ispa-tubes with yap:ce active windows for x and gamma ray … · 2000-06-04 · ispa-tubes with...
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ISPA-Tubes with YAP:Ce ActiveWindows for X and Gamma Ray
Imaging.
PIXEL 2000
International Workshop on SemiconductorPixel Detectors for Particles and X-Rays
Genova - Porto Antico - Magazzini del Cotone (Sala Libeccio)June 5-8, 2000
C. D'Ambrosio1, F. de Notaristefani2, H. Leutz1, D. Puertolas2, E. Rosso1
1 CERN, 2 INFN Section of Rome, Italy
D. P.
CERN
INFN-Roma III (HIRESPET* Collaboration)
Institute of Physics, Academy of Sciences-Prague
Alice and LHCb exp. at CERN
EP-TA2 and EP-MIC groups at CERN
Industrial partners: D.E.P. (NL)Crytur Ltd. (CZ)Edgetek (FR)
*http://www.roma1.infn.it/~hirespet/index.html
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
D. P.
OUTLINE
Short introduction to the ISPA-tube
“Conventional” designs of gamma camerasbased on ISPA-tubes and results
Present developments : scintillating windows(YAP:Ce)
Conclusions and future outlook
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
D. P.
Position-sensitive photon detection with an ISPA-tube
Signal out(pixel binaryreadout)
Signal out(global analog
readout)
Pixel electronics500µm x 50µm
Pixel detector500µm x 50µm
VACUUM
Photoelectron
Photon
Photocathode
Optical inputwindow
Solder bump
- + - +- + - +- + - +- + - ++ - + -+ - + -+ - + -+ - + -
Electron-hole pairs(typ. 5-6500)
H. V
. (ty
p . 2
0-2 5
kV
)B
ias
volt
age
(typ
. 50-
70 V
)
Pixel chip developedby CERN/EP-MIC
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
D. P.
The self-triggering principle
detector chip
electronics chip
Fast, analog and globalinformation
Trigger for strobe
Immediate calibration inphotoelectron or energy
Selection of a window inenergy possible
Pixel signals out (with presentchip, pixel response is binary
Precise space information
2-D imaging
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
D. P.
Photocathode (-25 kV)
Input window
Photoelectrons
Photons
Silicon pixel array (1024 elements)
Fast (10 ns) global analog information
Binary pixel pattern read out in 10 µs
VACUUM
30 lead-throughsBump bonds
Co source57
122 keV γ's
Lead phantom
YAP-detectorRear contact
Electronics pixel array (1024 elements)
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Detection of γγγγ-rays with an ISPA-tube
Ω chip assembly developed by RD19 collaborationPixel size 75mmx500mm
D. P.
γγγγ-imaging with an ISPA-tube coupled toYAP:Ce crystal detectors *
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Properties of pure YAPChemical formula YAlO3 (inert, non hygroscopic)Crystal structure Orthorhombic (no cleavage)Density g.cm-3 5.37Molecular weight 168.88Zeff 34Hardness Moh 8.6Refractive index n at 400 nm 1.97
at 500 nm 1.95Transparency nm 240 to >1000
Additional properties of YAP doped with CeLight emission peak nm 365Light decay (1/e) ns 27Radiation length cm 2.7Avr. K X-ray energy of Yttrium keV 15.2Refractive index n at 400 nm 1.92
at 500 nm 1.91
* Our YAP crystal detectors are produced by Crytur Ltd, Turnov, Czech Republic
Due to its properties YAP can be easily machined and optically polished.Arrays of small individual elements (1mm2 down to 300µm2 can be assembled)
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Performances of ISPA-tubes in imaging
The overall performances of the ISPA-tube rely on both
The input window arrangement: the goal is to collect as manyphotoelectrons as possible while preserving the “localisation” ofthe gamma event
The anode pixel chip: the goal is to detect as manyphotoelectrons Npe as possible on the detector plane (energyresolution considerations) and to get a binary patternreproducing the light spot on the photocathode with a number offiring pixels Nhit (<Npe) allowing a precise c.o.g calculation(analysis event per event)
