JPWO2007077680A1 - Glass composition - Google Patents

Abstract

To provide a radiation shielding glass that does not contain a lead component and has a shielding ability comparable to that of a lead glass in a glass containing a large amount of rare earth oxides, and has a high surface hardness and extremely high transparency in the visible range. . A glass composition containing, by mass% based on oxides, a total amount of Al2O3 and / or Ga2O3 and / or In2O3 of more than 5% and 35%, and a lead equivalent to 150 kV X-rays of 0.03 mmPb / mm or more It is. Further, by containing 20 to 90% of Ln2O3 (Ln represents one or more selected from the group consisting of Y, La, Gd, Dy, Yb, and Lu), the glass density can be further increased. It is possible to obtain a glass composition having a high radiation shielding ability and having a high surface hardness and high transparency in the visible region.

Description

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

  In facilities that handle radiation such as X-rays and γ-rays, radiation shielding glass is used in order to facilitate work and to protect people engaged in work from radiation. Such glass is required to have high transparency in the visible region 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, radiation shielding glass containing a large amount of the lead component is required to take measures for environmental measures when manufacturing, processing, and disposing of it. Had a problem. In addition, radiation shielding glass containing a large amount of lead components generates “burns” on the glass surface after cleaning the surface in order to remove dirt on the glass surface. Decreasing 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 radiation shielding glass containing no lead component has been developed. Patent Document 1 below is an SiO ₂ —BaO-based glass that essentially does not contain a lead component and has a density of 3.01 g. Radiation shielding glass that is greater than / cm ³ is disclosed. Patent Document 2 below essentially contains no lead component, contains SiO ₂ and Al ₂ O _{3, and} has a lead equivalent to 100 kV X-rays of 0.03 mmPb / mm or more. A radiation shielding 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.

  This invention is made | formed in view of the above subjects, and provides the glass composition which has high radiation shielding performance in the glass system which did not contain a lead component but contained a large amount of rare earth oxides.

As a result of intensive studies to solve the above problems, the inventor of the present invention contains Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O _3, and includes a rare earth oxide Ln ₂ O ₃ (Ln is Y, A glass composition containing a large amount of one or more selected from the group consisting of La, Gd, Dy, Yb, and Lu.) Shows a radiation shielding ability superior to that of lead glass, and has a higher surface than lead glass. The present invention has been completed by finding that it has hardness and transparency. More specifically, the present invention provides the following.

(1) The lead equivalent with respect to 150 kV X-rays containing a total amount of Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ of more than 5% and 35% by mass% based on oxide Is a glass composition of 0.03 mm Pb / mm or more.

According to this aspect, a glass composition having a high surface strength is easily provided by containing the total amount of Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ in excess of 5%. be able to. 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. Further, since the total amount of Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ exceeds 5%, rare earth oxide Ln ₂ O ₃ (Ln is Y, La, Gd, 1 or more selected from the group consisting of Dy, Yb, and Lu) can be contained in a larger amount, and the density of the glass can be increased.

(2) 20% to 85% of Ln ₂ O ₃ (Ln represents one or more selected from the group consisting of Y, La, Gd, Dy, Yb, and Lu) in terms of mass% based on oxide. The glass composition as described in (1).

It is known that the shielding ability against high-energy radiation such as X-rays is proportional to the density. According to the glass composition of the present invention, by containing a large amount of Ln ₂ O ₃ (Ln is one or more selected from the group consisting of Y, La, Gd, Dy, Yb, and Lu), Since the density of the glass can be increased, high radiation shielding ability can be easily obtained.

(3) The total amount of SiO ₂ and / or B ₂ O ₃ and / or GeO ₂ and / or P ₂ O ₅ is ₅ to 70%, ZnO is 0 to 25%, and RO is mass% based on oxide. 0-10% (R represents one or more selected from the group consisting of Ba, Sr, Ca, Mg), Rn ₂ O 0-10% (Rn is a group consisting of Li, Na, K, Cs) 1 or more selected from above.), The glass composition according to (1) or (2), wherein each component is contained in a total amount of Sb ₂ O ₃ and As ₂ O ₃ in the range of 0 to 5%. .

According to this aspect, SiO ₂ and / or B ₂ O ₃ and / or GeO ₂ and / or P ₂ O ₅ , ZnO, RO (R is one selected from the group consisting of Ba, Sr, Ca, Mg) As described above), since it contains components such as Rn ₂ O (Rn represents one or more selected from the group consisting of Li, Na, K, and Cs), the glass has excellent meltability, A glass composition that is stable against devitrification and has high surface strength can be easily produced.

