Transcript 2012 IEEE_NSS-MIC 유현준x(4748677)

Design of SiPM based Electrical Personal Dosimeter
Hyunjun Yoo, Yewon Kim, Hyunduk Kim and Gyuseong Cho*
Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
E-mail : [email protected]
Ⅰ. Abstract
The SiPM(Silicon Photo-Multiplier) has been developed for various applications such as the medical diagnostics PET and astro-particle physics for the last decade[1-2]. As an
additional application of the SiPM, we are proposing an SiPM based EPD (Electrical Personal Dosimeter) which composed of a small size scintillator and gamma-ray pulse
processing electronics basically. For this application, the SiPM has a number of advantages over other photo-detectors such as PIN diodes and PMTs (Photo-Multiplier Tube), for
example, the lower mass production cost, the smaller size and the lower bias voltage than the PMT [3]. To maximize the probability of radiation detection, EPD needs the large area
of detector. But there are more dark current when SiPM area is larger. The number of photo peak counts from energy spectrum means the signal that events of human being exposed
from maximum energy gamma ray. And dark current means the noise of SiPM by thermal generation or tunneling process. From the experimental results, peak count rate starts to
saturation from 40mm2 detector size. So, we optimize the SiPM area for EPD in 40mm2 . The 5.3% of Cs-137 energy resolution from charge adder preamplifier is well operated
with 9ch SiPM. But, voltage adder preamplifier can not take the energy spectrum because of high electronics noise. So we decided that charge sensitive preamplifier is more suitable
to confirm the gamma ray full peak energy for EPD to increase the radiation detection probability.
Ⅱ. Materials and Methods
10
1
0
10
20
30
0
40
0
20
40
[Dark current is proportionally increased by SiPM area]
In this experiment, we used the Cs-137 isotope and LYSO array scintillator.
From the experimental results, photo-peak count that have full gamma-ray
energy is increased with SiPM area, but, photo-peak count rate is saturated over
the 40mm2 SiPM area. So, we have to optimized the detector area in 40mm2 to
increasing the probability of radiation detection what have full gamma ray
energy human exposed.
32
LSO,Cs-137
1ch
4ch
9ch
Count
60000
30
3.69%
4.40%
40000
20000
3.39%
 Electronics for Signal Processing
0
0
500
1000
 Preamp
1500
28
26
24
22
2000
0
20
40
MCA Channel
These experiments use the 2 types of charge sensitive preamplifiers developed by
SensL and KAIST. SensL’s preamplifier is used to check the reference
characteristics of preamplifier. The latter has 2 types of operations, first is charge
adder and second is voltage adder, both are used to find the difference among each
SiPM area. It can select the number of SiPM channel from 1 to 9 by deep switch.
[SPMmicro_v2, SensL]
[Preamplifier developed by KAIST]
 NIM Module
MCA
100
Energy Spectrum
80000
[CsI(Tl) Scintillator]
 10 x 10 x 10mm
80
2
[Dark current of 3 types of SiPM area]

60
Pixel Area [mm ]
Voltage(33V)
 Scintillator
-
200
Operation
Reverse Bias [V]
[Detector area for each channel]
[ 4x4 LYSO array scintillator]
 Same area with SiPM & 20mm thickness
400
Photo-count/Total-count [%]
[3 types of SiPM channel]
101.7uA
0.1
[SensL’s SPMArray4]
600
355.0uA
100
0.01
9ch
732.6uA
Dark Current [uA]
Dark Current [uA]
- For optimizing the SiPM area, we use the 16 channel SiPM Array (SensL’s
SPMArray4) for 3 types as 1ch, 4ch, 9ch. Each types are consisted by summing the
number of anodes to a single bunch.
4ch
Operation Voltage : 33V
1000
 Silicon Photo Multiplier
1ch : 3.16x3.16 𝑚𝑚2
4ch : 6.32x6.32 𝑚𝑚2
9ch : 9.48x9.48 𝑚𝑚2
1ch
4ch
9ch
10000
 Detector for Radiation Measurement
1ch
800
100000
60
80
100
2
Area [mm ]
[The rate of photo-count is saturated over 40 mm2 ]
[Energy spectrum of 3 types of SiPM area]
 Experiments of Multi-Channel Preamp
-
We develop the multi-channel preamplifier for SiPM array. There are two ways
preparing the experimental setups. The first, the all anodes of each SiPM
channels are connected to the one bunch and a preamplifier, so the summed
charge signal is processed for dose calculation. The second, the each SiPM is
connected to 16-channel preamplifiers, so each charge signal from an SiPM is
processed independently. From the results, voltage adder preamplifier has very
low SNR. But charge adder preamplifier has the photo peak in 5.3% energy
resolution, so it can be used to calculate the personnel dose from this
experimental setup, but it needs the noise filter to eliminate the electronics noise.
[Basic schematic of preamplifier of KAIST]
70000
Graphic User Interface
10000
Voltage Adder
Cs-137, CsI(Tl)
60000
Energy Resolution:5.3%
50000
40000
6000
Count
Count
8000
30000
4000
20000
2000
0
[Spectroscopy Amplifier, Ortec]
[TRUMP-PCI, Ortec]
[MAESTRO V6.05, Ortec]
10000
Charge adder
Cs-137,9ch
0
500
1000
1500
2000
MCA Channel
[Energy spectrum of charge adder preamplifier]
Ⅲ. Experimental Results
 Optimizing the SiPM Area
 SiPM Dark Current
-
For optimizing the SiPM area to maximize the probability of radiation detection,
there are two important factors dark current and rate of photo-peak count. Dark
current is generated by thermally or tunneling process in a silicon wafer. So it is
dominant phenomenon prohibiting the accurate measurement of the low energy
gamma-ray from the environments[4]. From the experimental results, dark current is
proportionally increased by SiPM area.
0
500
1000
1500
2000
MCA Channel
[Energy spectrum of voltage adder preamplifier]
Ⅳ. Reference & Acknowledgement
[1] Dennis R Schart, et al, A novel, SiPM-array-based, monolithic scintillator detector for PET, Phys.
Med. Biol.54 3501-3512(2009)
[2] Razmick Mirzoyan, et al, SiPM and ADD as advanced detectors for astro-particle physics, Nuclear
Instruments and Methods in Physics Research A 572 493-494(2007)
[3] P.Buzhan, el al, An advanced study of silicon photomultiplier, ICFA Instrumentation Bulletin(2001)
[4] E Sciacca, Silicon planar technology for Single photon optical detectors, IEEE Transactions on
electron devices, Vol. 50, No. 4(2003)
“This work was supported by the Center for Integrated Smart Sensors funded by the Ministry of
Education, Science and Technology as Global Frontier Project" (CISS-2012-0006361)