**3. Experimental**

The RPL glass dosimeter , the OSL dosimeter and the DIS dosimeter developed as the passive dosimeter were used in the environmental natural radiation monitoring. Figure 6 shows photographs of a personal glass dosimeter of type GD-450 used in this study. The GD-450 is made of Ag+-doped phosphate glass (AGC Techno Glass Co., Ltd.), supplied by Chiyoda Technol Corp.

Fig. 6. Photographs of the GD-450 (left) and of glass used in GD-450 (right).

The OSL dosimeters (Luxel badge: S-type) used in this study as shown in Fig.7 (left) were supplied by Nagase Landauer Co., Ltd. (Kobayashi, 2004). In this study, the OSL dosimeter, which was made of an Al2O3:C phosphor material, was used for environmental natural radiation monitoring. The Al2O3:C phosphor emit 420 nm OSL emission with intensity in proportion to the exposure dose under optical stimulation with the wavelength of 523 nm.

Fig. 7. Photographs of the OSL dosimeter (Type S) as shown the left photo picture and of the DIS dosimetr (Type DIS-1) as shown in the right photo picture.

The RPL glass dosimeter , the OSL dosimeter and the DIS dosimeter developed as the passive dosimeter were used in the environmental natural radiation monitoring. Figure 6 shows photographs of a personal glass dosimeter of type GD-450 used in this study. The GD-450 is made of Ag+-doped phosphate glass (AGC Techno Glass Co., Ltd.), supplied by

Fig. 6. Photographs of the GD-450 (left) and of glass used in GD-450 (right).

The OSL dosimeters (Luxel badge: S-type) used in this study as shown in Fig.7 (left) were supplied by Nagase Landauer Co., Ltd. (Kobayashi, 2004). In this study, the OSL dosimeter, which was made of an Al2O3:C phosphor material, was used for environmental natural radiation monitoring. The Al2O3:C phosphor emit 420 nm OSL emission with intensity in proportion to the exposure dose under optical stimulation with the wavelength of 523 nm.

 Fig. 7. Photographs of the OSL dosimeter (Type S) as shown the left photo picture and of the

DIS dosimetr (Type DIS-1) as shown in the right photo picture.

**3. Experimental** 

Chiyoda Technol Corp.

The DIS as shown in Fig.7 (right) was supplied from RADOS Technology, Finland. The basic principle of the DIS is as follows; a nonvolatile solid-state memory cell is stored in the form of electric charge being trapped on the floating gate of a MOSFET transistor in air or gas space surrounded by a conductive wall. The DIS dosimeter is based on Analog-EEPROM (Analog Electrically Erasable Programmable Read Only Memory). The DIS responds to X, γ, β-rays and neutron. This dosimeter has an excellent energy characteristic and can be read repeatable without quenching of the data. The DIS dosimeter can widely detect a radiation dose within the range from 1 μSv to 40 Sv

The personal dosimeters GD-450, Luxel badge (Type S) and DIS-1 were set on 7 points in Ishikawa prefecture as shown in Fig.8.

Each of 7 points are represented as alphabet of from A to G. (A: Tsurugi-machi, B: Tatsunokuchi, C: Inside of house of Mt. Shishiku, D: Outside of Mt. shishiku, E: Inside of Ogoya Mines, F: Outside of Ogoya Mines, G: Public Health and Environmental Science). Each data was obtained monthly. Photographs of local points in which the dosimeters were set up are shown in Fig.9. Data were obrained monthly. The each accumulated monthly data was divided into daily data and multiplied 30 days. The each data was compensated appropriately with the each formula for the dosimeters (Sarai, 2004). The same point data were averaged and the standard deviations were calculated. The data of GD-450 were compared with the data of the other dosimeters.

Fig. 8. Map of seven points such as Tsurugi-machi (◆), Tatsunokuchi (●), outside of Mt.Shishiku (■), inside of house in Mt.Shishiku, (▲), outside of Ogoya Mines (◇), Inside of Ogoya Mines (○) and rooftop of Ishikawa Prefecture Institute of Public health and Environmental Science (□). in Ishikawa prefecture, in which the environmental radiation dose using the glass dosimeter were measured.

