ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray … · 2000-06-04 · ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging. PIXEL 2000 International Workshop

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


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


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


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)


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 *


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.


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


Fibre opticwindow

X- or γγγγ-ray

X- or γγγγ-ray

YAP:Ce array

YAP:Ce plate



Photons

PhotonsPhotons

Different possible configurations


(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


D. P.


Current ISPA prototype


Photons YAP:Ce window

X- or γγγγ-ray


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.


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.


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


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.


0

1000

2000

3000

4000

5000

0 20 40 60 80 100 120 140 160 180 200


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


coun

ts [a

.u.]

5.9 keV



109Cd

55Fe

D. P.




0

1000

2000

3000

4000

0 100 200 300 400 500 600 700


coun

ts [a

.u.]

279.2 keV

two K lines(72.19 keV) 203Hg

D. P.


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


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


distance of the two holes = 0.90 mm on chipFWHMxmeas. = 0.452 mm

D. P.


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.


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.


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.


D. P.


FUTURE OUTLOOK

Developments on heavier Ce-doped scintillatorsand of larger dimensions.

Implementation of ALICE chip.

Possible use of thinned detector unit.

D. P.


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.


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)

Documents

ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray … · 2000-06-04 · ISPA-Tubes with YAP:Ce Active Windows for X and Gamma Ray Imaging. PIXEL 2000 International Workshop