Ag-doped phosphate glass with high weathering resistance for RPL dosimeter

Radiation Measurements 140 (2021) 106492

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Radiation Measurements
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Ag-doped phosphate glass with high weathering resistance for
RPL dosimeter
Masaru Iwao a, *, Hironori Takase a, Daiki Shiratori b, Daisuke Nakauchi b, Takumi Kato b,
Noriaki Kawaguchi b, Takayuki Yanagida b
a
b

Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-Chome, Otsu-shi, Shiga, 520-8639, Japan
Nara Institute of Science and Technology (NAIST), 8916-5 Takayama-cho, Ikoma-shi, Nara, 630-0192, Japan

A R T I C L E I N F O

A B S T R A C T

Keywords:
Radiophotoluminescence
Glass dosimeter
High weathering resistance
Phosphate glass

Ag-doped phosphate glass employed in the commercial dosimeter named FD-7 is used globally as one of the most
reliable dosimeter materials. The luminescence phenomenon is well known as radiophotoluminescence (RPL). In
this work, a new RPL glass material was developed for dosimeters that are used under high humidity conditions.
The glass material that contains Ag2O as an activation center was produced by the melt-quenching method. The
radiation properties and the optimal amount of Ag2O concentration required for achieving the best performance

of the glass were evaluated using the RPL read-out system employing the photon counting method. On exposure
to UV laser light radiation, the new RPL glass developed in this work emitted light of an approximate wavelength
of 650 nm after radiation exposure, and the RPL intensity was proportional to the exposed dose. In addition, the
glass material exhibited high reusability owing to the repeated operation of irradiation and reset. On conducting
the weathering resistance test for a long duration, it was found that the new RPL glass exhibited the same RPL
intensity and appearance as its initial values.

1. Introduction
A larger variety of passive personal dosimeters are used in radiation
control areas such as medical facilities, science laboratories, mining
industry, and nuclear power plants. These dosimeters are convenient for
the end-users because of their low price, accuracy, shock resistance, and
lack of electric power. The number of dosimeter users is more than five
million worldwide (Pradhan et al., 2016). The RPL dosimeter has many
advantages over TLD, such as a small fading effect at room temperature
(Lee et al., 2009), good dose linearity, and high reproducibility (Rano­
gajec-Komor et al., 2008). The mechanism of the luminescence phe­
nomenon by Ag ions in the RPL glass dosimeter and the luminescence
process with build-up have been discussed by many researchers. (Huang
and Hsu, 2011; Miyamoto et al., 2011; McKeever et al., 2019; Kurobori
et al., 2020; Sholom and Mckeever, 2020; Yamamoto et al., 2020). When
the Ag-doped phosphate glass is irradiated by an ionizing radiation,
electrons and holes are generated and the electrons are captured by Ag+
in the glass structure and become Ag0. However, holes are trapped in the
PO4 tetrahedron, but migrate over time to Ag+, forming the more stable

Ag2+ ions. Ag2+ is the main RPL centers, shows the orange light under
ultraviolet excitation light. There is another possibility regarding the
orange RPL centers that Ag+ diffuses to Ag0 to forms Ag+
2.

Over fifty years, the RPL dosimeter named FD-7 glass (Yokota and
Nakajima, 1965) has been produced using the same chemical compo­
sition as when it was first produced because of its high reliability.
However, abnormally luminescent signals derived from the surface
degradation of the RPL glass have been reported by some researchers
(Yamanishi et al., 2003; Hashimoto et al., 2004). This phenomenon is
considered to occur when the surface degradation of the glass is accel­
erated by a high humidity environment. In general, from the perspective
of glass structure science, the phosphate glass network structure has
poor weathering resistance, because the P–O–P bond (phosphate oxygen
bond) is disconnected from the attack of OH− ions in the atmosphere
(Bunker et al., 1984). To achieve a strong network structure of the
phosphate glass, Al2O3, Fe2O3, and Pb2O3 are generally added (El-Deen
et al., 2008; Lim et al., 2010; Weyl and Kreidl, 1941). Further, for
improving the weathering resistance, in our previous study (Ikeda,
2019), it was found that by adding a small amount of SiO2 in phosphate

* Corresponding author. Development Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-Chome, Otsu -shi, Shiga, 5208639, Japan.
E-mail address: (M. Iwao).
/>Received 27 August 2020; Received in revised form 19 November 2020; Accepted 23 November 2020
Available online 30 November 2020
1350-4487/© 2020 The Authors.
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M. Iwao et al.