Environmental Background Radiation Monitoring Utilizing Passive Solid Sate Dosimeters 129

1.0 Excitation spectrum Emission spectrum

Fig. 10. Typical RPL emission and excitation spectra of Ag+-doped phosphate glass after xray irradiation. The peak separation of the excitation and emission spectra of RPL indicated

5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5

Energy [eV]

using dashed lines were carried out using the component separation of Gaussian

Fig. 11. Formation of RPL luminescence centers such as Ag0 and Ag2+ ions in x-ray

almost linearly increased with x-ray absorption dose up to 10 Gy.

The RPL emission images as a function of x-ray absorbed dose, when the x-ray irradiated Ag+-doped phosphate glass is excited using UV light, are shown in Fig. 12, where it is seen that the intensity of yellow color emission increases with the absorbed dose. This result coincides with that of previous report (Shih-Ming Hsu, 2007), in which RPL intensity was

bands(dashed lines).

0.0

0.2

0.4

0.6

Normalized RPL intensity

0.8

irradiated Ag+-doped phosphate glass.

Fig. 9. Photographs of 4 points such as (a) point D, (b) point E, (c) point Fand (d) point G in Ishikawa prefecture, in which the dosimeters were set up.

#### **4. Results and discussion**

#### **4.1 Basic characteristics of RPL glass dosimeter**

Typical RPL emission and its excitation spectra of x-ray irradiated Ag+-doped phosphate glass are shown in Fig.10. It can be seen that the RPL emission spectrum consists of two emission bands peaked at about 2.70 eV (460 nm) and 2.21 eV (560 nm). On the other hand, the RPL excitation spectrum consists of two excitation bands peaked at about 3.93 eV (315 nm) and 3.32 eV (373 nm). The fact that RPL emission spectrum consists of two emission bands such as yellow color emission and blue color emission has been reported in previous report (Miyamoto, 2010). The radiative lifetime of yellow and blue RPL peaks are estimated. The lifetime is 2~4 μs for yellow RPL and 2~10 ns for blue RPL, respectively, which was dependent on the irradiation dose (Kurobori, 2010). The RPL emission mechanism is explained using Fig.11 as follows; when the Ag+-doped phosphate glass is exposed to ionizing radiation such as x-ray, the electron-hole pair will be produced. The electrons are captured into Ag+ ions in the glass structure and then the Ag+ ions change to Ag0 ions. On the other hand, the holes are captured by the PO4 tetrahedron at the begining of migration and then produce Ag2+ ions owing to interaction with Ag+ ions over time. It has been reported that both Ag0 and Ag2+ ions can be played in role as luminescence centers for blue and yellow RPL, respectively (Miyamoto, 2010).

(a) (b)

(c) (d)

Fig. 9. Photographs of 4 points such as (a) point D, (b) point E, (c) point Fand (d) point G in

Typical RPL emission and its excitation spectra of x-ray irradiated Ag+-doped phosphate glass are shown in Fig.10. It can be seen that the RPL emission spectrum consists of two emission bands peaked at about 2.70 eV (460 nm) and 2.21 eV (560 nm). On the other hand, the RPL excitation spectrum consists of two excitation bands peaked at about 3.93 eV (315 nm) and 3.32 eV (373 nm). The fact that RPL emission spectrum consists of two emission bands such as yellow color emission and blue color emission has been reported in previous report (Miyamoto, 2010). The radiative lifetime of yellow and blue RPL peaks are estimated. The lifetime is 2~4 μs for yellow RPL and 2~10 ns for blue RPL, respectively, which was dependent on the irradiation dose (Kurobori, 2010). The RPL emission mechanism is explained using Fig.11 as follows; when the Ag+-doped phosphate glass is exposed to ionizing radiation such as x-ray, the electron-hole pair will be produced. The electrons are captured into Ag+ ions in the glass structure and then the Ag+ ions change to Ag0 ions. On the other hand, the holes are captured by the PO4 tetrahedron at the begining of migration and then produce Ag2+ ions owing to interaction with Ag+ ions over time. It has been reported that both Ag0 and Ag2+ ions can be played in role as luminescence centers for blue

Ishikawa prefecture, in which the dosimeters were set up.

