JP7438893B2 - Radiation detection system and radiation detection method - Google Patents

Description

Embodiments of the present invention relate to radiation detection technology.

Conventionally, with an ionization chamber survey meter, after the first measurement, a cap is attached to the tip of the probe to block the incidence of beta rays, and only gamma rays are measured. I am trying to get the value of the line. In other words, in order to obtain the respective values of β-rays and γ-rays, it is necessary to perform two measurements at the same location, which not only complicates the work procedure, but also requires the processing to obtain the difference between the first and second measurements. Therefore, the measurement error increases. Therefore, there is something called a phoswitch detector. This Phoswitch detector is a detector that uses different penetrating powers depending on the type of radiation. For example, two layers of scintillators are arranged, and the type of radiation can be identified based on the value detected in the first layer and the value detected simultaneously in the first and second layers. Here, a technique is known in which the type of radiation is determined by comparing the integration results of pulse signals. Furthermore, a technique is known that uses a three-layer scintillator to determine α-rays, β-rays, and γ-rays.

Patent No. 5027124 Japanese Patent Application Publication No. 2012-242369

In conventional technology, different types of scintillators measure different radiations, so the magnitude of the peak value differs for each scintillator. By evaluating the decay time of pulse signals originating from these scintillators, we identify the scintillators to which radiation has reacted. However, data may be incorrectly determined due to errors caused by differences in the magnitude of the pulse signals.

The embodiments of the present invention have been made in consideration of such circumstances, and an object thereof is to provide a radiation detection technique that can improve the accuracy of determining the type of radiation.

A radiation detection system according to an embodiment of the present invention includes a detection unit that outputs a pulse signal having different characteristics depending on the type of incident radiation, and a signal amplification unit that amplifies the pulse signal and shapes the waveform of the pulse signal. a waveform data acquisition section that acquires the waveform shaped by the signal amplification section; a time change calculation section that calculates the amount of change over time of the waveform acquired by the waveform data acquisition section; and at least the time change calculation section. a data determination unit that determines the type of radiation based on the data acquired by the unit, and the time change calculation unit calculates the amount of time change using a filter that calculates a change in the time course of the waveform. seek .

Embodiments of the present invention provide radiation detection technology that can improve the accuracy of determining the type of radiation.

FIG. 1 is a configuration diagram showing a radiation detection system according to a first embodiment. A graph showing differences in pulse signal waveforms due to differences in scintillator fluorescence decay time. 5 is a graph showing an example of a waveform acquired by a waveform data acquisition unit and an output value of a time change calculation unit. 7 is a graph showing another example of the waveform acquired by the waveform data acquisition unit and the output value of the time change calculation unit. 7 is a graph showing an example of a difference in the output mode of a time change calculation unit due to a difference in fluorescence decay time of a scintillator. 7 is a graph showing another example of a difference in the output mode of a time change calculation unit due to a difference in fluorescence decay time of a scintillator. Flowchart showing radiation detection processing. FIG. 2 is a configuration diagram showing a radiation detection system according to a second embodiment. FIG. 7 is a configuration diagram showing a radiation detection system according to a third embodiment.

(First embodiment)
Hereinafter, embodiments of a radiation detection system and a radiation detection method will be described in detail with reference to the drawings. First, a radiation detection system according to a first embodiment will be described using FIGS. 1 to 7.

Reference numeral 1 in FIG. 1 is a radiation detection system according to the first embodiment. This radiation detection system 1 detects ionizing radiation such as α-rays, β-rays, γ-rays, and X-rays. For example, a worker who performs a detection work detects radiation by holding the detection unit 2 as a probe and bringing the detection unit 2 close to a predetermined radiation source. In particular, the radiation detection system 1 is used to measure doses in the working environment and work place of a nuclear power plant where a severe accident has occurred.

When an event occurs that damages nuclear fuel, nuclides that emit alpha and beta rays are generated. At nuclear power plants where such severe accidents have occurred, areas, equipment, and parts that have been contaminated with or exposed to melted nuclear fuel material or fission products are subject to radiation control.

For example, it is necessary to manage alpha rays emitted from nuclear fuel materials such as uranium, plutonium, and americium. Furthermore, regarding fission products, it is necessary to manage high-energy and high-intensity β-rays emitted from Sr-90/Y-90.

Since the range of alpha rays in the air is about 4 cm, it is necessary to prevent internal exposure caused by the attachment, expansion, and diffusion of contaminants in the air, rather than external exposure to alpha rays. Therefore, it is important to monitor the density of surface contamination and the concentration of pollutants in the air.

On the other hand, the maximum range of β-rays emitted from nuclides in the air is about 1 meter, so it is important to prevent not only internal exposure but also external exposure. In particular, the equivalent dose limit to the crystalline lens of a radiation worker's eye is set at 50 mSv per year and 100 mSv over 5 years. Therefore, it is necessary to measure and understand the dose equivalent rate of β-rays in the working environment and workplace. Therefore, the radiation detection system 1 of the first embodiment is used.

The radiation detection system 1 includes a detection section 2, a signal amplification section 3, a waveform data acquisition section 4, a time change calculation section 5, and a data determination section 6.

The detection unit 2 outputs a pulse signal having different characteristics depending on the type of radiation incident thereon.

The signal amplification section 3 amplifies the pulse signal output from the detection section 2 and shapes the waveform of this pulse signal. This signal amplifying section 3 is a so-called amplifier, and amplifies the pulse signal output from the detecting section 2 to a measurable level. For example, a charge amplifier method or a current amplifier method can be used. Note that the signal amplifying section 3 requires a frequency response that can amplify a waveform that depends on the attenuation process of the pulse signal output from the detecting section 2.

