JPH0293393A - Radiation dose rate meter - Google Patents

Abstract

PURPOSE:To compensate energy by the same machinery by providing an averaging square circuit of an AC component while providing a square circuit to said circuit and correcting the energy characteristics of the sensitivity response of a detector on the basis of the square average value output data of said circuit. CONSTITUTION:The current signal of a radiation detector 1 is split into two systems A, B through a preamplifier 2. In the system A, a signal is sent to a function generator 4 through an A/D converter 3 and, on the basis of each value calculated by the function generator 4, a radiation dose rate D is operated by an operation circuit 8. The radiation dose rate of this operation result is displayed on a display part 9. If necessary, data is transmitted to a central operation room. By this method, energy can be compensated without taking external treatment for providing a shield body to the outside of the detector with respect to a radiation dose rate meter of current mode measurement at all.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a dose rate meter that measures the current value generated by incident γ-rays to determine the irradiation dose rate.
The present invention relates to a compensation means suitable for compensating a sensitivity response depending on linear energy to a predetermined value.

[Conventional technology]

The conventional gamma ray energy sensitivity response compensation a (hereinafter abbreviated as energy compensation) method, regardless of whether the ammeter J1 remote or the pulse A eye 1 remote, This was done by changing the type, thickness, etc. of the outer cylinder and the insulation material installed on the outside. This compensation method depends on the structure of the detector.

It is highly dependent on materials, etc., and it is extremely difficult to compensate for a predetermined response. “Photon energy dependence of electrodeposited surfaces of various shapes and materials” Health Physics, 22° 153-157 (1
987) describes an example of an attempt to calculate energy compensation for an ionization chamber, but according to this document, the sensitivity response changes significantly depending on the type, material, and shape of the gas filled in the FF11 chamber. Recognize. Generally, the material, thickness, etc. of the externally provided barrier are varied, and the optimum conditions are often selected experimentally. Since the sensitivity response of a detector differs depending on the nine types of detector structures, conditions outside the detector, etc., it is necessary to select optimal conditions for each type of detector.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into account the provision of an easier energy compensation method based on the basic principle of radiation detection, and requires a large amount of materials, time, and effort for energy compensation. There was a problem. Furthermore, in the conventional technology, one detector signal is set in pulse measurement mode in the low dose rate region and current measurement mode in the high dose rate region.
It was impossible to widen the measurement range. This is because the pulse mode and the current mode have completely different energy responses, so one detector cannot compensate for the energy in both measurement modes.

The purpose of the present invention is to provide a new means to replace the conventional method of utilizing radiation attenuation of shielding materials and structural materials for the energy compensation method of the current measurement mode, and to provide a new means for the energy compensation method of the current measurement mode, and to provide a new means for the energy compensation method of the current measurement mode. The goal is to enable energy compensation.

[Means to solve the problem]

The above purpose is based on the detection signal itself of current mode measurement.
By extracting the energy component of the gamma rays incident on the detector, energy compensation can be achieved using a signal processing circuit provided after the detector.

FIG. 1 shows a block diagram of the technical means of the present invention. A detection signal (current signal) from a radiation detector 1 is branched into two signal processing systems via a preamplifier 2. One of the channels (2) is sent to a function generator 4 via an A/D (analog/digital converter) 3. The other system is the RMS value (root mean square value) extraction circuit 5 of the output signal of the preamplifier 2 and the A/D
6 to the function generator 4. In these two systems of signal processing, the former is the DC component of the radiation detection signal (,1! current value)
The latter extracts the RMS value included in the AC component of the radiation detection signal. In addition, the physical meaning of these two systems of signal processing is that the former extracts a value that depends on the counting rate of radiation, and the latter extracts the energy component of the radiation incident on the detector and a value that depends on the counting rate. This means that The arithmetic circuit 8 determines the energy-compensated irradiation dose rate based on the signals from both systems. The irradiation dose rate is externally displayed on the display 9 in R/h units or Sv/h units. If energy compensation becomes possible with these two signal processing circuits, there will be no need for energy compensation using an external barrier or the like as in the past.

[Effect]

Hereinafter, the basic operations of current mode measurement and pulse mode measurement will be explained, and how the energy compensation method of the present invention works will be explained.

FIG. 2 shows the basic shape of a pulse generated by incident radiation. The rise time (indicated by a in FIG. 2) of this pulse is extremely fast at several n5 ec, and the trailing edge (referred to as tail) is gentle at several m5 ec.

The waveform in FIG. 2 represents the shape when one radiation is incident, and as the number of incident radiation increases, the tails of each pulse overlap, resulting in the waveform in FIG. 3. In this state, the DC component of the signal (indicated by α in Figure 3) increases,
The signal is the base of the DC component α plus the fluctuation of the rising edge of the incident radiation. Generally, each pulse in Figure 2 has a small current value (measuring the current value is difficult), and the radiation dose is determined by pulse measurement. Pulse measurement is a method of counting pulses that exceed a certain peak value. Identification of the constant peak value is performed using a discriminator. Moreover, this peak value directly depends on the energy of the incident radiation. Under the high count rate condition shown in FIG. 3, it becomes impossible to identify individual pulses, making pulse measurement impossible.