D. P.
X- or γγγγ-ray
Photons
YAP:Ce array
Quartz window
Photoelectroncluster
X- or γγγγ-ray
YAP:Ce plate
Photoelectroncluster
Fibre opticwindow
X- or γγγγ-ray
X- or γγγγ-ray
YAP:Ce array
YAP:Ce plate
Photoelectroncluster
Photoelectroncluster
Photons
PhotonsPhotons
Different possible configurations
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
(FWHM)~2-2.5 mm (FWHM)>3.5 mm
(FWHM)~crystal elements (FWHM)~2mm
D. P.
Result summary
Fibre window ISPA-tube:
++ excellent spatial resolutionfrom 100 µm (array) to 300 µm (plate)
-- poor E-resolution (only a few photoelectrons)
Quartz window ISPA-tube:÷ acceptable spatial resolution
from 500 µm (array) to 700 µm (plate)
+ good E-resolution at 122 keVfrom 20% FWHM (plate) to 40% FWHM (array) 200 p.e. 80p.e.
see IEEE TNS, vol. 42, no6, p. 2221 and vol. 44, no5, p.1747
ISPA-tube with larger active surface (40 mm diameter)+ The demagnification (~4) principle has been also successfully appliedfor gamma imaging applications, with sub-millimeter spatial resolution
see NIM, A442, (2000), p.279
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Current ISPA prototype
Photoelectroncluster
Photons YAP:Ce window
X- or γγγγ-ray
Photoelectroncluster
Photons YAP:Ce plate
X- or γγγγ-ray
quartz window
LHC1* chip implementationnew electronics amplifier 100 ns peaking time, globally adjustable
threshold, adjustable delay line, coincidence logic and memory
smaller pixel size (50x500µm)Electrical tests ~7.5% (150) pixels are masked (noisy)
test input ~4900e- γ=1710 (~85%) pixels respond with an efficiency of ~95%
≠
* The LHC1 chip has been developed at CERN by the RD19 and the EP/MIC group
YAP:Ce scintillating window
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Quantum efficiency of S20 photocathodeon YAP:Ce scintillating window
Perfect stability observed over 2 years
0
5
10
15
20
25
30
200 250 300 350 400 450 500 550 600 650 700 750 800
Q.E YAP-window HPMTQ.E Quartz-window HPMTQ.E. YAP-window ISPAQ.E. Quartz-window ISPA
Qua
ntum
Eff
icie
ncy
[%]
Wavelength [nm]
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
0
1000
2000
3000
4000
5000
0 50 100 150 200 250 300 350
Number of photoelectrons
coun
ts [a
.u.]
122 keV(FWHM) ~ 22%
Compton edge(39 keV)
Pb ~ 80 keV+ b. sc.
0
1000
2000
3000
4000
5000
0 50 100 150 200 250
Number of photoelectrons
coun
ts [a
.u.]
60 keV(FWHM) ~ 26.5%
Compton edge(11keV)
Energy spectra of some different sourcesEmissions converted in the YAP:Ce window of the ISPA-tube
Pulse height distributions measured on the silicon chip rear side
57Co
241Am
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
0
1000
2000
3000
4000
5000
0 20 40 60 80 100 120 140 160 180 200
Number of photoelectrons
coun
ts [a
.u.]
22 keV(FWHM) ~ 40%
Y escape(6.3 keV)
(x20)
88 keV
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20
Number of photoelectrons
coun
ts [a
.u.]
5.9 keV
Energy spectra of some different sourcesEmissions converted in the YAP:Ce window of the ISPA-tube
Pulse height distributions measured on the silicon chip rear side
109Cd
55Fe
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Energy spectra of some different sourcesEmissions converted in the YAP:Ce window of the ISPA-tube
Pulse height distributions measured on the silicon chip rear side
0
1000
2000
3000
4000
0 100 200 300 400 500 600 700
Number of photoelectrons
coun
ts [a
.u.]