Radiation Measurements 140 (2021) 106492

glass, its surface appearance could be improved as compared to that of a
phosphate glass without SiO2. The improvement in weather resistance
by introducing SiO2 into phosphate glass was first reported by Izumitani
(1998). It has also been reported that the weather resistance changes
depending on the amount of SiO2 introduced. It is presumed that when
the amount of SiO2 introduced was small, the 6-fold coordinated Si
crosslinked the network of the chain phosphate and the network became
stronger, resulting in improved weather resistance. On the other hand,
when the introduction amount was further increased, the weather
resistance decreased. It was suggested that 4-fold coordinated Si enters
as a tetrahedron between the tetrahedrons of PO4, breaking the chain of
phosphoric acid and making phosphoric acid a single molecule. Phos­
phoric acid is easily eluted by becoming a single molecule. It is known by
the study of Miyabe et al. (2005) that the 6-fold coordination and 4-fold
coordination of Si are actually formed by introducing SiO2 into phos­
phate glass using nuclear magnetic resonance (NMR).

As it is important to increase the reliability of materials to conduct an
accurate dosimetry, the aim of the present study was to develop a new
glass material having a high weathering resistance for its use in an RPL
dosimeter and investigate its radiation characteristics. Furthermore, we
established a read-out system for evaluating its luminescence decay

time.
2. Experimental methods and materials
2.1. Experimental setup
The RPL intensity was evaluated using an RPL read-out system that
employs photon counting. According to Nomura et al. (2002), the
luminescence in the FD-7 phosphate glass consists of three components:
the luminescence due to the dirt on glass surface in a very short decay
time region (of the order of ns), the RPL in the middle decay time region
(a few μs), and a predose in the long decay time region having a low
intensity. The RPL intensity (the number of photons) obtained by inte­
grating the area of the decay curve in the range of 2–7 μs Thus, the RPL
intensity of all glass samples was evaluated from the luminescence decay
time using the RPL read-out system. Here, the predose is the amount of
light emitted by the sample itself before the radiation is irradiated. It is
the luminescence of the glass itself and is treated as the background
before the measurement in this study. Fig. 1(a) shows the schematic of
the RPL read-out system. The light source used for the irradiation is an
ultraviolet (UV) pulse laser having an excitation wavelength of 355 nm.

Fig. 1. (a) Schematic of the RPL read-out system. (b) Luminescence observed from the 0.1Ag:PANS glass after γ-ray irradiation. The orange line corresponds to the
luminescence obtained from the glass excited by a UV laser.
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Radiation Measurements 140 (2021) 106492

Fig. 1(b) shows a photograph of the light emitted from the glass sample
in this study directly captured by a digital still camera. Its emission
spectrum is the same as Fig. 5(a) shown later.
The pulsed laser was selected as a Q-switched solid-state laser con­
sisting of Nd:YAG. Its pulse frequency and pulse width were set to 10
kHz and 10 ns Laser expose time was performed 1 ms. The average light
power was set to 1.0 or 20 μW and monitored using a power meter (PD300R, Ophir). The average light power varied depending on the irradi­
ation dose. In the case of predose and small dose evaluation, the average
light power was set to 20 μW. In contrast, a large dose evaluation was
carried out using a small light power of 1.0 μW. According to the study
by Maki et al. (2011), a laser beam with a significant amount of pulsed
energy and repetition rate causes annealing of the RPL centers and un­
derestimates the radiation dose. In this study, although a high repetition
rate of the laser beam was used, the annealing effect did not occur. The
maximum pulsed energy was estimated to be 0.002 μJ, which is a very
small value. Thus, the laser beam condition did not affect the results of
the intensity measurement. Regarding the error of the RPL measure­
ment, the same sample was measured 10 times in this read-out system,
consequently, the variation was ±3.5%. The laser device was cooled
with air fans to stabilize the optical laser power. As shown in Fig. 1(a),
the laser beam entered perpendicularly in the central portion of the side
of the glass sample, which was precisely positioned with a movable XYZ
stage. A photomultiplier tube (PMT, H10682-01, Hamamatsu Pho­
tonics), a photon counting board (M9003-01, Hamamatsu Photonics) as
the photon counter, and a pulse delay generator (C10149, Hamamatsu
Photonics) were connected to each other via signal cables and connected

