JP6108394B2 - Radiation energy distribution detection method and detection apparatus therefor - Google Patents

Description

  The present invention estimates the radiation energy distribution of charged particles emitted from a high-intensity radiation source or electromagnetic waves converted into the charged particles, thereby affecting the effect of quality hardening of transmitted X-rays, which is a problem in X-ray CT and the like. The present invention relates to a radiation energy distribution detection method and a detection apparatus thereof.

  Radiation, especially X-rays, is widely used for medical and industrial purposes. Examples of X-ray generators include radioactive materials that emit X-rays, X-ray tubes, X-ray sources using electron linear accelerators, and radiation facilities. X-ray tubes and electron linear accelerators are often used for medical industry applications. An X-ray source using an X-ray tube or an electron linear accelerator uses a bremsstrahlung X-ray generated at that time by accelerating an electron beam and entering the target. The bremsstrahlung x-ray is not monochromatic but has a continuous energy spectrum.

  X-ray imaging and X-ray CT using X-rays having a continuous energy spectrum have a problem of beam quality hardening (beam hardening). X-rays are attenuated in the subject, but the attenuation coefficient depends not only on the type and density of the substance but also on the energy. That is, the energy distribution of X-rays that have passed through the subject changes. In the region of about 10 MeV from the region of the X-ray energy that can be generated by the X-ray tube, the attenuation coefficient becomes lower than the X-ray energy. Low-energy X-rays decrease, and high-energy X-rays pass through the subject without decreasing relatively. Therefore, the phenomenon of quality hardening that the energy distribution of transmitted X-rays becomes a distribution closer to the higher one is seen. This quality hardening is known to have serious effects (artifacts) such as density distortion in CT images during image reconstruction in X-ray CT, and various correction means have been proposed. ing.

  In patent document 1, it is going to remove the influence of a quality hardening by the X-ray energy distribution information obtained with the X-ray detector which operate | moves in photon counting mode. However, since the operation in the burst mode in which a large number of photons are simultaneously incident on the detector cannot be performed, the measurement time has to be long.

  In Patent Document 2, X-rays having different energy distributions are generated by applying different voltages to the X-ray tube, and respective images are acquired and reconstructed. However, the same image must be irradiated twice with X-rays, and there is a concern that the patient's exposure will increase.

  Artifacts caused by radiation hardening occur in the medical field near bones, artificial bones, and other parts such as metal, where X-ray absorption is greater than other parts, and this is a serious problem that affects diagnostic results. . Even in industrial applications, for example, artifacts occur in the steel frame portion of reinforced concrete.

  In order to know the energy distribution of X-rays, the deposit in the detector of the total energy of the photons is usually measured in the photon counting mode in which the X-ray photons are incident on the detector in a time-discrete state. It is needed. When two or more photons are incident on the detector simultaneously and deposit energy, the total energy is provided as a signal. Therefore, in the burst mode where a large number of photons are simultaneously incident on the detector, only the total energy is known.

  As far as soft X-rays are concerned, it is not impossible to measure burst mode energy distribution by applying a wavelength dispersion type X-ray measurement method. However, a wavelength dispersion type X-ray measurement method uses a crystal lattice. Since this method involves taking out X-rays of specific energy and measuring the intensity, it takes time to measure the energy distribution by changing the angle of the crystal lattice and performing an energy scan. In addition, the apparatus becomes large. On the other hand, in the case of hard X-rays of several hundred keV or more, the efficiency of reflection by the crystal lattice is lowered, which is not practical.

  Patent Document 3 discloses a method of using a Cherenkov counter in order to eliminate, for example, “noise” coming out of low energy scattered gamma rays by utilizing sorting by energy bands as in the present invention. However, the present invention is not used for the purpose of obtaining information on the hardening of the wire quality by detecting the distribution of radiation energy. Also, no consideration is given to stacking Cherenkov counters.

  Patent Document 4 discloses a multicolor X-ray measurement in which X-ray detectors are stacked and the intensity ratio for each energy of a plurality of monochromatic X-rays is measured using the difference in the linear attenuation coefficient according to the X-ray energy. A method has been proposed. However, in this method, a plurality of monochromatic X-rays whose energies are known are to be measured, and for each monochromatic X-ray, the detection efficiency of the X-ray detector and the transmission efficiency until it enters the detector are verified beforehand. Need to ask. For this reason, it is not easy to apply to a method of detecting energy distribution by subdividing X-rays having a continuous energy spectrum for each energy, and the versatility is poor.

  In Non-Patent Document 1, magnetized iron is installed between two Cherenkov counters, each having airgel and air, to cause a change in transmittance due to X-ray spin between the two Cherenkov counters. A short pulse gamma ray knitting extreme measuring device is disclosed. Of the two Cherenkov counters, the rear air Cherenkov counter measures the intensity of X-rays that have passed through magnetized iron, and is installed to measure the energy distribution of incident X-rays (gamma rays). is not. Furthermore, the maximum energy of X-rays (gamma rays) described in the text of Non-Patent Document 1 was estimated by using a theoretical formula from the energy of the electron beam and the wavelength of the laser beam, not the value measured by the Cherenkov counter. Is. The magnetized iron described in Non-Patent Document 1 corresponds to a subject to be inspected in the present invention.

JP 2010-82031 A JP 2008-154784 A Japanese Patent No. 3569227 Japanese Patent No. 4839050

Masashi Fukuda, “Polarization Measurement of Short-Pulse Gamma Rays Produced through Inverse Compton Scattering of Circularly Polarized Laser Beams”, JAHEP-Japan Association of High Energy Physicists, High Energy News Research Introduction, Vol. 23, No. 2, 2004 , P57-62

  The present invention provides information on energy distribution necessary for obtaining an accurate CT image free from artifacts due to radiation hardening in an image configuration by radiation imaging or radiation CT, that is, in a radiation detector in the burst mode described above. An object of the present invention is to provide a radiation energy distribution detection method and a detection apparatus for acquiring information related to the energy distribution of radiation of known type in a short time.

  In order to solve the above problems, the present inventor has provided a plurality of Cherenkov counters having different energy thresholds when Cherenkov radiation occurs with respect to the incident direction of charged particles that are radiation or electromagnetic waves converted into the charged particles. It was found that the radiation energy distribution can be estimated more accurately than before by arranging in series and obtaining the radiation intensity existing in a predetermined range of the energy threshold value by each Cherenkov counter. That is, the present invention has the following configuration.

  In the present invention, a plurality of Cherenkov counters having different energy thresholds when Cherenkov radiation occurs are arranged in series with respect to the incident direction of charged particles that are radiation or electromagnetic waves converted into the charged particles, and the plurality of Cherenkov counters are arranged in series. In each of the above, by converting the radiation intensity existing in a predetermined range of the energy threshold from the light intensity measured by the photodetector provided in the Cherenkov counter, the radiation energy distribution for estimating the radiation energy distribution is calculated. It is a detection method. Here, the energy threshold when the Cherenkov radiation occurs is controlled by the refractive index of the optical medium included as the Cherenkov radiator in the Cherenkov counter, and the conversion of the radiation intensity existing in a predetermined range of the energy threshold is known. Calibration is performed by using the relationship between the energy and the light intensity, or by simulation calculation.

