JPS6116032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation energy measuring method and an element used in the method. More specifically, the present invention relates to a radiation energy measuring method using a thermal fluorescence dosimeter element having a specific thermal fluorescence, and a thermal fluorescence dosimeter element having the above-mentioned specific thermal fluorescence used in the method.

As is well known, a thermal fluorescent dosimeter (hereinafter abbreviated as "TLD") is a thermal fluorescent dosimeter (hereinafter abbreviated as "TLD") that absorbs radiation when it is heated after absorbing radiation. This is a radiation dosimeter that utilizes the property of exhibiting thermal fluorescence with an amount or intensity proportional to the radiation dose. This TLD uses a thermal fluorescent dosimeter element (hereinafter referred to as "TLD element"), which is a TL phosphor molded into an appropriate shape, as a radiation detection element, and the TLD element that has absorbed radiation is heated by a reading device. , by measuring the amount of thermal fluorescence emitted from the TLD element in a specific heating temperature range or the intensity of thermal fluorescence at a specific heating temperature, the radiation dose absorbed by the TLD element is measured. . TLD has the advantages of being able to measure a wide range of doses with a single TLD element, being highly sensitive and capable of measuring doses as low as 10 mR or less, and being easy to handle and providing measurement results immediately. Recently, it has become widely used as a dosimeter for managing personal radiation exposure.

Traditionally, TL phosphors include magnesium-activated lithium fluoride phosphor (LiF:Mg), manganese-activated lithium borate phosphor (Li ₂ B ₄ O ₇ :Tb), and thulium-activated calcium sulfate phosphor ( CaSO ₄ :Tm), terbium-activated magnesium silicate phosphor (Mg ₂ SiO ₄ :
Tb) etc. are known, and these TL fluorophores are
These TL
Conventional TLD using a TLD element made of phosphor
As mentioned above, the radiation dose can only be determined by measuring the thermal fluorescence amount or thermal fluorescence intensity that is proportional to the radiation dose absorbed by the TLD element. However, when managing radiation exposure, it is desirable to know both the dose and energy of the radiation to which the human body is exposed in order to evaluate the effects of radiation on the human body. There is a need for a TLD for personal exposure management that can simultaneously measure

The present invention has been made in view of the above-mentioned situation, and an object of the present invention is to provide a method of measuring radiation energy using a TLD element.

Another object of the present invention is to provide a TLD element that can measure not only the dose of radiation but also its energy.

In order to achieve the above object, the present inventors
Various studies have been conducted on the thermal fluorescent properties of various TL phosphors that can be used as TLD devices. As a result, in the TL phosphor, there are multiple peaks in the curve showing the relationship between the heating temperature of the phosphor and the thermal fluorescence intensity, that is, the glow curve, and among the multiple peaks, It has been discovered that there is a TL phosphor that has thermal fluorescent properties such that the ratio of the heights of two specific peaks of the phosphor changes depending on the energy of the irradiated radiation. After the TLD element made of the TL phosphor having the above-mentioned thermal fluorescent properties absorbs radiation, the TLD element is heated and a glow curve is measured.
The inventors have discovered that the energy of the absorbed radiation can be determined by determining the ratio of the heights of the two peaks, and have completed the present invention.

The radiation energy measuring method of the present invention is applicable to a glow curve in which a plurality of peaks exist and the height ratio of two specific peaks among the plurality of peaks changes depending on the radiation energy. A TLD element made of a TL phosphor having thermal fluorescent properties is made to absorb radiation, and then the TLD element is heated to measure the glow curve, and the heights of the two specific peaks in the glow curve are determined. The method is characterized in that the energy of the absorbed radiation is determined by determining the ratio of .

In addition, the TLD for radiation energy measurement of the present invention
The element has a thermal fluorescence property in which a plurality of peaks exist in a glow curve, and a height ratio of two specific peaks among the plurality of peaks changes depending on radiation energy. It is characterized by being made of TL phosphor powder or its molded product.

The present invention will be explained in detail below.

