JPS59214787A - Radiation dose measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a dose rate linearity and an even energy characteristic in a wide range by arranging a semiconductor detection body in a metal shield and providing a hole in the metal shield. CONSTITUTION:A shield 3 made of a lead or a lead-tin alloy has a hole 5 corresponding to the sensitivity per unit area and transmits a photon below 60keV to obtain an even energy characteristic. The thickness of the shield is 0.3-1.0mm. when the semiconductor uses a material with the atomic number of 30-45 and 1.0-2.0mm. when the atomic number is 45-60. A pulse signal generated from a compound semiconductor detection body 1 with the atomic number exceeding 30 is counted with a pulse counting section 9 through an FET7 and an amplification circuit 9 and the results are indicated on a calculation display section 10 as does value. This apparatus will be used for a pocket sized alarm dosimeter, a portable dose range meter and the like to enable a dose measurement at a high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates primarily to an X-ray and γ-ray radiation dosimetry device used primarily for personal radiation exposure management or radiation work management.

Conventional configuration and its problems Linearity can be achieved over a wide range by changing the range from low dose rates of 0.1 mR/hour or less to thick dose rates of about 1000 R/hour or more.
As a measuring method capable of measuring radiation, a radiation detector using a compound semiconductor having an atomic number of 30 or more as a detector was developed (Japanese Patent Application No. 57-210761). However, this is mainly for radiation detection, and depends on photon energy vs. dose sensitivity (
It cannot be used as a dosimeter in workplaces where radiation with a wide range of photon energies is present.

Regarding a method for improving the energy characteristics of a semiconductor detector, a method of improving the energy characteristics using pulse height information from the detector (Japanese Patent Application Laid-Open Nos. 67-100364 and 67-10)
No. 0365) has been developed in recent years, but since the pulse pitch is converted into time in principle, high speed is sacrificed, which causes deterioration of linearity at thick dose rates. For this reason, energy for dose measurement targeting large dose rates;
This is not suitable as a silgi correction method. In addition, in this method, the stability of the pulse height greatly affects the stability of the measured value, so a high degree of stability is required for the detector and circuit system, and it is suitable for equipment that requires small size, light weight, and low power consumption. There are difficulties in its application.

Furthermore, if the object to be detected is a thin layer (0.1 to 0.6 thickness), it is not possible to completely match the pulse height and the incident photon energy, so the energy correction by the pulse height is sufficient. I can't afford anything.

Conventionally, as a simple energy correction method, a metal shield has been used in thermal fluorescence dosimeters, etc., but the energy correction range is also small, about 10 times the sensitivity of the reference energy, and as in the present invention, it is several hundred times more sensitive. There is no method to correct the double sensitivity ratio.

Furthermore, it was discovered that the energy characteristics of semiconductor detectors change significantly depending on the thickness of the sensing body, so it was necessary to develop a new shield.

Purpose of the Invention The present invention provides a simple radiation dosimeter that has linearity over a wide range from low dose rate to high dose rate and has uniform energy characteristics over a wide energy range from 30 keV to IMeV or more. The purpose is to

Structure of the Invention The radiation dosimeter of the present invention has one part of a semiconductor detector,
A metal shield made of lead alone or lead and other metals with an appropriate thickness is arranged in the 4π direction, and a resin layer with a thickness of at least 0.5 mm is further formed on the inner surface of the metal shield. By using the absorption edge of lead, incident photons are selectively transmitted with a boundary of 90 keV, and among the above energy characteristics, the region of 60 keV or more is improved. Provides holes and allows photons of 60 keV or less to pass through,
The energy characteristics below 60 keV are also improved, and the transmitted photons are measured using a pulse measurement method. This allows dose measurement to be performed with high accuracy.

DESCRIPTION OF EMBODIMENTS Figure M1 shows the basic configuration of the apparatus of the present invention. In the figure, 1 is a compound semiconductor detector, 2 is its electrode, 3 is a shield made of lead or a lead-tin alloy, and 4 is a resin layer. The 1-7 field 3 has holes 6 corresponding to the sensitivity per unit area, and is configured to mainly transmit photons of 60 keV or less and to obtain uniform energy characteristics as a whole. A voltage of approximately 6 to soV is applied to the compound semiconductor detector 1 from a power source 6. The pulse signal generated from the compound semiconductor detector 1 is transmitted to the load resistor 8.
The signal is amplified through an input FET (field effect transistor) 7 and an amplifier circuit 9. Then, this amplified pulse signal is counted by the pulse counting section 9, and the calculation/display section 1
0 is displayed as a dose value.

FIGS. 2(a), (b), and (C) show typical examples of shapes of metal shields. FIG. 2 (-) shows a spherical shell type, which allows consideration of directional characteristics in all directions with respect to j-, with the sensing body at the center. Figure 2 (b) is a hemispherical shell type, (C
) is a box-shaped metal shield. Considering that the shape of a small pocket dosimeter is excellent in terms of circuit mounting and is worn on the body, problems with the rear direction characteristics are unlikely to occur. Figure 2 (a), (b) (
The shape of the gap shown on each side in C) is an example of a practical one, and various shapes are possible.

The shield thickness is based on the reference photon energy characteristics and 70
It is determined by the energy characteristics of photons between keV and 200 keV. Lead is used as the shielding material, but
This has an absorption edge at 90 keV, so
This is because below this point, the sensitivity increases rapidly and it is possible to make the energy characteristics uniform. This effect is noticeable when lead alone is used, and there is a possibility that the error will be magnified by photons with a single energy around 100 keV. Therefore, when lead is 0.5 mm thick or more, it is necessary to use it together with tin. Sometimes used. In the energy characteristic correction method using the lead absorption edge in the present invention, the weight ratio of lead and tin in the shield thickness is 6°keV and 100keV.
Considering the absorption of lead and tin in V, it is sufficient that the lead content is 60% or more.