  Further, the present invention provides a plurality of Cherenkov counters each having at least two different refractive indexes selected from the group consisting of gas, gel, liquid and solid in order to change the energy threshold when Cherenkov radiation occurs. It is composed of charged particles in the order of a Cherenkov counter having the Cherenkov radiator having a relatively low density and a low refractive index, and a Cherenkov counter having the Cherenkov radiator having a relatively high density and a high refractive index. It arrange | positions in series with respect to the incident direction of a radiation. In addition, in order to change the energy threshold, the plurality of Cherenkov counters use at least two or more solids having different refractive indexes as Cherenkov radiators, respectively, and the energy threshold is low and the refractive index is relatively high. The Cherenkov counter having the Cherenkov radiator may be arranged in the order of the Cherenkov counter having the Cherenkov radiator having a high energy threshold and a relatively low refractive index.

  Further, the present invention provides the photodetector for detecting the Cherenkov light by installing a plurality of photodetectors in one Cherenkov counter and shielding at least one of the photodetectors so that the Cherenkov light does not enter. And a radiation energy distribution detection method for measuring the intensity of the Cherenkov light from a difference in electrical signal between the light detector and the photodetector that shields the Cherenkov light. In addition to this, there are a plurality of optical fibers as means for transmitting the Cherenkov radiator or Cherenkov light to the photodetector for changing the energy threshold, so that at least one of the optical fibers does not receive Cherenkov light. The intensity of the Cherenkov light may be measured from the difference in electrical signal between the optical fiber and the optical fiber that is not shielded.

  According to the method for detecting a radiation energy distribution of the present invention, a main detector comprising a scintillation counter or a semiconductor radiation detector is replaced with a Cherenkov counter arranged at the end of a plurality of Cherenkov counter groups or at the end of the Cherenkov counter group. And measure all the radiation intensity transmitted through the subject by the main detector, and convert all the radiation intensities and the intensity signals measured by the photodetectors in each of the plurality of Cherenkov counters. This is a method for estimating the influence of radiation hardening on the radiation energy distribution by comparing with the radiation intensity existing in a predetermined range of the energy threshold.

  When detecting the energy portion of X-rays emitted from the X-ray tube, at least one of the Cherenkov counters has a converter plate for converting X-rays into charged particles on the front surface on the X-ray incident side. . Here, the solid used as the Cherenkov radiator of the Cherenkov counter may be at least one selected from the group of high refractive index glass, cubic zirconia, diamond, strontium titanate, moissanite, and rutile.

  The radiation energy distribution detection apparatus of the present invention has a plurality of Cherenkov counters arranged in series with different energy thresholds when Cherenkov radiation occurs with respect to the incident direction of charged particles that are radiation or electromagnetic waves converted to the charged particles. And a processing device for converting radiation intensity existing in a predetermined range of the energy threshold from light intensity measured by a photodetector provided in the Cherenkov counter in each of the plurality of Cherenkov counters. Have Here, the Cherenkov counter includes at least a Cherenkov radiator having a refractive index corresponding to an energy threshold when the Cherenkov radiation occurs, and a photodetector that detects the Cherenkov light, and has a predetermined energy threshold. The processing apparatus for converting the radiation intensity existing in the range includes means for performing calibration using a relationship between known energy and light intensity, or performing simulation calculation.

  Further, in the radiation energy distribution detection apparatus of the present invention, the means for converting the radiation intensity existing in the predetermined range of the energy threshold, the structure of the Cherenkov counter and the optical medium incorporated therein, and the detection means by the photodetector Has the same configuration as that adopted in the detection method of the radiation energy distribution described above. Here, an optical fiber may be used as means for transmitting the Cherenkov radiator or Cherenkov light for changing the energy threshold to the photodetector.

  In addition, the radiation energy distribution detection device of the present invention uses a scintillation counter or a semiconductor radiation detector as a means for measuring all the radiation intensities that pass through a subject in order to estimate the influence of radiation hardening on the radiation energy distribution. The main detector is arranged at the end of the plurality of Cherenkov counter groups or instead of the Cherenkov counter arranged at the end of the Cherenkov counter group.

  According to the detection method of the present invention, it is possible to estimate the energy distribution of X-rays not in the photon counting mode but in the burst mode. There is no need to perform a wavelength scan (sweep) as in the conventional wavelength dispersion type, and if the X-ray intensity is strong, the X-ray energy distribution can be estimated in one shot in principle.

  Further, according to the detection apparatus of the present invention, it is possible to estimate an X-ray energy distribution in a one-dimensional or two-dimensional space by configuring an array of Cherenkov counter groups instead of a single Cherenkov counter group.

  Furthermore, in the detection method and detection apparatus of the present invention, by using a high refractive index material as a Cherenkov radiator, X-ray energy distribution estimation in a range emitted by an X-ray tube having a normal tube pressure (about 120 kV) can be performed. It becomes possible. For this reason, in CT using an X-ray tube, X-ray quality hardening can be estimated even if X-ray bombardment is performed only once. In addition, tungsten or molybdenum is frequently used for the X-ray target of the X-ray tube, and the X-ray tube emits characteristic X-rays depending on the target material in addition to the bremsstrahlung X-rays. In that case, it is possible to distinguish the Ka line and the Kb line by optimizing the optical medium used as the Cherenkov radiator in consideration of the energy threshold of characteristic X-rays by tungsten or molybdenum.

  In addition, the energy distribution of X-rays by an electron linear accelerator having an electron beam energy of less than 1 MeV is about 100 keV to 300 keV. By using various optical glasses (refractive index 1.43-2.14), it is possible to know the detailed energy distribution.

  As a result, artifacts resulting from X-ray CT quality hardening can be corrected based on the measured values, and the accuracy of image diagnosis and the like is improved. This is expected to improve diagnostic accuracy in the medical field, leading to a reduction in misdiagnosis.

It is a figure which shows the relationship between the refractive index of an optical medium, and the emission threshold value of Cherenkov light with respect to the kinetic energy of an electron. It is a figure which shows one Example of the detection apparatus of the radiation energy distribution by this invention. It is sectional drawing which shows the structure of the Cherenkov counter used for this invention. It is sectional drawing which shows another structure of the Cherenkov counter used for this invention. It is sectional drawing which shows the detection apparatus of the radiation energy by this invention which has arrange | positioned two of the Cherenkov counters which have an optical fiber in series. FIG. 5 is a diagram showing a configuration of another embodiment of the radiation energy distribution detection apparatus according to the present invention. It is a schematic diagram of the X-ray source using an electron linear accelerator. In Example 5 of this invention, it is a schematic diagram of the apparatus which measures the maximum energy of a X-ray.