(4) The glass composition according to any one of (1) to (3), wherein 0 to 10% of Ce ₂ O ₃ is contained in mass% based on the 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. Therefore, it is possible to easily provide a glass composition having transparency in glass even after long-term use.

(5) The glass composition according to any one of (1) to (4), which contains 0 to 15% of TiO _{2 in} mass% based on oxide.

According to this aspect, TiO ₂ is a component having an effect of improving the surface hardness of glass, and a glass composition having a high glass surface hardness can be easily provided.

(6) Contains 1 to ₂ % of ZrO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO _{3 in} a total of 0 to 30% by mass% based on the oxide (1) to (5 ) The glass composition according to any one of the above.

  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 composition containing the said component is used suitably as radiation shielding glass.

(7) The glass composition according to any one of (1) to (6), 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, high radiation shielding ability can be easily obtained.

  (8) The glass composition according to any one of (1) to (7), 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. object.

  According to this aspect, 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. Therefore, transparency in the visible region is high, and radiation such as X-rays and γ-rays is handled. When used as a facility shield, it is possible to easily provide a glass composition that facilitates observation of the interior of a facility or the like.

(9) The glass composition according to any one of (1) to (8), wherein the Knoop hardness is 500 N / mm ² or more.

According to this aspect, since the Knoop hardness (HK) is 500 N / mm ² or more, it is possible to easily provide a glass composition having high mechanical strength that hardly damages the glass surface.

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

  According to this aspect, the glass composition has a radiation shielding ability of 0.03 mmPb / mm or more with a lead equivalent to 150 kV X-rays, high transparency in the visible range, excellent transparency, and surface hardness. Since it is high, it is more suitable as a radiation shielding glass.

Since the glass composition of the present invention contains a total amount of Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ in excess of 5% as a glass component, the surface strength of the glass is high. In order to make it possible to contain a higher amount of rare earth oxide Ln ₂ O ₃ (Ln is one or more selected from the group consisting of Y, La, Gd, Dy, Yb, and Lu). To provide a glass composition that can easily increase the density of glass, increase the lead equivalent, and has a radiation shielding ability comparable to that of a glass containing a lead component without containing a lead component. Can do.

2 is a diagram showing a spectral transmittance curve in the glass composition of Example 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION

  Next, 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 specification, the content of each component is described in mass% (also referred to as wt%) unless otherwise specified. In addition, all the glass compositions represented by the mass% in this-application specification are represented by the mass% on the basis of an 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>
The components of Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ are effective in improving the meltability and stability of glass, and are also effective in improving the hardness of the glass surface. . Moreover, it becomes possible to incorporate more Ln ₂ O ₃ components into the glass by containing Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ components. The density is improved and the radiation shielding ability tends to be higher. In order to obtain the above effects, the total amount needs to exceed 5%. However, if it exceeds 35%, the stability of the glass tends to be greatly impaired. Therefore, the preferable range of the total content is 5% as a lower limit, the upper limit is 35%, more preferably 30%, and most preferably 25%. Among these components, the Al ₂ O ₃ component is particularly effective, so it is preferable to contain at least 5%.

Ln ₂ O ₃ component (Ln represents one or more selected from the group consisting of Y, La, Gd, Dy, Yb, and Lu) increases the density of the glass and imparts high radiation shielding ability to the glass. Therefore, it is a component useful for achieving the object of the present invention. However, if the Ln ₂ O ₃ component 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 lower limit of the amount of Ln ₂ O ₃ is 20%, more preferably 26%, most preferably 35%, and the upper limit is preferably 85%, more preferably 80%, and most preferably 75%. Among the Ln ₂ O ₃ components, particularly the components of Gd ₂ O ₃ and Lu ₂ O ₃ are more effective, so it is preferable to include either or both.

The components of SiO ₂ and / or B ₂ O ₃ and / or GeO ₂ and / or P ₂ O ₅ are glass-forming oxides and are particularly useful for obtaining highly transparent glasses without devitrification, If the content is too large, the radiation shielding ability of the glass tends to be lowered, and if it is too little, the stability of the glass tends to be lowered. Therefore, the lower limit of the total amount is 5%, more preferably 8%, and the upper limit is preferably 70%, more preferably 65%.