Typically this condition is 3 x 103-104 pulses/sec. Furthermore, as the counting rate increases, the DC component of the 'fS3 diagram becomes larger, and it becomes possible to determine the radiation dose rate from the current measurement value. This is the "ammeter" remote.

Now, to explain the energy compensation method of the present invention, the output signal of the preamplifier 2 in a state where the number of incident radiations is extremely large and can be measured in the current mode is as shown in FIG. Third
The pulse interval in the figure becomes even narrower, resulting in an output signal in which the alternating current component AC is superimposed like noise on the direct current component α. This alternating current component AC is a superposition of the rising (peak value) components of the pulses explained in FIGS. 2 and 3. That is, this alternating current component AC is based on the energy component of each incident radiation. Although it is difficult to identify individual peak values from this alternating current component AC, it can be said that the average peak value per unit time depends on the RMS value. Letting this RMS value be β, it can be expressed by the following equation.

T: AC component of unit time 5sffi flow mode output signal This RMS value β
is an important parameter for extracting the average energy of radiation incident on the detector 1. By clarifying the relationship between this RMS value β and the number of incident radiations (irradiation dose rate=current value α) and the average energy, energy compensation of the sensitivity response can be achieved. First, regarding the relationship between the in rate (current value α) and the RMS value β, the RMS value β increases depending on the radiation dose rate, and the ratio is expressed by the formula (1
), it depends on r-. FIG. 5 shows the relationship when the energy of incident radiation is constant. In order to achieve energy compensation, the dependence of the RMS value β on the dose rate α is normalized. θ(α) shown in FIG. 5 is a coefficient for correcting dose rate dependence. In this example, the standard is 103 nA, which allows current mode measurement. A specific correction method is to obtain θ(α) as a function of the current value α measured in current mode, and correct the RMS value β.

Next, the relationship between the energy E of incident radiation and the RMS value will be explained. FIG. 6 shows the relationship between E and RMS value when the dose rate α is kept constant. In this figure, △ and O marks are experimental values. This figure also shows the energy sensitivity response in current mode. From these relationships, it is possible to determine the relationship between the RMS value β(E) using the radiation incident energy E as a parameter and the energy compensation coefficient φ(E) that makes the sensitivity response a predetermined value. FIG. 7 shows the relationship between the RMS value β(E) and the energy compensation coefficient φ(E).

As described above, energy compensation can be achieved using the current mode measurement value α and the RMS value β. Figures 6 and 7 are examples in which energy compensation is compensated for sensitivity response in units of mR/h.
inter national CommiCommls
sionRadiolo Units and mea
The dose equivalent evaluation (S
energy compensation (in volts) can also be easily achieved. Specifically, we express the forward mode energy sensitivity response in Fig. 6 as a response in units of Sv, and calculate the energy compensation coefficient φ(E
) can be created by creating a new relationship.

The energy-compensated irradiation dose rate D (mR/h) is determined by the following formula.

D=α・φ(E)・F...(2)φ
(E)=φ(β・θ(α)) φ(E): Energy compensation coefficient F: Irradiation dose rate conversion constant The above is the basic operation content of the present invention.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

The ffi signal from the radiation detector 1 is branched into two systems (2) via a preamplifier 2. ■In the system, A/D converter 3
A signal is sent to the function generator 4 via the function generator 4.

Here, the correction value of the DC component α of the current signal and the RMS value β,
Find θ(α). ■In the system, RMS value extraction circuit 5 and A
Determine the RMS value β of the current signal via the /D converter 6,
φ(E) is determined by the function generator 4 at the subsequent stage. Function generator 4
The calculation circuit 8 calculates the irradiation dose rate based on each value obtained. The irradiation dose rate as a result of this calculation is displayed on the display section 9. Information will also be transmitted to the central control room, etc., as necessary.

According to the present invention, for a current mode measurement irradiation dose rate meter,
Energy compensation can be easily achieved without any external processing such as providing a shield body outside the detector. The above-mentioned function generator 4° arithmetic circuit 8 can be easily configured with a single-chip computer system,
It can be applied to energy compensation for any current mode measurement. This revolutionizes the conventional energy compensation method and allows energy compensation to be achieved with the same equipment regardless of the type of detector. sex.

This has the great effect of reducing costs by more than 50% in terms of inspection man-hours, etc.

