JP2019182672A - Method for producing glass for radiation detection - Google Patents

Abstract

To provide a method for producing a glass for radiation detection having a low pre-dose value.SOLUTION: The present invention provides a method for producing a glass for radiation detection by heating and melting raw materials for molding. The raw materials for AlOused herein are aluminum metaphosphate with an average particle size Dof 50-500 μm.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a radiation detection glass suitable for measuring a dose equivalent of radiation.

Radiation detection glass is widely used as a detection substance for measuring the radiation exposure dose in fields dealing with radiation, such as the medical field and the nuclear field. Here, radiation refers to beta rays, gamma rays, X-rays, or the like. In general, silver phosphate glass is used for radiation detection glass (see, for example, Patent Document 1). When this glass is irradiated with radiation, holes and electrons are generated in the glass, and the generated 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, fluorescence is emitted (radioluminescence phenomenon, hereinafter referred to as “RPL phenomenon”).

  Since the fluorescence intensity due to the RPL phenomenon is proportional to the dose equivalent (hereinafter referred to as “radiation dose”) of the irradiated radiation, the radiation dose can be measured by measuring the fluorescence intensity. The fluorescence detection sensitivity with respect to the radiation dose of the glass varies depending on the composition of the glass. The fluorescence center generated in the glass by the RPL phenomenon is stabilized by the interaction with the coordinating coordination atom, and the disappearance of the fluorescence center does not occur at room temperature. Therefore, the radiation dose can be measured over a long period of time. Moreover, since the fluorescence center produced | generated in glass lose | disappears by heat processing, it can be used repeatedly.

Japanese Patent Laid-Open No. 2006-145145

  However, the glass described in Patent Document 1 has a problem that there is a lot of fluorescence (hereinafter referred to as “pre-dose”) that the glass itself has when not irradiated with radiation, which hinders measurement of radiation dose.

  In view of the above, an object of the present invention is to provide a method for producing a glass for radiation detection having a low predose value.

As a result of various experiments, the present inventors have found that the particle diameter of aluminum metaphosphate used as the Al ₂ O ₃ raw material greatly affects the pre-dose value of the radiation detection glass. Specifically, Al ₂ O ₃ greater aluminum metaphosphate particle size having a high melting point Al ₂ O ₃ tends undissolved when melted as starting materials, hard spots of Al ₂ O ₃ is generated in the glass for radiation detection Cheap. The generated Al ₂ O ₃ bumps cause multiple scattering and raise the pre-dose value of the glass for radiation detection. In addition, when aluminum metaphosphate having a small particle diameter is used as the Al ₂ O ₃ raw material, aluminum metaphosphate and other raw materials (especially carbonate raw materials) easily react at the initial stage of melting, and a large amount of gas such as CO ₂ is used. Occurs. Since the generated gas lowers the oxygen partial pressure of the molten atmosphere, it was found that the glass was reduced and Ag ⁰ was generated, increasing the pre-dose value of the radiation detection glass. In the present invention, those represented by the chemical formula Al (PO ₃ ) ₃ are collectively referred to as “aluminum metaphosphate”.

That is, the method for producing a radiation detection glass of the present invention is a method for producing a radiation detection glass by heating and melting a raw material and molding the raw material, and an average particle diameter D ₅₀ is 50 to ₅₀ as an Al ₂ O ₃ raw material. It is characterized by using aluminum metaphosphate having a thickness of 500 μm. Controlling the particle diameter of aluminum metaphosphate in this way makes it easy to produce a radiation detection glass having a low pre-dose value.

The method of manufacturing the radiation detection glasses of the present invention, the radiation detection glass, in _{mol%, SiO 2 + B 2 O} 3 0.1~30%, SiO 2 0~20%, B 2 O 3 0~10% _{, P 2 O 5 40~70%,} Al 2 O 3 10~30%, Na 2 O 10~35%, preferably contains Ag 2 O 0.01~2%.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the glass for radiation detection which has a low predose value can be provided.

Method for manufacturing the radiation detection glasses of the present invention, Al as ₂ O ₃ raw material, the average particle diameter D _50, characterized in that the heating and melting a raw material with aluminum metaphosphate is 50 to 500 [mu] m.

As described above, when aluminum metaphosphate having an average particle diameter D50 of ₅₀ to 500 μm is used as the Al ₂ O ₃ raw material, it is difficult to generate Al ₂ O ₃ flutter and Ag ⁰ that increase the pre-dose value, and radiation. The pre-dose value of the detection glass can be lowered.

