investigation of a transmission-line readout for building
TRANSCRIPT
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Investigation of a Transmission-Line Readout for Building PET Detector Modules
Contents1. Introduction2.Simulation Setup3.Results4.Summary and Plans
Heejong Kim, Univ. of Chicago
Pico-Second Workshop VII, Feb. 28, 2009
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Idea of Multi-threshold sampling•Conventional PET DAQ.
ADC for EnergyCFD Discriminator for Timing
•Pulse sampling at the pre-defined Voltage.
•Pulse reconstruction using timing readoutExtract Energy.
Multi timing hits on the rising edgeEvent timing.
TOP : Waveform with 20Gsps sampling.3 M-T sampled signal superimposed.
Bottom : Rising part only.
Waveform from R9800PMT+LSO
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M-T board and Setup
M-T Board( left)4 channels implemented.
HPTDC(CERN)(right)readout timing from M-T board.8 channels with ~25ps resolution.
Na-22 for coincidence source.Signal from R9800+LSO Connected to M-T board
with 4 different Threshold levels.HPTDC readout through LabView.
input
output
HPTDC
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Energy &Timing Resolution
Pulse reconstruction using M-T sampling.4~8 points from 2~4 thresholds.Exponential fit to falling edge.18% Energy resolution( ~14% using 20Gs sampling waveform)
Linear fit on the rising edges.Coincidence timing resolution~350ps
( ~300ps using 20Gs sampling)
cf, “A multi-threshold sampling method for TOF-PET signal processing”,NIMA, In Press(doi:10.1016/j.nima.2009.01.100)
Energy of 511keV gammma Coincidence time
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Introduction•Micro-Channel Plate(MCP) PMT shows fast time response.( 200~500ps anode rise time, 20~50ps TTS)
•Transmission Line(TL) Board can be a efficient way to readout multiple channels.
•MCP+TL Board can be an attracting option for PET detector design.
•Sandwich configuration: MCP + LSO + MCPHigh Sensitivity ( ~80% detection efficiency)3D positioning with resolution < ~4mm.<~500ps coincidence timing resolution.
•Need optimization before building proto type detector module.
•Preliminary study was done using Geant4 simulation.
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MCP & Transmission line Board
Wavelength(nm)200 250 300 350 400 450 500 550 600 650 700
Eff
icie
ncy(
%)
0
5
10
15
20
25
30Q.EQ.E
2inch square head-on MCP(Burle/Photonis).10um, 25um pore size.Anode #: 32x32 ( 1.6mm pitch)7.5x10e5 gain at 2,600V( 85011-spec)
TL Board : readout MCP anodes with 32x2. Modified to 12x12 anodes for this simulation.
Q.E of Planacon(Burle) MCP(From Fukun’s slides)
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Simulation Setup(Geant4)
•Dimension : 51x51x33mm3•LSO( 1 pixel => 4x4x25mm3)
pixelated into 12x12(left)Crystal pitch : 4.25mm
•MCP(51x51x4mm3) •Photocathode embedded in MCP.•Module = LSOs between 2MCPs.
LSO : Decay time 40nsLightout : 30,000/MeV
511keV two gammas at the center.180 deg angle between two gammas.50mm separation between two modules.Surface: “groundbackpainted”
(Unified model)
(not to scale)X-25.5 25.50
0
25.5
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Single Electron Responses
Time(ns)−1 0 1 2 3 4
Am
plit
ude(
mV
)
0
1
2
3
4
5
6
7
8
9
1. Pulse Shape~500ps rise time(top)( real measurement by J-F)similar value for falling timeassume asymmetric gausian shape
2. Average gain factor : 10e6 Single electron gain~70% in FWHM.
3. Transit Time Spreadsigma = 50ps( real measurement by J-F).
Simulated pulse shape
real measurement
cf.Seng’s slides at Picosecond workshop at Lyon08
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Signals at anodes
Detect photons at photocathode.Apply Q.E of MCPApply single electron response to photoelectron.Sum up pulse at each anode.
0 50 100 150 2000
50
100
150
200
250
h_t2_up_6_5_0
0 50 100 150 2000
50
100
150
200
250
h_t2_up_6_6_0
-4 -2 0 2 40
50
100
150
200
250
h_t2_up_6_5_0
-4 -2 0 2 40
50
100
150
200
250
h_t2_up_6_6_0
Simulated signal shape at anodesBeam was on the right anode.Signal is localized.
Top : Time( -10 ~ 200ns)Bottom : Time( -5 ~ 5ns)
Example : maximum signal anode and neighbor
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Data Set
x yA 2.125 2.125
4.0C 4.5 4.5D 6.375 2.125
B 4.0
A
B
D
1) Two gamma ( along Z direction)
Z(mm)
a 3.125
b 6.25
c 9.375
d 12.5
e 18.75
2) DOI measurement( varying Z)
a b c
25mm4mm
C
d e
Front Back
5,000 events generated for each set.