The waveform data acquisition section 4 acquires the waveform of the pulse signal amplified and shaped by the signal amplification section 3. Note that the waveform data acquisition section 4 is capable of measuring time-based peak value information regarding the waveform of the pulse signal.

The time change calculation section 5 calculates the amount of time change of the waveform acquired by the waveform data acquisition section 4. For example, the time change calculation unit 5 calculates a time change in the time transition of the peak value measured by the waveform data acquisition unit 4. The temporal change calculation unit 5 only needs to be capable of at least numerical calculation processing.

Further, the time change calculation unit 5 calculates the amount of time change using a filter that calculates a change in the time course of the waveform. In this way, it is possible to calculate the change in the time course of the waveform of the pulse signal.

The time change calculation unit 5 uses a method of obtaining an approximate curve of an arbitrary function for the latest plurality of data and differentiating it, a method of calculating a simple amount of change per time, a method of Savitzky-Golay (SG) method, a flattening method, etc. Arithmetic processing can be performed using a differential method, a moving average method, a weighted moving average method, etc. For example, a differential filter, an SG filter, or the like can be used as a filter used by the time change calculating section 5. Note that the SG filter is also called a digital smoothing polynomial filter, a least squares smoothing filter, or the like. In the following description, a mode using an SG filter will be exemplified.

The data determination unit 6 determines the type of radiation based on the data acquired by the waveform data acquisition unit 4 and the data acquired by the time change calculation unit 5. Note that the data determination section 6 can also determine the type of radiation based only on the data acquired by the temporal change calculation section 5.

The data determination unit 6 identifies the type of data by identifying characteristic values from the waveform of the pulse signal or the waveform output by the time change calculation unit 5. The data determination unit 6 may be used as long as it is capable of evaluating data by at least numerical calculations or comparison calculations.

The data determination section 6 includes a comparison evaluation section 7 , an occurrence location identification section 8 , and an energy information acquisition section 9 . These are realized by the CPU executing programs stored in the memory or HDD.

At least the data determination unit 6 of this embodiment has hardware resources such as a CPU, ROM, RAM, and HDD, and when the CPU executes various programs, information processing by software is realized using the hardware resources. It consists of computers. Furthermore, the radiation detection method of this embodiment is realized by causing a computer to execute various programs.

The detection unit 2 of the first embodiment includes a photodetector 10, a first scintillator 11, a second scintillator 12, a third scintillator 13, a shield 14, and a housing 15 that accommodates these.

The scintillators 11, 12, and 13 are plate-shaped members. These scintillators 11, 12, and 13 emit light upon interaction with radiation. Further, the photodetector 10 detects light emission from the scintillators 11, 12, and 13. The photodetector 10 outputs a pulse signal in response to detection of light emission. In this way, the scintillators 11, 12, 13 and the photodetector 10 can constitute the detection section 2 that detects radiation.

Note that the detection unit 2 uses a unit whose pulse signals have different attenuation times so that the waveform of the pulse signal generated by the radiation changes.

As the photodetector 10, a photomultiplier tube can be used, which has high light sensitivity and a wide variety of aperture options. Moreover, various photodetection devices such as a photodiode, an avalanche photodiode, a silicon photomultiplier (SiPMT), and a multi-pixel photon counter (MPPC) can also be used for the photodetector 10. Any device may be used as the photodetector 10 as long as the emission wavelengths of the scintillators 11, 12, and 13 match.

A plurality of scintillators 11, 12, and 13 are stacked on each other inside the casing 15. The plurality of scintillators 11, 12, 13 are of different types. The mode of light emission differs depending on the type of these scintillators 11, 12, and 13, and the characteristics of the pulse signal output by the photodetector 10 also differ. In this way, it is possible to configure the detection section 2 that outputs pulse signals with different characteristics depending on the type of radiation.

The housing 15 is a cylindrical member, and has an opening 16 formed at one end thereof. This opening 16 is closed with a thin film 17. This thin film 17 has radiation transmittance, as well as light blocking and electromagnetic shielding properties. Radiation enters through this opening 16 and hits the scintillators 11, 12, and 13.

Among the plurality of scintillators 11 , 12 , 13 stacked on each other, the first scintillator 11 is provided at a position closest to the opening 16 of the housing 15 . The second scintillator 12 is provided inside the first scintillator 11. The third scintillator 13 is provided inside the second scintillator 12. In this way, since the penetration distance differs depending on the type of radiation, it is possible to configure the detection unit 2 that outputs a pulse signal with different characteristics depending on the type of radiation.

In the first embodiment, the first scintillator 11 is formed thinner than the second scintillator 12. The second scintillator 12 is formed thinner than the third scintillator 13. Furthermore, the third scintillator 13 is formed thicker than the combined thickness of the first scintillator 11 and the second scintillator 12.

The shield 14 is a plate-shaped member. This shield 14 is provided between the second scintillator 12 and the third scintillator 13. The shield 14 blocks some types of radiation while transmitting light. The shielding body 14 is made of a material that is transparent to the emission wavelengths of the scintillators 11 and 12. For example, it is made of glass, acrylic, etc. Note that the shield 14 is formed to be thicker than the combined thickness of the first scintillator 11 and the second scintillator 12.

The housing 15 blocks some types of radiation while transmitting gamma rays. For example, the housing 15 blocks radiation having low penetrating power such as alpha rays and beta rays. These radiations with low penetrating power are incident from an incident direction 18 facing the aperture 16 . That is, the incidence of α rays and β rays is limited to the opening 16 of the housing 15. On the other hand, γ-rays with high penetrating power are incident not only from the opening 16 but also from an incident direction 19 on the side of the housing 15 . In this way, α-rays and β-rays with low penetrating power can be easily distinguished from γ-rays with high penetrating power, so it is possible to particularly improve the detection accuracy of γ-rays.