Next, a modification of the present invention will be described. FIG. 8 shows a comparison of the measurement ranges of current mode measurement and pulse mode 31 measurement of the semiconductor detector. In current mode measurement, the lower limit of the range is determined by the leakage current of the detector. In pulse mode measurement, the upper limit is determined by the pulse resolution time of the measurement circuit. By continuously measuring the measurement range from low-level irradiation doses to high-level irradiation doses using pulse mode measurement and current mode measurement, it is possible to increase the range by more than four orders of magnitude compared to conventional irradiation dose rate meters.

However, the reason why this wide range could not be achieved using conventional techniques is that the energy responses of current mode measurement and pulse mode measurement are completely different.

FIG. 9 shows energy characteristics in pulse mode and current mode. This figure shows a comparison of the energy characteristics of a detector that compensates energy within ±25% for pulse mode measurements by simply performing current mode measurements.Compared to pulse mode measurements, current mode measurements are A large difference occurs on the low energy side, making it impossible to maintain the accuracy (±25%) required for energy compensation. This is because in pulse mode, a discriminator is provided in the measurement circuit, so radiation below this discriminatory level (energy) does not contribute to detection sensitivity, and in current mode, radiation in all energy ranges affects detection sensitivity. By contributing. By using the present invention, it is easily possible to compensate the current mode sensitivity response to be identical to the pulse mode sensitivity response. FIG. 10 shows a modified example of widening the range using one detector using the present invention. The detector 1 is provided with a barrier material 10 for energy compensation for pulse mode measurement. For low-level irradiation dose rates, a switch 11 provided after the preamplifier 2 connects to the pulse mode measurement system ◎. The pulse measurement system is a linear amplifier 12. Discriminator 13. Counter 14. A signal is sent to the dose rate display section 9 via the switch 15 to display the irradiation dose rate.

The limiter 16 switches the switches 11 and 15 based on the output value of the counter 14. The irradiation dose rate becomes thick (becomes), and the output value of the counter 14 reaches the upper limit of pulse measurement (
For example, if 5X103CPS) is reached, limiter-1
6 is a current mode measurement system (■,
■ side).

In current mode system, RMS value extractor5. A/D converter 3,
6. Function occurrence @4. The arithmetic circuit 8 is used to compensate the energy of the current mode plan using the technical means of the present invention. Through this process, the irradiation and tl rate output to the display unit 9 via the switch 15 can be made the same as the energy characteristics of pulse mode measurement. This makes it possible to widen the measurement range from low irradiation dose rate to high irradiation dose rate.

This makes it possible to expand the conventional dynamic range of 3 to 4 digits to more than 8 digits, and it is possible to exhibit performance that could not be achieved with conventional irradiation B dose rate meters.

In addition, as another modification, R M used in the present invention
A similar function can be achieved by using an AC component averaging circuit instead of the S value extractor. However, this method slightly degrades compensation accuracy.

Similarly, in place of the RMS value extractor, it is possible to use the integral value or self-correlation value of the power spectrum.

〔Effect of the invention〕

According to the present invention, in the current mode radiometer subsystem,
It becomes possible to perform energy compensation using a signal processing circuit after preamplification, and it also becomes possible to perform energy compensation for various types of detectors with different energy characteristics using a single type of signal processing circuit. This eliminates the need for energy compensation work for different types of detectors, which was conventionally performed, and can significantly reduce the mass production of the measurement system and the inspection process, achieving a cost reduction of more than 50%.

Furthermore, the measurement dynamic range of one detector can be significantly improved from the conventional four digits to eight digits.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a single pulse shape for radiation measurement, FIG. 3 is a pulse shape in a high count rate state, and FIG. 4 is a signal of the current mode meter 8111, Figure 5 shows the relationship between the RMS value and the irradiation vA rate (current value), Figure 6 shows the energy of incident gamma rays, the RMS value, and the energy characteristics of current mode measurement, and Figure 7 shows the RMS value converted into energy and energy compensation. The relationship between the coefficients, Figure 8 shows the relationship between the irradiation dose rate, the current value of the current mode meter, and the counting rate of the pulse mode measurement, Figure 9 shows the energy characteristics, and Figure 10 shows a modification of the present invention. be. 1... Detector, 2... @ stationary amplifier, 3... A/D converter, 4... Function generator, 5... RMS value extractor,
6... A/D converter, 8... Arithmetic unit, 9... Display section, 1
0...Shiyahei body, 11.15...Switcher, 12.
・Linear amplifier, 13・Discriminator, 14・
...Counter, 16...Limiter.

Claims (1)

[Claims] 1. In an irradiation dose rate meter that detects a DC component of a current generated by the incidence of radiation, an AC component mean square circuit is provided, and the root mean square value output information of the circuit is provided. An irradiation dose rate meter characterized in that the energy characteristic of the sensitivity response of the detector is corrected based on. 2. The dosimeter according to claim 1, wherein an irradiation dose rate meter is provided with an AC component averaging circuit, and corrects the energy characteristic of the sensitivity response of the detector based on the output information of the circuit.