JP2007290899A - Glass composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass composition having a shielding ability comparable to lead glass, high surface hardness, and extremely high transparency in the visible region, in a glass system that contains no lead component and contains a rare earth oxide and fluorine simultaneously. <P>SOLUTION: The glass composition comprises 1-85% of Ln<SB>2</SB>O<SB>3</SB>(wherein Ln represents one or more selected from the group consisting of La, Y, Gd, Tb, Dy, Yb, and Lu) and 0.1-20% of fluorine, by mass in terms of oxide, wherein the glass composition has a lead equivalent to X-rays of 150 kV of 0.03 mmPb/mm or more. Further, a glass composition, which is stable against devitrification, has high surface hardness, and is excellent not only in transparency but also in radiation shielding ability, can be obtained by bringing the total content of SiO<SB>2</SB>and/or B<SB>2</SB>O<SB>3</SB>and/or GeO<SB>2</SB>and/or P<SB>2</SB>O<SB>5</SB>to 10-70%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a glass composition, and more particularly to a glass composition containing a large amount of rare earth oxide and fluorine.

  In facilities handling radiation such as X-rays and γ-rays, a glass composition having radiation shielding properties is used to facilitate work and to protect people engaged in work from radiation. Such glass is required to have high transparency in the visible range and excellent shielding ability (absorption ability) against radiation. Since shielding ability is proportional to the mass absorption coefficient and density of glass, lead glass with high density has been used since ancient times.

  However, since the lead component is a harmful substance, the glass composition containing a large amount of the lead component is required to take measures for environmental measures when manufacturing, processing, and disposing of it, which increases the cost. Had a problem. In addition, glass compositions containing a large amount of lead components cause “burns” on the glass surface after surface cleaning to remove dirt on the glass surface, and this “burns” significantly reduces the transparency of the glass. Was also a problem.

  Further, since the surface hardness is low, the surface is easily scratched in processing steps such as polishing and cutting, and the glass may be broken due to the scratch.

Accordingly, a glass composition containing no lead component has been developed. Patent Document 1 essentially contains no lead component and is a SiO ₂ —BaO-based glass having a density of 3.01 g / cm 3. A radiation shielding glass of ³ or more is disclosed. Patent Document 2 essentially does not contain a lead component, contains SiO ₂ and Al ₂ O ₃ , and has a radiation shielding that has a lead equivalent to 100 kV X-rays of 0.03 mmPb / mm or more. Glass is disclosed.
Japanese Patent Laid-Open No. 6-127773 Japanese Patent Laid-Open No. 2003-315489

  However, since the radiation shielding glasses of Patent Documents 1 and 2 have considerably lower shielding ability than lead glass, their use is limited mainly to places where radiation with low energy is handled.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a glass composition having high radiation shielding ability in a glass system that does not contain a lead component and contains a rare earth oxide and fluorine. And

  As a result of intensive studies to solve the above problems, the present inventor can produce a glass containing a large amount of rare earth oxide by introducing fluorine into the oxide glass, and the glass has an excellent radiation shielding ability. In addition, the present inventors have found that it has high transparency and surface hardness, and completed the present invention.

  More specifically, the present invention provides the following.

(1) Ln ₂ O ₃ (Ln represents one or more selected from the group consisting of Y, La, Gd, Tb, Dy, Yb, and Lu) in an oxide-based mass% of 1 to 85%, A glass composition containing 0.1 to 20% by mass of fluorine with respect to the total of components expressed on an oxide basis and having a lead equivalent to 150 kV X-rays of 0.03 mmPb / mm or more.

It is known that the shielding ability against high-energy radiation such as X-rays is proportional to the density. According to this aspect, Ln ₂ O ₃ (Ln represents one or more selected from the group consisting of Y, La, Gd, Tb, Dy, Yb, and Lu) and fluorine are contained simultaneously. _{Since a} large amount of ₂ O ₃ component can be contained in the glass and the density of the glass can be increased, high radiation shielding ability can be easily obtained. Moreover, since the lead equivalent with respect to 150-kV X-ray is 0.03 mmPb / mm or more, it can be used suitably also when handling high energy radiation.

