JP7022386B2 - Manufacturing method of glass for radiation detection - Google Patents

Description

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

Radiation detection glass is widely used in fields dealing with radiation such as medical fields and nuclear fields as a detection substance for measuring radiation exposure dose. 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 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, 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 fluorescence detection sensitivity of this glass to the radiation dose varies depending on the composition of the glass. The fluorescent center generated in the glass by the RPL phenomenon is stabilized by the interaction with the close-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, since the fluorescent center generated in the glass disappears by the heat treatment, it can be used repeatedly.

As the radiation detection glass, glass or the like containing SiO ₂ which is a component for improving the fluorescence detection sensitivity is used (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-145145

However, the glass described in Patent Document 1 has a large amount of fluorescence (hereinafter referred to as "predose") possessed by the glass itself when not irradiated with radiation, and has a problem of hindering the measurement of radiation dose.

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

When melted using a SiO ₂ raw material, SiO ₂ having a high melting point tends to remain undissolved, and the lumps of SiO ₂ are likely to occur in the radiation detection glass. Therefore, as a result of conducting various experiments, the present inventors have found that the generated SiO ₂ lumps cause multiple scattering and increase the predose value of the radiation detection glass when measuring the radiation dose. I stopped.

The method for producing a glass for radiation detection of the present invention is characterized in that a raw material is heated and melted using a silica glass crucible having a thickness of 5 mm and a linear transmittance of 0.1 to 30% at a wavelength of 800 nm. In this way, infrared rays, which are a heating source, are scattered on the inner wall of the crucible and irradiate the entire molten glass, so that the glass can be heated uniformly. Therefore, the SiO ₂ raw material is easily melted, and the lumps of SiO ₂ are less likely to occur in the radiation detection glass. As a result, a glass for radiation detection having a low predose value can be produced.

In the method for producing a glass for radiation detection of the present invention, it is preferable that the surface roughness Ra of the silica glass crucible is 1 to 100 μm.

In the method for producing the radiation detection glass of the present invention, the radiation detection glass is mol%, SiO ₂ 0.1 to 20%, B ₂ O ₃₀ to 10%, P ₂ O ₅ 40 to 70%, Al. It preferably contains ₂ O ₃ 10 to 30%, Na ₂ O 10 to 35%, and Ag ₂ O 0.01 to 2%.

According to the present invention, it is possible to provide a method for producing a glass for radiation detection having a low predose value.

The method for producing a glass for radiation detection of the present invention is characterized in that a raw material is heated and melted using a silica glass crucible having a thickness of 5 mm and a linear transmittance of 0.1 to 30% at a wavelength of 800 nm.

As described above, when the glass is heated using a silica glass crucible having a thickness of 5 mm and a linear transmittance of 0.1 to 30% at a wavelength of 800 nm, the lumps of SiO ₂ that increase the predose value are less likely to occur.

Next, the silica glass crucible will be described.

The linear transmittance at a wavelength of 800 nm at a thickness of 5 mm of the silica glass crucible is 0.1 to 30%, preferably 0.2 to 29%, particularly preferably 0.5 to 28%. If the linear transmittance is too low, infrared rays are easily reflected by the outer wall of the crucible, making it difficult to heat the glass. On the other hand, if the linear transmittance is too high, infrared rays are less likely to be scattered on the inner wall of the crucible and it is difficult to uniformly heat the glass.

The surface roughness Ra of the silica glass crucible is preferably 1 to 100 μm, 2 to 90 μm, and particularly preferably 5 to 80 μm. If the surface roughness Ra is too small, infrared rays are less likely to be scattered on the inner wall of the crucible, and it is difficult to uniformly heat the glass. If the surface roughness Ra is too large, infrared rays are easily reflected by the outer wall of the crucible, making it difficult to heat the glass.

The silica glass crucible is manufactured by firing a SiO ₂ raw material, and its linear transmittance and surface roughness Ra can be controlled by the particle size, firing temperature, and firing time of the SiO ₂ raw material. Further, it is also possible to control the surface roughness Ra of the obtained silica glass crucible by buffing, wet blasting, sandblasting or the like, or etching with an acid or an alkali.

The silica glass crucible preferably contains ₂₉₀ % or more, particularly 92% or more, in terms of mass%. In a silica glass crucible, the SiO ₂ component may elute into the glass, and the composition of the glass may be designed in consideration of the amount of the SiO ₂ elution. However, if the content of SiO ₂ in the silica glass crucible is too small, components other than SiO ₂ may elute into the glass. As a result, problems such as not being able to obtain glass having a desired composition are likely to occur.

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 method for manufacturing the glass for radiation detection will be described in detail.

First, the raw material powder is prepared so as to have a desired composition. Next, the prepared raw material powder is put into the silica glass crucible described above 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.