The TL phosphor constituting the TLD element of the present invention used in the radiation energy measurement method of the present invention has, for example, a composition formula of MgO.xSiO ₂ :yTb,zA (where A is lithium, potassium, cobalt, nickel, and thulium at least one of the following, x, y and z are each 0.2≦x≦1.0,
Examples thereof include magnesium silicate-based phosphors expressed by the following formulas: 10 ^-5 ≦y≦2×10 ⁻² and 10 ⁻⁶ ≦z≦3×10 ⁻² . This magnesium silicate phosphor is a novel
It is a TL phosphor and is manufactured by the manufacturing method described below.

First, the raw materials for the phosphor are magnesium oxide (MgO) and nitrate.
At least one compound selected from the group consisting of magnesium compounds that can be easily converted to MgO at high temperatures, such as carbonates, sulfates, hydroxides, and halides; silicon dioxide (SiO ₂ ), and silicic acid that can be easily converted to MgO at high temperatures. At least one compound selected from the group of compounds consisting of silicon compounds that can be converted into SiO ₂ at high temperatures, terbium oxide (Tb ₄ O ₇ ), and nitrates, carbonates, sulfates, halides, etc. that can be easily converted into oxides at high temperatures. At least one compound selected from the group of compounds consisting of terbium compounds
a first compound group consisting of lithium oxide (Li ₂ O), potassium oxide (K ₂ O), cobalt oxide (Co ₂ O ₃ ), nickel oxide (NiO) and thulium oxide (Tm ₂ O ₃ ), as well as nitrates, carbonates,
Lithium compounds, potassium compounds that can be easily converted to Li ₂ O, K ₂ O, Co ₂ O ₃ , NiO and Tm ₂ O ₃ at high temperatures, such as sulfates, hydroxides, halides, etc.
At least one compound selected from the compound group consisting of the second compound group consisting of cobalt compounds, nickel compounds, and thulium compounds is used. The above phosphor raw materials are stoichiometrically MgO x SiO ₂ :yTb, zA (where A is at least one of lithium, potassium, cobalt, nickel, and thulium, and x, y, and z are each 0.2 ≦x≦1.0,
(The number satisfies the following conditions: 10 ^-5 ≦y≦2×10 ^-2 and 10 ^-6 ≦z≦3×10 ^-2 ). Mix thoroughly. Next, the obtained phosphor raw material mixture is filled into a heat-resistant container such as an alumina crucible or a quartz crucible, placed in an electric furnace, and fired in air at a temperature of 1500°C to 1800°C. After firing, the resulting fired product is crushed, washed with water, dried,
Pass through a sieve to obtain phosphor.

The magnesium silicate-based phosphor manufactured as described above has two peaks in its glow curve, and the ratio of the heights of the two peaks seems to change depending on the energy of the irradiated radiation. It has thermal fluorescent properties. Note that the TL phosphor used in the TLD element of the present invention has a plurality of peaks in the glow curve, and the height ratio of two specific peaks among the plurality of peaks is determined by the irradiation. Any TL phosphor may be used as long as it has thermal fluorescent properties that change depending on the energy of the radiation, and is not limited to the above-mentioned magnesium silicate-based phosphor.

The structure of the TLD element of the present invention is exactly the same as that of a conventional TLD element except that a TL phosphor having the above-mentioned thermal fluorescent properties is used as the TL phosphor. 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 capillary with an inert gas, compressed with a molding agent such as potassium bromide to form a tablet, or a heat-resistant material such as fluororesin or silicone resin is used. The element is formed into a desired shape by appropriate means such as embedding it in resin and molding, and then it is ready for use. Figure 1 shows the present invention.
These are examples of TLD elements, where a and b are elements sealed in a glass tube with a handle, c is a rod-shaped element, and d
is a sheet-like element, and e is a disk-like element.

