cm
radiography
Imaging detectors based on the GEM scintillation light, F.A.F. Fraga, L.M.S.
Margato, S. T. G. Fetal, I. Ivaniouchenkov,, R. Ferreira Marques, A.J.P.L
Policarpo, presented at the IEEE NSS 1999
High pressure Xe X-ray detector
• A 25 mm thick conversion volume at 5 bar Xe
will have ~ 90% detection efficiency for 17.5 keV
X-rays!
• 50 mm will be needed to get 80% efficency at 25
keV
•
Performance of high pressure Xe/TMA in GEMs for neutron and
X-ray detection, R. Kreuger, C. W. E. van Eijk, F. A. F. Fraga,
M. M. Fraga, S. T. G. Fetal, R. W. Hollander, L. M. S. Margato,
T. L. van Vuure, presented at the IEEE NSS 2001
High pressure Xe / TMA
1000
0
2
4
100
10
Xe +5%TMA (1bar)
%TMA
8
10
12
Xe/TMA 3bar
6
150.0
Charge Gain
Gain
• Xe-TMA strong Penning
effect
• TMA ion. pot 8.1 eV
• Xe metastable pot. 8.3
• Operation at a lower
voltage
Xe +2.5%TMA (3bar)
Xe +2.5%TMA (5bar)
1
150 200 250 300 350 400 450 500
Vgem=320 V
100.0
VGEM (V)
50.0
single GEM 60/70/140
0.0
0
50
100
150
200
PT MA (mbar)
250
300
350
Operation of Xe - TMA at 5 bar (light)
Xe/TMA - 3 bar
0,625%TMA
1,25%TMA
2.0E-09
Xe+5%TMA - 3 bar
Xe+5%TMA - 5 bar
2,5%TMA
5%TMA
Step = 2 nm
Slit aperture = 1 mm
Gas Gain ~ 100
1.0E-09
5.0E-10
2.0E-09
#Counts/e
1.5E-09
#Counts/e
Xe+5%TMA - 1bar
1.5E-09
Step=2nm
Slit aperture=1mm
Gas Gain ~50
1.0E-09
5.0E-10
0.0E+00
250 270 290 310 330 350 370 390
 (nm)
0.0E+00
250 270 290 310 330 350 370 390
 (nm)
•Light yield
•~ 0.3 ph/ sec. electron
•~104 ph / keV with gas gain 700
•Scintillators have 20-50 ph/ keV
UV CCD system
~40 keuro, CCD chip ~10 keuro
Radiography of a small dog-whelk
double GEM, 5mm absorption space, Xe-2.5%TMA at 5bar,
molybdenium X-ray tube at 40 kV
Radiography of a small snail ~8mm
double GEM, 5mm absorption space, Xe-2.5%TMA at 5bar,
molybdenium X-ray tube at 30 and 40 kV
The width of the shell fissure is similar to the GEM picth
Images of a 50 micron slit
collimator
• X-ray voltage 30kV
• Collimator length 25
mm
• Collimator slit 50 m
•  ~ 65 m
CCD readout of high pressure xenon-TMA GEM detectors for X-ray
imaging, L. M. S. Margato , F. A. F. Fraga*, M. M. F. R. Fraga*, S. T. G. Fetal*,
R. Ferreira Marques*, A. J. P. L. Policarpo*, T.L. van Vuure, R. Kreuger,
C.W.E. van Eijk and R.W. Hollander, presented at the SAMBA 2002, Trieste,
2002
Xe-2.5%TMA rise-time at 1 and 3
bar versus collection field
Double GEM Xe+2.5%TMA (1bar)
Ed=0.5kV/cm.bar, Et=2kV/cm.bar
Double GEM Xe+2.5%TMA (3bar)
Ed=0.5kV/cm.bar, Et=0.25kV/cm.bar
charge (5.9 keV)
PMT (5.9 keV)
250
200
200
Rise Time (ns)
Rise Time (ns)
charge (5.9 keV)
PMT (5.9 keV)
250
150
100
150
100
50
50
0
0
0.0
0.5
1.0
1.5
2.0
Ec (kV/cm.bar) (collection Field)
2.5
0.0
0.5
1.0
1.5
2.0
Ec (kV/cm.bar) (collection Field)
2.5
Energy resolution using Xe2.5% TMA 5bar (light signals)
Double GEM Xe+2.5%TMA (5bar)
PMT signals
109Cd (22.1keV)
2500
#counts
2000
1500
1000
500
0
0
100
200
300
channel
400
500
Recoil detector for fast neutron (1-10
MeV) spectroscopy
• Single event energy resolution
• Efficiency is expected to be more than two
orders of magnitude better than current Li
foil detectors (~10-7)
• Gaseous media
• GEM multiplication
• Scintillation read by CCD
Recoil neutron spectrometer
• We have to measure
– Energy of the recoil
• Total light measurement
– Angle of the recoil
nucleus
• ratio between track real
length (estimated from the
recoil energy) and
projection read by the CCD
Gas selection
(neutron recoil spectrometer)
• Maximal track length should be around
5 cm
• Efficient scintillator
neutron energy (MeV) 4He recoil energy (64%)
0.8
1.6
7.8
15.6
0.5
1.0
5.0
10.0
range (cm)
He
Ne
1.8
0.7
2.8
1.1
18.3
6
57
16.9
Ar
0.3
0.5
3.7
10.5
Kr
Xe
0.3
0.4
2.6
7
Simulated using SRIM-2000 (J.F. Ziegler, J.P. Piersack)
Experimental measurements with alpha particles are being carried on
to estimate the accuracy of the spectrometer
Tests will be done at the Democritos (Greece) neutron accelerator
facility
0.2
0.3
1.9
5.2
Medical applications
• Dose imaging in radioteraphy
GEM2
GEM1
kapton
mylar
Window
window
Proton Beam
Mirror
3.5 mm
(E = 150 MeV)
3 mm
L1
L1+L2 ~ 2m
L2
Cathode
CCD camera
D
C
B
A
Dose imaging in radiotherapy with an Ar-CF4 filled scintillating GEM,S.
Fetal, C.W.E. van Eijk, F. Fraga, J. de Haas, R. Kreuger, T.L. van Vuure
and J.M. Schippers, PSD6, submitted to NIM
Other projects
• Thermal neutron imaging
– Solid converter detector with GEM active
scintillator readout
– Groups integrating the TECHNI collaboration
• X-ray polarization
– GEM polarimeter with optical readout
• GEM coating with p-terphenyl
Conclusions
• Active scintillators using GEMs can be used with a
large variety of gases Ar-CO2, Ar-CF4, Ar-TEA, HeCF4, Xe-CO2, Xe-TEA, Xe-TMA,...
• Very large number of emitted photons per detected
event
– typically 2-3 orders of magnitude than solid
scintillators
• Can achieve high resolution
• Large area
• Fast signals, high count rates(>105c/s/mm2)
• promising with APDs and position sensitive PMTs
Acknowledgements
• Current work on GEM luminiscence is supported by the contract
CERN/P/FIS/ 2001/2567 with the Portuguese FCT.
• This work was done with the collaboration of the GDD,
CERN(F.Sauli), TUD (C. van Eijk) and SDN, ILL (B. Guerard)
Photon-counting position
sensitive devices APD arrays
• Hamamatsu S8550