**6. Physical characteristics of radio-photoluminescence glass dosimeter**

The pulse ultra-violet laser excitation system improves the readout accuracy of RPLGD and also shortens the readout time. The improvement in the luminescent material lowers the detectable dose limit. These improvements make the applications of RPLGD in radiation measurements growing rapidly. There are three major types of RPLGD in the market; the SC-1 for environmental radiation dose monitor; the GD-450 for personal external radiation dose monitor; and the Dose Ace for research purposes. All those three types use FD-7 glass, manufactured by Asahi, Japan, as shown in Figure 7.

The SC-1 is a plate-type RPLGD with outside capsule volume of 30 x 40 x 9 mm3.The dimension of FD-7 glass inside the capsule is 16 x 16 x 1.5 mm3. There are two layers of tin filters, one on the top and another at the bottom, over of the capsule with a dimension of 0.75 mm and 3 mm respectively. These tin filters are used as energy compensator to estimate the radiation energy and to lower the energy dependence effect. The FD-7 in GD-450 has a dimension of 33 x 7 x 1 mm3. There are five different types with different thickness of filters in the capsule of GD-450; namely, 0.2 mm acrylic plate; 0.5 mm acrylic plate; 0.7 mm aluminum filter; 0.2 mm copper filter; and 1.2 mm tin filter. The functions of these filters in

luminescence model for RPLGD. We believe that the color centers of RPLGD may be structured among the orbital electrons in the compound. The various continuous energy levels are formed with different bonding structures among elements. Those energy levels can store free electron energy which is produced by the excitation process. Therefore, its excitation energy gap has a continuous value (from 1.78 to 2.07 eV) which releases 600 nm –

Fig. 6. There are many continuous energy levels in RPLGD color centers.

manufactured by Asahi, Japan, as shown in Figure 7.

**6. Physical characteristics of radio-photoluminescence glass dosimeter** 

The pulse ultra-violet laser excitation system improves the readout accuracy of RPLGD and also shortens the readout time. The improvement in the luminescent material lowers the detectable dose limit. These improvements make the applications of RPLGD in radiation measurements growing rapidly. There are three major types of RPLGD in the market; the SC-1 for environmental radiation dose monitor; the GD-450 for personal external radiation dose monitor; and the Dose Ace for research purposes. All those three types use FD-7 glass,

The SC-1 is a plate-type RPLGD with outside capsule volume of 30 x 40 x 9 mm3.The dimension of FD-7 glass inside the capsule is 16 x 16 x 1.5 mm3. There are two layers of tin filters, one on the top and another at the bottom, over of the capsule with a dimension of 0.75 mm and 3 mm respectively. These tin filters are used as energy compensator to estimate the radiation energy and to lower the energy dependence effect. The FD-7 in GD-450 has a dimension of 33 x 7 x 1 mm3. There are five different types with different thickness of filters in the capsule of GD-450; namely, 0.2 mm acrylic plate; 0.5 mm acrylic plate; 0.7 mm aluminum filter; 0.2 mm copper filter; and 1.2 mm tin filter. The functions of these filters in

700 nm visible lights.

GD-450 are the same as that of SC-1; to estimate radiation energy and to lower the energy dependence effect. The GD-450 dosimeters are the major personal dosimeters used in Japan.

Fig. 7. Three types of RPLGD; above: SC-1 system for environmental radiation monitor; below left: GD-450 system for personal dose monitor; and below right: small volume Dose Ace system for research

The Dose Ace type RPLGD is mainly for research purposes. It is a cylindrical shape with three different models; GD-302M, GD-352M, and GD-301. The GD-302M and GD-352M have a length of 12 mm and a diameter of 1.5 mm, while GD-301 has a length of 8.5 mm and a diameter of 1.5 mm. GD-301 and GD-302M, without filters in capsule, are used to measure the dose of high energy photons as in radiotherapy. However, there is a Tin filter in the capsule for GD-352M to lower the energy dependence effect. The GD-352M can be used for measuring the dose from low energy photons as in diagnostic radiology. In the process of dose readout, based on the dose values, the dose ranges are divided into two categories, low dose range (10 Gy – 10 Gy) and high dose range (1 Gy - 500 Gy).The readout system can automatically distinguish the dose range according to different readout magazine used by the users. On the top of that, there are different readout areas in RPLGD for different dose ranges too. The readout area for high dose range is located at between 0.4 mm and 1 mm, a total length of 6 mm and a total volume of 0.47 mm3, from the non-series end in the