FIG. 2 is a graph showing the glow curve of the TLD element of the present invention comprising MgO・0.4SiO ₂ :0.001Tb, 0.02K phosphor contained in the above-mentioned magnesium silicate-based phosphor, and curves a and b are respectively This is a glow curve when the TlD element is irradiated with 50 KVp X-rays and ⁶⁰ Co gamma rays. As is clear from Figure 2, the TLD element made of MgO・0.4SiO ₂ :0.001Tb, 0.02K phosphor had glow curve peaks around 200℃ and 330℃, and was irradiated with 50KVp of X-rays. 2 of the glow curve when irradiated with ⁶⁰ Co gamma rays.
The ratio of the heights of the two peaks changes. In addition, Figure 2
MgO・0.4SiO ₂ : Consists of 0.001Tb, 0.02K phosphor
Although this figure shows the glow curve of the TLD element, the glow curve of the TLD element made of other phosphors included in the above-mentioned magnesium silicate-based phosphor also has two peaks as in Figure 2. It was confirmed that the ratio of the heights of the two peaks changes depending on the irradiated radiation energy. For example, TLD elements made of magnesium silicate phosphors in which the terbium coactivator (A in the above compositional formula) is lithium, cobalt, nickel, and thulium, respectively.
The glow curve has peaks at 190℃ and 420℃, 180℃ and 340℃, 190℃ and 405℃, and 90℃ and 230℃, and the ratio of the heights of these two peaks depends on the energy of the irradiated radiation. It changes over time.

FIG. 3 shows the TLD element of the present invention made of the above-mentioned magnesium silicate-based phosphor after irradiating the TLD element with various radiations having different energies.
The obtained result is obtained by heating the TLD element, measuring the glow curve, and determining the ratio of the height of the peak on the high temperature side and the height of the peak on the low temperature side of the glow curve (this value is α) for each radiation energy. 3 is a graph showing the relationship between the calculated α value and the irradiation radiation energy, and the straight lines a, b, c, d and e in _FIG .
MgO・0.4SiO ₂ :0.001Tb, 0.02K phosphor, MgO・
0.3SiO ₂ :0.001Tb, 0.00001Co phosphor, MgO・
0.5SiO ₂ :0.001Tb, 0.00001Ni phosphor and
This is the case of a TLD element made of MgO・0.3SiO ₂ :0.0002Tb, 0.0002Tm phosphor. In addition, the α value is
It is shown as a relative value with α value of 1 for ⁶⁰ Co gamma rays (1.25 MeV).

As is clear from Figure 3, in the TLD element made of the above-mentioned magnesium silicate-based phosphor, the height of the peak on the high temperature side of the glow curve is equal to the height of the peak on the low temperature side for high-energy radiation. Conversely, for low-energy radiation, the height of the peak on the high temperature side of the glow curve tends to be relatively high relative to the peak height on the low temperature side; The ratio of the peak height to the peak height on the low-temperature side, that is, the α value, changes linearly in response to radiation energy (the α value decreases linearly in response to an increase in radiation energy). Therefore, after the TLD element absorbs radiation, the energy of the absorbed radiation can be determined by heating the TLD element, measuring the glow curve, and determining the α value. Among the above-mentioned magnesium silicate-based phosphors, TLD elements made of magnesium silicate phosphors whose terbium co-activator is potassium and magnesium silicate phosphors whose terbium co-activator is cobalt are α
Since the slope of the straight line representing the relationship between radiation energy and radiation energy is large (Fig. 3 b and c, respectively),
Radiation energy can be measured more accurately. Therefore, among the TLD elements made of the above magnesium silicate-based phosphor, it is particularly preferable to use these TLD elements.

The radiation energy measuring method of the present invention has been explained above with reference to FIG.
Used in the radiation energy measurement method of the present invention
TLD elements are not limited to TLD elements made of this magnesium silicate-based phosphor, but have multiple peaks in the glow curve, and the height of two specific peaks among the multiple peaks. When using a TLD element made of the magnesium silicate-based phosphor described above, any TLD element may be used as long as it is made of a TL phosphor having thermal fluorescent properties such that the ratio of It can be used to measure radiation energy in the same way as .