279.2 keV
two K lines(72.19 keV) 203Hg
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
y = 1.7468x - 0.203R2 = 0.9994
0
50
100
150
200
250
300
350
400
450
500
550
0 50 100 150 200 250 300
Energy [keV]
Num
ber
of p
hoto
elec
tron
s
203 Hg γ
241 Am γ
203 Hg K
109 Cd γ
203 Hg L
57 Co γ
109 Cd Ag X 55 Fe Mn X
Photoelectron numbers versus the energies of totalabsorption peaks for several gamma sourcesmeasured with the YAP-window ISPA-tube
D. P.
Image of a 60 keV γγγγ-source (241Am) through a2-holes (0.35 mm φφφφ) lead collimator (5 mm thick)
~1 mm
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
20 k-events
D. P.
0
5
10
15
20
25
30
35
40
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00
c.o.g. coordinate projection x(mm)
mean1 = 2.80 mmsigma1 = 0.195 mmmean2 = 3.70 mmsigma2 = 0.190 mm
Intensity profile of the two holes along the X-direction
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
distance of the two holes = 0.90 mm on chipFWHMxmeas. = 0.452 mm
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Average number of firing pixel per gamma event: Nhit
0
100
200
300
400
500
600
0 10 20 30 40 50 60 70 80 90 100 110 120
Number of hits per event
mean at ~50 hits
Note: Nhit ~50 is < to Npe~100. The greatest part of the difference isdue to “overlap” effect
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
0
5000
10000
15000
20000
25000
30000
-4 -3 -2 -1 0 1 2 3 4
c.o.g. residuals x(mm)
Center-of-gravity residual projection along the X-direction
=(FWHM)resX = 1.50 mm on chip
D. P.
2
2
2 )(FWHMN
FWHM
hit
res =
+φ
(FWHM)resX = 1.50 mm; (FWHM)resY = 1.46 mm; Nhit ~50
x 0.352 + 0.2142 = 0.4102 <===> FWHMxmeas. = 0.452 mm
y 0.352 + 0.2062 = 0.4062 <===> FWHMymeas. = 0.435 mm
The difference between the estimated values and the measured ones canbe related to the tails in the residual distributions, which worsens theprecision in the c.o.g. calculation.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
The estimation of the spatial resolution is simply given by:
D. P.
CONCLUSIONS
First results with the YAP:Ce window ISPA-tube are very encouraging (cluster size /2, Npex1.2).
They can be used to detect a wide range ofenergies (window thickness can be adjusted).
Better matching of refractive index if coupledto other standard crystals.
The performances can be further improvedwith those of future pixel chip anode.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
FUTURE OUTLOOK
Developments on heavier Ce-doped scintillatorsand of larger dimensions.
Implementation of ALICE chip.
Possible use of thinned detector unit.
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Attenuation coefficients of Cerium-doped RE3+
perovskyte scintillators
0.1
1
10
100
0.01 0.1 1Energy (MeV)
Line
ar a
ttenu
atio
n co
effic
ient
(cm
-1)
YAP
LuAP
Lu0.1Y0.9AP
Lu0.3Y0.7AP
140 keV(99mTc)
D. P.
ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging.
Rel. L. Y. Density Peak emission Light decay%NaI(Tl) (g.cm-3) (nm) (ns)
NaI(Tl) 100 3.67 415 230
BGO 20 7.13 480 300
YAP:Ce 40 5.37 365 27
Lu0.1Y0.9AP:Ce - 5.73 - -
Lu0.3Y0.7AP:Ce - 6.19 - -
LuAP:Ce 20-50 8.34 360-370 <20
Some properties of Cerium-doped RE3+
perovskyte scintillators
@ 140 keV with a 3-mm thick scintillating window:
YAP;Ce ~30% efficiency (~55% total absorption)Lu0.1Y0.9AP:Ce ~45% efficiency (~70% total absorption)Lu0.3Y0.7AP:Ce ~65% efficiency (~80% total absorption)LuAP:Ce ~95% efficiency (~95% total absorption)