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 1993Towards 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

• 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

-100 -50 0 50 100

0

10

20

30

40

50

60 GEM 80/70GEM 60/50GEM 45/35

E (

kV/c

m)

z (micron)

Study of luminiscence of GEMs

• Both charge and light signals were digitized

X-ray

Camberra 2006

Camberra 2005

DigitizerTektronixTDS 7104

2mm

2mm

5mm

Vd

V1

V2

V3

V4

Ed

Et

Ei

Drift Grid

GEM1

GEM2

Induction Grid

PMT

P.A

P.A

Typical light signal shape using He-40%CF4

• The light signal risetime at the preamplifier output is 39ns

Average rise time of the light and charge signals versus induction field, Ei

• 55Fe

• Ed=0.5kV/cm

• Et= Ei = 2kV/cm

• double GEM gain ~ 3.1x103.

Double GEM, He+40%CF 4 (1bar),

Ed=0.5kV/cm, Et=2kV/cm,

Effective Gain ~3.1x10 3

0

20

40

60

80

0 1 2 3 4 5Ei (kV/cm)

Ris

e T

ime

(ns)

Charge

Light

Energy resolutionDouble GEM, He+40%CF4 -1bar

Ed=0.5kV/cm, Et=Ei=2kV/cm, Effective Gain ~ 9x104

55

Fe (5.9keV)

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0 100 200 300 400Channel

#Cou

nts

Charge (R~20%)

Light (R~20%)

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

• Quantum efficiency of the Quantix 1400 camera versus wavelengh

0

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300 400 500 600 700 800 900 1000 1100

Wavelength (nm)

Qun

atum

effi

cien

cy (%

)

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

Radiation source

-Vdrift

Front electrode Back electrode

GEM

Glass window

Minimum focusing distance~30cm

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

•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

0

50

100

250 300 350 400 450

Vgem

ligh

t/cu

rren

t (a

.u.)

Ar(1) Ar(3)

Ar(2) Ar2.5%Co2

Ar5%CO2 Ar5%CO2

Ar10%CO2 Ar10%CO2

Ar10%CO2

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

• 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

10

100

1000

300 350 400 450 500 550 600

Vgem (Volt)

Gai

n

Ar+5%CO2Ar+5%CF4

Ar+80%CF4100%CF4

0

5

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15

20

25

30

300 350 400 450 500 550 600

Vgem (Volt)

Lig

ht Y

ield

(a.

u./e

)

Ar+5%CO2

Ar+5%CF4

Ar+80%CF4

100%CF4

500 550 600 650 700 750 800 850

0

1

2

3

Ar + 67% CF4

G=40

I no

rm (

a.u

.)

(nm)

500 550 600 650 700 750 800 850

0

1

2

3

Ar + 10% CF4

G=90

500 550 600 650 700 750 800 850

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1

2

3Ar + 5% CF

4

G=40

1 10

0,1

0,2

0,3

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0,5

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0,7

5% CF4

10% CF4

67% CF4

Np

h/e

-

Gain

Visible and NIR emission spectra of Ar-CF4 mixtures, normalized to the light intensity at 620 nm.

Nº of photons emitted, between400 and 1000 nm, per secondaryelectron, as a function of the effective gain, in Ar-CF4 mixtures.(Measurements performed withthe photodiode).

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

• Gain saturates for smaller holes at lower pressures as reported in NIMA 419(1998)410

• 60 m hole GEMs have higher light yield

1

10

100

1000

35 45 55 65 75 85

Hole diameter (micron)

Gai

n

0,4 bar (420 V) 1 bar (560 V)2 bar (740 V) 3 bar (740 V)

Data on CF4 + HeCF4 pressure = 400mbar, He = 0.6 and 3.6 bar

1

10

100

1000

10000

300 350 400 450 500 550

VGEM (V)

Gai

n

GEM 140/80: He-CF4 (600/400 mbar)GEM 140/60: He-CF4 (600/400 mbar)GEM 140/45: He-CF4 (600/400 mbar)

1

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1000

10000

300 350 400 450 500 550 600

VGEM (V)

Gai

n

GEM 140/80: He-CF4 (3600/400 mbar)GEM 140/60: He-CF4 (3600/400 mbar)GEM 140/45: He-CF4 (3600/400 mbar)

0E+00

2E-06

4E-06

6E-06

8E-06

1E-05

300 350 400 450 500 550 600

VGEM (V)

Lig

ht Y

ield

(a.u

./e)

100%CF4GEM 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)

Photon yield 0.077 photons/secondary electron at 1 bar He-60%CF4

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) radiographyX-ray energy ~8keVXe-10%CO2 at 1barabsobtion 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

• Xe-TMA strong Penning effect

• TMA ion. pot 8.1 eV• Xe metastable pot. 8.3• Operation at a lower

voltage

Xe/TMA 3bar

0.0

50.0

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150.0

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PTMA (mbar)

Cha

rge

Gai

n

0 2 4 6 8 10 12%TMA

Vgem=320 V

1

10

100

1000

150 200 250 300 350 400 450 500

VGEM (V)Ga

in

Xe +5%TMA (1bar)

Xe +2.5%TMA (3bar)

Xe +2.5%TMA (5bar)

single GEM 60/70/140

Operation of Xe - TMA at 5 bar (light)Xe/TMA - 3 bar

0.0E+00

5.0E-10

1.0E-09

1.5E-09

2.0E-09

250 270 290 310 330 350 370 390

(nm)

#Cou

nts/e

0,625%TMA

1,25%TMA

2,5%TMA

5%TMA

Step = 2 nmSlit aperture = 1 mmGas Gain ~ 100

Step=2nmSlit aperture=1mmGas Gain ~50

0.0E+00

5.0E-10

1.0E-09

1.5E-09

2.0E-09

250 270 290 310 330 350 370 390 (nm)

#Cou

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Xe+5%TMA - 1bar

Xe+5%TMA - 3 bar

Xe+5%TMA - 5 bar

•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-whelkdouble GEM, 5mm absorption space, Xe-2.5%TMA at 5bar,

molybdenium X-ray tube at 40 kV

Radiography of a small snail ~8mmdouble 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

0

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250

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Ec (kV/cm.bar) (collection Field)

Rise

Tim

e (ns

)

charge (5.9 keV)PMT (5.9 keV)

Double GEM Xe+2.5%TMA (3bar)Ed=0.5kV/cm.bar, Et=0.25kV/cm.bar

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250

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Ec (kV/cm.bar) (collection Field)

Rise

Tim

e (n

s)

charge (5.9 keV)PMT (5.9 keV)

Energy resolution using Xe-2.5% TMA 5bar (light signals)

Double GEM Xe+2.5%TMA (5bar)PMT signals

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channel

#cou

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109Cd (22.1keV)

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%) range (cm)He Ne Ar Kr Xe

0.8 0.5 1.8 0.7 0.3 0.3 0.21.6 1.0 2.8 1.1 0.5 0.4 0.37.8 5.0 18.3 6 3.7 2.6 1.9

15.6 10.0 57 16.9 10.5 7 5.2

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

Medical applications• Dose imaging in radioteraphy

Cathode

GEM2

B

3.5 mm 3 mm

kapton

Windowmylar

window

GEM1

D C A

Proton Beam

(E = 150 MeV)

Mirror

L1+L2 ~ 2mL2

L1

CCD camera

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, He-CF4, 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