(2) By mass% based on oxide, the total amount of SiO ₂ and / or B ₂ O ₃ and / or GeO ₂ and / or P ₂ O ₅ is 10 to 70%, M ₂ O ₃ (M is Al, 1 to at least one selected from the group consisting of Ga and In. 0 to 35%, 0 to 10% BaO, and RO (R is one selected from the group consisting of Zn, Sr, Ca and Mg) 0 to 30%, Rn ₂ O (Rn is at least one selected from the group consisting of Li, Na, K, and Cs) is 0 to 15%, and TiO ₂ is 0 to 15%. %, the glass composition according to the total amount of _Sb 2 _{O 3} and _As 2 _{O 3} containing each ingredient in the range of 0 to 5% (1).

According to this aspect, at least one or more selected from components such as SiO ₂ , GeO ₂ , B ₂ O ₃ , P ₂ O ₅ , M ₂ O ₃ , RO, Rn ₂ O, and TiO ₂ is contained. Therefore, a stable glass having no devitrification, high surface hardness and high transparency can be easily produced.

(3) It contains 0 to 40% in total amount of one or more of ZrO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ in mass% based on oxide (1) or The glass composition as described in (2).

  According to this aspect, since the said component is effective in the radiation shielding capability and the improvement of the surface hardness of glass, the glass containing the said component is used suitably as a glass composition.

(4) The glass composition according to any one of (1) to (3), wherein 0 to 5% of Ce ₂ O ₃ is contained by mass% based on an oxide.

According to this aspect, Ce ₂ O ₃ is a component that contributes to an improvement in radiation shielding capability, and in particular, is a component that has an effect of preventing coloring due to radiation irradiation. Accordingly, it is possible to provide a glass composition having transparency in glass even after long-term use.

(5) The fluorine is contained by AlF ₃ and / or LnF ₃ (Ln represents one or more selected from the group consisting of La, Y, Gd, Tb, Dy, Yb, and Lu) (1 ) To (4).

According to this embodiment, when fluorine is contained by AlF ₃ and / or LnF ₃ (Ln represents one or more selected from the group consisting of La, Y, Gd, Tb, Dy, Yb, and Lu), Since the glass does not devitrify and it is easy to contain a larger amount of rare earth oxide, a glass having higher radiation shielding ability and transparency can be easily obtained.

(6) The glass composition according to any one of (1) to (5), wherein the density is 3.2 g / cm ³ or more.

According to this aspect, since the density is 3.2 g / cm ³ or more, it has a high shielding ability.

  (7) The glass composition according to any one of (1) to (6), wherein the transmittance at a wavelength of 400 nm is 40% or more and the transmittance at a wavelength of 550 nm is 80% or more in the glass composition having a thickness of 10 mm. object.

  According to this aspect, since the transmittance at a wavelength of 400 nm is 40% or more and the transmittance at a wavelength of 550 nm is 80% or more, it is easy to provide a glass composition having high transparency in the visible region. .

(8) The glass composition according to any one of (1) to (7), wherein the Knoop hardness of the glass is 420 N / mm ² or more.

According to this aspect, since the Knoop hardness (HK) is 420 N / mm ² or more, the surface hardness of the glass is increased, and the glass composition having high mechanical strength that hardly scratches the surface is easily provided. Can do.

  (9) A radiation shielding glass which is the glass composition according to any one of (1) to (8).

  Since the glass composition as described in (1)-(8) is excellent in the capability to shield a radiation, it is useful as a glass for radiation shielding.

Since the glass composition of the present invention can contain many Ln ₂ O ₃ components in the glass by simultaneously containing Ln ₂ O ₃ and fluorine as glass components, the density of the glass increases, Lead equivalent can be increased. Moreover, even if it does not contain a lead component, the glass composition which has the radiation shielding ability comparable to the glass containing a lead component can be provided easily.

  Hereinafter, specific embodiments of the glass composition of the present invention will be described.

[Glass component]
The composition range of each component which comprises the glass composition of this invention is described below. In the present invention, the content of each component is described in mass% unless otherwise specified. In the present invention, the glass composition represented by mass% is all represented by mass% based on oxide. Here, the “oxide standard” means that the oxide, nitrate, etc. used as a raw material of the glass component of the present invention are all decomposed and changed into oxides when melted, and the mass of the generated oxide Is a composition in which each component contained in the glass is described with the total of 100% by mass.