Radio-Photoluminescence Glass Dosimeter (RPLGD) 563

In Figure 9, it shows the readout reproducibility for GD-352M and TLD-100H respectively with a C.V. (coefficient of variation) of 0.46 – 3.11 for GD-325M and C.V. of 0.71 – 3.87 for TLD-100H. The figure shows that the C.V. is smaller for RPLGD as compared to that of TLD because of different manufacture methods. Each RPLGD is made after glass material melted at high temperature and results in a smaller variation among each RPLGD. On the other

0 5 10 15 20 25 Number of Dosimeter

Figure 10 shows the dose linearity for GD-352M and TLD-100H respectively in a range of 0.105 mGy and 50.4 mGy. The measured dose points are at 0.105 mGy, 0.168 mGy, 0.672 mGy, 1.05 mGy, 2.1 mGy, 6.3 mGy, 25.2 mGy, and 50.4 mGy with five RPLGDs for each measured point. The correlation coefficient is close to unity for both GD-325M and TLD-100H. It shows that the dose irradiated is proportional to the dose estimated from

Figure 11 shows the energy dependence for GD-302M, GD-352M, and TLD0-100H respectively. The values shown in figure 11 are normalized to the readout from Cs-137 irradiation. When un-filtered GD-302M irradiated with low energy photons, the interactions between photons and RPLGD are increased because of the photoelectric effect. Therefore the luminescence signal is increased too. For filtered GD-352M, the Tin filter can stop the low

Table 3 shows the characteristics comparisons of different passive dosimeters. It demonstrates that the physical characteristics of OSLD are better than that of TLD. And the physical characteristics of RPLGD are better than that of OSLD because of different readout system and different luminescence material. Therefore, RPLGD could become one of the

Fig. 9. The readout reproducibility of GD-352M and TLD-100H

energy photons; hence, the energy dependence effect is less.

important dose measurement tools in the future.

TLD-100H GD-352M

hand, the TLD is made with growing crystal, therefore the variation is greater.

0.8

readout.

0.9

1

Relative response

1.1

1.2

readout area (as shown in Figure 8); while the low dose range is located from 1 mm to 6 mm with a volume of 0.47 mm3. The high dose readout area can be used for the measurement of dose with high gradient too. The Table 2 shows the characteristics of various RPLGDs.

Fig. 8. The high dose readout area for GD-320M; the series end is located on the left side, the readout area is located at 0.4 mm to 1.0 mm from the non-series end, the diameter of incident pulse ultra-violet laser is 1 mm (Hsu).


Table 2. The characteristics of RPLGD

readout area (as shown in Figure 8); while the low dose range is located from 1 mm to 6 mm with a volume of 0.47 mm3. The high dose readout area can be used for the measurement of dose with high gradient too. The Table 2 shows the characteristics of various RPLGDs.

Fig. 8. The high dose readout area for GD-320M; the series end is located on the left side, the

12.04 12.04 12.04

± 3%

(0 ~ 80 degree)

10 μGy - 10 Gy 10 μGy - 10 Gy 10 μGy - 10 Gy

1.2(with energy compensator filter)

1 Gy - 500 Gy

3.4(w/o energy compensator

(0 ~ 80 degree)

0

filter)0.8(with energy compensator filter)

readout area is located at 0.4 mm to 1.0 mm from the non-series end, the diameter of

Type SC-1 GD-450 Dose Ace

1.2(with energy compensator filter)

Fading effect < 5 % / yr < 5 % / yr < 5 % / yr

Repeatable readout yes yes yes

(0 ~ 80 degree)

incident pulse ultra-violet laser is 1 mm (Hsu).

Effective atomic

The dose linearity

Energy dependency (20 keV / 137Cs )

Angular dependency ± 8%

Table 2. The characteristics of RPLGD

number

range

In Figure 9, it shows the readout reproducibility for GD-352M and TLD-100H respectively with a C.V. (coefficient of variation) of 0.46 – 3.11 for GD-325M and C.V. of 0.71 – 3.87 for TLD-100H. The figure shows that the C.V. is smaller for RPLGD as compared to that of TLD because of different manufacture methods. Each RPLGD is made after glass material melted at high temperature and results in a smaller variation among each RPLGD. On the other hand, the TLD is made with growing crystal, therefore the variation is greater.