Note that the housing 15 may be made of any material as long as it can provide a shielding effect against some types of radiation. Furthermore, the housing 15 may also serve as an electromagnetic shield.

Although the reaction between γ rays and certain substances is different from that of β rays, the scattered electrons generated when γ rays react with substances are physically the same as β rays. In order to suppress the influence of γ rays, it is preferable to make the first scintillator 11 and the second scintillator 12 thin. However, if the first scintillator 11 and the second scintillator 12 are made thinner, the sensitivity to γ-rays decreases, and the sensitivity to γ-rays incident from the incident direction 19 on the side of the housing 15 changes. Therefore, in the first embodiment, the third scintillator 13 is provided for detecting gamma rays. Furthermore, a shield 14 is also provided.

For example, the maximum energy of charged particles such as β rays to be detected by the first scintillator 11 and the second scintillator 12 is assumed. Then, the shield 14 is provided which is thicker than the maximum range of these charged particles. In this way, even if the β rays pass through the second scintillator 12, they will not reach the third scintillator 13. Therefore, the third scintillator 13 only emits light based on γ-rays.

In the detection unit 2 of the first embodiment, the second scintillator 12 can be made thin as long as it falls within the range of conditions that allow energy from the β rays to be detected. In this way, the gamma rays can be detected by the third scintillator 13 while reducing the event (probability) of the gamma rays reacting with the first scintillator 11 and the second scintillator 12.

The radiation detection system 1 can detect at least three types of radiation: β-rays with a first energy, β-rays with a second energy higher than the first energy, and γ-rays. In this radiation detection system 1, it is possible to discriminate which type of radiation has been detected in a single detection operation. In the following description, the first energy β-ray will be referred to as a low-energy β-ray. The second energy β-rays are referred to as high-energy β-rays.

Next, a description will be given including the effects passively produced by the operation of the radiation detection system 1.

For example, in the case of α rays or β rays, which are charged particles, their penetrating power is low and they are blocked by the casing 15, so that they enter only through the opening 16 of the casing 15. Then, the α rays or β rays incident through the aperture 16 hit the scintillators 11 and 12.

When α-rays or β-rays are incident on the inside of the housing 15, energy is given to the first scintillator 11 closest to the aperture 16 among the plurality of scintillators 11, 12, 13, and light emission occurs. Based on this light emission, the photodetector 10 generates a pulse signal.

When the penetrating power of the incident radiation is low, all the energy is given to the first scintillator 11 and the radiation stops. However, when the penetrating power of the radiation is high, energy is also given to the second scintillator 12 to generate light emission, and the photodetector 10 generates a pulse signal. In other words, a pulse signal caused by the first scintillator 11 is always generated.

On the other hand, in the case of light, that is, gamma rays or X-rays, which are a type of electromagnetic waves, they do not necessarily react with the housing 15 or the first scintillator 11, but depend on the energy thereof, the material of the first scintillator 11, etc. React with a predetermined probability. Therefore, a pulse signal based on the light emission of the first scintillator 11 may not be generated.

Here, by setting the material and size of the first scintillator 11 to those that are difficult for gamma rays to react with, radiation with weak penetrating power (alpha rays, beta rays) and radiation with high penetrating power (gamma rays, lines) can be distinguished.

For example, when the purpose is to distinguish between β rays and γ rays, a plastic scintillator with a low density is used as the first scintillator 11. Furthermore, the thickness of the first scintillator 11 is, for example, about 0.3 mm. Furthermore, a plastic scintillator with low density is also used for the third scintillator 13. Further, as a material for the second scintillator 12, calcium fluoride (CaF2 (Eu)) to which europium is added is used. Note that the third scintillator 13 has a longer fluorescence decay time than the first scintillator 11.

Here, the fluorescence decay time of the scintillators 11, 12, and 13 is a constant representing the time it takes for the initial light intensity of the fluorescence pulse (light emission from the scintillators 11, 12, and 13) to decay to 1/e. Note that the light intensity of the fluorescence pulse is at its maximum value at the moment it is generated (initial value I(0)). Here, the initial light intensity is the value of the light intensity at the moment when this occurs. Since a fluorescence pulse is generated instantaneously and attenuates (attenuates) exponentially, the attenuated light intensity I(t) at time t is calculated using the initial value I(0) at time t=0. It can be expressed in the form I(t)=I(0)·exp(−t/τ). This τ is the fluorescence decay time and is also the time constant of the exponential decay response.

The low energy β rays of about 250 keV or less stop at the first scintillator 11 . When this low energy β ray is incident, a pulse signal corresponding to the fluorescence decay time of the first scintillator 11 is output.

High-energy β-rays exceeding 250 keV pass through the first scintillator 11 and reach the second scintillator 12. When this high-energy β ray is incident, a pulse signal corresponding to the fluorescence decay time of the first scintillator 11 and the second scintillator 12 is output.

Furthermore, the γ rays, which have higher energy than the high energy β rays, pass through the first scintillator 11 and the second scintillator 12 and reach the third scintillator 13. Furthermore, the light is also incident from the incident direction 19 on the side of the casing 15 and reaches the third scintillator 13 . When this γ ray is incident, a pulse signal corresponding to the fluorescence decay time of the first scintillator 11, the second scintillator 12, and the third scintillator 13 is output.

Here, the second scintillator 12 made of CaF2(Eu) has a higher density and can be made thicker than the first scintillator 11 made of plastic. Therefore, the events (light emission and output of pulse signals) occurring in the second scintillator 12 can be relatively increased. That is, it is possible to obtain pulse signal waveforms with different characteristics depending on low-energy β-rays, high-energy β-rays, and γ-rays.

