JPH058795B2 - - Google Patents

Description

Detailed Description of the Invention A. Purpose of the Invention Industrial Field of Application The present invention relates to a gamma ray irradiation dose rate measurement/recording device, and more specifically, to a gamma ray irradiation dose rate measurement/recording device, which measures radiation levels ranging from natural radiation levels to high radiation levels during a nuclear reactor accident, etc. inside and outside a nuclear facility. The present invention relates to a portable wide-range gamma-ray irradiation dose rate measuring and recording device that can automatically record measured values of irradiation dose rates over a wide range of levels up to 2000 yen, and is small, lightweight, and portable.

Conventional technology In the conventional technology, the measurement of irradiation dose rate over a wide range of levels using a portable gamma ray irradiation dose rate measuring device is carried out using multiple measuring devices depending on the radiation level, and furthermore, these measurement devices are Since the measuring device is large and requires a battery power source or an external power source, there are problems with speed and portability when carrying out mobile measurements and recording.

Problems to be Solved by the Invention The present invention solves the problem of the wide range of γ in the prior art described above.
This was done to solve the problem that the radiation dose rate cannot be measured with a single measuring device and that it is difficult to carry when carrying out measurements on the go.

The object of the present invention is to provide a gamma ray detector with a lead shield of a special structure, and to generate pulses proportional to the irradiation dose of incident gamma rays from the detector at low dose rates, depending on the level of the irradiation dose rate in the measurement field. By automatically selecting measurement using signals and measurement using current signals using the current measurement method at high dose rates, it is possible to measure a wide range of irradiation dose rates with a single measurement device, and the degree of integration has also been increased. It is an object of the present invention to provide a portable wide-range gamma ray irradiation dose rate measurement/recording device whose entire device is miniaturized by using small, lightweight, and low power consumption parts.

(b) Means for solving the structural problems of the invention Gamma ray irradiation dose rate is measured using a conventional 2"φ x 2" thallium activated sodium iodide NaI (Tl) scintillation detector at high irradiation dose rate. When the current measurement method is used in this region, this detector exhibits an overresponse in sensitivity in the region where the energy of the gamma rays measured is approximately 200 KeV or less. Therefore, in order to improve the energy characteristics in the low energy region, the present invention adds a separately developed lead shield with a special structure to the detector to improve the characteristics and systemize it. This configuration reduces the gamma ray energy.
A measurement accuracy of ±10% of the irradiation dose rate was obtained over a wide range from 80KeV to 3MeV, and good directional characteristics were obtained. Also, other shapes of NaI (Tl) and plastic luncillators can be used in the apparatus of the present invention to improve the energy and directional characteristics by means of shields, etc.

Embodiment FIG. 1 is a block diagram showing an embodiment of the portable wide range gamma ray irradiation dose rate measuring and recording device of the present invention. When measuring in the low irradiation dose rate range from natural radiation levels to less than approximately 5 mR/h using the lead-shielded detector 1 using the pulse measurement method, the pulse signal from the detector 1 is converted to gamma ray energy by the preamplifier 2. It is converted into a pulse signal with a proportional wave height. After waveform shaping, this pulse signal is amplified by the linear amplifier 3 so that the pulse height corresponding to 3 MeV of γ-ray energy becomes 6V. This output signal of the linear amplifier 3 is subjected to energy compensation by a pulse height discriminator bias modulation circuit 4 to flatten its energy characteristics, and is converted into a pulse train signal proportional to the irradiation dose rate. This measurement method is called the DBM measurement method.

In addition, when measuring in a high irradiation dose rate range of 5 mR/h or more using the current measurement method, the anode current output signal from the detector 1 is converted into a voltage signal, and then the voltage signal is converted into a frequency by the V/F converter 5. , a pulse train signal proportional to the irradiation dose rate is obtained.

In order to switch between these two measurement methods according to the level of the irradiation dose rate at the measurement field, first, the count value of the output signal of the DBM circuit is converted into the irradiation dose rate.
This irradiation dose rate is compared with the preset level from the level switching unit 6 for the DBM measurement method and the current measurement method in the comparison section 12, and if the converted irradiation dose rate is higher than this level, that is, the high irradiation dose. If it is in the rate range, a level switching signal is output to the calculation section 7. Further, when the converted irradiation dose rate is smaller than the switching level, that is, in the low irradiation dose rate region, the signal obtained by the DBM measurement method is outputted to the calculation unit 7 via the gate circuit 8.
An arbitrary value can be set as the switching level. Arithmetic unit 7
calculates the irradiation dose rate from the obtained counting rate and preset calibration constants and correction coefficients. This calculation result is displayed on the liquid crystal display section 9 at predetermined time intervals, and at the same time, the measurement time and the average irradiation dose rate within the measurement time are automatically printed on the stored digital printer 10.
recorded. Further, the measurement results in the low irradiation dose rate region are displayed on the rate meter 11 and can also be output to the external recorder 13.

