JP2010271153A - Radiation monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation monitor confirming operation of a detector by direct response of the detector to a radiation, without using a bug source. <P>SOLUTION: The radiation monitor includes a radiation detection element, including a radioactive material existing naturally, a photomultiplier for converting light from the radiation detection element into an electric signal, and a wave height discriminator for discriminating a peak value at which a peak appears from the electric signal output from the photomultiplier. The radiation detection element generates light caused by a radiation from a radioactive material existing naturally and included in itself, and a light caused by radiation from the outside. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radiation monitor used for an area monitor or the like of a nuclear power plant, and more particularly to a soundness confirmation of the radiation monitor.

  Conventionally, a radiation monitor used for an area monitor or the like of a nuclear power plant or the like has installed a weak radioactive substance called a bug source in the vicinity of a radiation detector in order to confirm the soundness of operation. However, since a bug source is a radiation source, there are various restrictions on handling and it is inconvenient.

  Patent Document 1 describes a method for confirming the soundness of operation by utilizing fluctuations in counting due to radiation derived from nature as a radiation monitor that does not use a bug source. Patent Document 2 describes a method for confirming the soundness of operation by making light generated by a light emitting diode enter a radiation detector instead of a bug source. Patent Document 3 describes a radiation monitor having a structure in which a bug source is installed in the vicinity of a radiation detection element in order to confirm the soundness of operation with a bug source having a small radiation dose.

Japanese Patent Laid-Open No. 6-214039 JP-A-2-128184 Japanese Patent Application No. 2006-22796

  The method described in Patent Document 1 requires a special detection system for fluctuation detection. In addition, since this method uses counting by natural radiation outside the radiation detector, the counting rate is small and it takes time to check the soundness of the operation. The method described in Patent Document 2 uses the response of a radiation detector due to photons generated by light emitting diodes as an alternative to the response due to radiation. Therefore, it is not possible to directly confirm the soundness of the operation for radiation. The method described in Patent Document 3 also uses a radiation source installed outside the radiation detection element. Therefore, various restrictions are imposed on handling.

  An object of the present invention is to provide a radiation monitor that can confirm the operation of a detector without using a bug source and by a direct response of the detector to radiation.

  According to the present invention, the radiation monitor includes a radiation detection element containing a radioactive substance that exists in nature, a photomultiplier tube that converts light from the radiation detection element into an electrical signal, and an electrical signal output by the photomultiplier tube. And a wave height discriminator for discriminating a wave height value at which a peak appears.

  The radiation detection element generates light caused by radiation from a naturally occurring radiation substance contained in itself and light caused by radiation from the outside.

  ADVANTAGE OF THE INVENTION According to this invention, the radiation monitor with easy handling which can confirm the soundness of the operation | movement with respect to radiation can be provided, without using a bug source.

It is a block diagram of the 1st example of the radiation monitor of this invention. It is a figure which shows the structural example of the radiation detection element and photomultiplier tube of the radiation monitor of this invention. It is a figure which shows an example of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows an example of the time change of the count rate of each area | region of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the count rate of each area | region of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the count rate of each area | region of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the count rate of each area | region of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the count rate of each area | region of the peak value spectrum obtained by the radiation monitor of this invention. It is a block diagram of the 2nd example of the radiation monitor of this invention. It is a figure which shows an example of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows an example of the time change of the net count rate of each peak of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the net count rate of each peak of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the net count rate of each peak of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the net count rate of each peak of the peak value spectrum obtained by the radiation monitor of this invention. It is a figure which shows another example of the time change of the net count rate of each peak of the peak value spectrum obtained by the radiation monitor of this invention.

  A configuration example of the radiation monitor of the present invention will be described with reference to FIG. The radiation monitor of this example includes a radiation detection element 1 containing a radioactive substance, a photomultiplier tube 2 that converts light from the radiation detection element into an electrical signal, an amplifier 3 that amplifies the electrical signal from the photomultiplier tube, and a peak A wave height discriminator 4 for discriminating wave height values that appear, a counter 5 for counting counts in one or a plurality of wave height areas, a count rate meter 6 for converting the count of each area from each counter into a count rate, and each area Has a monitor 7 for displaying the count rate.