Next, a series of steps of regenerating after measuring the fluorescence intensity using the glass for radiation detection will be described.

(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), 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 under the following heat treatment conditions to stabilize the fluorescence intensity, the fluorescence intensity is measured by irradiating with ultraviolet light. 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 value tends to decrease. Specifically, the heat treatment temperature is preferably 105 to 200 ° C., particularly preferably 110 to 180 ° C. The heat treatment time is preferably 10 to 120 minutes, particularly preferably 20 to 70 minutes. If the heat treatment time is too short, heat is not easily transferred 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 decrease.

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

The heat treatment temperature 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) to ( Glass transition point −15 ° C.), particularly preferably (glass transition point −25 ° C.) to (glass transition point −20 ° C.). If the heat treatment temperature 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 heat treatment temperature 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 heat treatment temperature is preferably 420 to 500 ° C., 430 to 490 ° C., 440 to 480 ° C., and particularly preferably 450 to 470 ° C. The heat treatment time is preferably 20 to 150 minutes, 30 to 120 minutes, 40 to 90 minutes, and particularly preferably 50 to 70 minutes. If the heat treatment 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 heat treatment 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. By regenerating the glass, it can be used repeatedly. Needless to say, the more times you use it, the lower the cost. It is preferable that the heat treatment conditions for eliminating the fluorescent center formed by natural radiation are the same as described above.

Next, the radiation detection glass manufactured by the present invention will be described.

The glass for radiation detection is mol%, SiO ₂ 0.1 to 20%, B ₂ O ₃₀ to 10%, P ₂ O ₅ 40 to 70%, Al ₂ O ₃ 10 to 30%, Na ₂ O 10 It preferably contains ~ 35% and Ag ₂ O 0.01 ~ 2%.

The reasons for limiting the glass composition as described above are shown below. In the description of the content of each component, "%" means "mol%" unless otherwise specified.

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 0.1 to 20%, 0.2 to 19%, 0.3 to 18%, 0.5 to 17%, 0.7 to 16%, 1 to 15%, especially 1.5. It is preferably ~ 10%. If the content of SiO ₂ is too small, the weather resistance tends to decrease. On the other hand, 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%, 0.1 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 10 to 30%, 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 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%. 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 heat treatment temperature described above becomes high, so that B ₂ O ₃ , P ₂ O ₅ , and Na ₂ O evaporate during the heat treatment, and composition deviation is likely to occur, making it difficult to obtain desired characteristics. .. The lower limit of the glass transition point is not particularly limited, but is actually 300 ° C. or higher.

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.

Table 1 shows Examples (No. 1 to 5) and Comparative Examples (No. 6) of the present invention.

First, a glass batch prepared to have a composition of SiO _{22%, P 2 O 555%, Al 2 O 3 13%, Na 2 O 29.9%, and Ag 2 O 0.1 % in mol %} . Was put into a silica glass crucible having the linear transmittance and surface roughness Ra shown in Table 1 and melted in an electric furnace at the melting temperature and melting time shown in Table 1. 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. For each of the obtained samples, the presence or absence of lumps caused by SiO ₂ and the predose value were evaluated. The surface roughness Ra of the silica glass crucible was controlled by sandblasting. The linear transmittance of the silica glass crucible was measured by a spectroscopic analyzer, and the surface roughness Ra was measured by a surface roughness measuring instrument.

The lumps caused by SiO ₂ were evaluated as follows. The obtained sample was observed with an optical microscope. Those in which no lumps were observed were marked with "○", and those in which lumps were observed were marked with "x".

For the evaluation of the predose value, a sample polished so that both sides had an optically polished surface (mirror surface) was used. The fluorescence intensity measured by irradiating the optically polished surface of the sample with ultraviolet light after eliminating the fluorescence center formed by natural radiation by heat-treating the sample at 400 ° C. for 1 hour was used as the predose value.

As is clear from Table 1, No. 1 which is an embodiment of the present invention. No lumps were confirmed in the samples 1 to 5, and the predose value was as low as 49 to 64. On the other hand, No. In the sample No. 6, the lumps caused by SiO ₂ were present, and the predose value was as high as 199.

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

Claims (2)

The raw material is heated and melted using a silica glass crucible having a thickness of 5 mm and a linear transmittance of 0.1 to 30% at a wavelength of 800 nm , and the surface roughness Ra of the silica glass crucible is 1 to 100 μm. A method for manufacturing glass for radiation detection. Radiation detection glass is mol%, SiO ₂ 0.1 to 20%, B ₂ O ₃₀ to 10%, P ₂ O ₅ 40 to 70%, Al ₂ O ₃ 10 to 30%, Na ₂ O 10 The method for producing a glass for radiation detection according to claim 1, which contains ~ 35% and Ag ₂ O 0.01 to 2%.