JP7094492B2 - Treatment method of glass for radiation detection - Google Patents

Description

The present invention relates to a method for treating a glass for radiation detection.

Radiation detection glass is widely used as a detection substance for measuring radiation exposure dose in fields dealing with radiation such as the medical field and the nuclear power field. Here, radiation refers to beta rays, gamma rays, X-rays, and the like. Generally, as the radiation detection glass, for example, phosphate glass containing silver ions is used. When this glass is irradiated with radiation, holes and electrons are generated in the glass, and the formed holes and electrons are captured by Ag ⁺ ions in the glass to become Ag ²⁺ and Ag ⁰ . When Ag ²⁺ and Ag ⁰ in glass are excited by ultraviolet light having a wavelength of 300 to 400 nm, they fluoresce (radiophotoluminescence phenomenon, hereinafter referred to as "RPL phenomenon").

Since the fluorescence intensity due to the RPL phenomenon is proportional to the dose equivalent of the irradiated radiation (hereinafter referred to as "radiation dose"), the radiation dose can be measured by measuring the fluorescence intensity. The fluorescent center formed in the glass by the RPL phenomenon is stabilized by the interaction with the proximity coordinating atom, and the fluorescent center does not disappear at room temperature, so that the radiation dose can be measured for a long period of time. Further, it is possible to eliminate the fluorescent center formed in the glass by the heat treatment. (For example, refer to Patent Document 1) That is, since the glass can be regenerated in a state where the fluorescent center does not exist, it can be used repeatedly.

Japanese Unexamined Patent Publication No. 2016-145145

However, when the glass is heat treated to eliminate the fluorescent center, the glass may be colored. The colored glass has a problem that it cannot be used repeatedly because the glass itself has a lot of fluorescence (hereinafter referred to as "predose") when it is not irradiated with radiation and hinders the measurement of the radiation dose.

In view of the above, it is an object of the present invention to provide a method for treating glass for radiation detection, which can suppress the coloring of glass generated when the glass is heat-treated.

As a result of repeating various experiments, the present inventors have found that the cause of coloration of glass is Ag ⁰ generated during heat treatment. The mechanism by which Ag ⁰ is generated is as follows. First, Ag ⁺ inside the glass and water (H ⁺ ) in the atmosphere adhering to the glass surface exchange ions, and Ag ⁺ moves to the glass surface. The transferred Ag ⁺ reacts with CO ₂ in the atmosphere to generate Ag ₂ CO ₃ on the glass surface. When the glass is heat-treated in this state, Ag ₂ CO ₃ is decomposed into Ag O and CO ₂ , and Ag O is decomposed into Ag and O ₂ . That is, Ag is generated on the glass surface during the heat treatment, and Ag diffuses into the glass as a colloid (Ag ⁰ ). In addition, Ag ⁰ not only colors the glass, but also increases the predose value of the glass.

The method for treating radiation detection glass of the present invention based on the above findings is to wash the radiation detection glass made of silver phosphate glass with water and then heat-treat it to eliminate the fluorescent center generated in the glass. It is characterized by that.

Since Ag ₂ CO ₃ is more soluble in water than an organic solvent such as alcohol, it is possible to remove Ag ₂ CO ₃ generated on the glass surface by washing the glass with water. The glass from which Ag ₂ CO ₃ has been removed is less likely to be colored even by heat treatment and tends to have a low predose value. Here, "water" refers to ion-exchanged water, pure water, tap water, and the like.

In the method for treating radiation detection glass of the present invention, silver phosphate glass has a composition of mol%, SiO ₂ + B ₂ O ₃ 0.1 to 30%, SiO _{20 to 20%, B 2 O 3} It preferably contains 0 to 10%, P ₂ O ₅ 40 to 70%, Al ₂ O ₃ 5 to 30%, Na ₂ O 10 to 35%, and Ag ₂ O 0.01 to 2%.

In the method for treating radiation detection glass of the present invention, the relative humidity of the heat treatment atmosphere is preferably 80% RH or less. The higher the temperature and humidity, the more actively the ion exchange between Ag ⁺ in the glass and the water (H ⁺ ) in the atmosphere adhering to the glass surface is performed, but the relative humidity of the heat treatment atmosphere is controlled to 80% RH or less. Thereby, ion exchange can be suppressed. As a result, the glass is less likely to be colored even after heat treatment and tends to have a low predose value.

In the method for treating radiation detection glass of the present invention, it is preferable that the rate of temperature rise to the maximum temperature during heat treatment is 1 to 40 ° C./min.