The radiation detection element 1 is made of a radiation material. This radioactive material generates light having an intensity corresponding to its energy by alpha rays or gamma rays generated from itself. In addition, this radiation substance generates light having an intensity corresponding to the energy of the incident radiation even when radiation 9 such as gamma rays is incident from the outside. Examples of such a radiation substance include lanthanum bromide (LaBr ₃ (Ce)), lutetium silicate (Lu ₂ SiO ₅ (Ce)), and the like. The lanthanum contained in lanthanum bromide naturally exists in two types having a mass number of 137 and 138. Lanthanum 138 having a mass number of 138 is a radioactive substance that emits gamma rays with energy of 0.79 MeV and 1.44 MeV. Moreover, alpha ray emitting nuclides such as polonium 214 are naturally contained in the production process of lanthanum bromide. In lutetium contained in lutetium silicate, two kinds having a mass number of 175 and 176 exist naturally. Lutetium 176 having a mass number of 176 is a radioactive substance that emits gamma rays with energy of 0.08 MeV, 0.20 MeV, and 0.31 MeV.

  The radiation detection element 1 generates light due to radiation 9 from the outside or radiation emitted inside. This light is converted into an electric signal by the photomultiplier tube 2, amplified by the amplifier 3, and sent to the wave height discriminator 4. The peak discriminator 4 discriminates the signal from the amplifier for each peak value region. The peak value has a peak at a value corresponding to the energy of alpha rays or gamma rays. The counter 5 counts for each peak value region having a predetermined width, and calculates a count rate for each peak value region. The count rate is a count per unit time. A graph of the time variation of the count rate for each peak value region is displayed on the monitor 7. In this example, since the count rate is calculated for each peak value region, it is not necessary to obtain the peak value spectrum shown in FIG.

  The user can determine whether or not the radiation monitor is operating normally from the graph of the temporal change in the count rate for each peak value region displayed on the monitor 7.

  An example of the structure of the radiation detection element 1 and the photomultiplier tube 2 will be described with reference to FIG. The photomultiplier tube 2 has a cylindrical glass tube 206, the inside of which is evacuated. A glass tube 206 includes a photocathode 202 that converts light into electrons, a converging electrode 203 that converges photoelectrons, a plurality of metal plates 204 that emit secondary electrons, and an anode 205 that receives secondary electrons. A window 201 is formed on the end surface of the photomultiplier tube 2 on the photocathode 202 side. A cylindrical radiation detection element 1 is mounted so as to cover the window 201.

As described above, the radiation detection element 1 is made of a radiation material such as lanthanum bromide (LaBr ₃ (Ce)) or lutetium silicate (Lu ₂ SiO ₅ (Ce)).

  The outer surfaces of the radiation detection element 1 and the photomultiplier tube 2 are covered with a shielding film that shields light. However, external radiation 9 passes through this shielding film.

  The radiation detection element 1 generates light due to radiation 9 from the outside or radiation emitted inside. This light is received by the photocathode 202 through the window 201 on the end face of the photomultiplier tube 2 and converted into electrons. When these electrons collide with the first metal plate 204, secondary electrons are generated. When the secondary electrons collide with the next metal plate 204, secondary electrons are further generated. Thus, secondary electrons are successively generated by the plurality of metal plates 204 and finally reach the anode 205.

  FIG. 3 shows an example of a peak value spectrum of light generated by the radiation detection element 1. The horizontal axis is the peak value, and the vertical axis is the count. The peak value is proportional to the energy of the radiation. The higher the peak value, the greater the radiation energy. The count is a count value of photoelectrons detected by the photomultiplier tube 2 and represents the intensity of radiation. The radiation 9 from the outside of the radiation detection element forms a peak in the peak value spectrum according to the energy of the radiation. The peak value regions where the peaks appear are defined as region a1, region a2, and region a3. Further, the radiation from the radioactive substance contained in the radiation detection element also forms a peak in the peak value spectrum according to the energy of the radiation. The peak value regions where the peaks appear are defined as region b1, region b2, and region c. The width of the peak value region is set in advance. The peak height discriminator 4 classifies the peak value region where these peaks appear.