to a personal computer. The RPL read-out process was as follows: The
glass sample was irradiated by a pulsed ultraviolet laser, after which
luminescence light was emitted from the glass sample. The PMT detec­
ted the light emitted from the glass sample, and the photon counter
counted the number of photons. A UV band pass filter and long pass filter
were placed in front of the laser source and the glass sample, respec­
tively. This read-out system uses the UV cut filter to detect and monitor
the luminescence lifetime for wavelengths above 560 nm with PMT. The
read-out system including the laser source, PMT, and sample stage was
covered with a black almite box. Orange light emitted from glass sam­
ples was observed after irradiating the samples with the UV laser light.

2.3. Types of tests conducted and the instruments used
To evaluate the absorption properties of the glass samples doped
with different concentrations of Ag2O, their transmittance spectra were
measured. A spectrometer (V670, JASCO) was used for measuring the
spectral range from 190 to 3000 nm with an interval of 0.1 nm. The RPL
emission was evaluated using a fluorescence spectrophotometer (F7000, Hitachi High-Tech Corporation) in the spectral range of 400–800
nm with an interval of 0.2 nm. A UV cut filter was installed on the
fluorescence spectrometer to prevent secondary light from the excitation
source. The spectra are corrected for the wavelength response of this
detection system.
Subsequently, 137Cs γ-ray and X-ray radiation instruments were used
for irradiating the glass samples. The dosage of the samples irradiated by
137
Cs γ-ray was between 0.1 m and 20 Gy. The following 137Cs γ-ray
instruments were used. The samples were irradiated in the range of
0.1–100 mGy using an original γ-ray irradiation instrument from the
Nuclear Science Research Institute of Japan Atomic Energy Agency. The
samples were irradiated in the range of 1–20 Gy by PS-3200T (PONY

INDUSTRY CO., LTD) at the Tokyo Metropolitan Industrial Technology
Research Institute. These irradiated samples were evaluated in terms of
the following properties: linearity of the radiation response, RPL in­
tensity evaluation before and after the weathering resistance test, and
repeated read-out.
X-ray irradiation of the prepared samples was carried out in the
sensing device laboratory of the Nara Institute of Science and Technol­
ogy. The dose amount was set at 1000 mGy. The samples irradiated with
X-rays were evaluated in a reusability test, i.e., the cyclic test of the
generation of activation centers due to radiation exposure and the reset,
i.e., the recombination of electron and hole due to annealing. Further,
the RPL intensity evaluation of the PANS glass containing different
concentrations of Ag2O activator was carried out.
The preheating temperature required for accelerating the build-up
and reset temperature corresponding to the disappearance of the acti­
vation centers in the Ag:PANS glass was estimated from the glass tran­
sition temperature (Tg) and corresponded to the same heating conditions
of FD-7, as shown in previous studies (Kurobori, 2015, 2018). According
to these studies, the preheat temperature and reset temperature were in
the range of 70–100 ◦ C and 360–400 ◦ C, respectively. Tg of the Ag:PANS
glass and FD-7 composition glass measured using differential thermal
analysis (DTA) were 514 ◦ C and 448 ◦ C, respectively, which are 66 ◦ C
higher than that obtained for the FD-7 composition glass. Based on these
results and those from previous studies, the preheat temperature and
reset temperature of the Ag:PANS glass was determined as follows. The
preheat temperature was set at 100 ◦ C for FD-7 composition glass and
160 ◦ C for Ag:PANS glass for 30 min after irradiation. The reset tem­
perature was set at 400 ◦ C for 1 h for the FD-7 composition glass and
440 ◦ C for 1 h for the Ag:PANS glass after irradiating them with 137Cs
γ-ray and X-rays.

To evaluate the weathering resistance, the weathering resistance test
was carried out at 40 ◦ C and 90% relative humidity in a constant tem­
perature and humidity chamber using deionized water. This condition
was referred to in the International Electrotechnical Commission stan­
dard (IEC 62387). The glass samples were taken out of the chamber after
several days, and their luminescence was measured using the RPL readout system.

