JPS6123837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermal fluorescent phosphors and thermal fluorescent dosimeter elements. More specifically, the present invention relates to an alkaline earth metal fluoride thermal fluorescent phosphor activated with a rare earth element and a thermal fluorescent dosimeter element using this phosphor.

Thermal fluorescent phosphor (hereinafter referred to as "TL phosphor")
is mainly used as an element in a thermal fluorescence dosimeter (hereinafter referred to as "TLD") that utilizes the proportional relationship between the relative thermal fluorescence intensity and the irradiated radiation dose. Conventional
Many TL fluorophores are known, but in fact TLD
There are only a few that can be used as elements, and currently
The TL phosphors used as TLD elements are magnesium-activated lithium fluoride phosphors (LiF:Mg).
Manganese-activated calcium fluoride phosphor ( _CaF2 :
Mn), dysprosium-activated calcium fluoride phosphor (CaF ₂ :Dy), silium-activated calcium sulfate phosphor (CaSO ₄ :Tm), terbium-activated magnesium silicate phosphor (Mg ₂ SiO ₄ :Tb) There are only a few types. Looking at the recent spread of TLD, due to its high sensitivity, ease of handling, and high measurement accuracy, it is being used not only for personal radiation exposure control but also for microdose control such as environmental radiation control. Under these circumstances, it is desired to develop a device with as high sensitivity as possible, that is, a TL phosphor with as high thermal efficiency as possible.

The present invention was made in view of these demands, and an object of the present invention is to provide a novel TL phosphor with high sensitivity.

A further object of the present invention is to provide a novel high-sensitivity TLD device using the TL phosphor of the present invention.

In order to achieve the above object, the present inventors mainly selected a phosphor matrix for alkaline earth metal fluorides, selected an activator for activating the matrix and its additive amount, and determined the combination of the matrix and the activator. Various considerations were made regarding alignment, etc. As a result, a composite fluoride consisting of calcium fluoride, strontium fluoride, or both is used as a matrix, and this is combined with Tb, Pr,
The phosphor activated with at least one rare earth element among Tm, Ho, Sm, and Ce exhibits thermal fluorescent properties with higher sensitivity than conventionally known alkaline earth metal fluoride TL phosphors. They discovered this and arrived at the present invention.

Rare earth activated alkaline earth metal fluoride of the present invention
The compositional formula of the TL phosphor is M〓F ₂ :aX (where M〓 is at least one of Ca and Sr).
X is at least one of Tb, Pr, Tm, Ho, Sm and Ce, and a is a number satisfying the condition 10 ^-5 ≦a≦10 ^-2 . The same applies below. ). From the viewpoint of thermal fluorescence intensity, the more preferable a value range of the above composition formula is 5×10 ^-5 ≦a
≦2×10 ^-3 . The TL phosphor of the present invention represented by the above compositional formula is manufactured by the manufacturing method described below.

First, the phosphor raw materials include (1) at least one of CaF ₂ and SrF ₂ (2) fluorides of Tb, Pr, Tm, Ho, Sm, and Ce;
One or more compounds selected from the group consisting of oxides and compounds that can be easily converted into oxides at high temperatures, such as nitrates, chlorides, and sulfates, are used. The above two phosphor raw materials are stoichiometrically M〓F ₂ :aX (M〓 is at least one of Ca and Sr, and a satisfies the condition 10 ^-5 ≦a≦10 ^-2 ), and mix thoroughly using a ball mill, mortar, etc. From the viewpoint of thermal fluorescence intensity, the more preferable range of the a value of the above mixed composition formula is 5×10 ^-4 ≦a≦2×
10 ^-3 . Next, the phosphor raw material mixture is filled into an alumina crucible or a platinum crucible and fired in a weakly reducing atmosphere such as a carbon atmosphere, a nitrogen atmosphere containing hydrogen, or an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere. Firing temperature is 600℃ to 1100℃
°C is appropriate. The firing time varies somewhat depending on the amount of raw materials charged, but 0.5 to 5 hours is appropriate. In addition, if the phosphor raw material mixture is fired under the above firing conditions to produce a single-layer TL phosphor, and then re-fired once or twice or more under the same firing conditions as above, the thermal phosphor intensity will increase. A better TL phosphor can be obtained. After firing, wash if necessary.
Drying, sieving, and other operations often employed in the manufacture of phosphors may be performed. In this way, the rare earth activated alkaline earth metal fluoride TL phosphor of the present invention represented by the above-mentioned compositional formula can be obtained.