  It is known that Cherenkov radiation occurs when charged particles moving at a speed v close to the speed of light c are incident on an optical medium at a speed faster than the speed of light in the medium (v> c / n, n: refractive index of the medium). . If a = v / c, then a = 1 / n is a threshold value that determines whether Cherenkov radiation occurs.

が閾値となる(ｍは荷電粒子の質量である)。 For the total energy E of charged particles

Becomes the threshold (m is the mass of the charged particle).

が成り立つ。 For the kinetic energy K of charged particles,

Holds.

  The relationship between the refractive index of the optical medium and the emission threshold of Cherenkov light with respect to the kinetic energy of electrons is shown in FIG. As shown in FIG. 1, energy thresholds at which Cherenkov radiation occurs are different in optical media having different refractive indexes. When charged particles having a certain kinetic energy are incident on a plurality of optical media having different refractive indexes, an optical medium that generates Cherenkov radiation and an optical medium that does not generate the same appear depending on the refractive index.

  On the other hand, in order to observe the Cherenkov radiation, a Cherenkov detector (hereinafter referred to as a Cherenkov counter) is used. Therefore, only one Cherenkov counter can only obtain information on radiation having kinetic energy equal to or higher than the energy threshold corresponding to the refractive index of the optical medium contained therein, and cannot accurately grasp a wide range of energy distribution. . On the other hand, a plurality of optical media having different refractive indexes are arranged in the charged particle incident direction, and the presence or absence of Cherenkov radiation of each optical medium is detected. The kinetic energy can be measured over a wide range. In other words, the radiation intensity corresponding to the radiation energy is separated and measured by a plurality of Cherenkov counters each having a plurality of optical media having different refractive indexes, so that a wide energy range from a high energy component of radiation to a low energy component sequentially. It is possible to reliably detect the energy distribution while subdividing. Therefore, even if the radiation is incident on the radiation detector in the burst mode, the information on the energy distribution can be acquired accurately in a short time. The radiation energy distribution detection method and the detection apparatus thereof according to the present invention are based on this principle.

  In addition, it is known that an optical medium causing Cherenkov radiation can have two kinds of energy thresholds in one optical medium when the total reflection condition of light is used (Non-Patent Document: Yuta Sada, “Experiment Development of total reflection type glass Cerenkov detector for ”, Kyoto University Graduate School of Science, Master thesis J-PARC E15, 2010). Although this document uses optical media having different refractive indexes, the purpose is to identify the type of particles whose particle momentum is known, and the method for selecting the refractive index is different from that of the present invention.

  The radiation energy distribution detection method and the detection apparatus thereof according to the present invention will be described below with reference to examples.

<Example 1>
FIG. 2 is a diagram showing the configuration of the radiation energy distribution detection apparatus according to this embodiment. As shown in FIG. 2, the detection apparatus of the present invention uses a plurality of Cherenkov counters 1 (referred to as C1, C2, C3,. Group 2 is arranged in series with respect to the incident direction of radiation. As shown in FIG. 3, the Cherenkov counter 1 includes an optical medium (radiant) 6 that generates Cherenkov radiation, a photodetector 7 that detects Cherenkov light, a light shielding film that surrounds the optical medium, and a reflective film. As shown in FIG. 1, the optical medium (radiant) 6 is a radiator that determines whether or not Cherenkov radiation is generated. Therefore, the optical medium (radiant) is defined as “Cherenkov radiator 6” below. In the present invention, the Cherenkov light 1 may be reflected by the mirror 9 and guided to the photodetector 7 surrounded by the radiation shield 8. As shown in FIGS. 2 and 3, for detecting X-rays, a converter (metal plate) 5 is disposed in front of the Cherenkov radiator 6, and the X-rays are converted into charged particles (electrons, positrons). Convert. The converters 5 do not have to be installed in all the Cherenkov counters 1 constituting the Cherenkov counter group 2. The converter 5 may not be used when detecting the radiation energy of charged particles (electrons, positrons).

  The plurality of Cherenkov counters 1 shown in FIG. 2 are arranged so that energy thresholds when Cherenkov radiation occurs are different from each other. The present invention performs the following two methods for arrangement.

  The first method is a method in which the energy threshold is lowered in the order of C1, C2, C3,..., Cn. In this method, the radiation incident on the detection device shown in FIG. 2 is sequentially detected by each Cherenkov counter 1 from a high energy threshold value to a low energy threshold value according to the magnitude of the radiation energy. As a result, radiation having a relatively high energy is detected at the beginning of the plurality of Cherenkov counter groups 2, and radiation having a relatively low energy is detected as approaching the tail. Therefore, a wide range of energy can be measured. In this way, it is possible to accurately detect the radiation energy distribution for various types of radiation incident in the burst mode in a short time.

  As shown in FIG. 1, the energy threshold can be increased by reducing the refractive index of the Cherenkov radiator that causes Cherenkov radiation. In general, the refractive index can be adjusted by the polarizability and density of an optical medium used as a Cherenkov radiator. In this embodiment, each of the Cherenkov counters 1 (C1, C2, C3,..., Cn) has a density. The refractive index is controlled by using different Cherenkov radiators. Since a low-density material tends to have a low refractive index, the plurality of Cherenkov counters 1 are C1, C2, C3,... In order from those having a low-density Cherenkov radiator to those having a high-density Cherenkov radiator. ..., arranged as Cn. The reason why the plurality of Cherenkov counters 1 are arranged from those having a low-density Cherenkov radiator is as follows. If it is arranged from those having a high-density Cherenkov radiator, the radiation is absorbed and shielded by the high-density detector, and it is difficult for the radiation to reach the Cherenkov counter disposed behind. As a result, the effect of improving the detection performance due to the fragmentation of radiation energy cannot be obtained.

  The second method is a method in which all of the Cherenkov radiator is composed of a combination of solids having different energy thresholds. Here, each of the solid Cherenkov radiators is installed in the order of a plurality of Cherenkov counters 1 (C1, C2, C3,..., Cn) in ascending order of energy thresholds. The reason why the plurality of solids are arranged in order from the lowest energy threshold is as follows. In the solid Cherenkov radiator, radiation hardening appears more conspicuously than gas and liquid, so that radiation having low energy is absorbed in the middle. If a solid Cherenkov radiator with a low energy threshold is disposed behind, accurate measurement of low-energy radiation intensity becomes difficult. Therefore, in the case of a solid Cherenkov radiator, the intensity of radiation having low energy is detected first by placing a solid having a low energy threshold in front.