<About essential and optional components>
Ln ₂ O ₃ component (Ln represents one or more selected from the group consisting of Y, La, Gd, Dy, Tb, Yb, and Lu) increases the density of the glass and has high radiation shielding ability for the glass. Therefore, it is an essential component for achieving the object of the present invention. However, if Ln ₂ O ₃ is contained excessively, the stability of the glass tends to be impaired, and if it is too small, it becomes difficult to satisfy the object of the present invention. Therefore, the amount of Ln ₂ O ₃ is 1% or more, more preferably 5% or more, most preferably 10% or more as the lower limit, and the upper limit is preferably 85% or less, more preferably 80% or less, most preferably 75%. It is as follows. Among Ln ₂ O ₃ , Gd ₂ O ₃ is particularly effective, and therefore it is preferably contained.

The fluorine component has the effect of lowering the melting temperature of the glass and improving the transparency of the glass. Furthermore, by containing a fluorine component, it becomes possible to contain more rare earth oxides. As a result, the density of the glass is improved and the radiation shielding ability is increased. However, since an excessive amount of fluorine reduces the stability of the glass, in order to obtain a good effect, the upper limit of the content of the fluorine component is 20% or less, more preferably 15% or less, and most preferably 10% or less. Is 0.1% or more, more preferably 0.5% or more, and most preferably 1% or more. The fluorine component is preferably contained as AlF ₃ and / or LnF ₃ (Ln represents one or more selected from the group consisting of Y, La, Gd, Tb, Dy, Yb, and Lu).

The component of SiO ₂ and / or B ₂ O ₃ and / or GeO ₂ and / or P ₂ O ₅ is a glass-forming oxide, and preferably contains at least one of them in order to obtain a stable glass. In order to obtain a stable glass, the lower limit of the total amount of these component contents is preferably 10% or more, more preferably 12% or more, and most preferably 15% or more. Further, if the content of these components is too large, the radiation shielding ability is reduced. Therefore, in order to obtain a high radiation shielding ability, the upper limit of the content is preferably 70% or less, and 60% or less. More preferably, it is most preferable to set it as 50% or less.

The SiO ₂ and B ₂ O ₃ components can achieve the object of the present invention even if they are introduced alone into the glass. However, when used simultaneously, the melting property, stability and chemical durability of the glass are improved. Since it improves, it is preferable to use it simultaneously.

GeO ₂ component, since the same function as the SiO ₂ component, it is possible to replace some or all of the SiO ₂ component, because it is expensive, it is preferable to set the upper limit to 20% or less 15% or less is more preferable, and 10% or less is most preferable.

P ₂ O ₅ component, since the same function as SiO ₂ or _B 2 _{O 3} component, it is possible to replace some or all of the SiO ₂ or _B 2 _{O 3} component. However, if the amount is too large, the tendency of phase separation of the glass tends to become strong. Therefore, the upper limit is preferably 20% or less, more preferably 10% or less, and most preferably 5% or less.

The M ₂ O ₃ component (M represents one or more selected from the group consisting of Al, Ga, and In) is not essential, but can be added to improve the meltability and stability of the glass. However, if the amount is too large, the meltability and stability of the glass tend to decrease. Therefore, the upper limit of the total amount is preferably 35% or less, more preferably 25% or less, and most preferably 20% or less.

The Al ₂ O ₃ component is not essential, but is an ingredient that can be added because it is effective in improving the meltability and stability of the glass and further improving the surface hardness. However, when the amount exceeds 30%, the melting temperature increases and the stability of the glass tends to decrease. A preferred addition amount is 25% or less, and a particularly preferred addition amount is 20% or less.

The Ga ₂ O ₃ component is not essential, but it is an ingredient that can be added because it is effective in improving the meltability and stability of the glass and further improving the density. However, if the amount exceeds 20%, the melting temperature increases and the stability of the glass tends to decrease. A preferable addition amount is 15% or less.

The In ₂ O ₃ component is not essential, but it is an ingredient that can be added because it is effective in improving the meltability and stability of the glass and further improving the density. However, since it is expensive, it is preferably 10% or less, and more preferably 5% or less.

  The BaO component is effective in improving the meltability, stability and radiation shielding ability of the glass, but if the amount is too large, the stability of the glass tends to be lowered. Therefore, the upper limit value is preferably 10% or less, more preferably 8% or less, and most preferably 5% or less.