The average particle diameter D ₅₀ of aluminum metaphosphate is 50 to 500 μm, preferably 70 to 450 μm, and particularly preferably 100 to 400 μm. When the average particle diameter D ₅₀ is too small, the oxygen partial pressure of the molten atmosphere tends to deteriorate, Ag ⁰ glass is reduced is likely to occur. On the other hand, when the average particle diameter _{D 50} is too large, hard spots of _Al 2 _{O 3} is more likely to occur in the glass.

  Next, the manufacturing method of the glass for radiation detection is demonstrated concretely. However, the present invention is not limited to this.

First, raw material powder is prepared so as to have a desired composition. Here, aluminum metaphosphate having an average particle diameter D50 of ₅₀ to 500 μm is used as the raw material powder as the Al ₂ O ₃ raw material. Next, the prepared raw material powder is put into a glass melting crucible and melted until a homogeneous glass is obtained. Next, the molten glass is poured onto a carbon plate or the like, formed into a plate shape, and then slowly cooled to room temperature, thereby obtaining a radiation detection glass. As the slow cooling conditions, for example, it is preferable to lower the temperature from about 20 ° C. higher than the slow cooling point at about 2 ° C./min. Although it is preferred that the average particle size _{D 50} as _Al 2 _{O 3} raw material using only aluminum metaphosphate is 50 to 500 [mu] m, no problem even using other _Al 2 _{O 3} raw material up to 20% by weight.

Further, as described above, when the oxygen partial pressure at the time of melting is lowered, the Ag component is easily reduced, and Ag ⁰ is easily generated in the glass. Therefore, in addition to controlling the particle diameter of aluminum metaphosphate, a method of lowering the melting temperature to 1000 to 1400 ° C., a method of introducing an oxidizing gas into the molten atmosphere, and a method of using nitrate as an oxidant as a raw material When used together, the oxygen partial pressure at the time of melting becomes more difficult to decrease. Examples of the oxidizing gas include oxygen, ozone, and nitrogen oxides (nitrous oxide, nitrogen monoxide, nitrogen dioxide, etc.). Further, as the nitrate, silver nitrate, aluminum nitrate, sodium nitrate or the like can be used.

Examples of the material of the glass melting crucible include SiO ₂ and Al ₂ O ₃ . In addition, 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 pre-dose value of the radiation detection glass. Not suitable for.

  Next, a series of flows to be regenerated after measuring fluorescence intensity using radiation detection glass will be described.

(Disappearance of fluorescent center by natural radiation)
First, both surfaces of the obtained radiation detection glass are polished so as to be optically polished surfaces (mirror surfaces), and then heat-treated, so that the fluorescence centers formed by natural radiation disappear.

(Measurement of radiation dose)
Subsequently, the radiation dose received by the radiation detection glass is measured. Specifically, when radiation is applied to the radiation detection glass, Ag ²⁺ and Ag ⁰ are formed in the glass. Thereafter, heat treatment is performed under the following heat treatment conditions to stabilize the fluorescence intensity, and then ultraviolet light is irradiated to measure the fluorescence intensity. The radiation dose is calculated from this fluorescence intensity.

  The heat treatment temperature is preferably (glass transition point / 4) to (glass transition point / 2.5), particularly preferably (glass transition point / 3.5) to (glass transition point / 2.7). If the heat treatment temperature is too low, the fluorescence intensity is difficult to stabilize and the reproducibility of the radiation dose measurement value tends to be low. On the other hand, if the heat treatment temperature is too high, the fluorescence intensity tends to decrease during long-term storage, and the reproducibility of the radiation dose measurement values tends to be low. Specifically, the heat treatment temperature is preferably 105 to 200 ° C, particularly 110 to 180 ° C. Moreover, it is preferable that the heat processing time is 10 to 120 minutes, especially 20 to 70 minutes. If the heat treatment time is too short, heat is not easily transmitted to the inside of the glass, so that the fluorescence intensity is difficult to stabilize and the reproducibility of the radiation dose measurement value tends to be low. On the other hand, if the heat treatment time is too long, the fluorescence intensity tends to decrease during long-term storage, and the reproducibility of the radiation dose measurement value tends to be low.

(Regeneration of glass)
By heat-treating the glass after the fluorescence intensity measurement under the following heat treatment conditions, the glass can be regenerated (reused).