Figure 1 shows the thermal fluorescence curve of the TL phosphor of the present invention compared to that of a conventionally known alkaline earth metal fluoride TL phosphor.
The curve a is for the CaF ₂ :0.001Pr phosphor of the present invention, the curve b is for the SrF ₂ :0.001Tb phosphor of the present invention, and the curve c is for the SrF ₂ :0.001Tb phosphor of the present invention. This is a thermal fluorescence curve of a conventionally known CaF ₂ :Dy phosphor. As is clear from FIG. 1, the TL phosphor of the present invention has significantly higher thermal fluorescence intensity than the conventionally known CaF ₂ :Dy phosphor. (i.e. high sensitivity).
Note that the thermal fluorescence intensity of curve b is drawn reduced to 1/10. In addition, the TL phosphor of the present invention, especially
The CaF ₂ :Pr phosphor has a simple thermal fluorescence curve, and therefore, TLD devices using it are excellent in terms of dose linearity, measurement accuracy, etc. Furthermore, the peak of the thermal fluorescence curve of the TL phosphor of the present invention, particularly the SrF ₂ :Tb phosphor, is on the much higher temperature side than the peak of the CaF _{2 :} Dy phosphor. It has a higher ability to store radiation energy than the body and is characterized by less fading.

FIG. 2 shows one of the TL phosphors of the present invention.
2 is a graph showing the relationship between the a value of the CaF ₂ :aPr phosphor, that is, the number of grams of Pr added as an additive agent per 1 mole of CaF ₂ and the thermal fluorescence intensity. As is clear from Figure 2, the amount a of the additive Pr added is 5.
When in the range ×10 ^-5 ≦a≦2×10 ^-3 , especially TL
A strong TL phosphor can be obtained. Although phosphors other than CaF ₂ :aPr phosphor are not shown in Fig. 2, when a rare earth element other than Pr is used as an activator and as a matrix of the phosphor,
It was confirmed that when SrF ₂ or a composite fluoride of CaF ₂ and SrF ₂ was used, the relationship between the a value and the thermal fluorescence intensity had almost the same tendency as shown in FIG. 2.

As described above, the TL phosphor of the present invention has significantly higher sensitivity than the CaF ₂ :Dy phosphor, which has particularly high sensitivity among conventionally known alkaline earth metal fluoride TL phosphors, and also Its thermal fluorescent properties are stable and
It is an excellent phosphor for TLD devices. A TLD element using the TL phosphor of the present invention will be described below.

By using the TL phosphor of the present invention as a TL phosphor of a TLD device, a highly sensitive TLD device can be obtained. The TLD device using the rare earth-activated alkaline earth metal fluoride TL phosphor of the present invention obtained under optimal conditions has a sensitivity 6 to 50 times that of the conventional TLD device using CaF ₂ :Dy. of the present invention
By using a TLD element, the photometry mechanism of the TLD reader can be further simplified, and the dose detection limit can be lowered, thereby improving low dose measurement accuracy.

The TLD element of the present invention has a structure in which the rare earth-activated alkaline earth metal fluoride of the present invention is used as a TL phosphor.
Other than using a TL phosphor, it is exactly the same as a conventional TLD element. Generally, a TL phosphor is a powder, and a certain amount of it can be used as a TLD element as it is. However, it is difficult to handle it as a powder, so for example, it is sealed in a glass tube with an inert gas, compressed into tablets with a small amount of a molding agent such as potassium bromide, or made with a material such as fluororesin or silicone resin. Solidify by appropriate means such as embedding in heat-resistant resin,
In other words, it is elementized. In fabricating the TL phosphor of the present invention into a device, conventional methods can be used as is. FIG. 3 illustrates the TLD device of the present invention, in which a and b are glass-encapsulated elements with a handle, c is a rod-like element, d is a sheet-like element, and e
is a disk-shaped element.

As explained above, the TL phosphor of the present invention has excellent thermal fluorescent properties, and is suitable for use in TLD devices.
Can be used as a phosphor. As described above, the industrial value of the present invention is extremely large.