The method for treating radiation detection glass of the present invention is preferably used for regeneration of used radiation detection glass.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for treating glass for radiation detection, which can suppress the coloring of the glass generated when the glass is heat-treated.

In the method for treating radiation detection glass of the present invention, the radiation detection glass made of silver phosphate glass is washed with water and then heat-treated to eliminate the fluorescent center generated in the glass. The process of eliminating the fluorescent center of the radiation detection glass is mainly performed before the radiation dose is detected for the first time (the purpose is to eliminate the fluorescent center by natural radiation) and after the radiation dose is measured (the purpose is to regenerate the glass). It is generally done. The treatment method of the present invention can be applied to any of them, but it is particularly preferable to apply it at the time of regenerating glass.

The composition of silver phosphoric acid-based glass is SiO ₂ + B ₂ O ₃ 0.1 to 30%, SiO _{20 to 20%, B 2 O 30 to 10%, P 2 O 5 40 to} 70. %, Al ₂ O ₃₅ to 30%, Na ₂ O 10 to 35%, and Ag ₂ O 0.01 to 2%. The reason for limiting the glass composition range in this way will be described below. In the following description of the content of each component, "%" indicates "mol%" unless otherwise specified.

SiO ₂ and B ₂ O ₃ are important components for enhancing the weather resistance of the glass, and are components for enhancing the fluorescence detection sensitivity. The content of SiO ₂ + B ₂ O ₃ is 0.1 to 30%, 0.2 to 28%, 0.3 to 25%, 0.5 to 19%, 0.7 to 17%, 1 to 15%, In particular, it is preferably 1.5 to 10%. If the content of SiO ₂ + B ₂ O ₃ is too small, the weather resistance tends to be significantly reduced. On the other hand, if the content of SiO ₂ + B ₂ O ₃ is too large, it becomes difficult to vitrify, and conversely, the weather resistance tends to decrease. In addition, "SiO ₂ + B ₂ O ₃ " means the sum of the contents of SiO ₂ and B ₂ O ₃ .

The preferred range of the contents of SiO ₂ and B ₂ O ₃ is as follows.

SiO ₂ is an important component for enhancing the weather resistance of glass, and is also a component for enhancing fluorescence detection sensitivity and mechanical strength of glass. The content of SiO ₂ is 0 to 20%, 0.1 to 19%, 0.3 to 18%, 0.5 to 17%, 0.7 to 16%, 1 to 15%, especially 1.5 to 10. % Is preferable. If the content of SiO ₂ is too large, the meltability is lowered and vitrification is difficult, and devitrified crystals such as cristobalite are likely to precipitate.

B ₂ O ₃ is an important component for enhancing the weather resistance of glass, and is also a component for enhancing fluorescence detection sensitivity. The content of B ₂ O ₃ is 0 to 10%, 0.1 to 10%, 0.3 to 9%, 0.5 to 8%, 0.7 to 7%, 1 to 6%, especially 1.5. It is preferably ~ 5%. If the content of B ₂ O ₃ is too large, it becomes difficult to vitrify due to phase separation, and conversely, the weather resistance tends to decrease.

P ₂ O ₅ is a main component forming the skeleton of glass. The content of P ₂ O ₅ is preferably 40 to 70%, 45 to 67%, 47 to 65%, 50 to 63%, and particularly preferably 55 to 63%. If the content of P ₂ O ₅ is too small, the fluorescence detection sensitivity tends to decrease, and the glass tends to undergo phase separation and devitrification. On the other hand, if the content of P ₂ O ₅ is too large, the meltability is lowered and it becomes difficult to vitrify.

Al ₂ O ₃ is a component that enhances the weather resistance of glass and is a component that suppresses phase separation and devitrification. The content of Al ₂ O ₃ is preferably 5 to 30%, 8 to 29%, 11 to 28%, 13 to 26%, 14 to 24%, and particularly preferably 15 to 23%. If the content of Al ₂ O ₃ is too small, the weather resistance tends to decrease. On the other hand, if the content of Al ₂ O ₃ is too large, the meltability is lowered and it becomes difficult to vitrify.

P ₂ O ₅ / (SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ ) is preferably 1.5 or more, 1.6 or more, and particularly preferably 1.7 or more. If P ₂ O ₅ / (SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ ) is too small, phase separation and devitrification are likely to occur, and vitrification becomes difficult. Further, the upper limit of P ₂ O ₅ / (SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ ) is not particularly limited, but if P ₂ O ₅ / (SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ ) is too large, it is vitrified. It is preferably 5 or less, 4.5 or less, and particularly preferably 4 or less because it becomes difficult and the weather resistance tends to decrease. In addition, "P ₂ O ₅ / (SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ )" is the value obtained by dividing the content of P ₂ O ₅ by the total amount of SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ . Point to.