The components of SiO ₂ and B ₂ O ₃ are glass-forming oxides, and it is preferable that at least one of them is contained in order to easily obtain a stable glass. In order to obtain a stable glass, the lower limit of the total content of these components is preferably 5%, more preferably 8%, and most preferably 10%. In addition, if the content of these components is too large, the radiation shielding ability tends to decrease. Therefore, in order to obtain a high radiation shielding ability, the upper limit of the content is preferably 70%, and 60%. Is more preferable and 55% is most preferable.

The components of SiO ₂ and B ₂ O ₃ can achieve the object of the present invention even if they are introduced alone into the glass, but by using them simultaneously, the meltability, stability and chemical durability of the glass can be achieved. It is preferable to use them 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 30% or less 20% or less is more preferable, and 15% or less is most preferable.

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

  The ZnO component is an effective component for improving the meltability, stability, and chemical durability of the glass. However, if the amount is too large, devitrification is likely to occur and the radiation shielding ability is likely to be reduced. Therefore, the upper limit value is preferably 25%, more preferably 15%, and most preferably 10%.

  The RO component (R represents one or more selected from the group consisting of Ba, Sr, Ca, and Mg) is a component that is effective in improving the meltability and stability of the glass, but its amount is large. If it is too much, the stability of the glass tends to be lowered. Therefore, the upper limit is preferably 10%, more preferably 8%, and most preferably 5%. Of the RO components, the BaO component and the SrO component 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 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 is preferably 10%, more preferably 8%, and most preferably 5%.

  The SrO 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 is lowered. Therefore, the upper limit is preferably 10%, more preferably 8%, and most preferably 5%.

  The CaO component is an effective component 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. Accordingly, the upper limit is preferably 5%, more preferably 3%, and most preferably 1%.

  The MgO component is an effective component 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. Accordingly, the upper limit is preferably 5%, more preferably 3%, and most preferably 1%.

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 a component that is also effective for prevention. However, if the amount is too large, the stability of the glass tends to deteriorate, and the radiation shielding ability tends to decrease greatly. Therefore, the upper limit of the total amount is preferably 10%, more preferably 5%, and most preferably 3%. 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 a component that improves 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 decrease. Therefore, the upper limit is preferably 10%, more preferably 5%, and most preferably 3%.

The Na ₂ O component is a 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 10%, more preferably 5%, and most preferably 3%.

The K ₂ O component is a 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 10%, more preferably 8%, and most preferably 5%.

The Cs ₂ O component is a component that improves the meltability of the glass and contributes to the improvement of the radiation shielding ability. However, if the amount is too large, devitrification is likely to occur. Therefore, the upper limit is preferably 10%, more preferably 8%, and most preferably 5%.

The components of Sb ₂ O ₃ and As ₂ O ₃ 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, the As ₂ O ₃ component needs to take measures for environmental measures when glass is manufactured, processed, and discarded. Therefore, the total amount of Sb ₂ O ₃ and As ₂ O ₃ is preferably 5%, more preferably 3%, and most preferably 1%.

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 10% 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 optionally added, 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.

The ZrO ₂ component is a component that is effective in improving the radiation shielding ability and the surface hardness of the 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 20%, more preferably 15%, and most preferably 10%.

The SnO ₂ component is an optional component that is effective in improving the radiation shielding ability. However, if the amount is too large, the stability of the glass is easily lowered. Therefore, the upper limit value is preferably 15%, more preferably 10%, and most preferably 5%.

The Nb ₂ O ₅ component is a component that is effective in improving the radiation shielding ability. 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 20% or less, more preferably 15% or less, and more preferably 10% or less. Is most preferable.

The Ta ₂ O ₅ component is a component that is effective in improving the radiation shielding ability. 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%, more preferably 15%, and most preferably 10%.

The WO ₃ component is a component that is effective in improving the radiation shielding ability. 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 25% or less, more preferably 20% or less, and 15% or less. Is most preferable.

In order to further improve the stability of the glass, 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 may be 30%. Preferably, 20% is more preferable, and 10% is most preferable. Further, among these components, the ZrO ₂ and WO ₃ components are more effective in improving chemical durability, and therefore it is preferable to contain either one or both at the same time.

<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, the transition metal components such as V, Cr, Mn, Fe, Co, Ni, Cu, Ag, and Mo except Ti are colored even when they are contained in a small amount by combining them individually or in combination. Causes absorption at specific wavelengths in the region. Therefore, it is preferable that the glass composition of the present invention does not contain substantially. The term “substantially free” as used herein means that it is not contained artificially unless it is mixed as an impurity.

