JP7154538B2 - Method and apparatus for measuring radiation energy - Google Patents

Description

The present invention relates to a radiation energy measuring method and apparatus, and more particularly to a radiation energy measuring method and apparatus capable of measuring the energy of radiation with a wide energy distribution, such as cosmic ray muons, using a compact and inexpensive apparatus. .

As a method of measuring the energy of radiation such as protons, neutrons, and gamma rays, there is a method of deriving the energy from the amount of light emitted when the radiation is incident on a scintillator.

In a conventional radiation energy measuring device using a scintillator, for example, a photodetector such as a photomultiplier tube (also called a photomultiplier (PMT)) is arranged behind a plastic scintillator.

In such a measuring device, the amount of light emitted in the scintillator generally increases as the energy of the radiation of the same type increases. Therefore, the energy can be derived from the correlation between the amount of light emitted in the scintillator and the energy of the radiation.

The correlation between the amount of luminescence and radiation energy is obtained by irradiating radiation with known energy and systematically measuring the relationship between the amount of luminescence and energy in the scintillator, or by numerical calculation using a radiation simulation calculation code. be able to.

Glenn F. Knoll "Radiation Measurement Handbook 4th Edition" Ohmsha (September 25, 2013)

As illustrated in FIG. 1, when one low-energy radiation (.mu.) enters the scintillator 10, the radiation (.mu.) stops within the scintillator 10 while imparting its energy to the scintillator 10. FIG. In this case, since the total energy of the radiation is converted into the amount of light emitted in the scintillator 10, the energy can be accurately measured by a photodetector such as a photomultiplier tube 12. FIG. In the figure, 14 is a light guide.

However, for example, when high-energy radiation (μ) is incident on the scintillator, as illustrated in FIG. end up In this case, only part of that energy is imparted to the scintillator 10, and the rest of the energy retained by the transmitted radiation (μ') is unknown. Therefore, when the radiation has high energy enough to pass through the scintillator 10, it is difficult to accurately identify the energy.

Therefore, two methods are conceivable for measuring the energy of radiation while making the radiation stationary in the scintillator. 1, an energy absorbing material (absorber) is placed between the radiation source and the detector to attenuate the energy.

However, the former requires a larger scintillator and a higher manufacturing cost for the detector. In the latter, although the scintillator itself contained in the detector does not increase in size, the absorber is installed in front of the scintillator, so although it is possible to measure only radiation with a specific large energy, a wide energy distribution It is not possible to measure the energy of the radiation that has it, and it is not suitable for measuring the muon energy that comes in with various different energies, such as cosmic ray muons.

SUMMARY OF THE INVENTION The present invention has been made to solve the above conventional problems, and enables the measurement of the energy of radiation such as cosmic ray muons having a wide energy distribution with a compact and inexpensive device.

The present invention comprises a first scintillator that emits light from stationary radiation and is arranged along the direction of incidence of the radiation from the incident side of the radiation; Using a measuring device in which a first absorber that attenuates by a fixed amount and a second scintillator that passes through the first absorber and emits light due to radiation that is stationary inside, each of the first scintillator and the second scintillator When measuring the amount of light emitted and determining the energy of the radiation from the correlation with the energy of the radiation , a Monte Carlo simulation is performed to determine the energy loss rate of the radiation according to the type of absorber material in advance, depending on the measurement energy range and interval. The above problem is solved by selecting the type and thickness of the absorber and using the thickness and density of the absorber according to the size of the object to be measured and the size of the defect to be detected .

Here, the radiation is a layered structure in which two or more pairs of a scintillator that emits light due to the radiation that is stationary inside and an absorber that attenuates the energy of the incident radiation passing through the scintillator are paired in this order. and can be measured using a measuring device having a laminated structure including the first absorber as the absorber and the first scintillator and the second scintillator as the scintillators.

Also, the energy of the radiation can be attenuated by a predetermined amount by the second absorber before entering the first scintillator.

Also, the first absorber can be made of lead or iron.

Also, the second absorber can be made of lead or iron.

At least one of the first scintillator and the second scintillator may be a plastic scintillator.