  One of the first method and the second method can be selected and adopted according to the energy distribution range of the radiation to be measured based on the relationship shown in FIG. In some cases, the first and second methods may be combined. For example, in the first method, a combination of a plurality of solids having different energy threshold values is used instead of one type of solid as the Cherenkov radiator disposed at the end. A specific optical medium used as a Cherenkov radiator in the Cherenkov counter of the present invention will be described in detail later.

  Unlike the charged particles, the photodetector 7 provided in the Cherenkov counter 1 shown in FIGS. 2 and 3 is not directly sensitive to X-rays or gamma rays that are electromagnetic waves. However, it is known that X-rays and gamma rays emit electrons through the photoelectric effect, Compton effect, and electron pair generation in the material. Therefore, when detecting X-rays or gamma rays, a converter 5 made of metal or the like is installed in front of the Cherenkov counter 1, and the converter 5 converts the X-rays into electrons by photoelectric effect, Compton effect, and electron pair generation. It is possible. A similar reaction occurs in the Cherenkov counter, but it is preferable to install a converter in terms of conversion efficiency. Electrons emitted by the photoelectric effect have a kinetic energy almost equal to that of X-rays. Strictly speaking, the value is obtained by reducing the binding energy. The electrons are detected by the Cherenkov counter if the energy of the X-rays exceeds the threshold for the kinetic energy of the electrons of the Cherenkov counter.

であることが知られている。 Further, it is known that when the X-ray energy is several hundred keV or more, the Compton effect has a larger scattering cross section than the photoelectric effect. The maximum energy K _Rmax of the anti-view electrons emitted by the Compton effect is E _photon as the incident X-ray energy.

It is known that

  Furthermore, when the X-ray energy exceeds twice the mass energy of electrons, electron pair generation occurs. The maximum value of the kinetic energy of electrons or positrons generated by electron pair generation is a value obtained by subtracting twice the mass energy of electrons from the incident X-ray energy. Although it depends on the material, when the energy of X-rays exceeds 1 MeV, the photoelectric effect hardly occurs and electron pair production becomes dominant.

  Thus, as the energy threshold value of the X-ray detector, the maximum kinetic energy of electrons or positrons generated by photoelectric effect, Compton effect, or electron pair generation is used.

  The optimum value of the thickness of the converter 5 varies depending on the energy range used, but the probability that a photon is converted into an electron (positron) should not be so high as a few percent or less. If the converter 5 is too thick, the converted electrons are scattered in the converter or lose energy. In addition, the amount of photons reaching the subsequent stage is reduced. Generally, tungsten, iron, copper, or an alloy thereof is used as the material of the converter 5. Further, aluminum or lead as described in Non-Patent Document 1 may be used as the material of the converter 5. As for the material and thickness of the converter 5, there are many parts that depend on the energy and dose of the incident radiation, the intended purpose, and the design policy, and the details can be optimized by experiments. In some cases, it may be determined using a Monte Carlo simulation or the like, and an optimum configuration of the converter can be used if confirmation is finally made through experiments or the like.

  In the Cherenkov counter 1, if the photodetector 7 is installed behind the Cherenkov radiator 6, there is a risk of directly detecting X-rays or electrons. Therefore, as shown in FIG. 3, the photodetector 7 should be installed on the side surface of the Cherenkov radiator 6. It is common. Usually, the Cherenkov light is transmitted to the photodetector 7 by means for transmitting the Cherenkov light to the photodetector. For example, the mirror 9 shown in FIG. 3 is often used to collect light from behind the Cherenkov counter 1 in a direction perpendicular to the radiation incident direction. In this case, the mirror 9 and the mirror 9 to the photodetector 7 are often used. The light-shielded space 20 is functioned as an optical waveguide and corresponds to means for transmitting Cherenkov light to the photodetector. In addition, the light receiving surface of a photomultiplier tube often used as the photodetector 7 is glass and may emit Cherenkov light. When the Cherenkov radiator emits more Cherenkov light, A photomultiplier tube may be installed behind.

  Further, a wavelength conversion element may be interposed between the photodetector and the Cherenkov counter in order to convert the ultraviolet light of the Cherenkov light into the sensitivity wavelength of the photodetector. In addition to this, there is an optical medium doped with a wavelength conversion material as a Cherenkov radiator, so that it can also be used (see, for example, JP-A-2005-247661). The ultraviolet rays contained in the Cherenkov light can be observed as visible light by these methods, so that reliable detection can be performed even if the observed Cherenkov light is weak.

  As described above, since many photodetectors are sensitive to radiation, it is preferable to provide appropriate radiation shielding around the photodetector by a radiation shield 8 as shown in FIG.

  In FIG. 2, when the photodetector 7 is sensitive to radiation, scattered radiation or the like may be detected as a noise signal by the photodetector 7. In order to solve this problem, in the present invention, a plurality of photodetectors 7 are installed in one Cherenkov counter 1, and some (half) of them are shielded by a light shielding means such as an optical filter, and Cherenkov light is emitted. It is preferable not to enter the photodetector. In the case of detecting and shielding the Cherenkov light, the signal of Cherenkov light can be estimated based on the difference between the electric signal levels of the two. In that case, it is desirable that the light-shielding photodetector and the photodetector capable of detecting Cherenkov light be adjacent to each other as much as possible, and it is particularly desirable to install them within the same radiation shield.

  As described above, the Cherenkov radiator 6 and the photodetector 7 are usually optically coupled by means for transporting Cherenkov light to the photodetector. For example, in FIG. 3, the light-shielded space 20 from the mirror 9 to the photodetector 7 functions as an optical waveguide and corresponds to means for transmitting Cherenkov light to the photodetector. As a means for transporting the Cherenkov light to the photodetector, an optical fiber or the like can be considered. In addition to this, a cavity such as a reflection film installed on the inner side of the waveguide, and various optical elements not installed for the purpose of emitting Cherenkov light are conceivable. When the Cherenkov radiator 6 is a gas and the light detector is installed outside the gas container, the light extraction window is also included in the means for transmitting the Cherenkov light to the light detector. . The means for transmitting Cherenkov light to the photodetector is not necessarily insensitive to radiation. For example, there is a possibility of emitting Cherenkov light or scintillation light. Therefore, it may be necessary to remove noise signal light generated by the means for transmitting the Cherenkov light to the photodetector. In order to remove noise signal light generated by the means for transmitting the Cherenkov light to the photodetector, a plurality of means for transmitting the Cherenkov light to the photodetector are prepared, and at least one of them (generally, generally About the half), a means for blocking optical coupling with the Cherenkov radiator is provided. Specifically, a filter having a light shielding ability is inserted between the Cherenkov radiator and the means for transmitting the Cherenkov light to the photodetector. In this case, it is not necessary to block the light in the above-described photodetector 7. For example, the optical fiber and the photodetector 7 used as means for transmitting the Cherenkov light to the photodetector are one-to-one, one-to-many, many-to-one or Many-to-many optically coupled. However, what is not equipped with a filter should be separated.