  The RO component (R represents one or more selected from the group consisting of Zn, Sr, Ca, and Mg) is an optional component that is effective in improving the meltability and stability of the glass. If the amount is too large, the stability of the glass tends to be lowered. Therefore, the upper limit of the total amount is preferably 30% or less, more preferably 25% or less, and most preferably 15% or less. Of the RO components, the SrO and ZnO components are particularly important because they are effective in improving the radiation shielding ability, which is the object of the present invention, in addition to the above effects.

  The ZnO component is an optional component effective for improving the meltability and stability of glass and the radiation shielding ability. However, if the amount is too large, devitrification tends to occur. Therefore, the upper limit is preferably 30% or less, more preferably 20% or less, and most preferably 15% or less.

  The SrO component is an optional component that is effective in improving the meltability, stability, and radiation shielding ability of the glass, but if the amount is too large, the stability of the glass tends to be lowered. Therefore, the upper limit is preferably 30% or less, more preferably 20% or less, and most preferably 10% or less.

  The CaO component is an optional component effective for improving the meltability of the glass. However, if the amount is too large, devitrification is likely to occur, and the radiation shielding ability is likely to be lowered. Therefore, the upper limit value is preferably 10% or less, more preferably 5% or less, and most preferably 3% or less.

  The MgO component is an optional component effective for improving the meltability of the glass. However, if the amount is too large, devitrification is likely to occur, and the radiation shielding ability tends to be lowered. Therefore, the upper limit value is preferably 10% or less, more preferably 5% or less, and most preferably 3% or less.

The Rn ₂ O component (Rn represents one or more selected from the group consisting of Li, Na, K, and Cs) is effective in improving the meltability and stability of the glass and is colored by irradiation. It is an optional ingredient that is also effective for prevention. However, if the amount is too large, the stability of the glass deteriorates, and the radiation shielding ability tends to greatly decrease. Therefore, the upper limit of the total amount is preferably 15% or less, more preferably 10% or less, and most preferably 5% or less. In addition, when two or more Rn ₂ O components are combined, a great effect can be obtained by preventing coloring due to radiation irradiation.

The Li ₂ O component is an optional component that improves the meltability of the glass. However, if the amount is too large, devitrification tends to occur, and the radiation shielding ability tends to decrease. Therefore, the upper limit is preferably 8% or less, more preferably 5% or less, and most preferably 3% or less.

The Na ₂ O component is an optional component that improves the meltability of the glass. However, if the amount is too large, devitrification tends to occur, and the radiation shielding ability tends to decrease. Therefore, the upper limit value is preferably 10% or less, more preferably 5% or less, and most preferably 3% or less.

The K ₂ O component is an optional component that improves the meltability of the glass. However, if the amount is too large, devitrification tends to occur and the radiation shielding ability tends to decrease. Therefore, the upper limit value is preferably 10% or less, more preferably 5% or less, and most preferably 3% or less.

The Ce ₂ O ₃ component is a component having an effect of preventing coloring due to radiation irradiation. Although it is a component that can be optionally added, if the amount is too large, the absorption edge of the glass shifts to the long wavelength side, and the transparency in the visible region may be lowered. Therefore, the upper limit value is preferably 5% or less, more preferably 3% or less, and most preferably 1% or less.

The TiO ₂ component is a component that is effective in improving the stability of the glass and the hardness of the surface. Although it is a component that can be added arbitrarily, if the amount is too large, the stability of the glass tends to be low. Therefore, it is preferably 15% or less, more preferably 10% or less, and most preferably 5% or less.

In order not to decrease the stability of the glass, it is preferable to set the upper limit of the total amount of one or more of ZrO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ to 40% or less, It is more preferably 10% or less, and most preferably 5% or less.

Nb ₂ O ₅ component is a component that is effective in improving the shielding ability of glass. Although it is a component that can be added arbitrarily, if the amount is too large, the stability of the glass tends to decrease, so it is preferably 30% or less, more preferably 15% or less, and more preferably 5% or less. Is most preferable.

The WO ₃ component is a component that is effective in improving the shielding ability of glass. Although it is a component that can be arbitrarily added, if the amount is too large, the stability of the glass tends to decrease, so it is preferably 30% or less, more preferably 20% or less, and 15% or less Is most preferable.

