JP2021032753A - Radioactivity analysis device - Google Patents

Abstract

To provide a radioactivity analysis device that can always secure soundness of a detection part for detecting radiation emitted from a body to be measured even when characteristics of the detection part change, and that can analyze radiation with high accuracy.SOLUTION: The radioactivity analysis device comprises: a multi channel analyzer 13 that outputs a wave height spectrum corresponding to an electrical pulse signal outputted from a detection part 11 for detecting radiation irradiated with from an object to be measured 2; an inverse problem calculation part 14 that performs an inverse problem calculation using a response function on the wave height spectrum, and extracts an energy spectrum of radiation irradiated with from the object to be measured 2; and a light pulser 3 having a light source 31 whose light intensity changes according to magnitude of external power for the detection part 11. The inverse problem calculation part 14 performs an inverse problem calculation in order to extract an energy spectrum of the light source 31 of the light pulser 3 in addition to the energy spectrum of the radiation irradiated with from the object to be measured 2.SELECTED DRAWING: Figure 1

Description

The present application relates to a radioactivity analyzer.

Conventionally, a radioactivity analyzer that can display a wave height spectrum by combining a detector equipped with a scintillation detector using a scintillator such as sodium iodide (NaI) and a pulse height analyzer. The rough radiation energy distribution can be obtained, the energy distribution of the detected radiation can be known, and the radioactive nuclide can be identified.

In such a radioactivity analyzer, a radioactivity analysis function such as an inverse problem solving method (for example, unfolding calculation) is further added to the wave height spectrum obtained by the pulse height analyzer to convert the wave height spectrum into an energy spectrum. A technique for identifying a radioactive nuclei species (performing a nuclei species analysis) by calculating the energy of the detected radiation with higher accuracy has already been proposed (see, for example, Patent Document 1 below).

By the way, the detection characteristics of the scintillation detector constituting the detection unit for detecting the radiation emitted from the object to be measured may change due to a temperature change or the like. In particular, the ratio (gain) for amplifying the pulse signal, which is the output of the detector, has an undesired characteristic that it changes due to environmental temperature, aging deterioration, and the like. Therefore, it is necessary to automatically adjust the gain so that it does not fluctuate according to the environmental temperature or the degree of deterioration of the detector.

Therefore, in the prior art, in order to automatically adjust the gain, the gain is automatically adjusted using the total absorption peak of potassium-40 as an index, or a light pulser using a reference radiation source is added to the inside of the detector. In some cases, the gain is automatically adjusted using the total absorption peak of the standard obtained as an index.

In particular, the high-sensitivity main steam tube monitor installed in a nuclear power plant, for example, to which a conventional scintillation detector is applied, targets a wide range of energy bands, so a constant gain can be obtained in a wide range of energy bands. There is a request to keep. Therefore, the gain is automatically adjusted by using the total absorption peak of the reference obtained by adding a light pulser using a reference radiation source to the scintillation detector inside the detector as an index.

Here, the conventional light pulsar is configured by enclosing a reference radiation source such as Am-241 (Americium-241) in a case made of a light emitting body, and the light emitting body emits light by the reference radiation source. Therefore, the light intensity (light energy) of the conventional light pulsar is always fixed and cannot be changed by external power control or the like.

International Publication No. 2016/12945

As described above, the total absorption peak of potassium-40 or the light pulsar using the reference radiation source is applied as an index for gain adjustment applied to the conventional scintillation detector, and in particular, the conventional light pulsar is applied. The intensity of the light (light energy) is always fixed. Therefore, when the spectrum of the light energy of the light pulsar overlaps with the spectrum of the radioactivity to be measured, it becomes difficult to distinguish between the two, and it is hindered from using the light pulsar as a gain index. There's a problem.

In addition, since the scintillation detector that constitutes the detection unit adjusts the gain using the fixed light intensity (light energy) of the light pulser as an index, it is guaranteed that the energy band near this energy will have the correct gain. In the energy band outside the vicinity, it is difficult to always obtain a constant gain with high accuracy, and there is a problem that it depends on the linear performance of the amplifier circuit.

The present application discloses a technique for solving the above-mentioned problems, and adjusts the gain of the detection unit that detects the radiation emitted from the object to be measured so as not to be affected by the measurement environment, aging deterioration, etc. It is an object of the present invention to provide a radioactivity analyzer capable of reliably guaranteeing gain even in a wide energy band.