  The means for transmitting the Cherenkov light to the photodetector may consist of a plurality of parts, but the maximum energy of the radiation to be detected is known and in part or all of the means for transmitting the Cherenkov light to the photodetector When it is determined that there is no risk of noise signal generation, a filter is applied from a position close to the Cherenkov radiator 6 to a position where the noise signal closest to the Cherenkov radiator 6 can be generated to an arbitrary position between the Cherenkov radiators 6. Can also be installed.

  The photodetector 7 or the combination of the means 7 for transmitting Cherenkov light to the photodetector 7 and the photodetector 7 usually has an independent readout circuit (including ADC, etc.) (one-dimensional or two-dimensional light such as a CCD). This is not the case in the case of a detector), and is connected to an analysis processing device 4 (computer or the like). The difference of the signal level between the above-described detector that detects Cherenkov light and the one that is shielded from light can be performed by the analytical calculation device 4. It is also possible to perform a difference between both signal levels using a differential amplifier circuit in front of an ADC or the like.

  Next, the Cherenkov radiators having different densities provided in the plurality of Cherenkov counters 1 (C1, C2, C3,..., Cn) shown in FIG. 2 will be described. As described above, since the quality hardening also occurs in the Cherenkov counter, as a first method, the Cherenkov radiators are arranged in ascending order of density. Specifically, since it is necessary to increase the refractive index difference, that is, the density difference, so that the difference in energy threshold can be clarified, the silica airgel, liquid, and solid that increase in density sequentially from a gas with a lower density, respectively. It is preferable to arrange in the order of the Cherenkov counter. The present invention may use two or more Cherenkov radiators having at least different densities selected from the group of gas, silica aerogel, liquid and solid according to the energy threshold, and it is necessary to use Cherenkov radiators having different forms in combination. There is no. Even if they belong to the same form, they can be used as two or more Cherenkov radiators having different refractive indices by selecting ones having different densities.

  In the present invention, solids having different energy thresholds may be used in combination as the second method of arranging the Cherenkov radiator. Here, each solid Cherenkov radiator has a low energy threshold and a Cherenkov counter having a relatively high refractive index optical medium to a Cherenkov counter having a relatively low refractive index optical medium having a high energy threshold. Install in order. A combination of Cherenkov radiators composed of a plurality of solids is a solid optical medium disposed at the end when using at least two different refractive indexes selected from the group consisting of the gas, silica airgel, liquid, and solid. It may be adopted as one of the configurations.

  Air, carbon dioxide, nitrogen, argon and other gases, silica airgel, water and other liquids, acrylic resin, various optical glasses, diamond and diamond substitutes can be used as the Cherenkov radiator for the Cherenkov counter .

  For example, according to JP 2005-247661 A, the refractive index of silica airgel is 1.01 to 1.3. According to Makoto Tabata, a refractive index of 1.0022-1.265 is possible (Master's thesis, Graduate School of Natural Sciences, Chiba University) “See 2006.)

  Since the refractive index of gas depends on density, that is, temperature and pressure, it needs to be taken into consideration. Humidity cannot be ignored for air. A dry single gas is desirable. Conversely, by increasing the density by pressurizing the gas, it is possible to increase the refractive index and obtain a lower threshold. The refractive index strictly depends on the wavelength of light. When used as a Cherenkov radiator, these factors are taken into consideration and an optical medium having an optimum refractive index is selected for measurement. Examples of optical media used as Cherenkov radiators in this example are shown in Table 1 below.

When detecting charged particles instead of X-rays, the Cherenkov counter is made thinner with respect to the charged particle traveling direction in consideration of the range of charged particles in the Cherenkov radiator. Gas or silica aerogel is preferred over liquid or solid.

  When applied to X-ray detection, a solid material having a high refractive index, such as optical glass having a refractive index of 2 or more, diamond and cubic zirconia having a refractive index of 2.417, strontium titanate, moissanite, rutile, etc. When a diamond substitute is used as a Cherenkov radiator, it is possible to estimate the energy distribution of X-rays in the range emitted by an X-ray tube with a normal tube pressure (about 120 kV). Further, in CT using an X-ray tube, X-ray quality hardening can be estimated even if X-ray irradiation is performed only once.

  For the X-ray target of the X-ray tube, tungsten or molybdenum is frequently used. The X-ray tube emits characteristic X-rays depending on the target material in addition to the bremsstrahlung X-rays. For example, the characteristic X-rays of tungsten are Ka1 = 59.319 [keV], Ka2 = 57.982 [keV], Kb1 = 67.245 [keV], Kb2I = 69.101 [keV] (http://physics.nist.gov/PhysRefData (See /XrayTrans/Html/search.html). In contrast to the energy threshold values of diamond and cubic zirconia, it can be seen that the use of diamond and cubic zirconia can distinguish the Ka and Kb lines.

  In addition, the energy distribution of X-rays by an electron linear accelerator having an electron beam energy of less than 1 MeV is about 100 keV to 300 keV. If you have various optical glasses (refractive index 1.43-2.14), you can know the detailed energy distribution.

  As shown in FIG. 2, it is preferable to install a scintillation counter or a semiconductor detector capable of total X-ray absorption as the main detector 3 behind the Cherenkov counter group thus configured. The main detector 3 is normally arranged at the end of the Cherenkov counter group, but may be arranged so as to be provided in place of the Cherenkov counter arranged at the end of the Cherenkov counter group. By doing this, the entire X-ray transmittance of the subject is measured by the main detector, and all the radiation intensities measured in this way and each of the plurality of Cherenkov counters are measured by the photodetector provided in the Cherenkov counter. It is possible to estimate the influence of hardening of the radiation on the radiation energy distribution by comparing with the radiation intensity existing in a predetermined range of the energy threshold converted from the intensity signal. However, the installation of the main detector 3 is not essential.

  The signals of the Cherenkov counter group and the scintillation counter (or semiconductor detector) are input to an independent ADC after X-ray bombardment and are immediately read out by the analysis processor 4. However, this is not the case with a two-dimensional photodetector.

  One of the simplest detection methods for estimating the energy distribution of radiation according to the present invention by applying the detection apparatus shown in FIGS. 2 and 3 is as follows.

  In the Cherenkov counter group 2 composed of n Cherenkov counters 1 shown in FIG. 2, the individual Cherenkov counters 1 are arranged as C1, C2, C3,. The energy threshold of Ci (i = 1... N) is Si (i = 1... N), and the estimated radiation intensity (such as the number of X-ray photons) at Ci is Ni ((i = 1... N). And

The radiation intensity (such as the number of X-ray photons) estimated to be between the threshold value Si and S _{i + 1} can be simply obtained from N _{i + 1} −Ni. At this time, as a matter of course, the relationship between the actual signal level of each Cherenkov counter and the estimated radiation intensity (such as the number of X-ray photons) must be known by some method.