The Ta ₂ O ₅ component is a component that is effective in improving the shielding ability of glass. Although it is a component that can be optionally added, if the amount is too large, the stability of the glass is easily lowered. Therefore, the upper limit is preferably 30% or less, more preferably 20% or less, and most preferably 15% or less.

The ZrO ₂ component is a component that is effective in improving the glass shielding ability and the glass surface hardness. Although it is a component that can be optionally added, if the amount is too large, the stability of the glass is easily lowered. Therefore, the upper limit is preferably 20% or less, more preferably 10% or less, and most preferably 5% or less.

The SnO ₂ component is an optional component that is effective in improving the shielding ability of the glass, but if the amount is too large, the stability of the glass is easily lowered. Therefore, the upper limit value is preferably 10% or less, more preferably 5% or less, and most preferably 3% or less.

Sb ₂ O ₃ and As ₂ O ₃ components are components that can be optionally added for defoaming of glass melting. The total amount of Sb ₂ O ₃ and As ₂ O ₃ is sufficiently effective at 5% or less. Further, As ₂ O ₃ needs to take measures for environmental measures when manufacturing, processing, and discarding glass. Therefore, the total amount of Sb ₂ O ₃ and As ₂ O ₃ is preferably 5% or less, more preferably 3% or less, and most preferably 1% or less.

<About ingredients that should not be included>
Other components can be added as needed as long as the properties of the glass composition of the present invention are not impaired. However, even when each transition metal component excluding Ti, such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag, and Mo, is contained alone or in combination with a small amount, the glass is colored and visible. Causes absorption at specific wavelengths in the region. Therefore, it is preferable that the glass composition of the present invention does not contain substantially.

  Since each component of Pb, Th, Cd, Tl, and Os has tended to be refrained from being used as a harmful chemical material in recent years, not only the glass manufacturing process but also the processing process and environmental measures from disposal to commercialization. The above measures are required. Therefore, it is preferable not to include substantially when importance is attached to environmental influences.

  The glass composition of the present invention has high transparency in the visible region, and the transmittance at 400 nm is 40% or more and the transmittance at 550 nm is 80% or more in a glass having a thickness of 10 mm.

Moreover, the glass composition of this invention can obtain easily the density of 3.2 g / cm < ³ > or more. A more preferable density range is 3.8 g / cm ³ or more.

The Knoop hardness (HK) of the glass composition of the present invention is preferably 420 N / mm ² or more, more preferably 550 N / mm ² or more, and most preferably 600 N / mm ² or more.

  In the present invention, the radiation shielding ability is expressed in terms of lead equivalent. The lead equivalent is represented by the thickness of the lead plate having the same X-ray shielding ability, and the larger this value, the better the radiation shielding ability. The lead equivalent for 150 kV X-rays of the glass of the present invention was determined by converting the lead equivalent measured by a method according to JIS4501 to a thickness of 1 mm. The lead equivalent of the glass composition of the present invention is preferably 0.03 mmPb / mm or more, and more preferably 0.10 mmPb / mm or more.

  As described above, the glass composition of the present invention has excellent radiation shielding ability, high transparency in the visible range, excellent transparency, and excellent surface hardness, so that the radiation is shielded. It can be usefully applied as a shielding glass.

[Production method]
Although the glass composition of this invention will not be specifically limited if it is a method of manufacturing normal glass, For example, it can manufacture with the following method.

  A predetermined amount of each starting material (oxide, carbonate, nitrate, phosphate, sulfate, fluoride salt, etc.) is weighed and mixed uniformly. The mixed raw material is put into a quartz crucible, alumina crucible, platinum crucible, platinum alloy crucible or iridium crucible and melted at 1100-1500 ° C. for 1-10 hours in a melting furnace. Then, after stirring and homogenizing, it is lowered to an appropriate temperature and cast into a mold or the like to produce glass.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example and a comparative example, this invention is not limited to a following example.

[Examples 1 to 14]
The starting materials are weighed with the compositions of Examples 1 to 14 shown in Tables 1 and 2 (unit: mass%), mixed uniformly, and then placed in a platinum crucible and melted at 1250 to 1450 ° C. for 2 to 4 hours. Then, it cast into the metal mold | die and produced glass.