In addition, in the TLD element of the present invention, when the energy of the irradiated radiation is constant, the shape of the glow curve does not change, and like the conventional TLD element, it exhibits thermal fluorescence proportional to the irradiation dose. Therefore, for example, after measuring the energy of radiation by the radiation energy measurement method of the present invention described above, the dose of irradiated radiation can be determined by determining the height or area of any peak in the glow curve. can also be found.

As explained above, the present invention makes it possible to measure radiation energy, which was impossible with conventional TLDs. Further, the TLD element of the present invention can be used not only for measuring radiation energy, but also for measuring radiation dose like conventional TLD elements. Therefore, by using the TLD element of the present invention, more information regarding radiation can be obtained than with conventional TLD elements. As described above, the TLD device of the present invention has greater industrial utility value than conventional TLD devices as a TLD device for personal exposure management, environmental radiation measurement, etc.

[Brief explanation of the drawing]

FIG. 1 illustrates the TLD device of the present invention, in which a and b are elements enclosed in a glass tube with a handle, and c
is a rod-like element, d is a sheet-like element, and e is a disk-like element. Figure 2 shows MgO・0.4SiO ₂ :
This is a graph showing the glow curve of the TLD element of the present invention made of 0.001Tb, 0.02K phosphor, and curves a and b are the glow curves when the TLD element is irradiated with 50 KVp X-rays and ⁶⁰ Co gamma rays, respectively. be. FIG. 3 shows the ratio (α value) of the peak height on the high temperature side and the peak height on the low temperature side of the glow curve of the TLD element of the present invention made of a magnesium silicate-based phosphor. It is a graph showing the relationship with radiation energy that gives a glow curve,
Straight lines a, b, c, d and e are MgO・
0.4SiO ₂ :0.001Tb, 0.02Li phosphor, MgO・
0.4SiO ₂ :0.001Tb, 0.02K phosphor, MgO・
0.3SiO ₂・0.001Tb, 0.00001Co phosphor, MgO・
0.5SiO ₂ :0.001Tb, 0.00001Ni phosphor and
This is the case of a TLD element made of MgO・0.3SiO ₂ :0.0002Tb, 0.0002Tm phosphor.

Claims (1)

[Scope of Claims] 1. A thermal fluorescent material in which a plurality of peaks exist in a glow curve, and the height ratio of two specific peaks among the plurality of peaks changes depending on radiation energy. A thermal fluorescent dosimeter element made of a thermal fluorescent material having optical properties is made to absorb radiation, and then the thermal fluorescent dosimeter element is heated to measure the glow curve, and A radiation energy measuring method characterized in that the energy of the absorbed radiation is determined by determining the height ratio of the two specific peaks. 2 The thermal fluorescent phosphor has a composition formula MgO x SiO ₂ :yTb,zA (where A is at least one of lithium, potassium, cobalt, nickel, and thulium, and x, y, and z are each 0.2≦x≦1.0,
10 ^-5 ≦y≦2×10 ^-2 and 10 ^-6 ≦z≦3×10 ^-2 ) A method for measuring radiation energy according to claim 1. 3 Consisting of a powder of a thermally fluorescent phosphor or a molded product obtained by molding the same into an arbitrary shape, the thermally fluorescent phosphor has a plurality of peaks in its glow curve, and 1. A thermal fluorescence dosimeter element for measuring radiation energy, characterized in that it has thermal fluorescence characteristics such that the ratio of the heights of two specific peaks among the two peaks changes depending on the radiation energy. 4 The thermal fluorescent phosphor has the composition formula MgO x SiO ₂ :yTb,zA (where A is at least one of lithium, potassium, cobalt, nickel, and thulium, and x, y, and z are each 0.2≦×≦1.0,
10 ^-5 ≦y≦2×10 ^-2 and 10 ^-6 ≦z≦3×10 ^-2 ) A thermal fluorescence dosimeter element for measuring radiation energy according to claim 3.