Mihael Makek with D Bosnar V Gačić L Pavelić P Šenjug and P Žugec Department of Physics Faculty of Science University of Zagreb 2 nd Jagiellonian Symposium on Fundamental and Applied Subatomic Pysics Krakow 2017 ID: 633266
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Slide1
Performance of scintillation pixel detectors with MPPC read-out and digital signal processingMihael Makekwith D. Bosnar, V. Gačić, L. Pavelić, P. Šenjug and P. ŽugecDepartment of PhysicsFaculty of Science, University of Zagreb
2nd Jagiellonian Symposium on Fundamental and Applied Subatomic Pysics, Krakow, 2017Slide2
Motivation and outlineConstruct and test segmented detector arrays using state-of-the art SiPMs, scintillation materials and digital signal processing electronics; applications: PET, PALS, fundamental measurementsOutlineSimulation of detector efficienciesExperimental setupPerformance results of LFS scintillator pixels and MPPC array
Krakow, 2017Mihael Makek
2Slide3
Simulation of ideal detection efficiencytakes into account: density, Zeff, resolutionGeant4, geometry: 8x8 pixels, g impinging on either of 4 central pixelsShowing fraction of detected/incoming 511 keV gammasKrakow, 2017Mihael Makek
3
DetectorLYSO 20mm
E
dep.
>50 keV
E
dep.
~
511
keV
Single
0.57
0.43
Coincidence0.320.18
Detector
LFS 20mm
E
dep.
>50 keV
E
dep.
~
511
keV
Single
0.59
0.46
Coincidence
0.35
0.21Slide4
LFS scintillatorLutetium Fine Silicate (Zecotec patent)Krakow, 2017Mihael Makek4Crystal/Property
LFSLYSODensity [gcm-3
]7.357.1
Z
eff
64
66
Atten
.
Length [cm]
1.15
1.12
Decay constant [ns]
<33
41
Max.
emission [nm]
425
420
Light yield
[%
NaI]80-8570-80Refractive index1.811.81HygroscopicNo NoActiveYesYes
4x4 array
3.14 x 3.14 x 20 mm
3
1
layer
~0.06 mmSlide5
MPPC arrays4x4 MPPC array (S13361‐3050AE Hamamatsu)Main features:Number of micro-cells 3584/pixelMicro-cell pitch = 50 mmFill factor 74%Epoxy window, n=1.55Vbr ~ 53 VPDE (typical) ~ 40%Spectral range 320-900 nm(max at 450 nm) Krakow, 2017
Mihael Makek5
1 p.e.
2 p.e.
3 p.e.Slide6
Amplifiers16-channelPassive base:selectable cable lengthMatching base depending on the SiPM model and manufacturerSum output withselectable gain and offsetOutput signals:50 Ohmmaximum -2 V Rise-time ~ 10-15 ns
(depending on cable length)
Krakow, 2017Mihael Makek
6Slide7
DigitizersCAEN model V174316 channel, switched capacitor(based on SAMLONG chip)1024 samples/channel7 events/channel bufferUp to 3.2 GHz sampling rateSelectable trigger logic (after bugfixes on our request)Multi-board synchronization still in experimental phaseIndividual readout for all crystal channlesKrakow, 2017Mihael Makek
7Slide8
Setup and trigger Krakow, 2017Mihael Makek8
16 ch. Amp.
16 ch. Amp.
16 ch.
digitizer
OR
16 ch.
digitizer
OR
TRG IN
TRG IN
22
Na
ANDSlide9
Recorded at 1.6 GHz625 ps samplesVop = Vbr+1.5 VRise-time ~ 15 nsEnergy reconstruction
:Amplitude
Integral
Digitized s
ignals
Krakow, 2017
Mihael Makek
9Slide10
Reconstructed energy of 511 keV gammasKrakow, 2017Mihael Makek10
D
E/E=15%
D
E/E=13%
Integral linear with amplitude
Integral
provides
superior
energy resolutionSlide11
Non-linearity correctionLimited number of micro-cells causes saturation of large signalsThe relation between incident photons (Nph)and fired cells (Nfired):Apply correction:
where Nfired is obtained empirically:
Krakow, 2017Mihael Makek
11
M
is the total number of micro-cells,
PDE
is photon detection efficiency calculated as product of
QE(
l
),
P
av
(V,T) and fill factor
Original
Corrected
201 keV from
176
Lu
306 keV from
176
Lu
511 keV from
22
NaSlide12
Light sharingCalibration: sum of all fired channels = 511 keV Krakow, 2017Mihael Makek12
Energy
deposition
:
L
eading/total ~ 80%
S
1st neigh
bors
/total ~ 20%
2nd nei
ghors
/total ~
negligible
Single pixel energy
resolution degradation @511
keV
:
11%
13%
Light sharing significant
bewteen
adjacent pixels.
