RAD2012, Nis, Serbia
Positron Detector for radiochemistry on
chip applications
R. Duane, N. Vasović, P. LeCoz, N. Pavlov1,
C. Jackson1, A. Jakšić
1) Sensl technologies (www.sensl.com)
www.tyndall.ie
OUTLINE
•
Radiochemistry On Chip (ROC) European Project
– Production of radiotracers for Positron Emission Tomography (PET) analysis
•
Silicon Photomultiplier Technology
•
Miniature Radiation Probes
•
Summary
www.tyndall.ie
Positron Emission Tomography
Injection of positron emitting radiotracer
(e.g. F-18 combination with glucose biomarker = FDG)
www.tyndall.ie
Commercial production of Radiotracers
+
Cyclotron to produce the radioactive isotope
(e.g. F-18, C-11)
=
Hot-cells to combine radioisotopes with
biomarker such as glucose analog
Fludeoxyglucouse (FDG)
www.tyndall.ie
Radiochemistry on Chip (ROC) Motivation
Motivation: On-site production of PET radiotracers
Technical Goal: Microfluidic synthesis platform
www.tyndall.ie
Microfluidic Synthesis Platform
Waste Lines
RadioTracer
www.tyndall.ie
Radiation Detection Objectives
Waste Probe
Positron Probe
Flow Probe
microreactor
•Track movement of FDG radioactivity in 1m3 Lead Box
–High concentrations of positron and annihilation gammas (1Tbq total F18
activity)
•Shielded probes to quantify activity in waste and flow shielded chambers
•Unshielded positron probe to track small changes in positron activity in
microfluidic chips as “process monitor”
www.tyndall.ie
Shielded probe requirements/design
1. Activity: 3.7kBq/100uL (waste) to 740Mbq/uL (flow)
2. Size: approx 1-2cm3 (due to microfluidic chip sizes)
 Scintillator based detector
3. Magnetic Field Immunity due to proximity to mini-cyclotron
 Semiconductor (Silicon) based photodetector
4. Count linearity and stability (<5%)
 Gamma scintillation detector
5. Long cabling (5m)
 High gain photodetector
www.tyndall.ie
Scintillator and Photodetector Operation
High Energy Gamma
Scintillation Crystal
1) Conversion to lower energy
visible photons
Photodetector
With amplification
2) Detection and amplification
of visible photons
www.tyndall.ie
Silicon Photodetector types
Silicon PN photodiode (Gain=1)
Silicon Avalanche photodiode (Gain=100)
www.tyndall.ie
Geiger Mode photodetector (Gain>106)
Sensl Silicon Photomultiplier
Sensl Silicon Photomultiplier (SPM)
•
Silicon Photomultiplier (SPM) = Array of Geiger Mode photodiodes
-
•
•
•
3,640 35um geiger mode diodes per 3mm die
Replaces PhotoMultiplier Tube (PMT)
Low voltage 30V operation
Direct gamma hits are not an issue due to device design
• Expect good count linearity for gamma detector
Large signal to noise ratio results in simpler electronics and longer cabling
www.tyndall.ie
Sensl Silicon Photomultiplier Probes
Inorganic
Scintillator
SPM
www.tyndall.ie
CSI (TI) Probe Results
1600
511kev
1400
Ge-68
Cs-137
1200
667kev
1000
counts
800
600
400
200
0
-200
0
100
200
300
400
500
MCA channels
•CSI (TI) chosen as best spectral match (550nm) to SPM peak light absorption (520nm)
•Peak Resolution 8.7% Cs137 , 10.5% Ge68
www.tyndall.ie
CSI(TI) Probe Results
0
10000
20000
30000
40000
1000000
Counts/second
100000
139kBq peak
1.5kBq peak
background
139kBq total
1.5kBq total
1.35cm*1.35cm*1.35cm CSI(TI)
1mm source-detector distance
50000
1000000
100000
10000
10000
1000
1000
100
100
10
10
1
1
0.1
0
10000
20000
30000
40000
Minimum Waste
Background
0.1
50000
Time [sec]
•Distinguish minimum waste activity (1.5kBq) in lab environment at room
temperature
•Stability of 4.7% (139kBq) over 12 hour measurement (1s integration time)
— Meets 5% specification for flow probe
—Expect better stability for 740MBq flow activities
www.tyndall.ie
CSI(TI) Probe Linearity
0
20
40
60
80
100
35000
35000
Linear Fit=1
1.35cm probe
6mm detector source distance
30000
25000
25000
20000
20000
15000
15000
10000
10000
5000
5000
0
Linearity
30000
Counts/10s
0
120
5
10
15
20
25
30
1.0000
1.0000
0.9999
0.9999
0.9998
0.9998
0.9997
0.9997
0.9996
0.9996
0.9995
0.9995
0.9994
0.9994
0.9993
0.9993
0
0
20
40
60
80
100
120
0
5
Activity [kBq]
10
15
20
25
30
Acquisition Time [s]
•Good linearity for low waste activities(1.5kBq-139kBq) using peak counting
•Peak Sensitivity = 30counts/second/kBq (at 6mm distance from disc source)
www.tyndall.ie
CSI (TI) Flow Probe
• Saturation of measured counts (Peak counting)
–CSI(TI) scintillator 1ms pulse and associated 3ms shaping time
www.tyndall.ie
LSO Flow Probe
•LSO scintillator (3mm) investigated for flow probe
•Faster gamma response (40ns)
•Poorer spectral matching (440nm peak photon emission)
0
10
20
Counts
50000
30
40
50
60
70
80
90
100
110
50000
3mm*3mm*15mm LSO
Linear Fit (0.9995)
40000
40000
30000
30000
20000
20000
10000
10000
10s integration time
0
0
10
20
30
40
50
60
70
80
90
100
0
110
Activity [kBq]
www.tyndall.ie
LSO Flow Probe
109.74min F-18 half-life
5 second integration time
•Good fit to 1Gbq F-18 decay over 20 hours (Total counting)
www.tyndall.ie
SUMMARY
•
Silicon Photomultiplier based probes for radiochemistry
– CSI(TI) +SPM waste probe
– LSO + SPM flow probe
•
Preliminary results show good count linearity and stability
•
Temperature compensation circuitry for SPM gain in development
•
Welcome collaborators with access to high activity positron sources
– Stability, Linearity as a function of temperature
– Radiation Hardness
www.tyndall.ie
Thank you for your attention!!!
www.tyndall.ie