The radioactivity analyzer disclosed in the present application is a detection unit that detects radiation emitted from an object to be measured and outputs an electric pulse signal, and a pulse height spectrum that outputs a wave height spectrum with respect to the electric pulse signal from the detection unit. A wave height analyzer and an inverse problem calculation unit for extracting the energy spectrum of the object to be measured by performing an inverse problem calculation using a response function on the wave height spectrum from the pulse height analyzer are provided, and the detection unit is provided. A light pulser having a light source whose light intensity changes depending on the magnitude of external power is provided, and the inverse problem calculation unit adds the radiation energy spectrum of the object to be measured to the radiation energy spectrum of the object to be measured by the inverse problem calculation. The energy spectrum of the light pulser from the light source is extracted.

According to the technique disclosed in the present application, the gain adjustment for the detection unit that detects the radiation emitted from the object to be measured is not affected by the measurement environment, aging deterioration, etc., and the gain is reliably guaranteed even in a wide energy band. It is possible to obtain a radioactivity analyzer that can be used.

It is a block diagram which shows the structure of the radioactivity analyzer according to Embodiment 1 of this application. It is a figure which shows an example of the wave height spectrum which is the output of the pulse height analyzer of the radioactivity analyzer shown in FIG. It is a figure which shows an example of the energy spectrum which is the output of the inverse problem calculation part of the radioactivity analyzer shown in FIG. It is a block diagram which shows the structure of the radioactivity analyzer according to Embodiment 2 of this application. It is a figure which shows an example of the energy spectrum which is the output of the inverse problem calculation part of the radioactivity analyzer shown in FIG.

Embodiment 1.
FIG. 1 is a block diagram showing a configuration of a radioactivity analyzer according to the first embodiment.
In FIG. 1, the radioactivity analyzer 1 of the first embodiment is an apparatus for monitoring a substance containing radioactivity, and includes a detection unit 11, an amplifier 12, and a multi-wave height analyzer (MCA) 13. The inverse problem calculation unit 14 and the display unit 15 are provided. Further, a light pulser 3 is provided.

A scintillation detector that detects radiation emitted from the body 2 to be measured and outputs an electric pulse signal is applied to the detection unit 11. Although not shown, the scintillation detector in this case is configured by combining a scintillator that emits light by radiation and a photomultiplier tube.

The amplifier 12 amplifies the signal level of the electric pulse signal from the detection unit 11 and shapes the pulse waveform. Further, the pulse height analyzer 13 converts the electric pulse signal of the amplifier 12 into a digital value based on the wave height, discriminates it into multiple channels according to the magnitude of the digital value, and counts the number of signals corresponding to each channel. And output the wave height spectrum.

The inverse problem calculation unit 14 performs an inverse problem calculation on the wave height spectrum output by the pulse height analyzer 13 and converts it into a channel corresponding to the energy of the radiation incident on the detection unit 11, thereby converting the wave height spectrum into an energy spectrum. The amount of radioactivity of the object 2 to be measured is calculated by conversion. The content of the inverse problem calculation will be described in detail later. The display unit 15 displays the wave height spectrum which is the output of the pulse height analyzer 13 and the energy spectrum which is the output of the inverse problem calculation unit 14.

The light pulsar 3 is for injecting light of constant intensity onto the detection unit 11 to generate a peak simulating radiation detection on the wave height spectrum and the energy spectrum, and includes a light source 31 and a pulsar switch 32.

The light source 31 is composed of a light emitting element whose light intensity (light energy) changes depending on the magnitude of external power, for example, a light emitting element such as an LED (Light Emitting Diode), a semiconductor laser, or an organic EL (Electro Luminescence). , Light is emitted or extinguished by turning on / off the pulsar switch 32.

The light emitted by the light source 31 is received by the detection unit 11, the signal is amplified by the amplifier 12, the intensity of the incident light is analyzed by the pulse height analyzer 13, and the channel is counted as a channel suitable for the intensity of the light. It is displayed on the display unit 15 as a wave height spectrum. At the same time, the inverse problem calculation unit 14 performs an inverse problem calculation on the wave height spectrum and converts it into a channel corresponding to the light intensity (light energy), so that the energy spectrum is displayed on the display unit 15.

As described above, in the first embodiment, the light source 31 of the light pulser 3 generates light as a simulation of the radiation incident on the detection unit 11, but unlike ordinary radiation, the light intensity (light energy) of the light is generated. ) Can be changed by external power control, so when the wave height spectrum is converted to an energy spectrum by performing the inverse problem calculation described later, it is used by avoiding overlapping with the measurement energy band of the object 2 to be measured in advance. Channels can be set in any energy band determined by the person. Therefore, the light source 31 of the light pulser 3 can be used as an index for gain adjustment.

Next, the measurement method of the radioactivity analyzer 1 of the first embodiment configured as described above will be described.