2.2. Preparation of the new RPL glass samples
The glass of the commercial FD-7 material has an atomic weight
composition of 31.55% P, 51.16% O, 6.12% Al, 11.00% Na, and 0.17%
Ag, and the effective atomic number and density are 12.04 and 2.61 g/
cm3, respectively (Kurobori, 2018). The oxide mol fraction of FD-7
composition converted form the above atomic weight composition is
59P2O5‒13.2Al2O3‒27.7Na2O‒0.1Ag2O.
In this study, a new glass with a composition of
P2O5–Al2O3–Na2O–SiO2 (PANS) was developed by adding different
concentrations (0.05, 0.1, 0.2, and 0.4 mol) of Ag2O as an activator. SiO2
was added as it does not affect the visible transmission characteristics of
the glass and helps in improving the weathering resistance. Another way
to improve the weathering resistance of phosphate glass is to increase
the concentration of Al2O3. Therefore, the concentration of SiO2 and
Al2O3 in the PANS glass were set to 5 mol% and 19 mol%, respectively.
These Ag:PANS glass samples and FD-7 composition glass were
prepared using the following procedure. Reagent grade Na3PO4, AlPO4,
SiO2, and Ag2O were mixed and melted at 1200 ◦ C in an electric furnace
for 3 h. The melted glass was cooled rapidly in a carbon mold, and the
glass ingots thus obtained were placed in an annealing furnace at
approximately 500 ◦ C for 1 h. After annealing, the glass samples were
cut into 30 × 7 × 1 mm3 pieces and polished using a grinding equip­
ment. All glass samples were washed and cleaned using deionized water

and ethanol solution before every evaluation.

3. Results and discussion
Fig. 2 shows the typical decay curves, corresponding to the glass
samples prepared in this study, obtained after their irradiation with
137
Cs γ-ray of 10 Gy.
As can be seen from the figure, the Ag:PANS glass has the same decay
time as the FD-7 composition glass because it has almost the same
composition and activator. This indicates that the mechanism of RPL in
the PANS glass is the same as that occurring in the FD-7 composition
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Radiation Measurements 140 (2021) 106492

Fig. 4. Linear transmittance spectra of the as-melted glass samples having
different Ag2O concentrations. Inset is a partial expanded view of the range of
200–300 nm.

Fig. 2. Decay curves of the 0.1Ag:PANS glass (filled squares) and FD-7
composition glass (unfilled circles) excited at 355 nm using UV laser and
monitored the luminescence above 560 nm after irradiation with 137Cs γ-ray of
10 Gy.

glass. The decay curves for the samples before and after irradiation with
137
Cs γ-ray at a dose of 1 mGy are shown in Fig. 3.

It can be seen that there is a clear difference in the intensity before
and after irradiation in the short decay time range from a few μs to 20 μs
The density of the glass was measured using the Archimedes method
with distilled water, and the density and effective atomic number of the
PANS glass was 2.61 g/cm3 and 11.71, respectively. These values are
almost the same as those of FD-7. Therefore, it was assumed that the
dependence of the response of the PANS glass on the radiation energy is
close to that of FD-7.
Fig. 4 shows the transmittance spectra of the Ag-doped PANS glass
having different concentrations of Ag2O activator and FD-7 composition
glass. The transmittance spectra of all samples were as high as approx­
imately 90% in the visible range. In the short-wavelength region (under
350 nm), the starting point of the absorption spectra was approximately
340 nm, and the absorption edge was between 219 and 236 nm. It was
found that this absorption edge shifted to a longer wavelength with
increasing Ag2O concentration. In the long-wavelength region, it was
found that the transmittances decreased around 3000 nm. This trans­
mittance decreasing is thought to be derived from the absorption due to

Fig. 5. RPL spectra of 0.1Ag:PANS glass and FD-7 composition glass before and
after irradiation with γ-rays of dose 20 Gy.

the presence of OH groups in the glass and the P–OH bond (Rai et al.,
2011).
Fig. 5 shows the luminescence spectra of the Ag:PANS glass emitted
at 308 nm before and after γ-ray irradiation by employing a fluorescence
spectrophotometer. The samples irradiated with γ-rays of 20 Gy were
evaluated for luminescence after preheating. The excitation wavelength
at 308 nm was used as the absorption peak derived from Ag2+ in
phosphate glass (Kurobori et al., 2010). From the luminescence mea­

surement, the peak position of the luminescence intensity was obtained
at 634 nm (emission in orange color) for the 0.1Ag:PANS glass. This
emission peak was also observed for the FD-7 composition glass. This
suggests that the mechanism of RPL in Ag:PANS glass is similar to that in
the FD-7 composition glass. This inference is also supported by the result
that the Ag:PANS glass and FD-7 composition glass have almost the same
main components and Ag concentration. In addition, FD-7 composition
glass was a little higher than 0.1Ag:PANS glass in the maximum peak
intensity around 630 nm. This intensity difference is unclear, however,
as each sample contained the same Ag2O concentration, this result may
be influenced by the composition ratio of the components of each glass
sample. Incidentally, the luminescence around 450 nm of samples before
irradiation in Fig. 5 is the baseline noise peculiar to the device, not the
peak caused by the sample. It was observed without a sample.