Here, the case where lanthanum bromide (LaBr ₃ (Ce)) is used as the radiation detection element 1 will be described. Regions b1 and b2 are peak regions due to gamma rays. The energy of gamma rays from lanthanum 138 naturally contained in lanthanum bromide is 0.79 MeV and 1.44 MeV. Accordingly, the peak regions b1 and b2 appear in the peak value region of the same level as the peak caused by the external radiation. Region c is a region of peaks due to alpha rays. The energy of alpha rays from polonium 214 naturally contained in the production process of lanthanum bromide is as high as 7.7 MeV. Therefore, the peak region c appears in a high peak value region as compared with the peak caused by external radiation.

  The peak value spectrum shown in FIG. 3 can be obtained every unit time. Thereby, the time change of the peak value spectrum can be obtained. An example of the time change of the peak value spectrum will be described below.

  FIG. 4 shows an example of the change over time of the count rate in each region of the peak value spectrum. The horizontal axis is time, and the vertical axis is the count rate. The count rate is a count per unit time. The counting rate is the area a1, the area a2, and the area a3 corresponding to the radiation 9 from the outside, and the areas b1, b2, and c corresponding to the radiation from the inside of the radiation detection element 1. It is constant. Therefore, it can be determined that the radiation monitor is functioning normally.

  FIG. 5 shows another example of the change over time of the count rate in each region of the peak value spectrum. The horizontal axis is time, and the vertical axis is the count rate. Although the count rates of the area a1 and the area b1 increased instantaneously at the time t1, the count rates of other areas are constant. This is considered that the intensity of the external radiation having a peak in the region a1 is increased at the time t1, and the Compton scattering amount of the external radiation is added to the region b1. Therefore, it can be determined that the radiation monitor has normally detected that the intensity of external radiation having a peak in the region a1 has increased.

  FIG. 6 shows another example of the change over time of the count rate in each region of the peak value spectrum. The horizontal axis is time, and the vertical axis is the count rate. Although the count rates of the area a1 and the area b1 gradually increase from the time t2, the count rates of other areas are constant. As in the case of FIG. 5, it is considered that the intensity of the external radiation having a peak in the region a1 gradually increases from the time t2. Therefore, it can be determined that the radiation monitor has normally detected that the intensity of external radiation having a peak in the region a1 has increased.

  FIG. 7 shows another example of the change over time of the count rate in each region of the peak value spectrum. The horizontal axis is time, and the vertical axis is the count rate. The count rate for all areas is zero at time t3. This can be determined that the radiation monitor has failed at time t3.

  FIG. 8 shows another example of the change over time of the count rate in each region of the peak value spectrum. The count rate of all areas has increased from time t4. It is known that even if the intensity of external radiation increases, the count rate of the region c due to alpha rays from the natural radioactive material contained in the radiation detection element 1 does not change. Therefore, it can be determined that a failure has occurred in the radiation monitor at time t4.

  As described above, it is possible to confirm whether the radiation monitor is measuring normally or whether a failure has occurred from the graph of the temporal change in the count rate of each peak value region.

  With reference to FIG. 9, another configuration example of the radiation monitor of the present invention will be described. The radiation monitor of this example includes a radiation detection element 1 containing a radioactive substance, a photomultiplier tube 2 that converts light from the radiation detection element into an electrical signal, an amplifier 3 that amplifies the electrical signal from the photomultiplier tube, and an amplification. The peak discriminator 4 for discriminating the peak value of the signal, the peak count rate measuring device 8 for calculating the net count rate at each peak of the peak value spectrum discriminated by the pulse height discriminator, and the net count rate of each peak It has a monitor 7 for displaying.