[Comparative Example 1]
As Comparative Example 1, a lead-containing glass used as a radiation shielding glass was produced as follows.

  The starting materials were weighed so as to have the composition of Comparative Example 1 shown in Table 2, mixed uniformly, and then first melted at 1300 ° C. for 1 hour and 20 minutes using a quartz crucible to prepare cullet. Thereafter, the cullet was put in a platinum crucible and melted at 1320 ° C. for 2 hours and 30 minutes, and then cast into a mold to produce glass.

  Tables 1 and 2 show the density, Knoop hardness (HK), transparency, and lead equivalent of Examples 1 to 14 and Comparative Example 1. The density was measured by the Archimedes method. About the transmittance | permeability measurement, it carried out according to Japan Optical Glass Industry Association standard JOGIS02. In the present invention, the transmittance is shown not the degree of coloring. Specifically, a face-to-face parallel polished product having a thickness of 10 ± 0.1 mm was measured for a spectral transmittance of 200 to 800 nm in accordance with JISZ8722. The transmittance at wavelengths of 400 nm and 550 nm was determined and used as an index representing the transparency of the present invention. Knoop hardness (HK) was measured according to the Japan Optical Glass Industry Association Standard JOGIS09. The lead equivalent was measured at a tube voltage of 150 kV according to JIS4501.

  FIG. 1 shows a spectral transmittance curve in the glass of Example 1. The horizontal axis represents wavelength (nm) and the vertical axis represents spectral transmittance (%). These transmittances include reflection loss.

  As shown in FIG. 1, it can be seen that the glass of the present invention has extremely high transparency over the entire visible range. Moreover, it can be seen from Table 1 that the glass of the present invention has transparency far exceeding that of the existing lead glass.

  According to Tables 1 and 2, it can be seen that the Knoop hardness (HK) of the glass of the present invention is 1.5 times higher than that of lead glass.

  Further, according to Tables 1 and 2, the glass of the present invention has a high lead equivalent, and it is possible to realize a radiation shielding ability equivalent to or higher than that of lead glass.

It is a figure which shows the spectral transmittance curve in the glass of Example 1. FIG.

Claims (9)

Ln ₂ O ₃ (Ln represents one or more selected from the group consisting of Y, La, Gd, Tb, Dy, Yb, and Lu) in an oxide-based mass% of 1 to 85%, oxide-based A glass composition containing 0.1 to 20% by mass of fluorine with respect to the total of the components represented by formula (1) and having a lead equivalent to 150 kV X-rays of 0.03 mmPb / mm or more. The total amount of SiO ₂ and / or B ₂ O ₃ and / or GeO ₂ and / or P ₂ O ₅ is 10% to 70%, M ₂ O ₃ (M is Al, Ga, In 0-35%, BaO 0-10%, RO (R represents one or more selected from the group consisting of Zn, Sr, Ca, Mg). 0-30%, Rn ₂ O (Rn represents one or more selected from the group consisting of Li, Na, K, Cs) 0-15%, TiO ₂ 0-15%, Sb glass composition according to claim 1 containing the components a total amount of ₂ O ₃ and _As 2 _{O 3} in the range of 0-5%. % By mass on the oxide _{basis, ZrO 2, SnO 2, Nb} 2 O 5, Ta 2 O 5, according to claim 1 or 2 containing 0-40% by total weight of one or more of WO ₃ Glass composition. % By mass on the oxide basis, the glass composition according to claim 1 containing _Ce 2 _{O 3} 0 to 5% in 3 or. The fluorine is contained by AlF ₃ and / or LnF ₃ (Ln is one or more selected from the group consisting of La, Y, Gd, Tb, Dy, Yb, and Lu). The glass composition in any one. The glass composition according to claim 1, wherein the density is 3.2 g / cm ³ or more.   The glass composition according to any one of claims 1 to 6, wherein in the glass composition having a thickness of 10 mm, the transmittance at a wavelength of 400 nm is 40% or more and the transmittance at a wavelength of 550 nm is 80% or more. The glass composition according to any one of claims 1 to 7, wherein the Knoop hardness of the glass is 420 N / mm ² or more.   A radiation shielding glass, which is the glass composition according to claim 1.

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