  Each component of Pb, Th, Cd, Tl, and Os tends to be refrained from being used as a harmful chemical material in recent years. The above measures are required. Therefore, it is preferable not to include substantially when importance is attached to environmental influences.

Moreover, the glass composition of this invention can obtain a density of 3.2 g / cm < ³ > or more. A more preferable density range is 3.3 g / cm ³ or more.

  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 composition having a thickness of 10 mm.

The glass composition of the present invention has a Knoop hardness (HK) of 500 N / mm ² or more, more preferably 550 N / mm ² , and most preferably 600 N / mm ² .

  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. About the glass composition of this invention, the lead equivalent with respect to 150-kV X-rays calculated | required by converting the lead equivalent measured by the method according to JIS4501 into thickness 1mm. The lead equivalent of the glass composition of the present invention is preferably 0.03 mmPb / mm or more, and more preferably 0.05 mmPb / mm or more.

Thus, the glass composition of the present invention has a lead equivalent to 150 kV X-rays of 0.03 mmPb / mm or more, high transparency in the visible region, and a transmittance of 400 nm in a glass composition having a thickness of 10 mm. Since the transmittance at 550 nm is 80% or more at 40% or more and the Knoop hardness is 500 N / mm ² or more, it is suitable as a radiation shielding glass having high radiation shielding ability and excellent transparency.

[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 to 1550 ° C. for 1 to 10 hours in a melting furnace. Then, after stirring and homogenizing, the temperature 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 were weighed with the compositions of Examples 1 to 14 shown in Tables 1 and 2 (unit: wt%), mixed uniformly, and then put in a platinum crucible and melted at 1300-1500 ° C. for 2-4 hours. Then, it cast into the metal mold | die and produced glass.

<Comparative Example 1>
As a comparative example, a lead-containing glass used as a radiation shielding glass was produced.

  A batch was prepared so as to have the composition of Comparative Example 1 shown in Table 2. First, a cullet was prepared by melting at 1300 ° C. for 1 hour and 20 minutes using a quartz crucible. 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, transparency, Knoop hardness, 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 coloring degree. 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 T at wavelengths of 400 nm and 550 nm was obtained 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 JISZ4501.

  FIG. 1 shows a spectral transmittance curve in the glass composition 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 composition of the present invention has extremely high transparency over the entire visible range. Moreover, it turns out that the glass composition of this invention has transparency exceeding the existing lead glass so that Table 1 and Table 2 may be seen.

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

  According to Tables 1 and 2, it can be seen that the glass composition of the present invention has a high lead equivalent and has a radiation shielding ability equal to or higher than that of lead glass.

Claims (10)

The total amount of Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ is contained in excess of 5% and 35% by mass based on oxide, and the lead equivalent to 150 kV X-ray is 0. The glass composition which is 03 mmPb / mm or more. The Ln ₂ O ₃ (Ln is at least one selected from the group consisting of Y, La, Gd, Dy, Yb, and Lu) is contained in an amount of 20% to 85% by mass based on the oxide. The glass composition described in 1. The total amount of SiO ₂ and / or B ₂ O ₃ and / or GeO ₂ and / or P ₂ O ₅ is ₅ to 70%, ZnO is 0 to 25%, and RO is 0 to 10% by mass% based on oxide. % (R represents one or more selected from the group consisting of Ba, Sr, Ca, Mg), 0 to 10% Rn ₂ O (Rn is selected from the group consisting of Li, Na, K, Cs) represents one or more that.) the glass composition according to claim 1 or 2 containing the components a total amount of _Sb 2 _{O 3} and _As 2 _{O 3} in the range of 0-5%. % By mass on the oxide basis, the glass composition according to claim 1 containing _Ce 2 _{O 3} 0% to 3 either. % By mass on the oxide basis, the glass composition according to claim 1 containing TiO ₂ 0 to 15% in 4 either. % By mass on the oxide _{basis, ZrO 2, SnO 2, Nb} 2 O 5, Ta 2 O 5, wherein one of WO _3, or two or more of the preceding claims containing a total of 0-30% to 5 either Glass composition. 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 7, 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 8, wherein the Knoop hardness is 500 N / mm ² or more.   A radiation shielding glass, which is the glass composition according to claim 1.

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