**4.1 Basic characteristics of RPL glass dosimeter** 

and yellow RPL, respectively (Miyamoto, 2010).

**4. Results and discussion** 

Fig. 10. Typical RPL emission and excitation spectra of Ag+-doped phosphate glass after xray irradiation. The peak separation of the excitation and emission spectra of RPL indicated using dashed lines were carried out using the component separation of Gaussian bands(dashed lines).

Fig. 11. Formation of RPL luminescence centers such as Ag0 and Ag2+ ions in x-ray irradiated Ag+-doped phosphate glass.

The RPL emission images as a function of x-ray absorbed dose, when the x-ray irradiated Ag+-doped phosphate glass is excited using UV light, are shown in Fig. 12, where it is seen that the intensity of yellow color emission increases with the absorbed dose. This result coincides with that of previous report (Shih-Ming Hsu, 2007), in which RPL intensity was almost linearly increased with x-ray absorption dose up to 10 Gy.

Environmental Background Radiation Monitoring Utilizing Passive Solid Sate Dosimeters 131

dosimeter within a month was estimated tobe about 12μSv. On the other hand, the averaged self-doses accumulated in the Luxel badge also increases lienarly with increasing the time except for the bigining of measurement as shown in Fig.14. The value at the bigining of measurement is different from othe two values. This deviation may be caused by the exposure to the natural radiation during the transportation of dosimeters to Nagase Landauer in Tokyo by air. Except for the data point at the bigining of measurement, the

**average of five luxel badges**

Fig. 14. Self-dose of the luxel badge dosimeter. Each data point is averaged over doses of

**Thorium series**

**0 30 60 90**

**Time [days]**

.

**0 500 1000 1500 2000**

**Uranium series**

**K-40**

**Energy [keV]**

Fig. 15. Typical γ-ray spectrum obtained from the DIS dosimeter.

**0**

**20**

**40**

**60**

**Yield [counts/hr/kev]**

**80**

**100**

three Luxel badge units.

**0**

**20**

**Dose reading [**

**Sv]**

**40**

**60**

averaged self dose of the Luxel Badge is estimated to be about 9μSv.

Fig. 12. RPL emission images of Ag+-doped phosphate glass as a function of x-ray absorbed dose : (a) Ag+-doped phosphate glass under visible light, (b) Ag+-doped phosphate glass under UV light.

#### **4.2 Results of environmental natural background radiation monitoring**

Before the environmental background radiation monitoring was carried out, the self dose measurement and radioactive nuclide identification were made in an extremely low level background field of the tunnel of Ogoya Copper Mine (Ogoya underground laboratory of Kanazawa University), where muon intensity of cosmic ray is reduced to two orders of magnitude in comparison with the ground (Murata, 2002). The Luxel badge and DIS dosimeter were set in a shielding box of an ancient lead which contains few 210Pb isotope (half-life 22.3 years). Five units of the Luxel badge and the DIS dosimeter were prepared to measure the self-doses. Self-doses were measured by the month during three months.

Fig. 13. Self-dose of the DIS-1 dosimeter. Each data point is averaged over doses of five DIS units

Figure 13 shows self-dose of the DIS dosimeter. The average self-dose acumulated in the DIS dosimeter increases almost linearly with increasing time. The average self-dose of the DIS

Fig. 12. RPL emission images of Ag+-doped phosphate glass as a function of x-ray absorbed dose : (a) Ag+-doped phosphate glass under visible light, (b) Ag+-doped phosphate glass

Before the environmental background radiation monitoring was carried out, the self dose measurement and radioactive nuclide identification were made in an extremely low level background field of the tunnel of Ogoya Copper Mine (Ogoya underground laboratory of Kanazawa University), where muon intensity of cosmic ray is reduced to two orders of magnitude in comparison with the ground (Murata, 2002). The Luxel badge and DIS dosimeter were set in a shielding box of an ancient lead which contains few 210Pb isotope (half-life 22.3 years). Five units of the Luxel badge and the DIS dosimeter were prepared to measure the self-doses. Self-doses were measured by the month during three months.