The pulse signal output by the detection section 2 is amplified by the signal amplification section 3. Here, when using a charge amplifier type signal amplifying section 3 (amplifier) having an integration time longer than the extinction time of the scintillator, the shorter the wavelength (width in the time direction) of the pulse signal, the more the signal amplifying section 3 The rise time of the output waveform becomes shorter. Information about the fluorescence decay time of the scintillator appears at the rise time of the waveform. In other words, when the integration time of the signal amplifying section 3 is longer than the extinction time of the scintillator, the shape of the rising portion of the waveform changes depending on the fluorescence decay time of the scintillator.

On the other hand, if the pulse signal generated by the scintillator is directly amplified using an amplifier with an integration time shorter than the extinction time of the scintillator, information about the fluorescence decay time of the scintillator appears in the fall time of the waveform. In other words, when the integration time of the signal amplifying section 3 is shorter than the extinction time of the scintillator, the shape of the falling portion of the waveform changes depending on the fluorescence decay time of the scintillator.

For example, in the graph of FIG. 2, graph G1 is a waveform of a pulse signal caused by light emission from a scintillator with a fluorescence decay time of 24 nsec. Graph G2 is a waveform of a pulse signal caused by light emission from a scintillator with a fluorescence decay time of 285 nsec. Graph G3 is a waveform of a pulse signal caused by light emission from a scintillator with a fluorescence decay time of 940 nsec. Graph G4 is a waveform of a pulse signal when light emission from a scintillator with a fluorescence decay time of 24 nsec and light emission from a scintillator with a fluorescence decay time of 940 nsec are combined. As shown in these graphs G1 to G4, it can be seen that there is a difference in the shapes of the rising and falling portions of the waveform output from the signal amplifying section 3, depending on the fluorescence decay time of the scintillator.

When measuring the waveform, it is possible to use a high-speed digitizer or the like. However, in order to determine which scintillator's light emission is the signal, it is necessary to compare each data item. For example, when making a determination using data of the entire waveform of a pulse signal, the apparatus becomes very large-scale in terms of data transfer speed or data processing speed. Therefore, waveform feature amounts are used for actual determination.

In the prior art, the rise time of a waveform or the ratio of integral values in two sections (two-gate method) is used. However, for example, when using two layers of scintillators, a total of three types of light emission are determined: light emission from the first layer scintillator alone, light emission from the second layer scintillator alone, and simultaneous light emission from the first and second layers. There is a need. Furthermore, since the peak value obtained differs each time, it becomes difficult to make a determination based on a single index such as the rise time or the ratio of integral values.

Therefore, it is possible to increase the number of indicators that can be used for evaluation. The characteristic amount of the waveform depends on the type of the signal amplifying section 3, but the characteristic occurs in the rising portion or the falling portion of the waveform of the pulse signal. In the first embodiment, the waveform data acquisition unit 4 samples the peak value and calculates the slope of the signal by numerical calculation.

For example, the waveform of a pulse signal is measured at a sampling rate of 100 Msps. Then, the most recent five wave height values D _n are measured. Calculation is performed based on the following formula using data D ₁ to D ₅ of the past five peak values. Here, five stages of SG filter processing are performed, and the data SG after this SG filter processing is recorded as a time change amount.

SG=-2D ₁ -D ₂ +D ₄ +2D ₅

In this embodiment, the peak value is measured using data D ₁ to D ₅ of the past five peak values, but other methods may be used. For example, measurement may be performed using the wave height values of six or more times in the past.

Next, the results of output values output by processing the waveform acquired by the waveform data acquisition section 4 in the time change calculation section 5 will be explained with reference to FIGS. 3 to 4. For example, in the graph of FIG. 3, graph G5 is an example of a waveform acquired by the waveform data acquisition unit 4. Graph G6 is an output value output from the time change calculation unit 5 based on this waveform. Moreover, in the graph of FIG. 4, graph G7 is another example of the waveform acquired by the waveform data acquisition unit 4. Graph G8 is an output value output from the time change calculation unit 5 based on this waveform.

By processing in the time change calculation unit 5, when the amount of increase in the waveform per time is large, the output value of the time change calculation unit 5 becomes large. On the other hand, when the amount of decrease in the waveform per time is large, the output value of the time change calculation section 5 becomes a negative value. Alternatively, when the amount of change over time (shape of the waveform) approaches linearity, an output value near zero is output from the time change calculation section.

In this way, the maximum value of the output value of the temporal change calculating section 5 indicates the maximum change when the amount of temporal change increases. On the other hand, the minimum value of the output value of the temporal change calculation unit 5 indicates the maximum change when the amount of temporal change decreases. That is, depending on whether the output value of the time change calculating section 5 is positive or negative, it can be determined whether it corresponds to the rise time or fall time of the pulse signal.

In the prior art, these temporal changes were evaluated using the waveforms acquired by the waveform data acquisition section 4. In many cases, this was handled by evaluating values at different times. However, evaluation errors often occur due to changes in the magnitude of the pulse signal (maximum peak value).

In the first embodiment, the time change amount of the waveform acquired by the waveform data acquisition section 4 is analyzed by the time change calculation section 5, and the determination is made focusing on this time change amount, so that the influence of the peak value is suppressed. be able to. Furthermore, by using the waveform obtained by the waveform data acquisition section 4, it is possible to further suppress the influence of the peak value, and pulse signals can be separated with high accuracy.

Next, differences in the output mode of the time change calculation unit 5 due to differences in fluorescence decay time of the scintillator will be explained with reference to FIGS. 5 and 6.