  As a method of estimating the relationship between the actual signal level of each Cherenkov counter and the estimated radiation intensity (number of X-ray photons, etc.), (quasi) monochromatic X-rays with known energy and intensity (radiation from radioisotopes) There is a direct method of calibrating using X-rays or gamma rays). In addition, the conversion efficiency from X-rays to electrons etc. is obtained by Monte Carlo simulation, and the relationship between the signal level of charged particles and Cherenkov counters is determined as a single, single (single) charged particle (a particle beam generated by an accelerator, There is also a method in which a beta ray or the like emitted from a radioisotope is obtained by using a bending electromagnet or the like for energy selection. It is also possible to rely on calculation for everything.

  As described above, the radiation intensity (physical quantity reflecting the number of radiation photons) corresponding to the kinetic energy threshold of radiation is measured by each of a plurality of Cherenkov counters, so that an accurate radiation energy distribution can be obtained over a wide range of energy. Can be detected.

<Example 2>
FIG. 4 is a diagram showing a configuration of the Cherenkov counter 1 having a plurality of optical fibers as means for transmitting the Cherenkov radiator 6 or Cherenkov light for changing the energy threshold to the photodetector.

  FIG. 4A shows an example of a Turenkov counter when the optical fibers 10 and 11 are used as means for transmitting Cherenkov light emitted by the Cherenkov radiator 6 to the photodetector 7. FIG. 4 (b) shows that the Cherenkov radiator is not included in the Turenkov counter 1, and the optical fibers 13 and 14 are not only used as means for transmitting Cherenkov light to the photodetector, but also as Cherenkov radiators. It is an example of a Turenkov counter provided to bear the function of. Further, the Turenkov counter shown in FIG. 4C is an example in which an optical fiber is installed between the converter 5 and the filter 12. As a result, an effect of reducing an adverse effect on the measurement due to scattering of radiation generated between the converter 5 and the filter 12 can be obtained, and more precise measurement is possible. The filter 12 shown in FIGS. 4A to 4C is used to selectively measure only Cherenkov light having an energy threshold value to be measured. The detection apparatus of the present invention can be configured by arranging two or more Cherenkov counters shown in FIGS. 4A to 4C in the same manner as shown in FIG.

  FIG. 5 shows an example of a radiation energy detection device according to the present invention in which two Cherenkov counters shown in FIGS. 4A and 4B are arranged in series. The detection apparatus of the present invention shown in FIG. 5A is a series of two Cherenkov counters 1 that detect Cherenkov light emitted by the Turenkov radiator 6 with optical fibers 10 and 11 in series. On the other hand, FIG. 5B shows a light detection by arranging a Cherenkov counter 1 for detecting Cherenkov light emitted by the Turenkov radiator 6 with optical fibers 10 and 11 on the radiation incident side (upper stage in the figure). The Cerenkov counter 1 is provided in series on the radiation emission side (lower stage in the figure), not only as a Cherenkov light transmission means to the device, but also with optical fibers 13 and 14 serving as Cherenkov radiators. FIG. 5 shows an example of a detection device in which two Cherenkov counters are arranged, but in this embodiment, three or more can be arranged. The combination of the Cherenkov counters shown in FIGS. 4A and 4B can be freely selected according to the measurement accuracy of the radiation energy distribution.

  Although not shown in the figure, when any two or more of the Turenkov counters shown in FIGS. 4B and 4C are arranged in series, the Cherenkov counter arranged on the radiation emission side 1 includes an optical fiber whose energy threshold is lower than that of the Cherenkov radiator 6. For example, in the case of two, each Cherenkov counter arranged in series is provided with an optical fiber having a different energy threshold, and from the incident side of the radiation in the order of having an optical fiber having a high energy threshold and having an optical fiber having a low energy threshold. Deploy. Hereinafter, when three or more Cherenkov counters are arranged, the same configuration is adopted using optical fibers having different energy thresholds.

  As the optical fiber having a high energy threshold, one having a low refractive index of the core portion is selected. For example, a low refractive index liquid such as a quartz diameter optical fiber, a plastic optical fiber, silicone or fluorine oil has a lower refractive index. An optical fiber produced by encapsulating in a plastic clad material is mentioned. On the other hand, as an optical fiber having a low energy threshold, one having a high refractive index of the core part is used, and examples thereof include an optical fiber having a high refractive index glass or transparent ceramic core part. Since the optical fiber of this embodiment is used with a short length of several meters or less, there is no problem even if the light transmittance is not as high as that of the optical fiber for optical communication. Therefore, it is possible to use an optical fiber having the transparent ceramic core, an optical fiber having a high refractive index dopant in the core, or the like.

  The radiation energy distribution detection apparatus according to the present embodiment is generally sensitive to radiation because an optical fiber used as means for transmitting Cherenkov light from a Cherenkov radiator to a photodetector is generally made of solid or liquid. . As described above, when an optical fiber having the function of a photodetector is sensitive to radiation, scattered radiation or the like may be detected as a noise signal by the photodetector. In order to solve this problem, in this embodiment, a plurality of optical fibers (reference numerals 10, 11 and 13, 14 in FIG. 4) are installed in one Cherenkov counter 1, and one of them, for example, a filter 12 is installed. It is preferable that the material is made of a material that does not transmit light so that the light is blocked so that Cherenkov light does not enter the optical fibers 11 and 14. In the optical fibers 10 and 13 that detect the Cherenkov light and the light-shielded optical fibers 11 and 14, the signal of the Cherenkov light can be estimated from the difference between the electrical signal levels of both. 4 shows a Cherenkov counter having two optical fibers 10, 11 or 13, 14 as an example, but three or more optical fibers may be installed, some of which (about half) ) Is shielded, and the signal of Cherenkov light can be similarly estimated from the difference in the electrical signal level with the optical fiber that detects Cherenkov light. In this embodiment, by providing a plurality of optical fibers in the same Cherenkov counter and bringing them close to each other, a highly sensitive Cherenkov light signal with less noise can be obtained.

  The detection method for estimating the energy distribution of the radiation of the present invention performed by applying the detection apparatus shown in FIGS. 4 and 5 is performed in the same manner as in the first embodiment. The radiation energy detection method according to the present embodiment is the same as the Cherenkov counter group composed of n Cherenkov counters shown in FIG. 2, except that each Cherenkov counter is composed of a plurality of optical fibers. The actual signal level of the counter and the estimated radiation intensity can be measured based on the same principle as in the first embodiment.

  Further, in the present invention, not only a configuration in which all of the plurality of Cherenkov counters include a plurality of optical fibers but also a Cherenkov counter group in combination with a configuration of a Cherenkov counter having a Cherenkov radiator as shown in FIG. May be.