  The peak count rate measuring device 8 calculates the net count rate of each peak in the peak value spectrum shown in FIG. The net count rate is a value per unit time of the area of the remaining peak portion (mountain portion) by subtracting the background from each peak. In this example, in order to determine the peak area from the peak value spectrum, it is necessary to determine the peak value spectrum shown in FIG.

  FIG. 10 shows another example of a peak value spectrum of light generated by the radiation detection element 1. The horizontal axis is the peak value, and the vertical axis is the count. The radiation 9 from the outside of the radiation detection element forms a peak in the peak value spectrum according to the energy of the radiation. The peaks are referred to as peak d1, peak d2, and peak d3. Further, the radiation from the radioactive substance contained in the radiation detection element also forms a peak in the peak value spectrum according to the energy of the radiation. The peaks are referred to as a peak e1, a peak e2, and a peak e3. The peak discriminator 4 separates these peaks.

Here, the case where lutetium silicate (Lu ₂ SiO ₅ (Ce)) is used as the radiation detection element 1 will be described. Peak e1, peak e2, and peak e3 are peaks due to gamma rays. The energies of gamma rays from lutetium 176 naturally contained in lutetium silicate are energies of 0.08 MeV, 0.20 MeV, and 0.31 MeV. Therefore, the peak e1, the peak e2, and the peak e3 appear in the peak value region of the same level as the peak caused by the external radiation.

  FIG. 11 shows an example of a temporal change in the net count rate of each peak of the peak value spectrum. The peak d1, the peak d2, and the peak d3 corresponding to the radiation 9 from the outside, and the peak e1, the peak e2, and the peak e3 corresponding to the radiation from the inside of the radiation detection element 1 are all net. The count rate is constant. Therefore, it can be determined that the radiation monitor is functioning normally.

  FIG. 12 shows another example of the change over time of the net count rate of each peak of the peak value spectrum. The net count rate of peak d1 increases instantaneously at time t5, but the net count rates of other peaks are constant. This is considered that the intensity of the external radiation having the peak d1 increased at the time t5. Therefore, it can be determined that the radiation monitor is functioning normally.

  FIG. 13 shows another example of the change over time of the net count rate of each peak of the peak value spectrum. Although the count rate of the peak d1 gradually increases from the time t6, the count rates of the other peaks are constant. This is considered that the intensity of the external radiation having the peak d1 gradually increases from the time t6. Therefore, it can be determined that the radiation monitor is functioning normally.

  FIG. 14 shows another example of the change over time of the net count rate of each peak of the peak value spectrum. The count rate of all peaks is zero at time t7. This can be determined that a failure has occurred in the radiation monitor at time t7.

  FIG. 15 shows another example of the change over time of the net count rate of each peak of the peak value spectrum. The count rate of all peaks has increased from time t8. The peak e1, the peak e2, and the peak e3 are peaks due to radiation from a radioactive substance that naturally exists inside the radiation detection element. It is known that the net count rates of these peak e1, peak e2, and peak e3 do not change when normal. Therefore, it can be determined that a failure has occurred in the radiation monitor at time t8.

As described above, it can be confirmed from the graph of the change in the net count rate of each peak over time whether the radiation monitor is measuring normally or whether a failure has occurred.
As described above, according to this example, normal measurement and detector failure can be confirmed.

  Although the examples of the present invention have been described above, the present invention is not limited to the above-described examples, and it is easy for those skilled in the art to make various modifications within the scope of the invention described in the claims. Will be understood.

DESCRIPTION OF SYMBOLS 1 ... Radiation detection element, 2 ... Photomultiplier tube, 3 ... Amplifier, 4 ... Wave height discriminator, 5 ... Counter, 6 ... Count rate meter, 7 ... Operation check monitor, 8 ... Peak count rate measuring device, 9 ... External radiation

Claims (14)