(Front view)(Side View)
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Readout Scheme
TL direction
Front Side Back Side
•Readout signals from 12 horizontally (vertically) running TLs. •Total 12x2 channels for a module.•Position : Maximum signal TL coordinate.•Energy : Sum of two sides( e.g, 3 TL sum w.r.t the maximum for each side)•Timing : Average of maximum TL from each side.•DOI : Ratio of energies from two side( or timing)
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Detection Efficiency
Wavelength(nm)350 400 450 500 550 600
0
1000
2000
3000
4000
5000
310×
w/o Q.Ew/ Q.E
Beam position Efficiency(%)
A 76
B 75
C 74
D 77
Entries 4999Mean 1300RMS 656.2Integral 4999
/ ndf 2χ 31.26 / 33Constant 1056952± 2.202e+05 Mean 1232.4± 6337 Sigma 892.7± 1146
0 500 1000 1500 2000 25000
100
200
300
400
500
600
700 / ndf 2χ 52.67 / 50
Constant 4.1± 194
Mean 1.2± 1674
Sigma 0.93± 73.32
/ ndf 2χ 52.67 / 50
Constant 4.1± 194
Mean 1.2± 1674
Sigma 0.93± 73.32
TOP L: Photon Emission Spectrumdetected at photo-cathode
TOP R: # of photon per event.After Q.E applied.
‘# of photon > 1000’ required for efficiency.
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Energy ResolutionEntries 2868
Mean 254.3
RMS 29.7
Integral 2868
/ ndf 2χ 276.3 / 23
Constant 11560355185691923054592± 1.285e+22
Mean 59.2± 1914
Sigma 5.3± 173.2
Charge(pC)100 150 200 250 300 3500
50
100
150
200
250
300
Energy
/ ndf 2χ 38.34 / 19
Constant 8.0± 309.1
Mean 0.3± 264.9
Sigma 0.20± 12.49
/ ndf 2χ 38.34 / 19
Constant 8.0± 309.1
Mean 0.3± 264.9
Sigma 0.20± 12.49
Energy
Beam position FWHM(%)
A 11.1
B 11.2
C 11.3
D 11.1
Sum of 3 TLs signal w.r. t the maximum TL.Sum of two sides for a module.
Energy distrubution of 511keV
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Position Measurement•Use Anger logic with 3 highest TL’s signal.Xdet = Sum(Xi*Ei) / Sum(Ei) ( for Vertically running TL in Front)Ydet = Sum(Yi*Ei)/ Sum(Ei) ( for Horizontally running TL in Back)
B C
0 1 2 3 4 5 6 7 80
200
400
600
800
1000
1200
1400
h_x2_up_0Entries 2798Mean 5.601
RMS 3.598
Integral 2798
Reconstructed X coordinate.
Beam Entering Position(X cor)B : 4.0mmC : 4.5mm
Photon( Signal) is highly localizedwithin crystal pitchs( 4.25mm).
Position resol. for coincidence event~ 2mm
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Timing
Entries 2868Mean 0.006332RMS 0.2024Integral 2853
Time(ns)-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2
0
50
100
150
200
250
300
350
400
Coincidence Timing / ndf 2χ 65.35 / 21
Constant 9.9± 382.7
Mean 0.002748± 0.004347
Sigma 0.0025± 0.1447
/ ndf 2χ 65.35 / 21
Constant 9.9± 382.7
Mean 0.002748± 0.004347
Sigma 0.0025± 0.1447
Coincidence Timing
Beam position δ(T) (FWHM)
A 340psB 358psC 367psD 350ps
Timing of the maximum signal TL.Apply leading edge for timing pick-up( Threshold: 20mV)Transmission time was corrected depending on position.T0: Average of two maximum TL for a module.
Time difference between T0s from two modules.
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DOI measurement
•(Ef+Eb) is not dependent on DOI.Ef = Energy of Front sideEb = Energy of Back side
•Separate readout of front/backenable to use energy asymmetry.
•Energy Asymmetry : (Ef – Eb)/(Ef + Eb)*2*100(%)
•E Asymmetry vs Beam positionError bar is the spread the distribution.
length(mm)0 5 10 15 20 25
Energ
y Asy
mmery
(%)
-10
-5
0
5
10
length(mm)0 5 10 15 20 25
Energ
y Sum
( Fron
t + B
ack) (
pC)
200
210
220
230
240
250
260
270
280
290
300
Distance from front side(mm)
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Summary and Plans•A Geant4 study for PET detector design.LSO+MCP+TL Board.
•Preliminary results obtained.E resolution : ~12%Timing resolution : ~350psPosition resolution : ~4mmDOI : found tendency
•Need more data and investigations for optimization.Crystal(LaBr), dimension, # of readout channel.
•Try another readout scheme.•Validation with real tests.