JPH06127973A - Radiation shielding glass - Google Patents

Abstract

PURPOSE:To provide a glass excellent in light transmittance and excellently non-colorable without substantially containing lead. CONSTITUTION:A radiation shielding glass has a composition of 40-60% SiO2, 0-4% Al2O3, 0-3% MgO, 0-10% CaO, 3-23% SrO3, 7-27% BaO, 0-20% ZnO, 0-3% ZrO2, 1-12% Na2O, 1-12% K2O, 0-0.4% Li2O, 0-2% TiO2, 0.1-3% CeO2, 0-0.3% As2O3, 0-0.3% Sb2O3, 0-0.4% F2 and is 31-50% in sum of CaO, SrO and BaO, >=3.01g/cm<3> in density and is substantially free from PbO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation-shielding glass having a radiation-shielding ability, and more particularly to a glass having excellent shielding ability against γ-rays and non-coloring property and hardly causing dielectric breakdown.

[0002]

2. Description of the Related Art A radiation shielding window is provided for observing the inside of a hot cell or for remote control with a magic hand in a facility that handles radioactive substances. Therefore, the properties required for the glass used for this shielding window are
It has the ability to shield against lines, and the inside of the cell can be clearly seen, that is, the light transmittance is good.

When the glass is irradiated with strong γ rays,
With the irradiation time, the glass gradually turns brown and the light transmittance decreases remarkably, and static electricity is generated inside the glass, and the high voltage discharge caused by the accumulation of static electricity may cause glass destruction called dielectric breakdown. In addition to the above properties, the radiation shielding window is required to be free from such coloring and dielectric breakdown.

By the way, it is known that the shielding ability against high-energy radiation such as γ-rays is proportional to the density, and it is effective to use glass having a high density such as lead glass. It is also known that CeO ₂ is preferably contained in order to prevent coloring due to γ-ray irradiation.

However, glass containing a large amount of lead oxide (for example, glass having a PbO content of 72% by weight and a density of 5.2 g / cm ³ ) is excellent in radiation shielding ability, but particularly γ.
Line coloring is likely to occur, and dielectric breakdown is also likely to occur. On the other hand, in the case of glass that does not contain lead oxide at all or contains a small amount of it, γ-ray coloring and dielectric breakdown are difficult to occur, but since the density is low, the shielding ability is low, and all of the glass of the shielding window is completely Attempts to block the radiation result in a very thick window, which results in a significantly low light transmission.

Therefore, the glass currently constituting the shielding window is
Instead of one type, several types of glass having different compositions (usually three or more types) are used in combination. That is, on the hot side closest to the cell, a lead-free glass containing CeO ₂ is used, which may have a small shielding ability but does not cause coloring and dielectric breakdown even when exposed to strong γ rays. On the other hand, on the cold side, which is closest to the observer,
Since the rays are attenuated, it is not necessary to consider coloring or dielectric breakdown due to γ rays so much, but high lead glass containing no CeO ₂ is used because γ rays must be completely shielded.

The glass disposed between the two glasses has a high light transmittance, a high shielding ability against γ-rays, no coloring by γ-ray irradiation, and no dielectric breakdown. It is required to have all the characteristics described above, for example, Japanese Patent Publication No. 46-2586.
The CeO ₂ -containing lead glass as disclosed in Japanese Patent Laid-Open No. Hei 2-213331 and the like is used.

[0008]

When used in INVENTION Problems to be Solved by the way radiation shielding windows, but that thickness such glass was molded into a block of more than 10cm is used, the CeO ₂
Since the contained lead glass originally has a not so high light transmittance, there is a drawback in that a sufficient light transmittance cannot be obtained when it is made into a block body. Further, the non-coloring property with respect to γ-ray is also insufficient.
Therefore, a glass having further excellent light transmittance and excellent non-coloring property is desired.

Therefore, attempts have been made to use a high-density CeO ₂ -containing lead-free glass, but the fact is that none of the conventional lead-free glasses satisfy all the required characteristics described above. For example, the CeO ₂ -containing lead-free glass disclosed in Japanese Examined Patent Publication No. 63-44697 has a high density and has an excellent X-ray shielding ability, and thus is suitable for a face plate of a television picture tube, but has an electric resistance. Since it is high, dielectric breakdown is likely to occur, and it is impossible to use it for the application of the radiation shielding window as described above. An object of the present invention is to provide a radiation shielding glass that satisfies all the above-mentioned required characteristics.