Next, the present invention will be explained with reference to Examples.

Example 1 Calcium fluoride CaF ₂ 78 g Praseodymium oxide Pr ₂ O ₃ 0.16 g The above raw materials were sufficiently ground in a ball mill and mixed. The resulting mixture was filled into an alumina crucible and fired at a temperature of 800° C. for 2 hours in a carbon atmosphere. After baking, the baked product was cooled and passed through a sieve. In this way, CaF ₂ :0.001Pr was obtained. When this TL phosphor was irradiated with X-rays at a tube voltage of 120 KV _P for 5R and its thermal fluorescence intensity was measured, the main peak intensity was about 5 times that of the conventionally used CaF ₂ :Dy.

Example 2 Calcium fluoride CaF ₂ 78 g Praseodymium chloride PrCl _{3.7H 2} O 0.30 g The above raw materials were thoroughly ground and mixed in a ball mill. The resulting mixture was filled into an alumina crucible and fired at a temperature of 700° C. for 2 hours in a carbon atmosphere.
After baking, the baked product was cooled and passed through a sieve. In this way, CaF ₂ :0.0008Pr was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was approximately 6 times that of CaF ₂ :Dy, which has been used in conventional practice.

Example 3 Calcium fluoride CaF ₂ 78 g Thulium chloride TmCl _{3.7H 2} O 0.40 g The above raw materials were thoroughly ground and mixed in a ball mill. The resulting mixture was filled into an alumina crucible and fired at a temperature of 900° C. for 2 hours in an argon atmosphere. After baking, the baked product was cooled and passed through a sieve. In this way, CaF ₂ :0.001Tm was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was approximately twice as high as that of CaF ₂ :Dy, which has been used in conventional practice.

Example 4 Strontium fluoride SrF ₂ 125.6 g Terbium oxide Tb ₄ O ₇ 0.19 g The above raw materials were sufficiently ground in a ball mill and mixed. The resulting mixture was filled into an alumina crucible and fired at 900° C. for 2 hours in a carbon atmosphere. After baking, the baked product was cooled and passed through a sieve. In this way, SrF ₂ :0.001Tb was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was found that
It was about 50 times that of conventionally used CaF ₂ :Dy.

Example 5 Strontium fluoride SrF ₂ 125.6 g Terbium chloride TbCl ₃ ·6H ₂ O 0.37 g The above raw materials were thoroughly ground and mixed in a ball mill. The resulting mixture was filled into an alumina crucible and fired at 900° C. for 3 hours in a carbon atmosphere. After baking, the baked product was cooled and passed through a sieve. In this way, SrF ₂ :0.0001Tb was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was approximately 8 times that of CaF ₂ :Dy, which has been used in conventional practice.

Example 6 Strontium fluoride SrF ₂ 125.6 g Praseodymium oxide Pr ₂ O ₃ 0.16 g The above raw materials were sufficiently ground in a ball mill and mixed. The resulting mixture was filled into an alumina crucible and fired at 900° C. for 3 hours in a nitrogen atmosphere containing 2% hydrogen. After baking, the baked product was cooled and passed through a sieve. In this way, SrF ₂ :0.001Pr was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was approximately three times that of CaF ₂ :Dy, which has been used in conventional practice.

Example 7 Calcium fluoride CaF ₂ 3.9 g Strontium fluoride SrF ₂ 56.5 g Terbium fluoride TbF ₃ 0.11 g The above raw materials were sufficiently ground in a ball mill and mixed. The resulting mixture was filled into a platinum crucible and fired at a temperature of 900° C. for 2 hours in a carbon atmosphere. After baking, the baked product was cooled and passed through a sieve. In this way. (Ca0.1, Sr0.9) _F2 :0.0005Tb was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was found that it was approximately equal to that of conventionally used CaF ₂ :Dy.
It was 25 times hotter.

Example 8 Calcium fluoride CaF ₂ 78 g Holmium oxide Ho ₂ O ₃ 0.189 g The above raw materials were thoroughly ground and mixed in a ball mill. The obtained mixture was filled into an alumina crucible and fired at a temperature of 900° C. for 2 hours in a carbon atmosphere.
After baking, the baked product was cooled and passed through a sieve. In this way, CaF ₂ :0.001Ho was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was about 1.5 times that of CaF ₂ :Dy, which has been used in conventional practice.