FIG. 5 is a histogram of the number of positive output values of the time change calculation unit 5. Graph G9 is a graph of a plastic scintillator whose fluorescence decay time is about 2.4 nsec. Graph G10 is a graph of a plastic scintillator with a fluorescence decay time of about 300 nsec. Graph G11 is a graph of a CaF2 (Eu) scintillator with a fluorescence decay time of about 900 nsec.

FIG. 6 is a histogram showing the ratio of the maximum value of the output value of the time change calculation unit 5 and the maximum value obtained by the waveform data acquisition unit 4 for each fluorescence decay time. Graph G12 is a graph of a plastic scintillator whose fluorescence decay time is about 2.4 nsec. Graph G13 is a graph of a plastic scintillator with a fluorescence decay time of about 300 nsec. Graph G14 is a graph of a CaF2 (Eu) scintillator with a fluorescence decay time of about 900 nsec.

As shown in the graphs of FIGS. 5 and 6, it can be seen that the graphs change for each scintillator. By setting parameters for determination in advance based on the difference between these graphs, it becomes possible to determine which scintillator's light emission is the basis of the pulse signal. For example, the determination may be made using the number of positive output values of the time change calculation unit 5 in FIG. 5 as the first parameter, or the maximum value of the output value of the time change calculation unit 5 in FIG. 6 and the waveform The determination may be made using the ratio of the maximum values obtained by the data acquisition unit 4 as the second parameter. Furthermore, the first parameter and the second parameter may be used together for determination. In this way, highly accurate determination can be made regardless of the type of signal amplifying section 3 and regardless of the magnitude of the pulse signal.

As shown in FIG. 1, the comparison evaluation unit 7 compares each of at least two feature quantities of the waveform of the pulse signal with a feature quantity acquired in advance. For example, the determination is made by combining the first parameter and the second parameter. A logical formula for the determination result of the first parameter and the determination result of the second parameter is established and evaluated. If the positive number of the first parameter is greater than or equal to the first threshold and the number of the maximum value of the second parameter is greater than or equal to the second threshold, it is determined that the light emission is from a predetermined scintillator. In this way, waveform evaluation accuracy can be improved.

The signal amplifying section 3 of the first embodiment has a function of integrating and differentiating the pulse signal output from the detecting section 2. Furthermore, the signal amplification unit 3 is arranged such that the value of the integration time constant (signal decay time) of the signal amplification unit 3 is between the minimum value and the maximum value of the fluorescence decay times of the respective scintillators 11, 12, and 13. 3. In this way, it is possible to reduce the difference in maximum peak values that occur based on the types of scintillators 11, 12, and 13.

Here, the signal attenuation time of the signal amplifying section 3 is a constant representing the time it takes for the pulse signal (electrical signal) to attenuate until the maximum value becomes 1/e. reaches the maximum value after the waveform rises, and then decays (decreases) exponentially, so the attenuated value S(t) at time t can be calculated by using the maximum value S(max). It can be expressed in the form (t)=S(max)·exp(−t/τS). This τS is the signal decay time and is also the time constant of the exponential decay response.

For example, the fluorescence decay time of the first scintillator 11 is set to τ1, the fluorescence decay time of the second scintillator 12 is set to τ2, the fluorescence decay time of the third scintillator 13 is set to τ3, and the signal decay time of the signal amplification section 3 is set to τS. In this case, the following formula holds.

τ1<τ3<τS<τ2

When a charge amplifier method with a sufficiently long integration time is used as the signal amplification section 3, the peak value of the pulse signal waveform is determined by the energy given to each scintillator 11, 12, 13 and the scintillator 11, 12, 13. It is determined by the amount of light emitted depending on the material of No. 13.

In general, plastic scintillators have a low density and are not easily affected by gamma rays. On the other hand, plastic scintillators emit less light than inorganic scintillators such as CaF2 (Eu) scintillators.

Furthermore, when the scintillator is thin like the first scintillator 11, the amount of energy imparted from γ rays is also small, and the maximum value of the peak value is small overall. That is, in the case of a plastic scintillator, the peak value is smaller than that of a pulse signal of a CaF2 (Eu) scintillator. Therefore, the waveform data acquisition section 4 needs to be able to input a wide range of voltages.

In addition, when the difference between the respective pulse signals appears at the rising edge of the waveform, a very high-speed A/D converter is required to evaluate the amount of time change as fast as a few nanoseconds, such as with a plastic scintillator. . Therefore, the configuration of the radiation detection system 1 becomes complicated.

Therefore, in the first embodiment, by making the signal decay time τS of the signal amplification unit 3 smaller than the fluorescence decay time τ2 of CaF2(Eu), all of the light emission amount of the CaF2(Eu) scintillator is converted into a peak value. Try not to. In other words, the difference in maximum peak value due to the difference in type of scintillators 11, 12, 13 is reduced. Furthermore, the influence of the difference in fluorescence decay times of the scintillators 11, 12, and 13 also appears on the falling portion of the waveform of the pulse signal. Therefore, data can be determined based on the characteristics of both the rising and falling portions of the waveform of the pulse signal.

In addition to the number of data for which the output value of the time change calculation unit 5 was a positive value (FIG. 5), the number of data for which the output value of the time change calculation unit 5 was a negative value, or the number of data for which the output value of the time change calculation unit 5 was a negative value, or Features that can be used for determination will also appear in the maximum or minimum value of the output.

In the first embodiment, since three types of scintillators 11, 12, and 13 are combined, there are two to three types of events (emission of light and output of pulse signals) that occur.