[0010]

Means for Solving the Problems] As a means, by _{weight, SiO 2 40~60%, Al 2} O 3 0~4%, MgO
0-3%, CaO 0-10%, SrO 3-23%, Ba
_{O7~27%, ZnO0~20%, ZrO 2} 0~3%,
_{Na 2 O1~12%, K 2 O1~12} %, Li 2 O0~
0.4%, TiO ₂ 0 to 2%, CeO ₂ 0.1 to 3%, A
s ₂ O ₃ 0 to 0.3%, Sb ₂ O ₃ 0 to 0.3%, F ₂₀
It has a composition of 0.4%, the total amount of CaO, SrO, and BaO is 31 to 50%, and the density is 3.01 g / c.
The radiation-shielding glass is characterized by having m ³ or more and essentially not containing PbO.

[0011]

Function SiO ₂ is indispensable as a glass network structure forming component, but if the content is less than 40%, the weather resistance becomes poor, and if it exceeds 60%, a component for increasing the density should be sufficiently contained. I can't.

If Al ₂ O ₃ exceeds 4%, the meltability will deteriorate, so it is preferable that the amount be less than that. If the content of MgO exceeds 3%, devitrification tends to occur, so the content should be less than that.

CaO is a component for increasing the density of glass, but if its content exceeds 10%, devitrification tends to occur. S
rO is an essential component for increasing the density of glass, but if its content is less than 3%, its action is poor, and if it exceeds 23%, devitrification tends to occur. BaO is also an essential component for increasing the density of the glass, but if the content is less than 7%, its action is poor, and if it exceeds 27%, devitrification tends to occur. However, the total content of these three components of CaO, SrO, and BaO must be 31% or more and 50% or less, and if the content is less than 31%, the density is 3.01.
It is difficult to attain g / cm ³ or more, and if it exceeds 50%, devitrification tends to occur.

ZnO is a component for increasing the density of glass, but if its content exceeds 20%, devitrification tends to occur. Zr
O _{2 is} also a component to increase the density, but its content is 3%.
If it exceeds, surface devitrification is likely to occur.

Na ₂ O, K ₂ O and Li ₂ O are components contained in order to lower the electric resistance and prevent coloring due to γ-rays. In particular, Na ₂ O and K ₂ O are contained as essential components because of their great effect, but if the content of each of them is less than 1%, there is no effect, and if they exceed 12%, the weather resistance deteriorates. Further, the content of Li ₂ O is 0.
It is 4% or less, and if it exceeds this, the electric resistance is rather increased. That is, it is generally known that the electric resistance tends to decrease as the alkali content increases, but on the other hand, the electric resistance increases when the type of the alkali component increases. ₂ O content is 0.4
If it is more than%, the action of the latter becomes larger than that of the former and the electric resistance becomes high.

If the content of TiO ₂ exceeds 2%, γ-ray coloring is likely to occur. CeO
₂ is a component that prevents γ-ray coloring, but its content is 0.
If less than 1%, the action is poor, and if more than 3%, C
The glass becomes yellow due to the absorption of light by eO ₂ itself, and the light transmittance becomes low.

As ₂ O ₃ and Sb ₂ O ₃ function to cut bubbles when the glass is melted, but if both of them exceed 0.3%, surface devitrification is likely to occur. . If F ₂ exceeds 0.4%, it becomes a problem from the environmental aspect in glass production, so it is preferable that the amount be less than that.

The radiation-shielding glass of the present invention is characterized in that it essentially contains no PbO. There is a possibility that a small amount of PbO will be mixed as an impurity from the raw material, but it is necessary to pay attention so that PbO is not mixed in as much as possible in order to prevent a decrease in light transmittance and coloration due to γ rays. Finally, if the density is lower than 3.01 g / cm ³ , the γ-ray shielding ability will be insufficient, so a material having a density of 3.01 g / cm ³ or more is selected.