The present invention also includes a first scintillator which emits light by internally stationary radiation, which is arranged from the incident side of the radiation along the direction of incidence of the radiation, and the energy of the incident radiation passing through the first scintillator. a first absorber that attenuates by a predetermined amount, a second scintillator that passes through the first absorber and emits light by stationary radiation inside, and a light detector that detects each light emission of the first scintillator and the second scintillator means for determining the energy of radiation from the correlation between the amount of light emitted from the radiation and the energy of the radiation based on the output result from the photodetector ; a means for determining the rate in advance and selecting the type and thickness of the first absorber according to the measurement energy region and the interval, according to the size of the object to be measured and the size of the defect to be detected. A device for measuring radiation energy, which is characterized in that the thickness and density of the absorber are differentiated , likewise solves the above-mentioned problem.

Here, in the measuring device, two or more pairs of a scintillator that emits light due to radiation that is stationary inside and an absorber that attenuates the energy of the incident radiation passing through the scintillator by a predetermined amount are stacked in this order. It is possible to provide a laminate structure including the first absorber as the absorber and the first scintillator and the second scintillator as the scintillator.

Moreover, the incident surface of the measuring device can have a second absorber that attenuates the energy of the radiation by a predetermined amount before entering the first scintillator.

A light guide may be provided between the first scintillator and second scintillator and the photodetector to guide the light emitted from the first scintillator and second scintillator to the photodetector.

Further, the material or thickness of the absorbent body can be varied depending on the layers.

For a given size scintillator, it is possible to measure up to the energy of radiation perfectly stationary within it. In the present invention, two or more pairs of absorbers and scintillators are stacked along the incident direction of radiation (the absorber closest to the radiation may be omitted), and the energy is attenuated by passing through the absorbers. Stationary radiation is detected in either a plurality of scintillators or absorbers. Therefore, the energy distribution of a radiation flux having an energy distribution can be measured. In addition, since an absorber generally attenuates radiation energy more than a scintillator, the device can be smaller and less expensive than conventional devices.

A diagram showing light emission when one piece of low-energy radiation is incident on a scintillator of a conventional radiation detector. FIG. 4 is a diagram showing light emission when one high-energy radiation is incident on a scintillator of a conventional radiation detector, for explaining conventional problems; BRIEF DESCRIPTION OF THE DRAWINGS The perspective view which shows the structure of 1st Embodiment of this invention. Side view showing the same light guide part Similarly, the time change of the light emission intensity is compared between (A) the present invention and (B) the conventional example. The perspective view which shows the structure of 2nd Embodiment of this invention. The perspective view which shows the structure of 3rd Embodiment of this invention. Side view showing the same light guide part The perspective view which shows the structure of 4th Embodiment of this invention. The perspective view which shows the structure of 5th Embodiment of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the present invention is not limited by the contents described in the following embodiments and examples. In addition, the configuration requirements in the embodiments and examples described below include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that fall within the so-called equivalent range. Furthermore, the constituent elements disclosed in the embodiments and examples described below may be combined as appropriate, or may be selected and used as appropriate.

A first embodiment of the present invention in which the absorber closest to the radiation source 8 in the absorber/scintillator pair is omitted, as shown in FIG. a scintillator 21, a first absorber 31 that absorbs radiation transmitted through the first scintillator 21, and a second scintillator that transmits light through the first absorber 31 and emits light from the radiation stationary in the scintillator 22, a second absorber 32 that absorbs the radiation transmitted through the second scintillator 22, and a third scintillator 23 that transmits through the second absorber 32 and emits light from the radiation stationary in the scintillator. a third absorber 33 that absorbs the radiation transmitted through the third scintillator 23; a fourth scintillator 24 that transmits through the third absorber 33 and emits light from the radiation stationary in the scintillator; first, second, third and fourth light guides 41, 42, 43 and 44 for guiding light emitted by the first, second, third and fourth scintillators 21, 22, 23 and 24; , second, third and fourth light guides 41, 42, 43 and 44, and from the correlation between the output of the photomultiplier tube 51 and the energy of the radiation, and a data processing circuit 61 for determining the energy of the radiation.

The scintillators 21, 22, 23, 24 can be plastic scintillators, for example.

The absorbers 31, 32, 33 can be, for example, iron or lead.

The light guides 41, 42, 43, 44 are used to make the light outputs of the four scintillators 21, 22, 23, 24 incident on the light receiving surface of a common photomultiplier tube 51, as illustrated in FIG. .