For example, in the case of light emission of the first scintillator 11, in the case of light emission of the second scintillator 12, in the case of light emission of the third scintillator 13, in the case of light emission of the first scintillator 11 and the second scintillator 12, in the case of the second scintillator 12 and the third scintillator In the case of light emission from the scintillator 13, in the case of light emission from the first scintillator 11 and the third scintillator 13, in the case of light emission from all scintillators 11, 12, and 13, and in the case of no light emission, there are a total of eight cases.

Perform measurements in advance according to each condition. Then, the correlation between the radiation and the feature amount is acquired and recorded. By comparing these records with actual conditions, more detailed data can be identified. For these comparisons, a determination flow based on general conditional expressions may be used, or machine learning or the like may be used for determination.

Furthermore, in the radiation detection system 1 of the first embodiment, if it is possible to determine which scintillator 11, 12, 13 an event is based on, it is also possible to obtain the energy information thereof.

Here, the generation location identification unit 8 identifies which scintillator 11, 12, 13 the pulse signal is based on. For example, it is determined whether the pulse signal is based on light emission from the third scintillator 13 or not.

Furthermore, the energy information acquisition unit 9 acquires radiation energy information based on the types of scintillators 11, 12, and 13 specified by the generation location identification unit 8 and the maximum peak value of the pulse signal. In this way, in addition to the type of radiation, information on the energy of the radiation can also be acquired in one detection operation.

For example, in the case of gamma rays detected by the third scintillator 13, energy information (energy distribution) of the gamma rays can be obtained by obtaining information on the peak value of the gamma rays. This energy information can be used not only to measure the intensity of each nuclide, but also to evaluate the 1 cm dose equivalent.

Furthermore, in the case of high-energy γ-rays passing through the first scintillator 11 and the second scintillator 12, the energy given to the first scintillator 11 and the second scintillator 12 becomes smaller. Therefore, it is possible to distinguish between low-energy γ-rays that stop at the first scintillator 11 or the second scintillator 12 and high-energy γ-rays.

With the configuration of the detection unit 2 of the first embodiment, it is possible to measure γ-rays and also measure α-rays or β-rays, which are less susceptible to the influence of γ-rays.

Next, the radiation detection process executed by the radiation detection system 1 will be explained using the flowchart of FIG. A description will be given including the effects passively produced by the operation of this radiation detection system 1. Note that the configuration diagram shown in FIG. 1 will be referred to as appropriate. The following steps are at least some of the processes included in the radiation detection process, and other steps may be included in the radiation detection process.

As shown in FIG. 7, first, in step S11, the detection unit 2 outputs a pulse signal having different characteristics depending on the type of incident radiation.

In the next step S12, the signal amplification section 3 amplifies the pulse signal output by the detection section 2 and shapes the waveform of the pulse signal.

In the next step S13, the waveform data acquisition section 4 acquires the waveform amplified and shaped by the signal amplification section 3.

In the next step S14, the time change calculation section 5 calculates the amount of time change of the waveform acquired by the waveform data acquisition section 4.

In the next step S15, the comparison evaluation unit 7 compares each of the at least two feature quantities of the waveform acquired by the waveform data acquisition unit 4 with a feature quantity acquired in advance.

In the next step S16, the data determination unit 6 determines the type of radiation based on the data acquired by the waveform data acquisition unit 4 and the data acquired by the time change calculation unit 5.

In the next step S17, the occurrence point specifying section 8 specifies which scintillator 11, 12, 13 is based on the light emission of the pulse signal output by the detecting section 2.

In the next step S18, the energy information acquisition unit 9 acquires radiation energy information based on the types of scintillators 11, 12, and 13 specified by the generation location identification unit 8 and the maximum peak value of the pulse signal.

Then, the radiation detection system 1 ends the radiation detection process.

In the first embodiment, two scintillators, the first scintillator 11 and the second scintillator 12, are provided closer to the opening 16 than the shield 14, and one third scintillator 13 is provided deeper than the shield 14. However, the number of scintillators may be adjusted as appropriate. For example, three scintillators may be provided closer to the opening 16 than the shield 14, and the detection unit 2 may be configured with a total of four scintillators.

(Second embodiment)
Next, a radiation detection system 1A and a radiation detection method according to the second embodiment will be described using FIG. 8. In addition, the same reference numerals are given to the same constituent parts as those shown in the embodiments described above, and redundant explanation will be omitted.

The detection unit 2A of the second embodiment includes a photodetector 10, a first scintillator 11, a second scintillator 12, and a housing 15 that accommodates them. That is, in the detection unit 2A of the second embodiment, the third scintillator 13 and the shield 14 of the first embodiment are omitted.

As the first scintillator 11, a plastic scintillator with low density is used. Furthermore, the thickness of the first scintillator 11 is, for example, about 0.3 mm. Further, as a material for the second scintillator 12, calcium fluoride (CaF2 (Eu)) to which europium is added is used. Note that the second scintillator 12 has a longer fluorescence decay time than the first scintillator 11. In this way, it is possible to configure a radiation detection system 1A that can at least distinguish between β rays and γ rays.

(Third embodiment)
Next, a radiation detection system 1B and a radiation detection method according to a third embodiment will be described using FIG. 9. Note that the same components as those shown in the embodiments described above are given the same reference numerals and redundant explanations will be omitted.

The detection unit 2B of the third embodiment is a semiconductor detector. In this way, since the detection section 2B can be configured with a semiconductor detector, the number of parts can be reduced compared to the detection section 2 of the first embodiment.

Although the radiation detection system and radiation detection method according to the present embodiment have been described based on the first to third embodiments, the configuration applied in any one embodiment may also be applied to other embodiments. Alternatively, the configurations applied in each embodiment may be combined.