Fig. 3. Decay curves of the non-irradiated samples (filled circles) and after
137
Cs γ-ray irradiation of dose 1 mGy (unfilled circles) excited at 355 nm using
UV laser and monitored the luminescence above 560 nm.
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Radiation Measurements 140 (2021) 106492

Fig. 6 shows the variation in the RPL intensity as a function of Ag2O
concentration in the PANS glass. The vertical axis of Fig. 6 shows the
RPL intensity obtained by integrating the area of the decay curve in the
range of 2–7 μs The decay curve is the intensity obtained by irradiating

the excitation laser for 10 pulses at a repetition frequency of 10 kHz for
each measurement, that is, the intensity integrated 10 times. For a 0.1
mol% of Ag2O used in the PANS glass, the maximum intensity of RPL
was observed at an irradiation of 1000 mGy. As the Ag2O concentration
increased beyond 0.1 mol%, the RPL intensity of the PANS glass was
observed to decrease. This result is identical to that obtained by Hsu
et al. (2010). In general, the decrease in the RPL intensity with
increasing Ag2O concentration indicates the interaction with each
activator. This is called concentration quenching, in which the electrons
interact with each other causing nonradiative transitions when the
fluorescent centers are close to each other.
Fig. 7 shows the linearity of the dose response in the range 0.1
mGy–10 Gy for 0.1Ag:PANS glass. The intensity of the luminescence is
observed to increase depending on the irradiated dose. A linear regres­
sion of the measurement and predicted values yielded an R2 of 0.99,
indicating a reasonable agreement. According to IEC 62387, a mea­
surement range of 0.1 mSv–1 Sv is required for a personal dosimeter.
The results show that the PANS glass is able to measure the radiation
dosage in a range exceeding the required range in a personal dosimeter.
Fig. 8 shows the stability of the RPL intensity for the 0.1Ag:PANS
glass sample obtained by repeated read-out. Although the glass sample
was stored at room temperature, without controlling the humidity and
ambient light during the evaluation period, the RPL intensity showed
the constant intensity for a long period. This is equivalent to the stability
of a commercial FD-7 glass. As one of the characteristics of the RPL
phenomena, it is suggested that the activation center is not affected by
external environmental factors such as humidity, temperature, and
excitation light.
Fig. 9 shows the relative RPL intensity values before and after the
weathering resistance test. In this test, evaluation of the 0.1Ag:PANS

glass and FD-7 composition glass after their irradiation with γ-rays was
conducted. It was observed that 0.1Ag:PANS glass has a high weathering
resistance because the RPL intensities were constant for a long period. It
has been suggested that the addition of SiO2 to the glass strongly con­
nects the P–O and Si–O bonds, and strengthens the glass structure frame
against OH− attack. In contrast, the FD-7 composition glass was
observed to exhibit increasing luminescence after ten days of test. The
surface of the sample was observed to be covered with a sticky material
soon after taking it out from the test chamber. As the time elapsed, the

Fig. 7. Relationship between the absorbed dose and RPL intensity for PANS
glass containing 0.1 mol% of Ag2O concentration and irradiated with
137
Cs γ-ray.

Fig. 8. Stability of the RPL intensity in repeated read-out.

deviation in the measured values was observed to increase. It is assumed
that the surface degradation occurred owing to the elution of the
phosphoric acid component in the FD-7 composition glass. The increase
in the RPL intensity indicates that the difference in the refractive indices
at the phosphoric acid-air interface is smaller than the difference in the
refractive indices at the original glass-air interface, which facilitates
light extraction, and thus, increases the RPL intensity. The RPL intensity
of the FD-7 composition glass after 50 days in humidity test could not be
evaluated due to bonding of the sample with a sticky material.
Fig. 10 shows the appearance of the surfaces of the glass samples
after the weathering resistance test. The surface of the 0.1Ag:PANS glass
was clear after the test, whereas the FD-7 composition glass exhibited
dimming in a large area of the glass surface. The dimming could have

been caused by some compounds within the glass components coming
into contact with moisture in the atmosphere. This is because all ele­
ments, i.e., P, Na, and Al, were detected by the energy dispersive X-ray
spectroscopy and particle precipitations of the order of a few μm were
observed using an electron scanning microscope. The result of this
accelerated test suggests the possibility of inducing a dimming of the
glass material of the conventional RPL dosimeter due to its wear under
high humidity conditions for a long duration, similar to the internal

