Crystal growth and scintillation properties of strontium iodide scintillators Page: 3 of 5
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Fig. 1. Photograph of a SrI2:8% Eu ingot. The photograph on the left was
taken with ambient light, while the photograph on the right was taken with
the ingot placed on a light box.
Fig. 1 shows a photograph of a SrI2:8% Eu ingot. The ingot is
about 10 mm in diameter and 24 mm long. The yellowish color
of the ingot under ambient light is due to a thin layer of
mineral oil on the surface of the ingot. The bluish haze of the
ingot exposed to transmitting light is attributed to absorption
and emission of Eu2+. Almost all SrI2:Eu ingots are optically
clear, show minimal cracking and appear to have minimal Eu2+
segregation, whereas SrI2:Ce/Na ingots have a pale yellow tint
and show some Ce3" segregation.
III. SCINTILLATION PROPERTIES
A.Radioluminescence
Radioluminescence spectra were recorded with a Philips X-
ray tube having a Cu anode operated at 30 kV and 20 mA. The
scintillation light was dispersed through a McPherson 234/302
monochromator equipped with a holographic grating (1200
grooves/mm) and subsequently detected with a Hamamatsu
R2059 photomultiplier tube (PMT). Radioluminescence
spectra of SrI2:0.5% Eu and SrI2:0.5% Ce/Na are shown in Fig.
2. For SrI2:0.5% Eu the spectrum consists of a single broad
band due to Eu2+ 5d - 4f emission, peaking at 435 nm [6]. In
contrast, the spectrum of SrI2:0.5% Ce/Na exhibits a doublet
peaking at 404 and 435 nm attributed to Ce3+ luminescence,
while additional impurity - or defected - related emission isC
C300
400
500
0 -
0 -
0, -
o __C
C600
Wavelengty (nm)
Fig. 2. Radioluminescence spectrum of SrI2:0.5% Eu and SrI2:0.5% Ce/Na.1 _- Srl2:0.5 % Eu _
-- Srl2:0.5 % Ce/Na
0.1
0.01-
1E-30 500 1000 1500 2000
Time (ns)
Fig. 3. Scintillation decay time spectra of SrI2:0.5% Eu and SrI2:0.5% Ce/Na
under 137Cs gamma ray excitation.present at approximately 525 nm.
B. Scintillation Decay
Scintillation decay time spectra were recorded using a "'Cs
gamma ray source and a Tektronix TDS 220 oscilloscope
connected to the output of a PMT. Fig. 3 shows the
scintillation decay time spectra of SrI2:0.5% Eu and SrI2:0.5%
Ce/Na under 137Cs gamma ray excitation. A simple exponential
decay time model was used to fit the data. In the case of
SrI2:0.5% Eu, the scintillation decay curve can be described by
a single exponential decay time model with a time constant of
1.1 ps. For higher Eu concentrations, the time constant does
not change significantly. The scintillation decay curve of
SrI2:0.5% Ce/Na can be described by a two-component
exponential decay time model; a principle decay component
that contributes about 25% to the total light yield with a 27 ns
time constant, and a second decay component with a 450 ns
time constant. The principal decay component of SrI2:2%
Ce/Na contributes about 46% to the total light yield and has a
33 ns time constant. The remaining light is emitted by a 570 ns
decay component.
C.Light yield and Energy resolution
Pulse-height spectra were recorded with a Hamamatsu
R2059 PMT. The output of the PMT was connected to a
Canberra 2005 preamplifier and a Canberra 2020
spectroscopic amplifier. Crystals were optically coupled onto
the window of the PMT using Bicron BC-630 optical grease.
To minimize losses in light yield, crystals were wrapped in
several layers of 0.1-mm UV reflecting Teflon tape. Nitrogen
was flushed around the crystal to prevent hydration of the
surface during measurement. Light yields expressed in
photoelectrons per megaelectronvolt (MeV) of absorbed
gamma ray energy (phe/MeV) were determined by comparing
the peak position of the 662 keV full energy peak in the pulse
height spectra with the position of the peak in the spectrum of
single photoelectrons. The absolute light yield, expressed in- Srl2:0.5% Ce/Na
- Srl2:0.5% Eu2
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van Loef, Edgar; Wilson, Cody; Cherepy, Nerine; Payne, Steven; Choong, Woon-Seng; Moses, William W. et al. Crystal growth and scintillation properties of strontium iodide scintillators, article, June 1, 2009; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc930763/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.