<Example 3>
Each energy band estimated according to the present invention can be considered as a pseudo-monochromatic X-ray having an energy band width, so that it is a pseudo two-color or pseudo-multicolor for luggage inspection at airports and ports. The present invention can also be applied to an imaging apparatus (line sensor, flat panel detector, or X-ray CT apparatus). Recently, there has been a request for substance discrimination (UTNL-R-0476 Non-destructive inspection applied research using portable small X-ray source (http: / (See /www.nuclear.jp/utnl-w/0025/main0025.pdf), the present invention is suitable as a line sensor, for example, using a scintillator as disclosed in Japanese Patent Application Laid-Open No. 2011-112623. By applying the Cherenkov counter of the present invention instead of a scintillation counter in a two-stage X-ray detector, it is possible to adopt not only two stages but also three or more stages, thereby further subdividing the energy distribution. In this state, it becomes possible to detect with high accuracy.

<Example 4>
This embodiment can also be applied to simple energy measurement of charged particle beams such as electrons such as an electron beam accelerator or generated X-rays. Medical electron beam accelerators (linac, linac) with an electron beam energy of about 6 MeV are on the market. At present, the silica airgel having the lowest refractive index has an electron energy threshold of 7.2 MeV, which covers an electron beam kinetic energy of 6 MeV. At present, the silica airgel having the highest refractive index has an electron energy threshold of 0.29 MeV. Within this range, silica airgel of any refractive index can be obtained, although there is some variation. In this embodiment, two or more silica aerogels belonging to the same phase form called gel but having different density and refractive index are used as the Cherenkov radiator of the Cherenkov counter. Thereby, a plurality of silica airgels having appropriate refractive indexes are stacked, and each is independently shielded from light and connected to a photodetector surrounded by a radiation shielding material to constitute an electron beam energy analyzer.

  The electron beam taken out from the beam take-out window of the accelerator is made incident on the analyzing device using the detecting device of the present invention as an electron beam energy analyzing device. By analyzing the output of the photodetector and knowing which energy threshold silica airgel has emitted Cherenkov light, the energy of the electron beam can be known.

  However, since silica airgel has high electrical insulation and may lose energy and be charged by electrons stopped in the silica airgel, it is desirable to surround the silica airgel with a conductor such as an aluminum foil that also serves as a light reflecting film. .

  The simplest configuration is a configuration with two Cherenkov counters each having a silica airgel 1 and a silica airgel 2 as the Turenkov radiator 1 and the Turenkov radiator 2, and FIG. 6 (a) and FIG. And cross-sectional views respectively. Cherenkov light emitted inside each Turenkov counter is detected by the photodetector 7 in a manner perpendicular to the incident direction of the radiation. For example, if it is desired to guarantee a beam energy of 6.0 MeV ± 0.1 MeV, the energy threshold is set to 5.9 MeV and a Cherenkov counter of 6.1 MeV. The state in which the 5.9 MeV counter reacts and the 6.1 MeV counter does not react is a state in which a beam energy of 6 MeV ± 0.1 MeV is guaranteed.

  Whether or not each Cherenkov counter reacts can be determined from a signal taken into the analytical calculation device 4 by the ADC. Of the photodetectors 7 provided in each Cherenkov counter, the Cherenkov light It is also possible to take a difference between the electric signal level of the one detecting the light and the one shielded from light by a differential amplifier or the like and discriminate the signal by a comparator (or discriminator).

A charged particle beam generated by an electron beam accelerator or the like generally has a very large number of particles (much more than 10 ⁵ ), and a silica airgel can provide a sufficient amount of light even with a thickness of about 0.1 cm to 1 cm. To emit. In this embodiment, silica airgel is exemplified as the Cherenkov radiator. However, depending on the energy of the target radiation, a gas, liquid, solid or other material (called a metamaterial or photonic crystal) having an appropriate refractive index is used. Can be used as Cherenkov radiators.

  As described above, since this embodiment uses a clear energy threshold, it is an advantageous method for the purpose of obtaining the maximum energy of the incident radiation bundle. In short, since the energy distribution can be estimated by a clear energy threshold according to the present embodiment, it is more direct than the conventional method of estimating the intensity for each energy band from the signal intensity of the detector. That is, it can be considered that each energy band estimated by the present embodiment is pseudo-monochromatic radiation having the width of the energy band.

<Example 5>
The present invention can estimate the maximum energy or energy distribution of X-rays generated in the burst mode in the X-ray source. This method will be described in this embodiment.

  The X-ray generator and the radiation generator whose method of use is an X-ray source are required by law to generate X-rays with an electron beam of permitted energy. In Japan, X-ray sources with an electron beam energy of 1 MeV or higher are treated as radiation generators, and laws and regulations differ from X-ray sources of less than 1 MeV. In order to cope with such a case, it is important to easily know the maximum energy of the electron beam or X-ray. In addition, if the energy of X-rays generated by the X-ray source is unknown, the use of the X-rays will be hindered. Particularly in the case of cancer radiotherapy, it is necessary to estimate the absorbed dose at the affected area and other sites, and it is fatal that the maximum energy of X-rays is unknown.

  In the case of an X-ray tube, the energy of the electron beam is the high voltage voltage itself applied to the X-ray tube, so the maximum energy of the X-ray may be the voltage. However, in the case of an X-ray generator using an electron linear accelerator using a high frequency as an electron beam source and generating an bremsstrahlung X-ray by making the electron beam incident on the target, the energy of the electron beam is not obvious. The maximum energy of is not obvious.

  As shown in FIG. 7, the configuration example of the X-ray source 15 using the above-described electron linear accelerator includes an electron gun 17 directly connected to the acceleration tube 16 via a vacuum flange, and an acceleration tube 16 via a vacuum flange. The X-ray target 18 is directly connected. In some cases, the accelerating tube 16 has a short beam pipe 19 and an X-ray target 18 is connected to the end of the beam pipe 19 via a vacuum flange. Some large X-ray irradiation apparatuses for cancer treatment have a deflecting magnet of 90 to 270 degrees after a long (for example, 2 m long) accelerator tube. However, it is not preferable to provide a deflecting electromagnet from the viewpoint of miniaturization of the apparatus and portability. Further, since the electron beam tends to diverge in the lateral direction, it is desirable that the electron beam is incident on the X-ray target before the electron beam diverges. Alternatively, an apparatus that focuses an electron beam can be used, but it is disliked because it leads to an increase in the size of the apparatus. The inside of the electron linear accelerator is kept at a high vacuum.

  In order to measure the energy of the electron beam of the electron linear accelerator, a deflection electromagnet is usually used. However, it is often difficult to always provide the X-ray generator with a deflection electromagnet for measuring the energy of the electron beam. The above-described fourth embodiment is a method that can be considered to solve this problem, but the solution according to the fourth embodiment alone is not easy to solve. The reason is that the X-ray generator is provided with an X-ray target for generating X-rays, and the electron beam is designed to enter the X-ray target. Usually, in order to measure the energy of the electron beam of an X-ray generator that does not have a deflecting electromagnet, the X-ray target is removed and a beam extraction window is attached to extract the electron beam into the atmosphere, or the electron beam by the deflecting electromagnet An energy analyzer is attached to measure the energy of the electron beam. In order to carry out these methods, it is necessary to release the accelerator in a vacuum to the atmosphere for exchanging the X-ray target, etc., which is very time-consuming and takes time to recover the vacuum. , Takes a few days. Therefore, it is impossible to always monitor the maximum energy of X-rays by the above method.