  The heat treatment temperatures are (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) to ( It is preferable that they are (glass transition point -15 degreeC), especially (glass transition point -25 degreeC)-(glass transition point -20 degreeC). When the heat treatment temperature is too low, the fluorescent centers formed in the glass are not easily lost, and it is difficult to regenerate the glass. On the other hand, if the heat treatment temperature is too high, the silver ion concentration on the glass surface increases and the glass tends to be altered, making it difficult to regenerate the glass. Specifically, the heat treatment temperature is preferably 420 to 500 ° C, 430 to 490 ° C, 440 to 480 ° C, particularly 450 to 470 ° C. The heat treatment time is preferably 20 to 150 minutes, 30 to 120 minutes, 40 to 90 minutes, particularly 50 to 70 minutes. If the heat treatment time is too short, heat is not easily transmitted to the inside of the glass, so that the fluorescence centers formed in the glass are not easily lost and the glass is difficult to regenerate. On the other hand, if the heat treatment time is too long, the concentration of silver ions on the glass surface increases and the glass tends to be altered, making it difficult to regenerate the glass. In addition, it becomes possible to use repeatedly by reproducing | regenerating glass. It goes without saying that the more the number of uses, the lower the cost. In addition, it is preferable that the heat treatment conditions for erasing the fluorescent center formed by natural radiation are the same as described above.

  Next, the radiation detection glass produced in the present invention will be described.

The glass for radiation detection is mol%, SiO ₂ + B ₂ O ₃ 0.1-30%, SiO ₂ 0-20%, B ₂ O ₃ 0-10%, P ₂ O ₅ 40-70%, Al _{2. O 3 10~30%, Na 2 O} 10~35%, preferably contains Ag 2 O 0.01~2%.

  The reason for limiting the glass composition as described above is shown below. In the description of the content of each component, “%” means “mol%” unless otherwise specified.

SiO ₂ and B ₂ O ₃ are important components for increasing the weather resistance of the glass, and are components for increasing the fluorescence detection sensitivity. The content of SiO ₂ + B ₂ O ₃ is 0.1-30%, 0.2-28%, 0.3-25%, 0.5-19%, 0.7-17%, 1-15%, In particular, it is preferably 1.5 to 10%. When the content of SiO ₂ + _B 2 _{O 3} is too small, easy to weather resistance is significantly reduced. On the other hand, when the content of SiO 2 ₊ B ₂ O ₃ is too large, in addition to being difficult to vitrify, weather resistance tends to decrease conversely. “SiO ₂ + B ₂ O ₃ ” means the total content of SiO ₂ and B ₂ O ₃ .

Preferable ranges of the contents of SiO ₂ and B ₂ O ₃ are as follows.

SiO ₂ is an important component for increasing the weather resistance of glass, and is a component for increasing fluorescence detection sensitivity and mechanical strength of glass. The content of SiO ₂ is 0-20%, 0.1-20%, 0.2-19%, 0.3-18%, 0.5-17%, 0.7-16%, 1-15% In particular, it is preferably 1.5 to 10%. When the content of SiO ₂ is too large, in addition to meltability it becomes difficult to vitrify reduced devitrification crystals cristobalite tends to precipitate.

B ₂ O ₃ is an important component for increasing the weather resistance of the glass and is a component for increasing the fluorescence detection sensitivity. The content of B ₂ O ₃ is 0 to 10%, 0.1 to 10%, 0.1 to 9%, 0.5 to 8%, 0.7 to 7%, 1 to 6%, particularly 1.5. It is preferably ˜5%. When the content of B ₂ O ₃ is too large, in addition to being difficult to vitrification by phase separation, the weather resistance tends to decrease conversely.

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

Al ₂ O ₃ is a component that enhances the weather resistance of glass and a component that suppresses phase separation and devitrification. The content of Al ₂ O ₃ is preferably 10 to 30%, 11 to 28%, 13 to 26%, 14 to 24%, particularly preferably 15 to 23%. When the content of Al ₂ O ₃ is too small, the weather resistance tends to decrease. On the other hand, when the content of Al ₂ O ₃ is too large, the melting property becomes difficult to vitrify reduced.