In addition, in this embodiment, the determination of an arbitrary value (parameter) using a reference value (threshold value) may be a determination of "whether or not an arbitrary value is greater than or equal to the reference value" or a determination of "whether or not an arbitrary value is greater than or equal to the reference value". It may also be possible to determine whether or not the Alternatively, it may be determined whether or not an arbitrary value is less than or equal to a reference value, or it may be determined whether or not an arbitrary value is less than a reference value. Furthermore, the reference value is not fixed, but may be variable. Therefore, instead of the reference value, a value within a predetermined range may be used to determine whether an arbitrary value falls within the predetermined range. Alternatively, errors occurring in the device may be analyzed in advance, and a predetermined range including the error range centered on the reference value may be used for determination.

Note that although the flowchart of this embodiment shows an example in which each step is executed in series, the sequential relationship of each step is not necessarily fixed, and even if the sequential relationship of some steps is swapped. good. Also, some steps may be executed in parallel with other steps.

The system of this embodiment includes a control device with a highly integrated processor such as a dedicated chip, an FPGA (Field Programmable Gate Array), a GPU (Graphics Processing Unit), or a CPU (Central Processing Unit), and a ROM (Read Only memory) or RAM (Random Access Memory), external storage devices such as HDD (Hard Disk Drive) or SSD (Solid State Drive), display devices such as displays, and input devices such as mouse or keyboard. , and a communication interface. This system can be realized with a hardware configuration using a normal computer.

Note that the program executed by the system of this embodiment is provided by being pre-installed in a ROM or the like. Alternatively, this program may be installed as a file in installable or executable format on a non-transitory computer readable storage medium such as a CD-ROM, CD-R, memory card, DVD, or flexible disk (FD). It may also be stored and provided.

Further, the program executed by this system may be stored on a computer connected to a network such as the Internet, and may be downloaded and provided via the network. Further, this system can also be constructed by connecting separate modules that independently perform the functions of the constituent elements to each other via a network or a dedicated line and combining them.

Note that the radiation detection system 1 (data determination unit 6) may include a computer equipped with artificial intelligence (AI) that performs machine learning. Furthermore, the radiation detection system 1 may include a deep learning section that extracts a specific pattern from a plurality of patterns based on deep learning.

Analysis technology based on artificial intelligence learning can be used for the computer-based analysis of this embodiment. For example, a learning model generated by machine learning using a neural network, a learning model generated by other machine learning, a deep learning algorithm, a mathematical algorithm such as regression analysis, etc. can be used. Further, forms of machine learning include forms such as clustering and deep learning.

The system of this embodiment includes a computer equipped with artificial intelligence that performs machine learning. For example, the system may be configured with one computer equipped with a neural network, or may be configured with multiple computers equipped with neural networks.

Here, the neural network is a mathematical model that expresses the characteristics of brain function through computer simulation. For example, we will show a model in which artificial neurons (nodes) that form a network through synaptic connections change the strength of synaptic connections through learning and acquire problem-solving ability. Furthermore, neural networks acquire problem-solving ability through deep learning.

For example, a neural network is provided with an intermediate layer having six layers. Each layer of this intermediate layer is composed of 300 units. Furthermore, by allowing a multilayer neural network to learn in advance using learning data, it is possible to automatically extract features in patterns of changes in the state of a circuit or system. Note that for a multilayer neural network, any number of intermediate layers, any number of units, any learning rate, any number of learning times, and any activation function can be set on the user interface.

Note that deep reinforcement learning may be used for the neural network, in which a reward function is set for various information items to be learned, and an information item with the highest value is extracted based on the reward function.

For example, CNN (Convolution Neural Network), which has a proven track record in image recognition, is used. In this CNN, the middle layer is composed of a convolution layer and a pooling layer. The convolutional layer obtains a feature map by filtering nearby nodes in the previous layer. The pooling layer further reduces the feature map output from the convolution layer to create a new feature map. At this time, by obtaining the maximum value of pixels included in the region of interest in the feature map, it is possible to absorb some deviation in the position of the feature amount.

The convolution layer extracts local features of an image, and the pooling layer performs a process of combining local features. In these processes, the image is reduced while maintaining the characteristics of the input image. In other words, CNN can significantly compress (abstract) the amount of information an image has. Then, using the abstracted image stored in the neural network, the input image can be recognized and the image can be classified.

Note that deep learning includes various methods such as autoencoder, RNN (Recurrent Neural Network), LSTM (Long Short-Term Memory), and GAN (Generative Adversarial Network). These methods may be applied to the deep learning of this embodiment.

According to at least one embodiment described above, the accuracy of determining the type of radiation can be improved by including the time change calculation unit that calculates the amount of time change in the waveform acquired by the waveform data acquisition unit.

Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

1 (1A, 1B)... Radiation detection system, 2 (2A, 2B)... Detection section, 3... Signal amplification section, 4... Waveform data acquisition section, 5... Time change calculation section, 6... Data judgment section, 7... Comparison Evaluation section, 8... Occurrence point identification section, 9... Energy information acquisition section, 10... Photodetector, 11... First scintillator, 12... Second scintillator, 13... Third scintillator, 14... Shielding body, 15... Housing , 16...Aperture, 17...Thin film, 18, 19...Incidence direction.