**average of five DIS-1**

Fig. 13. Self-dose of the DIS-1 dosimeter. Each data point is averaged over doses of five DIS

**0**

**20**

**Dose reading [**

**Sv]**

**40**

**60**

**0 30 60 90**

**Time [days]**

Figure 13 shows self-dose of the DIS dosimeter. The average self-dose acumulated in the DIS dosimeter increases almost linearly with increasing time. The average self-dose of the DIS

**4.2 Results of environmental natural background radiation monitoring** 

under UV light.

units

dosimeter within a month was estimated tobe about 12μSv. On the other hand, the averaged self-doses accumulated in the Luxel badge also increases lienarly with increasing the time except for the bigining of measurement as shown in Fig.14. The value at the bigining of measurement is different from othe two values. This deviation may be caused by the exposure to the natural radiation during the transportation of dosimeters to Nagase Landauer in Tokyo by air. Except for the data point at the bigining of measurement, the averaged self dose of the Luxel Badge is estimated to be about 9μSv.

Fig. 14. Self-dose of the luxel badge dosimeter. Each data point is averaged over doses of three Luxel badge units.

Fig. 15. Typical γ-ray spectrum obtained from the DIS dosimeter.

Environmental Background Radiation Monitoring Utilizing Passive Solid Sate Dosimeters 133

radioactive nuclies are listed in Table 2. The 40K, 232Th and 238U have been contained in almost all dosimeters. So, it is difined that the self-dose of each dosimeter for a month is about 10-15μSv. Data was, therefore, compensated for each dosimeter which based on the

The environmental backgroung radiation dose at 7 points for one month were monitored using the glass dosimeter (GD-450) as well as the Luxel badge and the DIS dosimeters. The monitoring results of typical environmental background radiation dose in gray (Gy) as the absorbed dose using the GD-450 from March in 2008 to August 2009 are shown in Fig.16 for

Although natural background radiation doses with the GD-450 dosimeter at each point in Ishikawa prefecture were significantly different, the standard deviations were very small. Although the values were a little bit different between the GD-450 glass dosimeter and the Luxel badge (OSL dosimeter), the tendencies of the environmental dose at each point were very similar as shown in Fig.17. The higher dose at point B (Tatsunokuchi) than at other points is due to the use of radioisotopes at the Lowere Level Radiation laboratory in Kanazawa University. Morever, the values of the GD-450 dosimeter and the DIS dosimeter were very close and there was no significant difference between them as shown Fig.18. We have made the comparison of different types of RPL glass dosimeters such as Type: GD-450 for personal dosimeter and Type:SC-1 for enviromental monitoring, which were supplied from Chiyoda Technol Corp, as shown in Fig.19. It was found that there is no significant

Fig. 17. Dose response at each point in Ishikawa prefecture (A: Tsurugi-machi, B:

using GD-450 (blue bars) or Luxel badge (orange bars) dosimeters.

Tatsunokuchi, C: Inside of house of Mt. Shishiku, D: Outside of Mt. shishiku, E: Inside of Ogoya Mines, F: Outside of Ogoya Mines, G: Public health and Environmental Science)

A B C D E F G

GD-450 Luxel

sel-dose rate of about 12μSv/month.

7 points in Ishikawa prefecture.

difference at each points.

0

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

m

S

v


The origin of the self-dose was identified using high pure Ge semiconductor detector in the Ogoya underground laboratory. Typical gamma-ray spectrum obtained from the DIS dosimeter is shown in Fig.15.

Table 2. Identificated radioactive nuclides contained in each personal dosimeters.