By using components with a high degree of integration and low power consumption in the aforementioned circuit, we have succeeded in reducing the size and weight of the main body of the device. There are two power sources: built-in dry cell batteries and commercial 100V. The detector is attached to the main body for portability, but it can be removed from the main body for continuous measurement. Detector with special shield (2″φ) used in the device of the present invention
×2″ NaI (Tl)), by changing the G(E) function of the energy characteristic flattening circuit, that is, by replacing the ROMIC, 3″φ
Detectors, plastic scintillation detectors, etc. (improvement of energy characteristics can be achieved with special shielding bodies depending on the shape, etc.) can be used. Measurement accuracy can also be further improved by adding a temperature compensation circuit. In addition, if it is difficult to supply AC100V, it is possible to measure for a longer time by using a lead-acid battery, etc., and it can be used as a mobile monitoring post in emergencies or as an area monitor inside and outside the controlled area.

C. Effects of the invention The effects of the present invention are as follows:
Capable of measuring and recording irradiation dose rate over a wide range of levels of 10R/h, total weight 10Kg
It is easy to transport within 300 meters and can be powered by built-in dry batteries or a commercial power source.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the portable wide range gamma ray irradiation dose rate measuring and recording device of the present invention. 1...Detector, 2...Preamplifier, 3...Linear amplifier, 4...Bias modulation circuit, 5...V/
F converter, 6...Level switching section, 7...Calculating section, 8...Gate circuit, 9...Display section, 10...
Printer, 11... Rate meter, 12... Comparison section, 13... External recorder.

Claims (1)

[Claims] 1. A gamma-ray irradiation dose rate measuring and recording device that can automatically and continuously measure and record gamma-ray irradiation dose rates from natural radiation levels to high radiation levels using a thallium-activated sodium iodide scintillator as a detector. , a detector with a lead shield that detects gamma rays and outputs a pulse signal in a low irradiation dose rate region and outputs a current signal in a high irradiation dose rate region, and a detector that responds to the pulse signal from the detector. a low irradiation dose rate counter that outputs a pulse train signal proportional to the irradiation dose rate; and a low irradiation dose rate counter that converts the anode current signal of the detector into a voltage signal and then into a frequency signal, and outputs a pulse train signal proportional to the irradiation dose rate. A counter switching section that automatically selects the high irradiation dose rate counter and the low irradiation dose rate counter and high irradiation dose rate counter according to the dose rate level of irradiated gamma rays and switches the connection to the calculation section. a calculation section that calculates the gamma ray irradiation dose rate from the output signal of the counting section and preset calibration constants and correction coefficients; and a recorder that records the calculated gamma ray irradiation dose rate. A portable wide range γ featuring
Radiation dose rate measurement and recording device. 2. In claim 1, the low irradiation dose rate counter converts the output signal from the detector into γ
A preamplifier that converts the pulse signal into a pulse signal with a wave height proportional to linear energy, a linear amplifier that amplifies the output pulse signal from the preamplifier, and performs energy compensation to flatten the energy characteristics of the output pulse signal from the linear amplifier. An apparatus characterized by comprising a pulse height discriminator bias modulation circuit that converts the pulse train signal into a pulse train signal proportional to the irradiation dose rate. 3. The apparatus according to claim 1, wherein the high irradiation dose rate counting section comprises a voltage-frequency converter. 4. In claim 1, the counting section switching section includes a gate circuit, a comparison section that compares a reference switching level of 5 mR/h and an irradiation gamma-ray dose rate level, and an output from the comparison section. Accordingly, when the γ-ray irradiation dose rate is less than 5 mR/h, the low irradiation dose rate counter is connected to the calculation unit, and when the γ-ray irradiation dose rate is 5 mR/h or more, the high irradiation dose rate counter is connected to the calculation unit. 1. A device comprising: a level switching unit that operates a gate circuit; 5. In claim 1, a digital printer that prints and records the calculation results of the calculation unit, a liquid crystal display unit that visually displays the calculation results, and a rate that displays the output signal of the bias modulation circuit. A device characterized by comprising a meter.