Fig. 6. Relationship between Ag2O concentration and RPL intensity obtained
from the PANS glass irradiated by an X-ray dose of 1000 mGy.
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Radiation Measurements 140 (2021) 106492

Fig. 9. Relative RPL intensity before and after the weathering resistance test.
The filled circles correspond to 0.1Ag:PANS glass, whereas the unfilled triangles
correspond to FD-7 composition glass.

Fig. 11. The RPL intensity of 0.1Ag:PANS glass (orange dot) and FD-7 glass
(gray dot) integrating emission from 500 nm to 800 nm upon 310 nm excitation
as a function of elapsed time.

energy level of holes trapping due to defects in the glass structure
derived from the introduction of Si has changed. We think that the
relevance of these phenomena needs further investigations and have
room for investigation and discussion on the Si coordination number

and the RPL process of this glass by NMR and ESR measurements since
there are no reports investigating the state of structure defects due to Si
introduced into the phosphate glass.
The reusability of 0.1Ag:PANS glass was evaluated by repeating the
cycle of generation and elimination of the Ag activation centers. The
evaluation was carried out for measuring the RPL intensity after varying
the dose of the X-ray irradiation and the predose intensity after heating.
The heating conditions of the preheat for build-up and the reset to
evaluate the RPL and the predose were set at 160 ◦ C for 30 min and at
450 ◦ C for 1 h, respectively. The result of the reusability test is shown in
Fig. 12.
After ten cycles, no changes in the RPL intensity and the predose
intensity were observed regardless of the irradiated dose. The stable
measurement results obtained from the reusability test indicate the
following. In the case of a glass element having a low weathering

Fig. 10. Appearance of the glass samples after 50 h in the weathering resis­
tance test. The left sample is the Ag-doped PANS glass, whereas the right sample
is the FD-7 composition glass.

condition of the radiation protective clothing. Currently, the rule of
radiation exposure measurement established in each country is at most
four months. It can be inferred that the reliability can be sufficiently
ensured even if this PANS glass is worn for 8 h a day.
Regarding Ag:PANS glass, The addition of SiO2 and the increase in
Al2O3 in the glass increased Tg and improved weathering resistance. It
was also confirmed that the preheat temperature for build-up also rises
compared to FD-7. In addition, Fig. 11 shows the change in the RPL
intensity of 0.1Ag:PANS glass and FD-7 glass derived from Ag2+ after
irradiation, namely build-up curve. These glass samples were irradiated

with X-rays of 10 Gy, and the RPL excited at 310 nm as a function of
elapsed time was evaluated on the emission from 500 nm to 800 nm with
a fluorescence spectrophotometer (FP-8600, JASCO) at room tempera­
ture. The RPL intensity of 0.1Ag:PANS glass increased immediately after
the irradiation and continued to increase even after 14 h. Meanwhile,
that of FD-7 glass showed a constant value after 8 h. The result was
similar to that of Miyamoto et al. (2010). It was found that the build-up
time of 0.1Ag:PANS glass was longer than that of FD-7 glass. From these
results, it is suggested that the presence of Si and Al in the phosphate
glass, which improves weathering resistance, not only strengthened the
network of the phosphate glass, but also increased the energy barrier for
the diffusion of Ag ions. Furthermore, there is a possibility that the