Since the object 2 to be measured contains radioactivity, a part of the radiation emitted from the radioactivity is incident on the detection unit 11. When radiation enters the detection unit 11, it is converted into an electric pulse signal and output to the amplifier 12, and after the electric pulse signal is amplified and shaped by the amplifier 12, it is output to the pulse height analyzer 13.

The pulse height analyzer 13 reads the height of the pulse wave height of the input electric pulse signal and assigns it to each channel divided into, for example, about 1000 channels according to the height of the pulse wave height. That is, the maximum pulse height of the electric pulse signal that the pulse height analyzer 13 can accept is assigned to, for example, the 1000th channel of the maximum channel. The pulse height below the maximum pulse height is assigned to each channel proportional to the pulse height.

The pulse-height analyzer 13 integrates the counts of the pulse wave heights for each channel, and represents the pulse wave height channels on the horizontal axis and the counts for each channel on the vertical axis. For example, a wave height spectrum as shown in FIG. 2 is obtained. Output.

FIG. 2 shows a wave height spectrum when a sodium iodide (NaI) scintillation detector is used as the detection unit 11.

In FIG. 2, the energy of the radiation incident from the object 2 to be measured shows a peak at E1, and the periphery thereof has a spread, and the spread is referred to as a region Ra of the total absorption peak. The degree of spread of the region Ra of the total absorption peak is called the resolution of the detection unit 11 to be applied, and the narrower the spread of the region Ra, the better the resolution. This resolution is a characteristic of the detection unit 11 and is determined by its type and quality. The distribution of the energy region lower than the region Ra of the total absorption peak is called the Compton scattering region Rc, which is a region that always appears because the physical size of the detection unit 11 is finite. It can be said that the smaller the distribution area of the Compton scattering region Rc and the larger the distribution area of the region Ra of the total absorption peak, the better the performance of the scintillation detector.

Further, in the wave height spectrum shown in FIG. 2, L1 indicates a peak of the pulse wave height due to the light incidented by the light source 31 of the light pulser 3 (hereinafter, referred to as a pulser peak). When the pulsar peak L1 by the light source 31 of the light pulsar 3 overlaps with the spread of the region Ra of the total absorption peak of the radiation by the object 2 or the distribution of the Compton scattering region Rc, this is hidden, but the user previously asks. By adjusting the intensity of light (light energy) by the light source 31, when the wave height spectrum is converted into an energy spectrum by the inverse problem calculation by the inverse problem calculation unit 14 described later, the pulsapeak Ll by the light source 31 is the object to be measured. It is possible to avoid overlapping the measurement energy bands of 2.

The on / off of the light source 31 by the pulsar switch 32 per unit time affects the magnitude of the count number (vertical axis) of the wave height spectrum in FIG. 2, but the light intensity (light energy) (horizontal axis). Is not directly related.

Next, the content of the inverse problem calculation by the inverse problem calculation unit 14 will be described.
The output of the pulse height analyzer 13 is input to the inverse problem calculation unit 14. The inverse problem calculation unit 14 has a response function, and uses the response function to perform an inverse problem calculation on the wave height spectrum. That is, assuming that M is the wave height spectrum, R is the response function, and S is the energy spectrum excluding the influence of the interaction of radiation, the following (Equation 1) is established.

M = RS (expression 1)
Here, since the response function R generally forms a commutative group, there is an inverse element. Then, the inverse problem calculation unit 14 calculates (Equation 2), which is the inverse conversion in this (Equation 1), and extracts the energy spectrum S. In (Equation 2), (R-1) indicates the inverse element of the response function.

S = (R-1) · M (Equation 2)
Here, if the wave height spectrum M and the energy spectrum S are represented by vectors, that is, the count number corresponding to the number of channels is represented as a vector component, the response function R and the inverse element (R-1) of the response function are a matrix and an inverse matrix, respectively. Can be called.

Then, a feedback operation is performed by the sequential approximation method (reference: Ministry of Education, Culture, Sports, Science and Technology, radioactivity measurement method series 20 “spatial γ-ray spectrum measurement method”, (1990) Appendix 2), and the response function R calculated in advance by simulation. The energy spectrum S can be refined from the wave height spectrum M obtained by measuring the object 2 to be measured, and the target energy spectrum S can be obtained.

When the above successive approximation method is applied, the method of obtaining the energy spectrum S of (Equation 2) is as follows.
First, when the measured value M is substituted as it is as the initial value of the energy spectrum S, (Equation 3) is obtained.

Next, the following (Equation 4) and (Equation 5) are repeated in a feedback manner ^{until S (m + 1)} / S ^(m) converges.