Example 9 Example 8 except that 125.6 g of strontium fluoride (SrF ₂ ) is used instead of CaF ₂ as one of the raw materials.
Similarly, SrF ₂ :0.001Ho was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was about 25 times that of CaF ₂ :Dy, which has been used in conventional practice.

Example 10 Calcium fluoride CaF ₂ 78 g Samarium oxide Sm ₂ O ₃ 0.174 g The above raw materials were thoroughly ground and mixed in a ball mill. The obtained mixture was filled into an alumina crucible and fired at a temperature of 900° C. for 2 hours in a carbon atmosphere.
The baked product was cooled and passed through a sieve. like this
_CaF2 : 0.001Sm was obtained. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was found that
Conventional practical CaF ₂ :It was about 1.2 times that of Dy.

Example 11 Example 10 except that 125.6 g of strontium fluoride (SrF ₂ ) is used instead of CaF ₂ as one of the raw materials.
SrF ₂ :0.001Sm was obtained in the same manner as above. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was approximately 1.05 times that of CaF ₂ :Dy, which has been used in conventional practice.

Example 12 Strontium fluoride SrF ₂ 125.6 g Cerium oxide Ce ₂ O ₃ 0.164 g The above raw materials were sufficiently ground in a ball mill and mixed. The obtained mixture was filled into an alumina crucible and fired at a temperature of 900° C. for 2 hours in a carbon atmosphere.
The baked product was cooled and passed through a sieve. like this
SrF ₂ :0.001Ce was obtained. In the same manner as in Example 1,
When the thermal fluorescence intensity of this TL phosphor was measured, it was approximately 1.5 times that of CaF ₂ :Dy, which has been used in conventional practice.

Example 13 CaF ₂ :0.001Ce was obtained in the same manner as in Example 12 except that 78 g of calcium fluoride (CaF ₂ ) was used instead of SrF ₂ as one of the raw materials. When the thermal fluorescence intensity of this TL phosphor was measured in the same manner as in Example 1, it was approximately three times that of CaF ₂ :Dy, which has been used in conventional practice.

[Brief explanation of the drawing]

Figure 1 shows the thermal fluorescence curve of the rare earth activated alkaline earth metal fluoride TL phosphor of the present invention compared to that of the conventional CaF ₂ :Dy.
Curve a is the thermal fluorescence curve of the praseodymium-activated calcium fluoride phosphor of the present invention, and curve b is the thermal fluorescence curve of the terbium-activated strontium fluoride phosphor of the present invention. The light curve, curve c, is the thermal fluorescence curve of CaF ₂ :Dy. Note that the thermal fluorescence curve of curve b is drawn reduced to 1/10. Figure 2 is a graph showing the relationship between the a value (the number of grams of Pr added as an activator per 1 mole of CaF ₂ ) and the thermal fluorescence intensity in the Pr-activated calcium fluoride phosphor of the present invention. be. FIG. 3 illustrates the TLD element of the present invention.

Claims (1)

[Claims] 1. The compositional formula is M〓F ₂ :aX (where M〓 is at least one of Ca and Sr,
X is at least one of Tb, Pr, Tm, Ho, Sm, and Ce, and a is a number satisfying the condition 10 ^-5 ≦ a ≦ 10 ^-2 ) Metal fluoride thermal fluorescent phosphor. 2. The thermofluorescent phosphor according to claim 1, wherein a in the compositional formula is a number satisfying the following condition: 5×10 ^-5 ≦a≦2×10 ^-3 . 3 The compositional formula is M〓F ₂ :aX (where M〓 is at least one of Ca and Sr,
X is at least one of Tb, Pr, Tm, Ho, Sm, and Ce, and a is a number satisfying the condition 10 ^-5 ≦ a ≦ 10 ^-2 ) A thermal fluorescent dosimeter element using a metal fluoride thermal fluorescent material. 4. The thermal fluorescence dosimeter element according to claim 3, wherein a in the compositional formula is a number satisfying the following condition: 5×10 ^-5 ≦a≦2×10 ^-3 .