Fig. 12. Result of the RPL intensity (filled circle) and predose intensity (filled
triangle) of the 0.1Ag:PANS glass obtained from the reusability test at the
irradiation dose of 1000 mGy.
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Radiation Measurements 140 (2021) 106492

resistance, a structural change in the host glass material will occur
during its long-term use. Furthermore, as cycles of exposures/resets are
repeated, the electrons and holes generated by ionization are trapped in
the defects of the changed glass structure. There is a possibility that the
RPL intensity and predose intensity will exhibit values different from the
initial ones obtained for the glass having a low weathering resistance. In
this study, 0.1Ag:PANS glass was exposed to tens to thousands of times

of actual radiation dose, and this operation was repeated ten times. The
reason for setting this condition was that the number and the amount of
repeated valence changes for Ag ions in the glass are considered to affect
the number of reuses. In other words, these changes are reflected in the
RPL and predose intensities. The result in Fig. 12 shows that the elec­
trons and holes generated by the incident radiation completely formed
the activation centers of Ag even after repeated irradiation/reset,
because the variation in RPL intensity was not observed. This suggests
that the use of PANS glass as a dosimeter element can be expected to
prolong the lifetime of the individual/environmental dosimeters.

Hashimoto, T., Hashimoto, M., Ishikawa, M., Emori, S., 2004. Investigation on the
performance of dosimeters for individual monitoring applications at the O-arai
engineering center (in Japanese). Hoken Butsuri 39 (3), 231‒237. />10.5453/jhps.39.231.
Hsu, S.M., Yan, H.W., Huang, Y.H., Lee, J.H., Yu, C.Y., Liao, Y.J., Hung, S.K., Lee, M.S.,
2010. Chemical and physical characteristics of self-fabricated
radiophotoluminescent glass dosimeter. Radiat. Meas. 45, 553–555. />10.1016/j.radmeas.2009.11.045.
Huang, D.Y.C., Hsu, S.M., 2011. Radio-photoluminescence glass dosimeter (RPLGD). In:
Gali-Muhtasib, Hala (Ed.), Advances in Cancer Therapy. InTech Open, pp. 553–568.
/>Ikeda, H., 2019. Structure and weathering of SiO2 contained phosphate glass. In: 25th
International Congress on Glass, in Oral Presentation, ICG-SI-143-2019. The
American ceramics society.
Izumitani, T., 1998. Kougaku garasu to re-za garasu (in Japanese). Nikkan kogyo
shinbunshya, pp. 132–133.
Kurobori, T., Wahng, Z., Miyamoto, Y., Nanto, H., Yamamoto, T., 2010. The role of silver
in the radiophotoluminescent properties in silver-activated phosphate glass and
sodium chloride crystal. Opt. Mater. 32, 1231‒1236. />optmat.2010.04.004.
Kurobori, T., 2015. A glass imaging detector (in Japanese). FBNews 467, 1–5. http
s://www.c-technol.co.jp/cms/wp-content/uploads/2014/04/FBN467_web.pdf
(accessed 14 July 2020).

Kurobori, T., 2018. Performance characterization of a real-time fiber dosimetry system
using radiophotoluminescent glasses. Jpn. J. Appl. Phys. 57, 106402. https://doi.
org/10.7567/JJAP.57.106402.
Kurobori, T., Kada, W., Yanagida, Y., Koguchi, Y., Yamamoto, T., 2020. Variable periodic
time operated fibre-coupled dosimetry system using Ag-activated RPL glasses with
build-up. Radiat. Meas. 133, 106300. />radmeas.2020.106300.
Lee, J.H., Lin, M.S., Hsu, S.M., Chen, I.J., Chen, W.L., Wang, C.F., 2009. Dosimetry
characteristics and performance comparisons: environmental
radiophotoluminescent glass dosemeters versus thermoluminescent dosemeters.
Radiat. Meas. 44, 86‒91. />Lim, J.W., Schmitt, M.L., Brow, R.K., Yung, S.W., 2010. Properties and structures of tin
borophosphate glasses. J. Non-Cryst. Solids 356, 1379‒1384. />10.1016/j.jnoncrysol.2010.02.019.
Maki, D., Sato, F., Kato, Y., Yamamoto, T., Iida, T., 2011. Improvement of a dose reading
system for radiophotoluminescence glass dosimeters. Radioisotopes 60, 55‒61.
/>McKeever, S.W.S., Sholom, S., Shrestha, N., 2019. Observations regarding the build-up
effect in radiophotoluminescene of silver-doped phosphate glasses. Radiat. Meas.
123, 13–20. />Miyabe, D., Takahashi, M., Tokuda, Y., Yoko, T., Uchino, T., 2005. Structure and
formation mechanism of six-fold coordinated silicon in phosphosilicate glasses. Phys.
Rev. B 71, 172202. />Miyamoto, Y., Yamamoto, T., Kinoshita, K., Koyama, S., Takei, Y., Nanto, H.,
Shimotsuma, Y., Sakakura, M., Miura, K., Hirao, K., 2010. Emission mechanism of
radiophotoluminescence in Ag-doped phosphate glass. Radiat. Meas. 45, 546–549.
/>Miyamoto, Y., Takei, Y., Nanto, H., Kurobori, T., Konnai, A., Yanagida, T., Yoshikawa, A.,
Shimotsuma, Y., Sakakura, M., Miura, K., Hirano, K., Nagashima, Y., Yamamoto, T.,
2011. Radiophotoluminescence from silver-doped phosphate glass. Radiat. Meas. 46,
1480–1483. />Nomura, K., Ikegami, T., Juto, N., 2002. Development of dosimeters for personal
monitoring. I. Radiophoto-luminescent glass dosimeter (in Japanese). Radioisotopes
51, 85‒95. />Pradhan, A.S., Lee, J.I., Kim, J.L., 2016. On the scenario of passive dosimeters in
personnel monitoring: relevance to diagnostic radiology and fluoroscopy-based
interventional cardiology. J. Med. Phys. 41 (2), 81–84. />0971-6203.181634.
Rai, V.N., Sekhar, B.N.R., Tiwari, P., Kshirsagar, R.J., Deb, S.K., 2011. Spectroscopic
studies of gamma irradiated Nd doped phosphate glasses. J. Non-Cryst. Solids 357,