Figure 3 shows Cd with an effective atomic number of 6° as a compound semiconductor.
The energy characteristics are shown when a Te single crystal is used without a shield. It can be seen that the energy characteristics vary greatly depending on the thickness of the single crystal.

For detecting objects with a thickness of 0.1 to 0.6, which is the object of the present invention, if the standard energy is 1 ivfeV, there will be a sensitivity difference of about 100 times compared to 50 keV. In this region, there is a rapid change in sensitivity. Metal shields made of lead or the like have been used in some conventional thermal fluorescent dosimeters and GM tube-type point alarm meters, but in semiconductor dosimeters, the energy characteristics are significantly affected by the thickness of the sensing body. Because of the changing characteristics, it was not possible to follow conventional shield design concepts, and a completely new shield design technology was required.

Figure 4 shows the energy characteristics of a CdTe single crystal with a thickness of 0.3 mm provided with the lead shield. It is desirable that the characteristics of the dosimeter and the dosimeter be within ±3o coefficient with respect to the reference energy. This shows that for a CdTe detector with a throat thickness of 0.3, the optimal lead shield thickness is 1.0 to 1.4. Thinner shields provide flatter characteristics in low atomic number semiconductor materials. Ga As semiconductor with effective atomic number 32 0.3m
With respect to the thickness of m, good characteristics can be obtained with a thickness of 0.3 to 0.7 mm.

Figure 6 shows the energy characteristics when a CdTe single crystal with a thickness of 0.3 mm is used as the sensing object, and a lead shield with a thickness of 1.2 mm is used, with a gap of 1/100 per unit area in the shield. shows.

A low energy portion of 60 keV or less overlaps with that shown in FIG. 4, and excellent uniformity is obtained from around 30 keV to IMeV. For energy below 5okeV, there is an influence of the package, etc., but with these improvements, it is possible to achieve uniformity even for lower energies.

Resin inside the metal shield) is effective in making energy characteristics uniform in a high energy region of t\u, csookeV or higher. The thickness of this bright resin layer is determined by the range of electrons with energy equivalent to the target photon energy.

Effects of the Invention With the measuring device of the present invention as described above, 0.1 mR
It can exhibit uniform response characteristics to X-rays and γ-rays in a wide energy range from 30 ke'V or less to IMeV or more in a wide range of dose rates from low dose rates of 1000R/hour or less to thick dose rates of 1000R/hour or less. Because the dosimeter and dose rate meter can be manufactured using a semiconductor detector with a simple 7-wavelength structure, it is especially suitable for pocket dosimeters, pocket alarm dosimeters, or portable dose rate meters that require small size and light weight. They are used in batteries, etc., and contribute to the miniaturization and longer lifespan of batteries by saving power. Furthermore, since it is a measuring instrument that corrects energy using the absorption difference due to the metal shield,
Even if the circuit changes due to changes in power supply or temperature, if only the number of pulses corresponding to the incident radiation can be accurately measured, there will be no change in the energy characteristics, making it possible to maintain extremely stable measurements. . Therefore, there is a significant cost reduction effect due to stabilization of quality in mass production, reduction of variations in sensitivity between products, etc.

However, what is noteworthy is that the present invention allows semiconductor detectors, which have conventionally been expensive and unstable and have not been generally used as dosimetry devices, to be applied to highly accurate and inexpensive dosimeters. This type of measuring device, which was previously considered only as an auxiliary measuring device,
For example, pocket alarm meters can now replace dosimeters such as film badges and thermal fluorescent dosimeters. This makes the conventional dosimetry system more complete and greatly contributes to the safety management of radiation work.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of a radiation dose measuring device according to the present invention. Figure 2 (a); (b), (C
) are diagrams showing typical shapes of metal shields in this measuring instrument. Figure 3 shows the radiation detector and 1~
Figure 4 shows the photon energy characteristics when a CdTe single crystal with a thickness of 0.3+ nm is used as a radiation detector and the thickness of the detector is changed. Figure 5 shows the photon energy characteristics when the thickness is changed. A radiation detector using a CdTe single crystal with a thickness of 0.3 mm is used17, and the unit area ratio is 1 on the shield next to the lead 1.2. FIG. 3 is a diagram showing photon energy characteristics when a hole of /100 is formed. 1... Semiconductor detection section, 2... Electrode, 3
...Metal shield, 4...Resin layer, 5
...Vacancy, 6...Applied power, 7...
...Input FI! :T, 8...Load resistance, 9...
...Amplification circuit, 9...Pulse counting section, 1Q.
...Calculation/display section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure @ Figure 2 (α) Figure 3 Light, ) [Energy'- Figure 4 Light and Energy''-

Claims (3)

[Claims] (1) Radiation dose measurement characterized in that a semiconductor with an atomic number of 30 or more is used as a detection body, and the detection body made of the semiconductor is placed inside a hollow metal shield made of lead or having lead as a main component. vessel. (2) The thickness of the metal shield should be 0.3 to 1 when the semiconductor constituting the detector is a material with an atomic number of 30 to 46.
．． The radiation dosimeter according to claim 1, wherein the radiation dosimeter has a thickness of 1.0 to 2.0 mm when the material is made of a material with an atomic number of 46 to 6o. (3) A radiation dosimeter according to claim 1 or 2, characterized in that the metal shield has a hole having an area corresponding to the sensitivity with reference energy per unit area.