P ₂ O ₅ / (B ₂ O ₃ + Al ₂ O ₃ ) is preferably 1.5 or more, 1.6 or more, and particularly preferably 1.7 or more. If P ₂ O ₅ / (B ₂ O ₃ + Al ₂ O ₃ ) is too small, phase separation and devitrification are likely to occur, and vitrification becomes difficult. Further, the upper limit of P ₂ O ₅ / (B ₂ O ₃ + Al ₂ O ₃ ) is not particularly limited, but in reality, it is preferably 5 or less, 4.5 or less, and particularly preferably 4 or less. In addition, "P ₂ O ₅ / (B ₂ O ₃ + Al ₂ O ₃ )" refers to a value obtained by dividing the content of P ₂ O ₅ by the total amount of B ₂ O ₃ and Al ₂ O ₃ .

Na ₂ O is a component that lowers the viscosity of the glass melt to remarkably increase the meltability, and is a component that enhances the fluorescence detection sensitivity. The content of Na ₂ O is preferably 10 to 35%, 11 to 33%, 13 to 30%, 14 to 28%, and particularly preferably 15 to 25%. If the content of Na ₂ O is too small, the meltability tends to decrease and the fluorescence detection sensitivity tends to decrease. On the other hand, if the content of Na ₂ O is too large, the weather resistance tends to decrease.

Ag ₂ O is an important component for forming a fluorescent center by the RPL phenomenon. The content of Ag ₂ O is preferably 0.01 to 2%, 0.01 to 1%, and particularly preferably 0.01 to 0.5%. If the content of Ag ₂ O is too small, the fluorescence detection sensitivity tends to decrease. On the other hand, if the content of Ag ₂ O is too large, the weather resistance tends to decrease.

The radiation detection glass in the present invention may contain the following components in addition to the above components.

MgO is a component that enhances the weather resistance of glass. The content of MgO is preferably 0 to 10%, 0 to 7%, and particularly preferably 0 to 4%. If the content of MgO is too large, the liquidus temperature rises and devitrified crystals such as magnesium phosphate are likely to precipitate.

ZnO is a component that suppresses phase separation and devitrification of glass. The ZnO content is preferably 0 to 10%, 0 to 7%, and particularly preferably 0 to 4%. If the ZnO content is too high, the weather resistance and fluorescence detection sensitivity tend to decrease.

CaO, SrO and BaO are components that enhance the weather resistance of glass. The content of CaO + SrO + BaO is preferably 0 to 15%, 0 to 10%, and particularly preferably 0 to 5%. If the content of CaO + SrO + BaO is too large, the fluorescence detection sensitivity tends to decrease, the liquidus temperature decreases, and devitrified crystals such as phosphates tend to precipitate.

The preferable range of the contents of CaO, SrO and BaO is as follows.

The CaO content is preferably 0 to 15%, 0 to 10%, and particularly preferably 0 to 5%.

The content of SrO is preferably 0 to 15%, 0 to 10%, and particularly preferably 0 to 5%.

The content of BaO is preferably 0 to 15%, 0 to 10%, and particularly preferably 0 to 5%.

The glass transition point of the radiation detection glass is preferably 600 ° C. or lower, 550 ° C. or lower, and particularly preferably 530 ° C. or lower. If the glass transition point is too _high , the maximum _temperature during the heat _{treatment ,} which will be described later, will be _high . It becomes difficult. The lower limit of the glass transition point is not particularly limited, but is actually 300 ° C. or higher.

The shape of the radiation detection glass is not particularly limited, but it is usually a plate shape such as a rectangle.

Next, a method for manufacturing the radiation detection glass used in the present invention will be described.

First, the raw material powder is prepared so as to have a desired composition. Next, the prepared raw material powder is put into a crucible and melted until a homogeneous glass is obtained. Next, the molten glass is poured onto a carbon plate or the like, molded into a plate shape, and then slowly cooled to room temperature to obtain a glass for radiation detection. As the slow cooling condition, for example, it is preferable to lower the temperature at about 2 ° C./min from a temperature about 20 ° C. higher than the slow cooling point.