FIG. 5A shows an example of change in emission intensity over time in this embodiment. Waveforms 21A, 22A, 23A and 24A corresponding to scintillators 21, 22, 23 and 24 appear. On the other hand, when the integral scintillator 10 as illustrated in FIG. 1 is used, as shown in FIG. cannot be identified.

The combination of absorber and scintillator is selected according to the type of radiation to be measured and the energy region to be measured. Specifically, a Monte Carlo simulation is performed to determine in advance the radiation energy loss rate depending on the type of absorber material, and the type and thickness of the absorber are selected according to the measurement energy region and spacing.

For example, when measuring radiation with a wide energy distribution with an average number of GeV such as cosmic ray muon flux, when measuring at detailed energy intervals within a certain limited energy range, or when measuring a tendency for a wide energy range The present invention is effective when measuring at discrete energy intervals to obtain.

For example, an energy region suitable for energy window muography is a boundary region where muons are transmitted/not transmitted depending on the presence or absence of defects in the measurement object. Conventionally, it has been difficult to flexibly select the muon energy in muography. However, if the present invention is used in combination with a muography device, it becomes possible to select an energy window according to the type of defect by, for example, narrowing the energy interval to be measured in the boundary region. For example, for a bridge, the muon energy was measured at intervals of less than 1 MeV by an energy measuring device with a laminated structure consisting of a pair of a thin absorber (iron thickness of 0.5 mm) and a thin plastic scintillator (thickness of 5 mm) of the present invention. , to set the energy window.

Generally, in the energy window type muography inspection, when the object to be measured is large and the defects to be detected are large, high-energy muons are suitable and the energy window interval may be large. Therefore, it is advantageous to measure the energy at large intervals using a thick, high-density absorber that attenuates the energy greatly. On the other hand, when the object to be measured is small and the defects to be detected are small, low-energy muons are suitable, and a small energy measurement interval (energy window interval) is desirable. Therefore, it is effective to use a thin, low-density material for the absorber and measure the energy at fine intervals.

As for the radiation energy loss rate depending on the type of absorber material, it is possible to derive the radiation attenuation rate for absorbers with different atomic compositions, densities, thicknesses, etc. using Monte Carlo simulation codes such as PHITS, MCNP, and GEANT4. can.

As in the present embodiment, when one photomultiplier tube 51 detects the light emission amounts of a plurality of (four in the embodiment) scintillators 21, 22, 23, and 24, the second, third, and fourth scintillators A mechanism for identifying the amount of light emitted from the eyes is required. For example, since the light emitted from the scintillator 22 is generated with a time lag from the light emitted from the scintillator 21, the amount of emitted light can be identified. In order to derive the energy of the radiation from the amount of emitted light, as already described in the background art, it is necessary to have the correlation of the energy with the amount of emitted light derived experimentally or by simulation calculation. Moreover, even when several kinds of absorbers and scintillators having different materials and thicknesses are used, the energy of radiation can be determined by similarly obtaining the correlation of the energy of radiation with respect to the amount of light emitted in the scintillator.

In the first embodiment, there is one photomultiplier tube 51 as a photodetector, but as in the second embodiment shown in FIG. Multiplier tubes 51, 52, 53, 54 may be provided.

In this embodiment, light guides 41 , 42 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 , 43 are used in order to match the light output surfaces of the scintillators 21 , 22 , 23 , 24 with the light receiving surfaces of the photomultiplier tubes 51 , 52 , 53 , 54 . 44 are provided. If the light output surfaces of the scintillators 21, 22, 23 and 24 and the light receiving surfaces of the photomultiplier tubes 51, 52, 53 and 54 have the same shape, the ride guide can be omitted.

Further, when the number of photomultiplier tubes that can be used is limited, as in the third embodiment shown in FIG. 24) by means of light guides 41, 43 and light guides 42, 44 to one photomultiplier tube 51, 52 respectively.

FIG. 8 shows the connection relationship between the light guides 41, 42, 43 and 44 and the photomultiplier tubes 51 and 52 in this embodiment.

In the above embodiment, a photomultiplier tube is used as the photodetector, but the photodetector is not limited to this, and may be a multi-pixel photon counter (MPPC) or the like.