0,06 mm reflector too thin!Slide13
One photo-electon amplitudeMeasured on oscilloscopeMap temperature and voltage dependence for both detectors
Krakow, 2017Mihael Makek
13
V
br
(1) = 52.1 V
V
br
(2) = 52.2 VSlide14
Number of fired micro-cells @511 keVMean number of fired cellsat 511 keV vs:VoltageTemperatureKrakow, 2017Mihael Makek14
Reflects how PDE changes with temperature and voltage
Impact on energy resolutionSlide15
511 keV photo-peak amplitudeMean amplitude of the 511keV photo-peak vs V and t(Range limited by amplifier gain)Krakow, 2017
Mihael Makek15
Change of amplitude with V is ~equally governed by number of fired cells and 1p.e. amplitude
Change of amplitude with temp. is dominantly governed by 1p.e. amplitudeSlide16
Energy resolution @ 511 keVEnergy resolution improveswith U in the measured rangeNegligible dependence on temperature in the measured rangeKrakow, 2017
Mihael Makek16Slide17
Time resolutionPixel-to-pixel timingDetermined by fittinga straight line to the signalrising – edgeDt ~1.6 ns (FWHM)Limited by amplifier rise-time of ~15 nsKrakow, 2017
Mihael Makek
17Slide18
SummarySimulation shows LFS has potential to improve sensitivity of PET compared to LYSOLFS performace tests:energy resolution satisfactory, but can improve by reducing the light sharing between the pixels and running at higher overvoltageTime resolution must be checked with fast preamplifier MPPC arrays show stable performanceSaturation correction done on event-by-event basisSignal amplitudes scale linearly with voltage and temperatureTemperature variations under control without direct compensationKrakow, 2017Mihael Makek
18Slide19
BACKUP SLIDESKrakow, 2017Mihael Makek19Slide20
Single pixel full spectrumKrakow, 2017Mihael Makek20Slide21
Energy calibration procedureCorrect each channel for non-linearity (event-by-event)Equilibrate all channels by scaling each channel’s photo-peak to the same valueCalibrate the sum of all fired channels to 511 keVRepeat procedure for each run (approx 1h of data taking)
The self-calibration on coincidence data is stable wrt to temperature and voltage change no need to pre-calibrate the setup
Krakow, 2017
Mihael Makek
21Slide22
Uniformity of the response with distance from the MPPCA modified detector setup to test the uniformity:Krakow, 2017Mihael Makek22
Pb
collimator
22
Na
MPPC
d5
d4
d3
d2
d1
20 mmSlide23
Uniformity of the response with distance from the MPPCSelect photo-peak in the leading pixelKrakow, 2017Mihael Makek23
Leading pixel amplitude vs. distance
Leading/(sum of 1st neighbors)
vs. distance
Homogeneous response!Slide24
CeBr3 scintillatorKrakow, 2017Mihael Makek24Crystal/PropertyCeBr
3LYSODensity [gcm-3
]5.10
7.1
Z
eff
45.9
66
Decay constant [ns]
20
41
Max.
emission [nm]
380
420
Light yield
[%
NaI
]
160
70-80
Refractive index2.091.81HygroscopicYesNoActiveLow Yes SurfaceFine groundPolishedSlide25
Simulation of ideal detection efficiencytakes into account: density, Zeff, resolutionGeant4, geometry: 8x8 pixels, g impinging on either of 4 central pixelsShowing fraction of detected/incoming 511 keV gammasKrakow, 2017Mihael Makek
25
DetectorLYSO 20mm
E
dep.
>50 keV
E
dep.
~
511
keV
Single
0.57
0.43
Coincidence0.320.18
Detector
CeBr
3
20mm
E
dep.>50 keVEdep.~511keVSingle0.450.21Coincidence0.200.04