Further, when the oxygen partial pressure at the time of melting becomes low, the Ag component is easily reduced, and Ag ⁰ is easily generated in the glass. Examples of the method of suppressing the reduction of the Ag component include a method of lowering the melting temperature to 1000 to 1400 ° C., a method of introducing an oxidizing gas into the melting atmosphere, and a method of using nitrate as an oxidizing agent as a raw material. Examples of the oxidizing gas include oxygen, ozone, nitrogen oxides (nitrous oxide, nitric oxide, nitrogen dioxide, etc.) and the like. Further, as the nitrate, silver nitrate, aluminum nitrate, sodium nitrate and the like can be used.

Examples of the material of the glass melting crucible include SiO ₂ , Al ₂ O ₃ , and the like. Since Pt and Rh, which are general glass melting crucible materials, tend to reduce the glass to increase the amount of Ag ⁰ and increase the predose value of the radiation detection glass, the production of radiation detection glass is performed. Not suitable for.

Next, a series of steps of regenerating after measuring the fluorescence intensity using the glass for radiation detection will be described. By regenerating the glass, it can be used repeatedly. Needless to say, the more times you use it, the lower the cost.

(Disappearance of fluorescent center due to natural radiation)
First, both sides of the obtained radiation detection glass are polished so as to be an optically polished surface (mirror surface), washed with water, and then heat-treated to eliminate the fluorescent center formed by natural radiation.

(Measurement of radiation dose)
Then, the radiation dose received by the radiation detection glass is measured. Specifically, when the radiation detection glass is irradiated with radiation, Ag ²⁺ and Ag ⁰ are formed in the glass. Then, after heat-treating at 100 to 150 ° C. for 10 to 60 minutes to stabilize the fluorescence intensity, the fluorescence intensity is measured by irradiating with ultraviolet light. The radiation dose is calculated from this fluorescence intensity.

(Regeneration of glass)
Wash the glass after measuring the fluorescence intensity with water. The cleaning method is not particularly limited, but cleaning using an ultrasonic cleaner is preferable because the cleaning time can be shortened. A surfactant, a pH adjuster, an organic solvent such as alcohol, or the like may be added to the washing water in a total amount of up to 30% by mass.

As described above, since Ag ₂ CO ₃ generated on the glass surface can be removed by washing the glass with water, the glass is less likely to be colored even after heat treatment and tends to have a low predose value.

Next, the glass after cleaning is heat-treated under the following heat treatment conditions to regenerate the glass.

The relative humidity of the heat treatment atmosphere is preferably 80% RH or less, 70% RH or less, and particularly preferably 60% RH or less. If the relative humidity is too high, water tends to adhere to the glass surface during the heat treatment. As a result, Ag ⁰ is diffused in the glass, the glass is easily colored, and the predose value of the glass is easily increased. The lower limit of the relative humidity is not particularly limited, but in reality, it is 5% RH or more.

The maximum temperature during heat treatment is (glass transition point -80 ° C) to (glass transition point -10 ° C), (glass transition point -55 ° C) to (glass transition point -15 ° C), (glass transition point -40 ° C). )-(Glass transition point -15 ° C), particularly (Glass transition point -25 ° C) to (Glass transition point -20 ° C). If the maximum temperature during the heat treatment is too low, it is difficult to sufficiently eliminate the fluorescent center formed in the glass, and it is difficult to regenerate the glass. On the other hand, if the maximum temperature during the heat treatment is too high, the silver ion concentration on the glass surface increases and the glass tends to deteriorate, which makes it difficult to regenerate the glass. Specifically, the maximum temperature during the heat treatment is preferably 420 to 500 ° C., 430 to 490 ° C., 440 to 480 ° C., and particularly preferably 450 to 470 ° C. The holding time at the maximum temperature is preferably 20 to 150 minutes, 30 to 120 minutes, 40 to 90 minutes, and particularly preferably 50 to 70 minutes. If the holding time is too short, heat is not easily transferred to the inside of the glass, so that it is difficult to sufficiently eliminate the fluorescent center formed in the glass, and it is difficult to regenerate the glass. On the other hand, if the holding time is too long, the silver ion concentration on the glass surface increases and the glass tends to deteriorate, which makes it difficult to regenerate the glass. In addition, the time of exposure to high temperature becomes longer, and ion exchange between Ag ⁺ in the glass and water (H ⁺ ) in the atmosphere adhering to the glass surface becomes easier. As a result, the glass tends to be colored and the predose value tends to increase.