  A radiation detection element containing a radioactive substance that exists in nature, a photomultiplier tube that converts light from the radiation detection element into an electrical signal, and a peak value at which a peak appears from the electrical signal output by the photomultiplier tube A pulse height discriminator for discriminating; and a monitor for displaying a graph showing a temporal change in a count rate of peak values generated based on the crest value discriminated by the crest discriminator, and detecting the radiation A radiation monitor characterized in that the element generates light caused by radiation from a naturally occurring radiation substance contained in itself and light caused by radiation from the outside.   2. The radiation monitor according to claim 1, wherein a counter for counting a peak value for each peak area of a predetermined width based on the peak value discriminated by the peak discriminator, and a count for each peak area from the counter. A radiation rate monitor, wherein the monitor displays a graph showing a temporal change in the count rate of the crest value for each crest region.   The radiation monitor according to claim 1, further comprising: a peak count rate measuring device that calculates a net count rate for each peak of the peak value based on the peak value discriminated by the peak height discriminator, A radiation monitor, characterized by displaying a graph showing a temporal change in the net count rate for each peak of peak value.   2. The radiation monitor according to claim 1, wherein the radiation detection element is attached to an end surface of the photomultiplier tube, and a window through which light generated by the radiation detection element passes is passed through the end surface of the photomultiplier tube. A radiation monitor characterized by being formed.   The radiation monitor according to claim 1, wherein outer surfaces of the radiation detection element and the photomultiplier tube are covered with a shielding film that blocks light but transmits radiation.   The radiation monitor according to claim 1, wherein the radiation detection element includes a radioactive substance that emits at least one of alpha rays and gamma rays. The radiation monitor according to claim 1, wherein the radiation detection element is formed of lanthanum bromide (LaBr ₃ (Ce)) or lutetium silicate (Lu ₂ SiO ₅ (Ce)). monitor. Mounting a radiation detecting element containing a naturally occurring radioactive substance on the end face of the photomultiplier;
Converting light from the radiation detection element into an electrical signal by the photomultiplier;
From the peak value spectrum from the photomultiplier tube, generating a graph showing the time change of the count value of the peak value at which the peak appears;
Displaying the graph on a monitor;
Have
The radiation detection method, wherein the radiation detection element generates light caused by radiation from a naturally occurring radiation substance contained in the radiation detection element and light caused by radiation from the outside.   The radiation monitoring method according to claim 8, wherein the graph is a graph representing a change over time in a count rate of a peak value for each peak area.   9. The radiation monitoring method according to claim 8, wherein the graph is a graph representing a temporal change in a net count rate for each peak of a peak value.   9. The radiation monitoring method according to claim 8, wherein the radiation detecting element includes a radioactive substance that emits at least one of alpha rays and gamma rays. 9. The radiation monitoring method according to claim 8, wherein the radiation detection element is made of lanthanum bromide (LaBr ₃ (Ce)) or lutetium silicate (Lu ₂ SiO ₅ (Ce)). Radiation monitoring method.   A radiation detection element containing a radioactive substance that exists in nature, a photomultiplier tube that converts light from the radiation detection element into an electrical signal, and a peak value at which a peak appears from the electrical signal output by the photomultiplier tube A wave height discriminator for discrimination, a counter for counting wave height values for each wave height area of a predetermined width based on the wave height values discriminated by the wave height discriminator, and counting for each wave height area from the counter A counting rate meter that converts the rate into a rate, and a monitor that displays a graph representing a temporal change in the counting rate of the peak value for each of the peak regions, wherein the radiation detecting element is a naturally occurring radiation contained in itself. A radiation monitor characterized by generating light caused by radiation from a substance and light caused by radiation from the outside.   A radiation detection element containing a radioactive substance that exists in nature, a photomultiplier tube that converts light from the radiation detection element into an electrical signal, and a peak value at which a peak appears from the electrical signal output by the photomultiplier tube A peak height discriminator for discrimination, a peak count rate measuring device that calculates a net count rate for each peak of the peak value based on the peak value discriminated by the peak height discriminator, and a net for each peak of the peak value And a monitor for displaying a graph representing a change in counting rate over time, wherein the radiation detection element is caused by radiation from a naturally occurring radioactive substance contained in the radiation detection element and radiation from the outside. A radiation monitor characterized by generating light.

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