The information contained in the energy spectrum S obtained as described above indicates the type of radionuclide contained in the object 2 to be measured.

By solving this (Equation 2), the energy spectrum represented by S containing only the energy information of radiation can be extracted from the wave height spectrum represented by M. That is, the energy spectrum thus obtained excludes the influence of the interaction between the detection unit 11 and the peripheral structures of the object to be measured 2 and the influence of the statistical variation related to the detection unit 11. That is, by the calculation of (Equation 2), the energy information of the radiation can be accurately known, and the accuracy of the identification of the radioactive substance that emitted the detected radiation is improved. Then, the extracted energy spectrum is displayed on the display unit 15. At the same time, the wave height spectrum obtained based on the light source 31 of the light pulser 3 is also converted into an energy spectrum by the inverse problem calculation unit 14 and displayed on the display unit 15.

FIG. 3 shows an energy spectrum obtained by converting the wave height spectrum (FIG. 2), which is the output of the pulse height analyzer 13, by the inverse problem calculation unit 14.

For the radiation incident from the object 2 to be measured, the spread of the Compton scattering region Rc and the region Ra of the total absorption peak seen in the wave height spectrum is eliminated by the inverse problem calculation. Note that FIG. 3 shows a case where only one type of radiation having energy E1 is incident, but when a plurality of energies are incident, the count is also shown for channels other than energy E1. The number of counts for each of these channels, that is, for each energy, is the amount of radioactivity to be obtained.

In this way, when the radiation incident from the object 2 to be measured is converted into an energy spectrum by the inverse problem calculation unit 14, the spread of the Compton scattering region Rc and the region Ra of the total absorption peak seen in the wave height spectrum disappears. .. Further, since the position of the pulsar peak L1 by the light source 31 of the light pulsar 3 is set in advance so as not to overlap with the energy E1 of the radiation from the object to be measured 2, the amount of radioactivity of the object to be measured 2 appearing at the position of the energy E1 is used. It becomes clear where the position of the pulsar peak L1 by the light source 31 of the light pulsar 3 is located on the spectrum without being affected.

When the ratio (gain) for amplifying the pulse signal, which is the detection output of the radioactivity analyzer 1, is always constant, the position of the pulsar peak L1 of the light source 31 in the energy spectrum shown in FIG. 3 is always at the same position. On the other hand, if the gain fluctuates due to a change in the environmental temperature or aged deterioration of the detection unit 11, the energy of the radiation emitted by the object 2 to be measured also fluctuates accordingly, so that the radioactive nuclide or the like cannot be accurately identified. Further, the position of the pulsar peak L1 by the light source 31 also fluctuates.

In this case, the energy spectrum (FIG. 3) displayed on the display unit 15 is observed, and the gain of the amplifier 12 is adjusted so that the position of the pulsar peak L1 by the light source 31 of the light pulsar 3 is always at the same position. By adjusting the gain in this way, the gain of the radioactivity analyzer 1 can always be controlled to be constant without being affected by changes in the environmental temperature, aging deterioration of the detection unit 11, and the like.

As described above, according to the first embodiment, the light pulser 3 having the light source 31 whose amount of light changes depending on the magnitude of the external power is provided, and the light pulsar 3 is radiated from the object 2 to be measured by the calculation of the inverse problem calculation unit 14. Since the energy spectrum of the light source 31 of the light pulsar 3 is extracted in addition to the energy spectrum of the radiation, a channel corresponding to the energy of the light source 31 of the light pulsar 3 can be set in an arbitrary energy band determined by the user. Therefore, since the index for gain adjustment based on the light source 31 of the light pulser 3 can be obtained while avoiding the measurement energy band of the object to be measured 2, the detection unit 11 for detecting the radiation emitted from the object 2 to be measured can obtain the index. The soundness of the gain can be confirmed, and accurate gain adjustment can be performed. Therefore, accurate detection results can always be obtained.

Further, since the above-mentioned light pulsar 3 is configured by using a light source 31 such as an LED instead of using a conventional radiation source, it is not only possible to determine the intensity of light in advance, but also to turn on / on the light. It can be turned off. Therefore, when the gain index is not used, the light source 31 can be turned off so that only the radiation from the object 2 to be measured is incident.

Embodiment 2.
In the first embodiment, the light source 31 of the light pulsar 3 controls only on / off. However, if not only the on / off control but also the light intensity (light energy) is controlled, the light pulsar is controlled. The peak position of the energy spectrum of the light source 31 of No. 3 can be arbitrarily changed.