Fig. 16. Measured environmental radiation dose using the GD-450 glass dosimeter in seven points such as Tsurugi-machi (◆), Tatsunokuchi (●), outside of Mt.Shishiku (■), inside of house in Mt.Shishiku, (▲), outside of Ogoya Mines (◇), Inside of Ogoya Mines (○) and rooftop of Ishikawa Prefecture Institute of Public health and Environmental Science (□). in Ishikawa prefecture. The measurements of environmental radiation dose were carried out from March in 2008 to August 2009.

The sveral peaks under 1000 keV correspond to nuclides of 232Th and 238U series. The 40K peak with the energy of 1460 eV has been also detected. Measured parts and identified

The origin of the self-dose was identified using high pure Ge semiconductor detector in the Ogoya underground laboratory. Typical gamma-ray spectrum obtained from the DIS

> 210Pb (dpm)

2.00

232Th (dpm)

1.50 0.85

1.50

0.04 5.53

40K (dpm)

22.0 0.38

0.75

238U (dpm)

1.40

0.88 0.10 1.30 0.83 0.10

2.00

0.07 1.70

Table 2. Identificated radioactive nuclides contained in each personal dosimeters.

Fig. 16. Measured environmental radiation dose using the GD-450 glass dosimeter in seven points such as Tsurugi-machi (◆), Tatsunokuchi (●), outside of Mt.Shishiku (■), inside of house in Mt.Shishiku, (▲), outside of Ogoya Mines (◇), Inside of Ogoya Mines (○) and rooftop of Ishikawa Prefecture Institute of Public health and Environmental Science (□). in Ishikawa prefecture. The measurements of environmental radiation dose were carried out

3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8

TIME [month]

The sveral peaks under 1000 keV correspond to nuclides of 232Th and 238U series. The 40K peak with the energy of 1460 eV has been also detected. Measured parts and identified

dosimeter is shown in Fig.15.

Whole DIS Label Spring Al frame IC long IC fat Battery

Al2O3 crystal Ag filter Sn filter

from March in 2008 to August 2009.

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

dosimeter parts

DIS

Luxel

MEASUREMENTS [mGy]

radioactive nuclies are listed in Table 2. The 40K, 232Th and 238U have been contained in almost all dosimeters. So, it is difined that the self-dose of each dosimeter for a month is about 10-15μSv. Data was, therefore, compensated for each dosimeter which based on the sel-dose rate of about 12μSv/month.

The environmental backgroung radiation dose at 7 points for one month were monitored using the glass dosimeter (GD-450) as well as the Luxel badge and the DIS dosimeters. The monitoring results of typical environmental background radiation dose in gray (Gy) as the absorbed dose using the GD-450 from March in 2008 to August 2009 are shown in Fig.16 for 7 points in Ishikawa prefecture.

Although natural background radiation doses with the GD-450 dosimeter at each point in Ishikawa prefecture were significantly different, the standard deviations were very small. Although the values were a little bit different between the GD-450 glass dosimeter and the Luxel badge (OSL dosimeter), the tendencies of the environmental dose at each point were very similar as shown in Fig.17. The higher dose at point B (Tatsunokuchi) than at other points is due to the use of radioisotopes at the Lowere Level Radiation laboratory in Kanazawa University. Morever, the values of the GD-450 dosimeter and the DIS dosimeter were very close and there was no significant difference between them as shown Fig.18. We have made the comparison of different types of RPL glass dosimeters such as Type: GD-450 for personal dosimeter and Type:SC-1 for enviromental monitoring, which were supplied from Chiyoda Technol Corp, as shown in Fig.19. It was found that there is no significant difference at each points.

Fig. 17. Dose response at each point in Ishikawa prefecture (A: Tsurugi-machi, B: Tatsunokuchi, C: Inside of house of Mt. Shishiku, D: Outside of Mt. shishiku, E: Inside of Ogoya Mines, F: Outside of Ogoya Mines, G: Public health and Environmental Science) using GD-450 (blue bars) or Luxel badge (orange bars) dosimeters.