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 or devitrification is likely to occur, and vitrification becomes difficult. _The upper limit of _{P 2 O 5 / (SiO 2} + B 2 O 3 + Al 2 O 3) is not particularly _{limited, P 2 O 5 / (SiO 2} + B 2 O 3 + Al 2 O 3) is too large vitrification Since it becomes difficult and the weather resistance tends to decrease, it is preferably 5 or less, 4.5 or less, particularly 4 or less. “P ₂ O ₅ / (SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ )” is a 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. In addition, the upper limit of P ₂ O ₅ / (B ₂ O ₃ + Al ₂ O ₃ ) is not particularly limited, but practically, it is preferably 5 or less, 4.5 or less, particularly 4 or less. “P ₂ O ₅ / (B ₂ O ₃ + Al ₂ O ₃ )” indicates 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 and remarkably increases the meltability, and also increases the fluorescence detection sensitivity. The content of Na ₂ O is preferably 10 to 35%, 11 to 33%, 13 to 30%, 14 to 28%, particularly preferably 15 to 25%. When the content of Na ₂ O is too small, in addition to the meltability being easily lowered, the fluorescence detection sensitivity is liable to be lowered. On the other hand, when 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 fluorescence 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%. When the content of Ag 2 _O is too small fluorescence detection sensitivity is liable to decrease. On the other hand, the weather resistance tends to decrease when the content of Ag 2 _O is too large.

  The glass for radiation detection in the present invention may contain, for example, 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%, particularly preferably 0 to 4%. When there is too much content of MgO, liquidus temperature will rise and devitrification crystals, such as magnesium phosphate, will precipitate easily.

  ZnO is a component that suppresses phase separation and devitrification of glass. The content of ZnO is preferably 0 to 10%, 0 to 7%, particularly preferably 0 to 4%. When there is too much content of ZnO, a weather resistance and fluorescence detection sensitivity will fall easily.

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

  In addition, the preferable range of content of CaO, SrO, and BaO is as follows.

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

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

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

The glass transition point of the glass for radiation detection 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 above-described heat treatment temperature becomes high, so that B ₂ O ₃ , P ₂ O ₅ , and Na ₂ O evaporate during the heat treatment, and composition deviation tends to occur, making it difficult to obtain desired characteristics. The lower limit of the glass transition point is not particularly limited, but is practically 300 ° C. or higher.

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

  Table 1 shows examples (Nos. 1 to 5) and comparative examples (Nos. 6 and 7) of the present invention.

First, in _{mol%, SiO 2 2%, P} 2 O 5 55%, Al 2 O 3 13%, Na 2 O 29.9%, the glass batch which is prepared to have the Ag 2 O 0.1% of the composition Was put into a silica glass crucible and melted at 1200 ° C. for 4 hours. Here, as the Al ₂ O ₃ raw material, aluminum metaphosphate having an average particle diameter D ₅₀ described in Table 1 was used. Moreover, the raw material of other components selected the high purity raw material used for normal glass. The average particle diameter D ₅₀ was determined by laser diffraction method. Next, the molten glass was poured onto a carbon plate and formed into a plate shape, and then slowly cooled from a temperature about 20 ° C. higher than the annealing point to room temperature at 2 ° C./min to obtain a radiation detection glass. About each obtained sample, the roughness and the pre-dose value were evaluated.

  Evaluation was made as follows. The obtained sample was observed with an optical microscope. The case where no irregularities were observed was indicated by “◯”, and the case where irregularities were observed was denoted by “X”.

  For evaluation of the pre-dose value, a sample whose both surfaces were polished so as to be an optically polished surface (mirror surface) was used. The sample was heat treated at 400 ° C. for 1 hour so that the fluorescence center formed by natural radiation disappeared, and then the fluorescence intensity measured by irradiating the sample with optical light with ultraviolet light was defined as a pre-dose value.

  As is apparent from Table 1, No. 1 as an example of the present invention. In the samples 1 to 5, no irregularity was confirmed, and the pre-dose value was 48 to 65, which was low. On the other hand, No. which is a comparative example. Sample 6 had a high pre-dose value of 168. No. Sample No. 7 had bumps and had a high pre-dose value of 172.

The method for producing glass for radiation detection according to the present invention is suitable as a method for producing glass for radiation detection used for personal exposure dosimeters of radiation, radiation measurement in the environment, monitoring of patient exposure during radiation therapy, and the like. Here, radiation refers to beta rays, gamma rays, X-rays, or the like.

Claims (2)

A method for producing a glass for radiation detection by heating and melting a raw material,
Al as ₂ O ₃ raw material, manufacturing method of the glass for radiation detection, characterized in that the average particle diameter _{D 50} used aluminum metaphosphate is 50 to 500 [mu] m. The glass for radiation detection is mol%, SiO ₂ + B ₂ O ₃ 0.1-30%, SiO ₂ 0-20%, B ₂ O ₃ 0-10%, P ₂ O ₅ 40-70%, Al _{2. O 3 10~30%, Na 2 O} 10~35%, the manufacturing method of the radiation detecting glass according to claim 1, characterized by containing Ag 2 O 0.01~2%.