FIG. 4 is a block diagram showing the configuration of the radioactivity analyzer according to the second embodiment.
In the second embodiment, as the configuration of the light pulsar 3, the pulsar control unit 33 is provided in addition to the light source 31 and the pulsar switch 32. Then, the pulser control unit 33 can control the intensity (light energy) of the light generated from the light source 31.

In this case, as a specific control method by the pulsar control unit 33, for example, control such as changing the voltage applied to the light source 31 of the light pulsar 3 in synchronization with the on / off cycle of the balsa switch 32 is performed. Therefore, the intensity of the light emitted from the light source 31 is changed in time division.

FIG. 5 is a diagram showing an example of an energy spectrum which is an output of the inverse problem calculation unit 14 of the radioactivity analyzer shown in FIG.

As described above, the light emitted from the light source 31 is controlled by the pulsar control unit 33 to change the voltage applied to the light source 31 of the light pulsar 3 in synchronization with the on / off cycle of the balsa switch 32. Change the strength of. Then, even when the energy spectrum, which is the output of the inverse problem calculation unit 14 for the object 2 to be measured, exists over a plurality of channels (energy) E1, E2, E3, E4, ..., En, these peaks are avoided. For example, a pulsar peak by the light source 31 can be selected at each position of L1 and L2 shown in the figure. Therefore, even if the light emission control of the light source 31 of the light pulser 3 is continued, the measurement of the object to be measured 2 can be continued normally.

Further, when a scintillation detector showing a wide range of energy distribution, for example, for gamma ray detection, is used for the detection unit 11, it is important to have excellent gain linearity in a wide range of energy bands. Therefore, it is necessary to confirm the gain in a wide energy band. In the configuration of the second embodiment, the peak position of the energy spectrum can be changed over a wide range such as L1, L2, ... By controlling the light intensity of the light source 31 of the light pulser 3 according to the above necessity. Therefore, even when the measurement energy band of the object to be measured 2 is wide, it is possible to check the soundness of the gain by changing the position of the index gain.

As described above, as a scintillation detector for the purpose of detecting gamma rays of a wide range of energy, for example, there is a high-sensitivity main steam tube monitor installed in a nuclear power plant.

The high-sensitivity main steam tube monitor detects high-energy radiation of N-16 (6.13 MeV) and at the same time has a low-energy rare gas detection function, so the energy required for measurement is wide and the measurement energy is wide. There are many measurement targets. However, since the position of the pulsar peak in the energy spectrum can be changed over a wide range such as L1 and L2 by controlling the light intensity of the light source 31 of the light pulsar 3 by the pulsar control unit 33, the object to be measured 2 is the measurement target. It is possible to confirm the soundness of the gain over a wide range of energy bands by avoiding the influence of overlapping the spectral peaks of.

Further, in the second embodiment, the intensity of the light emitted from the light source 31 is changed by performing control such as changing the voltage applied to the light source 31 of the light pulsar 3, but the pulsar control unit 33 controls it. By changing the emission frequency of the light source 31, not only an arbitrary energy setting but also an arbitrary dose rate can be set. Therefore, the light pulser 3 can also be applied as a radiation detection test device.

Although various exemplary embodiments have been described in the present application, the various features, embodiments, and functions described in one or more embodiments may be applied to a particular embodiment. It is not limited and can be applied to embodiments alone or in various combinations.

Therefore, innumerable variations not illustrated are envisioned within the scope of the techniques disclosed in the present application. For example, it is assumed that at least one component is modified, added, or omitted, and further, at least one component is extracted and combined with the components of other embodiments. ..

1 Radioactivity analyzer, 2 Measured object, 3 Light pulser, 31 Light source,
32 pulsar switch, 33 pulsar control unit, 11 detector unit, 12 amplifier,
13 Pulse height analyzer, 14 Inverse problem calculation unit, 15 Display unit.

Claims (2)

From a detection unit that detects radiation emitted from the object to be measured and outputs an electric pulse signal, a pulse height analyzer that outputs a wave height spectrum with respect to the electric pulse signal from the detection unit, and a pulse height analyzer. It is provided with an inverse problem calculation unit for extracting the energy spectrum of the object to be measured by performing an inverse problem calculation using a response function on the wave height spectrum of the above.
A light pulser having a light source whose light intensity changes depending on the magnitude of external power is provided to the detection unit, and the inverse problem calculation unit adds the radiation energy spectrum of the object to be measured by the inverse problem calculation. A radioactivity analyzer that extracts the energy spectrum of the light pulser from the light source. The radioactivity analyzer according to claim 1, further comprising a pulsar control unit that controls the intensity of light from the light source by changing the magnitude of external power supplied to the light pulsar.

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