Moreover, an inorganic crystal, a liquid, or the like can be used as the scintillator. Also, a semiconductor detector, a nuclear emulsion plate, or the like can be used instead of the scintillator.

Furthermore, the laminated structure is not limited to the combination of the four layers of scintillators and the three layers of absorbers in the above embodiment, and two or more pairs of scintillators and absorbers may be laminated in this order. However, as in the fourth embodiment shown in FIG. 9, in order to remove low-energy radiation not to be measured, or in the configuration of the third embodiment, in order to attenuate the predetermined energy when the energy of the radiation is excessive. , a new absorber 30 can be added in front of the scintillator 21 of the first layer.

Furthermore, as in the fifth embodiment shown in FIG. 10, in a laminated structure similar to that of the fourth embodiment shown in FIG. 51 can also be connected.

Radiation to be measured is also not limited to muons.

21, 22, 23, 24... Scintillator 30, 31, 32, 33... Absorber 41, 42, 43, 44... Light guide 51, 52, 53, 54... Photomultiplier tube (photodetector)
61 data processing circuit

Claims (11)

arranged along the direction of incidence of the radiation from the side of incidence of the radiation;
a first scintillator that emits light by stationary radiation inside;
a first absorber that attenuates the energy of radiation incident through the first scintillator by a predetermined amount;
A second scintillator that passes through the first absorber and emits light by stationary radiation inside,
When measuring the amount of light emitted from each of the first scintillator and the second scintillator and determining the energy of the radiation from the correlation with the energy of the radiation ,
Perform Monte Carlo simulation, determine in advance the radiation energy loss rate depending on the type of absorber material, select the type and thickness of the absorber according to the measurement energy region and interval,
A method for measuring radiation energy, characterized by using different thicknesses and densities of absorbers according to the size of an object to be measured and the size of defects to be detected . The radiation has a laminated structure in which two or more pairs of a scintillator that emits light due to the radiation stationary inside and an absorber that attenuates the energy of the incident radiation passing through the scintillator by a predetermined amount are paired in this order. , the first absorber as the absorber, and the first scintillator and the second scintillator as the scintillator. How to measure. 3. The method of measuring radiation energy according to claim 1, wherein energy of radiation is attenuated by a predetermined amount by a second absorber before entering said first scintillator. 4. The method of measuring radiation energy according to claim 1 , wherein said first absorber is lead or iron. 5. The method of measuring radiation energy according to claim 3 , wherein said second absorber is lead or iron. 6. The radiation energy measuring method according to claim 1, wherein at least one of said first scintillator and said second scintillator is a plastic scintillator. arranged along the direction of incidence of the radiation from the side of incidence of the radiation;
a first scintillator that emits light by stationary radiation inside;
a first absorber that attenuates the energy of radiation incident through the first scintillator by a predetermined amount;
a second scintillator that passes through the first absorber and emits light with stationary radiation inside;
a photodetector that detects each emission of the first scintillator and the second scintillator;
means for determining the energy of radiation from the correlation between the amount of emitted radiation and the energy of radiation based on the output result from the photodetector;
means for performing a Monte Carlo simulation to determine in advance the energy loss rate of radiation depending on the type of absorber material, and selecting the type and thickness of the first absorber according to the measured energy region and interval;
with
A radiation energy measuring apparatus characterized by using different thicknesses and densities of an absorber according to the size of an object to be measured and the size of a defect to be detected . The measuring device has a laminated structure in which two or more pairs of a scintillator that emits light due to radiation that is stationary inside and an absorber that attenuates the energy of the incident radiation passing through the scintillator are paired in this order. 8. The apparatus for measuring radiation energy according to claim 7 , comprising a laminated structure including the first absorber as the absorber and the first scintillator and the second scintillator as the scintillator. 9. The radiation energy measuring device according to claim 7 , wherein the incident surface of the measuring device has a second absorber that attenuates the radiation energy by a predetermined amount before entering the first scintillator. . A light guide is provided between the first scintillator and the second scintillator and the photodetector to guide light emitted from the first scintillator and the second scintillator to the photodetector. A radiation energy measuring device according to any one of claims 7 to 9 . 11. A radiation energy measuring device according to claim 7 , wherein the material or thickness of said absorber differs from layer to layer.

Images