Fabricateion and Characterization of Rectangular Strontium Iodide
Scintillator Coupled to TSV-MPPC Array
K. Shimazoe1, A. Koyama1, H. Takahashi1, S. Sakuragi2, Y. Yasushi2
1
2
3
The University of Tokyo, Union Materials, Leading Edge Algorithm,
Introduction and Background
Rectangular SrI2(Eu) crystals
and Method
Europium doped Strontium Iodide (SrI2(Eu)) is a promising
scintillation detector for use in radiation detection because of its
high light output (80000 -110000 photons per MeV), excellent
energy resolution around 3 % and low background radiation.
These good characteristics make it promising for the gamma-ray
imaging in the environmental applications as an alternative of
Sodium Iodide (NaI(Tl)). Especially for Compton Imaging(Fig.1)
used in Fukushima [1], better energy resolution is required to
improve the position resolution.
For fabricating a compact radiation detectors, the coupling to solidstate photosensors, such as APD (Avalanche Photo Diode) and
silicon photomultiplier (SiPM), is necessary, which has typically a
square shape. The rectangular SrI2 scintillators (25.4 x 25.4 x 10
mm) are fabricated with “Liquinert” process for removal of water,
and evaluated with Photomultiplier, APD and TSV-type MPPC. The
initial results shows the excellent energy resolution around 3.6 %,
3.5 % and 3.9 % at 662 keV with PMT, APD and SiPM.
In general, single crystals of SrI2(Eu) are prepared by the vertical
Bridgman method in a quartz crucible. However, SrI2(Eu) has strong
hygroscopic nature, and therefore, we have to remove H2O from the
raw material completely before crystal growth to obtain high quality
single crystals. We have applied our original technology named
“Liquinert” process for this purpose [2]. The Liquinert process is an
effective technology for removing H2O from halide raw materials, and it
is suitable to prepare high quality metallic halides scintillation crystals.
We prepared several SrI2(Eu) single crystals with the size of φ15 mm
and approximately 80 mm length that contain 1.5 mol% of Eu. The
samples of cubic shape SrI2(Eu) were prepared as follows: (A) A 10
mm cubic crystal was cut from aφ15 mm crystal. (B) All surfaces of 10
mm Å~ 10 mm were ground with #600 SiC paper in the glove box with
moisture less than 0.1%. (C) The fine powdered SrI2(Eu) that resulted
from grinding was removed by a dried gauze. (D) Then, one face of the
crystal was polished with #4000 fine MgO powder to obtain a clear
surface. (E) The other five faces were wrapped with Teflon tape. (F)
The polished surface with a silicone grease was put
on the glass window of the aluminum case. (G) The crystal and the
aluminum case was closed using epoxy glue after the coverage of the
aluminum cap. (H) The preparation procedure was complete when the
glue was fixed. Figure 1 shows a picture of a fabricated SrI2(Eu)
detector encapsulated within an aluminum box.
10 x 10 x 10 mm3 [3], 12.5 x 12.5 x 12.5 mm3 and 25.4 x 25.4 x 10
mm3 crystals were fabricated.
Compton imaging in unmanned helicopter used in Fukushima
Fabricated strontium iodide crystals (10 mm, 12.5 mm and 25.4 mm)
Results
For characterization of crystals , PMT (R6231-10), APD (S8664-1010)
and SiPM (S12642-0404/0808PA-50) were used.
Figure shows the results with APD coupled to fabricated crystal.
137Cs
22Na
HV=351V 3µs @ 0 degC. 3µs @ 20 degC.
E.R (%) vs shaping time
Right figure shows the measurement
setup of APD based system. For
SIPM readout, CREMAT CR-113
charge amplifier was used.
Conclusion and Discussions
The performance of rectangular SrI2(Eu) crystal was
characterized using PMT, APD and SiPM. The energy
resolution less then 4% was observed in all devices. The
shaping time of 3 µs is optimal and the increase of bight
yield in lower temperature was observed. These rectangular
devices will be used in future Compton imaging system.
E.R (%) vs temperature
relative light yield vs temp.
Linearity
Figure shows the results with PMT and MPPC coupled to fabricated
crystal.
3.65%
R.T. PMT
Reference
[1] Jiang, Jianyong, et al. "A prototype of aerial radiation monitoring
system using an unmanned helicopter mounting a GAGG scintillator
Compton camera." Journal of Nuclear Science and Technology (2015):
1-9.
[2] S. Sakuragi et. al., 2014. Preparation of SrI2(Eu) scintillation crystals
by the Liquinert process and their scintillation property Proceedings of
the 28th workshop on Radiation Detectors and Their Uses, Jan. 2015
HV=64.1V 3 µs 5 deg.C sat. correction curve
[3] Shimazoe, K., et al. "Fabrication and characterization of cubic SrI 2
(Eu) scintillators for use in array detectors." Nuclear Instruments and
Methods in Physics Research Section A: Accelerators, Spectrometers,
Detectors and Associated Equipment 810 (2016): 59-62.