3757–3764. />ˇ Miljani´c, S., Veki´c, B., 2008. Characterisation of
Ranogajec-Komor, M., Kneˇzevi´c, Z.,
radiophotoluminescent dosimeters for environmental monitoring. Radiat. Meas. 43,
392‒396. />Sholom, S., McKeever, S.W.S., 2020. High-dose dosimetry with Ag-doped phosphate
glass: applicability test with different techniques. Radiat. Meas. 132, 106263.
/>Weyl, W.A., Kreidl, N.J., 1941. Phosphates in ceramic ware: IV, Phosphate glasses. J. Am.
Ceram. Soc. 24, 372–378. />Yamamoto, T., Yanagida-Miyamoto, Y., Iida, T., Nanto, H., 2020. Current status and
future prospect of RPL glass. Radiat. Meas. 136, 106363. />radmeas.2020.106363.
Yamanishi, H., Miyaka, H., Yamasaki, T., Komura, K., 2003. Self dose of TLD and
radiophoto-luminescence glass dosimeter measured in Ogoya tunnel (in Japanese).
Hoken Butsuri 38 (1), 45–49. />Yokota, R., Nakajima, S., 1965. Improved fluoroglass dosimeter as personnel monitoring
dosimeter and microdosimeter. Health Phys. 11 (4), 241–253. />10.1097/00004032-196504000-00001.

4. Conclusion
A new RPL glass material, namely Ag:PANS glass, was developed in
this work for its use in a radiation dosimeter. The following character­
istics have been observed from the tests conducted on it. As compared to
the conventional dosimeter material, namely, the FD-7 composition
glass, the weathering resistance property of Ag:PANS glass was observed
to be much superior. In addition, the RPL characteristics of the devel­
oped glass were found to be equivalent to that of the FD-7 composition
glass. This implies that Ag:PANS glass can be used in harsher environ­
ments, e.g., in hot and humid areas, or harsh working conditions. Since
the surface turbidity of the glass does not occur under high humidity, the
possibility of showing an abnormal value is reduced, its high reusability
can also contribute to improving the reusability rate of monitoring
service. This dosimeter material has many applications apart from its use
in personal/environmental dosimeters. For example, it can be used in
medical applications for surgical operations, because it can be produced
in different forms such as fibers, thin plates, and rings owing to the

advantage of the high degree of freedom of molding glass.
Funding
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
The authors thank H. Takeuchi, M. Kadomi and H. Ikeda of Nippon
Electric Glass Co., Ltd. for their support and useful discussions in this
work.
References
Bunker, B.C., Arnold, G.W., Wilder, J.A., 1984. Phosphate glass dissolution in aqueous
solutions. J. Non-Cryst. Solids 64, 291‒316. />(84)90184-4.
El Deen, L.M.S., Al Salhi, M.S., Elkholy, M.M., 2008. Spectral properties of PbO–P2O5
glasses. J. Non-Cryst. Solids 354, 3762–3766. />jnoncrysol.2008.03.032.

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