The rate of temperature rise to the maximum temperature during the heat treatment is preferably 1 to 40 ° C./min, 2 to 38 ° C./min, and particularly preferably 3 to 36 ° C./min. If the rate of temperature rise is too slow, the time of exposure to high temperature becomes long, and ion exchange between Ag ⁺ in the glass and water (H ⁺ ) in the atmosphere adhering to the glass surface becomes easy. As a result, the glass tends to be colored and the predose value tends to increase. On the other hand, if the heating rate is too fast, the glass is liable to break due to thermal shock.

It is preferable that the cleaning conditions and heat treatment conditions for eliminating the fluorescent center formed by natural radiation are the same as described above.

Hereinafter, the present invention will be described based on examples. The following examples are merely examples. The present invention is not limited to the following examples.

Tables 1 and 2 show the radiation detection glass (No. 1 to 14) used in the examples of the present invention and the radiation detection glass (No. 15 and 16) used in the comparative example.

(1. Preparation of glass for radiation detection)
First, high-purity raw materials used for ordinary glass such as oxides, hydroxides, carbonates, nitrates, and phosphates corresponding to each component are selected so as to have the glass composition in the table. A glass batch that was weighed and uniformly mixed was placed in a quartz glass pot and melted in an electric furnace at 1000 to 1300 ° C. for 1 to 5 hours until a uniform glass was obtained. For the purpose of homogenizing the glass and breaking bubbles, stirring was performed at the time of melting. Next, the molten glass was poured onto a carbon plate, molded into a plate shape, and then slowly cooled from a temperature about 20 ° C. higher than the slow cooling point to room temperature at 2 ° C./min to obtain a glass for radiation detection. Here, the glass transition point of the obtained radiation detection glass was measured by a thermomechanical analyzer (TMA).

(2. Disappearance of fluorescent center due to natural radiation)
Both sides of the obtained radiation detection glass are polished so as to be an optically polished surface (mirror surface), washed with pure water in an ultrasonic cleaner for 10 minutes, and then the dried sample is heat-treated under the conditions shown in the table. By doing so, the fluorescent center formed by natural radiation disappeared, and the optically polished surface of the sample was irradiated with ultraviolet light.

(3. Irradiation of X-rays)
Next, about 1 Gy of X-rays was irradiated from the vertical direction of the optically polished surface of the sample. After irradiation with X-rays, heat treatment was performed at 120 ° C. for 30 minutes to stabilize the fluorescence intensity, and then the optically polished surface of the sample was irradiated with ultraviolet light.

(4. Regeneration of glass (disappearance of fluorescent center by X-ray irradiation))
No. For the samples 1 to 14, the glass after ultraviolet light irradiation was washed with pure water in an ultrasonic cleaner for 10 minutes and then dried. No. For the samples 15 and 16, the glass after ultraviolet light irradiation was washed with ethanol in an ultrasonic cleaner for 10 minutes and then dried.

By heat-treating the dried sample under the conditions shown in the table, the fluorescent center formed by X-ray irradiation disappeared and the glass was regenerated.

(5. Evaluation of sample)
Coloring and predose values were evaluated for each sample thus obtained.

Coloring was evaluated as follows. The obtained sample was visually observed. Those for which coloring was not confirmed were designated as "○", and those for which coloring was confirmed were designated as "x".

The predose value was evaluated as follows. The fluorescence intensity measured by irradiating the optically polished surface of the obtained sample with ultraviolet light was used as the predose value.

As is clear from the table, No. 1 which is an embodiment of the present invention. The samples 1 to 14 were not confirmed to be colored and had a low predose value of 41 to 55, so that they could be reused. On the other hand, No. Coloration was confirmed in the samples 15 and 16, and the predose value was as high as 198 to 204, so that it was difficult to reuse them.

Claims (4)

As a composition, in mol%, SiO ₂ + B ₂ O ₃ 6.0 to 30%, SiO ₂ 6.0 to 20%, B ₂ O ₃₀ to 10%, P ₂ O ₅ 40 to 70%, Al ₂ O. Radiation detection glass made of silver phosphate-based glass containing 35 to 30%, Na 2 O 10 to 35%, and Ag 2 O 0.01 to 2% is _washed with _water and _then heat-treated in the glass. A method for treating glass for radiation detection, which comprises eliminating the fluorescent center generated in the glass. The method for treating radiation detection glass according to claim 1, wherein the relative humidity of the heat-treated atmosphere is 80% RH or less. The method for treating glass for radiation detection according to claim 1 or 2 , wherein the rate of temperature rise to the maximum temperature during heat treatment is 1 to 40 ° C./min. The method for treating radiation detection glass according to any one of claims 1 to 3 , wherein the used radiation detection glass is used for regeneration.