Environmental Background Radiation Monitoring Utilizing Passive Solid Sate Dosimeters 135

From the results as described above, Monitoring environmental natural background radiation dose with a personal GD-450 seems to be feasible and consequently, one can say that the GD-450 dosimeter can be suitable for monitoring environmental natural

Environmental natural background radiation dose values at 7 points in Ishikawa prefecture determined using the personal glass dosimeter, type GD-450 were compared with these determined some other personal dosimeters such as DIS dosimeter utilizing a MOSFET with an ioniization chamber and OSL dosimeter, Luxel budge, utilizing OSL phenomenon in Al2O3:C phosphor. The actual dose values were different from each other, however, the tendency of each dose at each point were very similar. It can be said that the personal glass dosimeter will be very useful for not only monitoring personal dose but also monitoring

The author wish to thank Dr.Yamamoto, Directer of the Research Center of Chiyoda Technol Corp. for his fruitful discussion and Dr.Kobayashi of Nagase Landauer Co. Ltd, Dr. Kakimoto of Ishikawa Prefecture Institute of Public health and Environment Science for

The work on the environmental natural background radiation monitoring using solid state passive dosimeters was partially supported by the foundation for Open-Research Center Program from the Ministry of Education, Culture, Sport, Science and Technology of Japan

Kobayashi, I, (2004), The detection of the Environmental radiation for DIS and Luxel badge,

Koyama, S., Miyamoto, Y., Fujiwara, A., Kobayashi, H., Ajisawa, K., Komori, H., Takei, Y.,

Murata, Y., Yamamoto, M. and Komura, K., (2002), Determination of low-level 54Mn in soils

Hsu, S.M., Yeh, S.H., Lin,M.S. and Chen, W.L., (2006), Comparison on characteristics of

Nanto.H, (1998), Photostimulated Luminescence in Insulators and Semiconductors,

J. Radiational Nucl. Chem, Vol.254, No.2, pp.249-257.

Radiation Effects & Defects in Solids, Vol.146, pp.311-321.

Radiation Protection Dosimetry, 119, 327-331.

Nanto, H., Kurobori, T., Kakimoto, H., Sakakura, M., Shimotsuma, Y., Miura, K., Hirao, K. And Yamamoto, T., (2010), Environmental Radiation Monitoring Utilizing Solid State Dosimeters, Sensors and Materials, Vol.22, No.7, 377-385. Miyamoto, Y., Takei, Y., Nanto, H., Kurobori, T., Konnai, A., Yanagida, T., Yoshikawa, A.,

Shimotsuma, T., Sakakura, M., Miura, K., Hirao, K., Nagashima, Y. and Yamamoto, T., (2011), Radiophotoluminescence from Silver-Doped phosphate Glass, Radiation

by ultra low-background gamma-ray spectrometry after radiochemical separation,

radiophotoluminescent glass dosimeters and thermoluminescent dosimeters,

background radiaiton dose.

natural background radiation dose.

**6. Acknowledgements** 

their excellent assistance.

and Chiyoda Technol Corp.

Ionizing Radiation, Vol.30, pp.33-43.

Measurements, in press.

**7. References** 

**5. Summary** 

Fig. 18. Dose response at each point in Ishikawa prefecture (A: Tsurugi-machi, B: Tatsunokuchi, C: Inside of house of Mt. Shishiku, D: Outside of Mt. shishiku, E: Inside of Ogoya Mines, F: Outside of Ogoya Mines, G: Public health and Environmental Science) using GD-450 (blue bars) or DIS (purple bars) dosimeters. There is no data at G for DIS.

Fig. 19. Dose response at each point in Ishikawa prefecture (A: Tsurugi-machi, B: Tatsunokuchi, C: Inside of house of Mt. Shishiku, D: Outside of Mt. shishiku, E: Inside of Ogoya Mines, F: Outside of Ogoya Mines, G: Public health and Environmental Science) using GD-450 (blue bars) or SC-1 (green line) dosimeters. The unit of the GD-45 and SC-1 are represented by mSv and mGy, respectively.

From the results as described above, Monitoring environmental natural background radiation dose with a personal GD-450 seems to be feasible and consequently, one can say that the GD-450 dosimeter can be suitable for monitoring environmental natural background radiaiton dose.