Number of Dosimeter

Figure 10 shows the dose linearity for GD-352M and TLD-100H respectively in a range of 0.105 mGy and 50.4 mGy. The measured dose points are at 0.105 mGy, 0.168 mGy, 0.672 mGy, 1.05 mGy, 2.1 mGy, 6.3 mGy, 25.2 mGy, and 50.4 mGy with five RPLGDs for each measured point. The correlation coefficient is close to unity for both GD-325M and TLD-100H. It shows that the dose irradiated is proportional to the dose estimated from readout.

Figure 11 shows the energy dependence for GD-302M, GD-352M, and TLD0-100H respectively. The values shown in figure 11 are normalized to the readout from Cs-137 irradiation. When un-filtered GD-302M irradiated with low energy photons, the interactions between photons and RPLGD are increased because of the photoelectric effect. Therefore the luminescence signal is increased too. For filtered GD-352M, the Tin filter can stop the low energy photons; hence, the energy dependence effect is less.

Table 3 shows the characteristics comparisons of different passive dosimeters. It demonstrates that the physical characteristics of OSLD are better than that of TLD. And the physical characteristics of RPLGD are better than that of OSLD because of different readout system and different luminescence material. Therefore, RPLGD could become one of the important dose measurement tools in the future.

Radio-Photoluminescence Glass Dosimeter (RPLGD) 565

0 10 20 30 40 50 60 Absorbed dose (mGy)

10 100 1000 Photon energy (keV)

Fig. 11. The energy dependence curves for GD-302M, GD-352M, and TLD-100H

Fig. 10. The dose linearity curves for GD-352M and TLD-100H, both C.V.s are less than 3.

GD-352M y = 1.019x - 0.0197 R2 = 1

> TLD-100H GD-352M

> > GD-302M GD-352M TLD-100H

TLD-100H y = 1.0282x - 0.1352 R2 = 0.9996

0

0

0.5

1

1.5

Relative response

(normalized for 662 keV)

2

2.5

3

3.5

10

20

30

Readout value (mGy)

40

50

60


Table 3. The characteristics comparisons of TLD, OSLD, and RPLGD

TLD OSLD RPLGD

dependent material-dependent good

reduced

material-dependent (10μGy - 10 Gy)

material-dependent (0 - 10 %/year)

dependent material-dependent ± 20%(having energy

yes yes yes

optically stimulated luminescence signal

radiophotoluminescence

yes, with the same

10μGy - 10 Gy 1 Gy - 500 Gy

less than 5%/year

compensation filter)

intensity

signal

luminescence

Repeatable readout no yes, but intensity

materialdependent (10μGy - 10 Gy)

materialdependent (5 - 20 % / quarter)

Re-useable yes no yes

Table 3. The characteristics comparisons of TLD, OSLD, and RPLGD

Luminescence material crystal crystal glass

Excitation source heat visible light ultra-violet laser

Geometrical shape chip and powder powder various shapes

signal

Sensitivity material-

Energy dependence material-

Range of measurement

Fading effect

Capability to

radiation

distinguish the types of

Principe of measurement

Fig. 10. The dose linearity curves for GD-352M and TLD-100H, both C.V.s are less than 3.

Fig. 11. The energy dependence curves for GD-302M, GD-352M, and TLD-100H

Radio-Photoluminescence Glass Dosimeter (RPLGD) 567

radiation monitor (Yasuda, Iyogi). Hsu et al. also applied RPLGD in prostate HDR (High Dose Rate Remote Afterloader) procedure to study the dose distributions (Hsu). Many institutes in US and Europe devote into the developments and the researches in the new luminescence material and readout techniques for RPLGD (Yasuda, Araki, Arakia, Nose,

With its small volume, RPLGD can be used in in-vivo dose measurements; e.g. dose evaluation in animal irradiation study. RPLGD can also be placed in the anthropomorphic phantom to evaluate dose received during the clinical procedures for diagnostic radiology and radiotherapy. With its characteristics of repeatable readout and small effective readout area, RPLGD can also be used in brachytherapy procedures to evaluate the dose delivery accuracy for each procedure as well as for entire course. On the top of that, with the help of dedicated tube to hold RPLGD, one can apply RPLGD in the area of adjacent critical organs to monitor the organ dose to avoid the dose exceeding the tolerance during the radiotherapy

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