[0019]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. First, No. 1 in Table 1. A raw material batch prepared so as to have a glass composition of 1 to 7 is converted into an oxide of 500.
It was weighed so as to be g (however, F ₂ is converted to CaF ₂ ). Next, the raw material batches were mixed by a vibration mill, put into a quartz crucible and melted at 1350 ° C. for 4 hours. Each sample piece was prepared by stirring with a platinum stir bar during glass melting to obtain a homogeneous glass, defoaming, pouring out on a carbon plate, transferring to a slow cooling furnace, cooling and cutting out. Table 1 also shows the results of measuring the density, light transmittance, γ-ray coloration degree, and electric resistance of each of these samples. The measuring method of each characteristic value is as follows.

Density: size 1 × 1 × 2 (cm)
The sample of No. 1 was immersed in water and determined by the Archimedes method. The unit of numerical values in the table is g / cm ³ .

Light transmittance: size 3 × 3 × 1 (cm)
Both surfaces of the sample (1) were optically polished, the light transmittance (%) at a wavelength of 590 nm was measured, and this value was converted to a thickness of 10 cm.

Γ-ray coloring degree ··· C in the sample after measuring the light transmittance
O ⁶⁰ γ-ray 5 × 10 ⁶ R / h was irradiated for 20 hours, and then the light transmittance was measured to calculate the ratio (%) of decrease with respect to the light transmittance before γ-ray irradiation.

Electric resistance: size 5 × 5 × 0.3 (c
The Ag paste was applied to both surfaces of the sample of m), and this was used as an electrode, and a DC voltage of 100 V was applied to obtain a current value flowing. The numerical values in the table are values at 250 ° C., and the unit is Ω-cm.

[0024]

[Table 1] In the table, No. Nos. 1 to 5 are examples of the present invention. 6 is
Example No. 1 described in the above-mentioned JP-A-2-212331. It is equivalent to 3. No. 7 is Japanese special public Sho6
Example No. 3 described in JP-A-3-44697. It is equivalent to 5.

As can be seen from Table 1, Example No. 1 of the present invention.
All of 1 to 5 had a density of 3.01 g / cm ³ or more, a transmittance of 85.8% or more, a γ-ray coloring degree of 4.0% or less, and an electric resistance of 9.3 Ω-cm or less. That is, since the density is high, the γ-ray shielding ability is excellent, the light transmittance is good, and the γ-ray coloring degree is low, so that it is easy to observe the inside of the cell, and the electric resistance is low, so that the dielectric breakdown is difficult to occur. .

On the other hand, in Comparative Example No. Although No. 6 had good density and electric resistance, it contained No. 6 having the same CeO ₂ content because it contained PbO. 1 was inferior in light transmittance and γ-ray coloring degree. In addition, N of the comparative example
o. 7, for containing a large amount of Li ₂ O with Na ₂ O, K ₂ O, the electrical resistance is high as 10.6Ω-cm, were those susceptible to dielectric breakdown.

[0027]

As described above, the glass of the present invention has a high density and therefore an excellent γ-ray shielding ability, and has a good light transmittance and a small γ-ray coloring degree, so that it is easy to observe the inside of the cell,
Since it has a low electric resistance and is unlikely to cause dielectric breakdown, it can be suitably used as a glass for a radiation shielding window.

Claims (1)

[Claims] 1. SiO ₂ 40-60% by weight, A
l ₂ O ₃ 0-4%, MgO 0-3%, CaO 0-10%,
SrO3-23%, BaO7-27%, ZnO0-20
%, ZrO ₂ 0 to 3%, Na ₂ O _{1 to} 12%, K ₂ O 1 to
12%, Li ₂ O 0 to 0.4%, TiO ₂ 0 to 2%, Ce
O ₂ 0.1-3%, As ₂ O ₃ 0-0.3%, Sb ₂ O ₃ 0
0.3%, has a composition of F ₂ 0 to 0.4%, and Ca
The total amount of O, SrO, and BaO is 31 to 50%,
It has a density of 3.01 g / cm ³ or more and is essentially PbO.
A radiation-shielding glass characterized by containing no.