Claims (13)

a detection unit that outputs a pulse signal with different characteristics depending on the type of incident radiation;
a signal amplification unit that amplifies the pulse signal and shapes the waveform of the pulse signal;
a waveform data acquisition unit that acquires the waveform shaped by the signal amplification unit;
a time change calculation unit that calculates a time change amount of the waveform acquired by the waveform data acquisition unit;
a data determination unit that determines the type of radiation based on at least the data acquired by the time change calculation unit;
Equipped with
The time change calculation unit calculates the amount of time change using a filter that calculates a change in the time course of the waveform.
Radiation detection system. a detection unit that outputs a pulse signal with different characteristics depending on the type of incident radiation;
a signal amplification unit that amplifies the pulse signal and shapes the waveform of the pulse signal;
a waveform data acquisition unit that acquires the waveform shaped by the signal amplification unit;
a time change calculation unit that calculates a time change amount of the waveform acquired by the waveform data acquisition unit;
a data determination unit that determines the type of radiation based on at least the data acquired by the time change calculation unit;
Equipped with
The types of radiation are β rays with a first energy, β rays with a second energy higher than the first energy, and γ rays.
Radiation detection system. a detection unit that outputs a pulse signal with different characteristics depending on the type of incident radiation;
a signal amplification unit that amplifies the pulse signal and shapes the waveform of the pulse signal;
a waveform data acquisition unit that acquires the waveform shaped by the signal amplification unit;
a time change calculation unit that calculates a time change amount of the waveform acquired by the waveform data acquisition unit;
a data determination unit that determines the type of radiation based on at least the data acquired by the time change calculation unit;
A radiation detection system comprising:
The detection unit includes:
a scintillator that emits light upon interaction with the radiation;
a photodetector that detects light emission from the scintillator;
Equipped with
A plurality of scintillators of different types and stacked on each other are provided inside a casing in which an opening through which the radiation enters is formed,
The mode of light emission differs depending on the type of the scintillator, and the characteristics of the pulse signal output from the photodetector differ,
The data determination section includes:
a generation point identifying unit that identifies which scintillator the pulse signal is based on, and
an energy information acquisition unit that acquires energy information of the radiation based on the type of the scintillator and the maximum peak value of the pulse signal identified by the generation location identification unit;
Equipped with
Radiation detection system. a detection unit that outputs a pulse signal with different characteristics depending on the type of incident radiation;
a signal amplification unit that amplifies the pulse signal and shapes the waveform of the pulse signal;
a waveform data acquisition unit that acquires the waveform shaped by the signal amplification unit;
a time change calculation unit that calculates a time change amount of the waveform acquired by the waveform data acquisition unit;
a data determination unit that determines the type of radiation based on at least the data acquired by the time change calculation unit;
A radiation detection system comprising:
The detection unit includes:
a scintillator that emits light upon interaction with the radiation;
a photodetector that detects light emission from the scintillator;
Equipped with
A plurality of scintillators of different types and stacked on each other are provided inside a casing in which an opening through which the radiation enters is formed,
The mode of light emission differs depending on the type of the scintillator, and the characteristics of the pulse signal output from the photodetector differ,
The signal amplification section has a function of integrating and differentiating the pulse signal,
The value of the integral time constant of the signal amplification section exists between the minimum value and the maximum value of the fluorescence decay time from when light emission occurs in each of the scintillators to when it completely disappears.
Radiation detection system. a detection unit that outputs a pulse signal with different characteristics depending on the type of incident radiation;
a signal amplification unit that amplifies the pulse signal and shapes the waveform of the pulse signal;
a waveform data acquisition unit that acquires the waveform shaped by the signal amplification unit;
a time change calculation unit that calculates a time change amount of the waveform acquired by the waveform data acquisition unit;
a data determination unit that determines the type of radiation based on at least the data acquired by the time change calculation unit;
A radiation detection system comprising:
The detection unit includes:
a scintillator that emits light upon interaction with the radiation;
a photodetector that detects light emission from the scintillator;
Equipped with
A plurality of scintillators of different types and stacked on each other are provided inside a casing in which an opening through which the radiation enters is formed,
The mode of light emission differs depending on the type of the scintillator, and the characteristics of the pulse signal output from the photodetector differ,
The plurality of scintillators include a first scintillator provided at the opening of the housing, a second scintillator provided inside the first scintillator, and a third scintillator provided inside the second scintillator. including
A shielding body is provided between the second scintillator and the third scintillator, which transmits light and blocks some types of the radiation.
Radiation detection system. the housing blocks some of the types of radiation while transmitting γ-rays;
The radiation detection system according to claim 5 . The time change calculation unit calculates the amount of time change using a filter that calculates a change in the time course of the waveform.
The radiation detection system according to any one of claims 2 to 6. The data determination unit determines the type of radiation based on the data acquired by the waveform data acquisition unit and the data acquired by the time change calculation unit.
The radiation detection system according to any one of claims 1 to 7 . The data determination unit includes a comparison evaluation unit that compares each of at least two feature quantities of the waveform with the feature quantity acquired in advance.
The radiation detection system according to any one of claims 1 to 8 . The detection unit includes:
a scintillator that emits light upon interaction with the radiation;
a photodetector that detects light emission from the scintillator;
Equipped with
The radiation detection system according to claim 1 or claim 2 . A plurality of scintillators of different types and stacked on each other are provided inside a casing in which an opening through which the radiation enters is formed,
The mode of light emission differs depending on the type of the scintillator, and the characteristics of the pulse signal output from the photodetector differ.
The radiation detection system according to claim 10 . The detection unit is a semiconductor detector,
The radiation detection system according to claim 1 or claim 2 . a step in which the detection unit outputs a pulse signal having different characteristics depending on the type of incident radiation;
a signal amplification section amplifying the pulse signal and shaping the waveform of the pulse signal;
a waveform data acquisition unit acquiring the waveform shaped by the signal amplification unit;
a step in which a time change calculation unit calculates a time change amount of the waveform acquired by the waveform data acquisition unit;
a data determination unit determining the type of radiation based on at least the data acquired by the time change calculation unit;
including ;
The time change calculation unit calculates the amount of time change using a filter that calculates a change in the time course of the waveform.
Radiation detection method.

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