  In order to solve such a problem, in this embodiment, as shown in FIG. 8, a converter (metal plate) 5 is installed in the apparatus of the X-ray source 15 so that X-rays can be converted into electrons. A device capable of measuring the maximum energy of the X-ray is installed between the X-ray source 15 and the subject or patient in the immediate vicinity of the X-ray generator. It is desirable to install a converter (metal plate) 5 for each Cherenkov radiator. In this way, the maximum energy of X-rays can be estimated without removing the X-ray target, and the energy of the electron beam that is the source can also be estimated. Therefore, the maximum energy of X-rays and the energy of electron beams can be estimated by installing the apparatus in the immediate vicinity of the X-ray source when necessary. The installation location of the apparatus is preferably on the X-ray emission axis, but may be located off the X-ray emission axis.

  The method for estimating the maximum energy of X-rays is in principle equivalent to the method shown in the fourth embodiment. For example, if it is desired to guarantee an X-ray energy of 6.0 MeV ± 0.1 MeV, the energy threshold value is 5.9 MeV and a Cherenkov counter of 6.1 MeV. A state in which the counter of 5.9 MeV reacts and the counter of 6.1 MeV does not react is a state in which X-ray energy of 6 MeV ± 0.1 MeV is guaranteed. However, since the energy slightly decreases when the X-ray is converted into an electron beam, this energy decrease is taken into consideration as necessary.

  By making the converter (metal plate) 5 and Cherenkov radiator of the above device as thin as the signal level permits, the influence on generated X-rays can be reduced and the maximum energy of X-rays and the energy of electron beams can be estimated. it can. This makes it possible to constantly monitor the maximum energy of the X-ray and the energy of the electron beam while using the X-ray while using the apparatus as a front detector. If the X-ray energy is the same, the intensity of the X-ray is proportional to the intensity of Cherenkov light. Therefore, if the signal level is calibrated, the intensity of the X-ray can always be monitored.

  In the present embodiment, it goes without saying that the number of Cherenkov radiators and converters (metal plates) 5 can be increased to 3 or more, and the energy distribution can be estimated.

  Thus, according to the present embodiment, each energy band can be considered to be a pseudo monochromatic X-ray having the width of the energy band, and the same as the fourth embodiment in the detection of the X-ray energy distribution. An effect is obtained. Therefore, the present embodiment is a more direct X-ray energy distribution detection method than the method of estimating the intensity for each energy band from the signal intensity of the detector as disclosed in Patent Document 4 described above. is there. Of course, it goes without saying that X-rays transmitted through the subject or patient can be detected by the radiation detector according to the present invention.

DESCRIPTION OF SYMBOLS 1 ... Cherenkov counter, 2 ... Cheurenov counter group, 3 ... Main detector, 4 ... Analysis processing device, 5 ... Converter, 6 ... Cherenkov radiator, 7 ... Photodetector, 8 ... radiation shield, 9 ... mirror, 10 ... optical fiber for detecting Cherenkov light, 11 ... shielded optical fiber, 12 ... filter, 13 ... An optical fiber for detecting Cherenkov light, 14 ... a shielded optical fiber, 15 ... an X-ray source, 16 ... an accelerator tube, 17 ... an electron gun, 18 ... an X-ray target, 19 ... Beam pipe, 20... Space as a means for transmitting Cherenkov light to the photodetector.

Claims (18)

  A plurality of Cherenkov counters having different energy thresholds when Cherenkov radiation occurs are arranged in series with respect to the incident direction of charged particles that are radiation or electromagnetic waves converted to the charged particles, and in each of the plurality of Cherenkov counters, An energy distribution of the radiation is estimated by converting a radiation intensity existing in a predetermined range of the energy threshold from a light intensity measured by a photodetector provided in the Cherenkov counter. Detection method. The energy threshold when the Cherenkov radiation occurs is controlled by the refractive index of an optical medium included as a Cherenkov radiator in the Cherenkov counter,
The light intensity measured by the photodetector provided in the Cherenkov counter exists within a predetermined range of the energy threshold by performing calibration using a relationship between known energy and light intensity or by performing simulation calculation. The radiation energy distribution detection method according to claim 1, wherein the radiation energy distribution is converted into radiation intensity.   A plurality of the Cherenkov counters are used as the Cherenkov radiator, each of which has at least two different refractive indexes selected from the group consisting of gas, gel, liquid and solid to change the energy threshold when Cherenkov radiation occurs, From the Cherenkov counter having the Cherenkov radiator having a relatively low density and low refractive index to the Cherenkov counter having the Cherenkov radiator having a relatively high density and high refractive index, in the incident direction of the radiation composed of charged particles. The radiation energy distribution detection method according to claim 1, wherein the radiation energy distribution is detected in series.   The plurality of Cherenkov counters use at least two or more solids having different refractive indices as Cherenkov radiators to change the energy threshold when Cherenkov radiation occurs, respectively, and the energy threshold is low and the refractive index is relatively high. The Cherenkov counter having the Cherenkov radiator is arranged in series with respect to the incident direction of the radiation composed of charged particles in the order of the Cherenkov counter having the Cherenkov radiator having a high energy threshold and a relatively low refractive index. The method of detecting a radiation energy distribution according to claim 1, wherein the radiation energy distribution is detected.   A plurality of photodetectors are installed in one Cherenkov counter, and at least one of the photodetectors is shielded so that Cherenkov light does not enter, thereby shielding the photodetectors that detect the Cherenkov light and the Cherenkov light. The method of detecting an energy distribution of radiation according to any one of claims 1 to 4, wherein the intensity of the Cherenkov light is measured from a difference of an electric signal with the photodetector.   The plurality of Cherenkov counters each have a plurality of optical fibers as means for transmitting the Cherenkov radiator or the Turenkov light to the photodetector for changing the energy threshold, and at least one of the optical fibers does not receive the Cherenkov light. The intensity of the Cherenkov light is measured from the difference in electrical signal between the optical fiber that detects the Cherenkov light and the optical fiber that shields the Cherenkov light. 6. The method for detecting a radiation energy distribution according to any one of 5 above.   A main detector consisting of a scintillation counter or a semiconductor radiation detector is arranged at the end of the Cherenkov counter group in which a plurality of the Cherenkov counters are arranged in series, or in place of the Cherenkov counter arranged at the end of the Cherenkov counter group, The main detector measures all radiation intensities that pass through the subject, and is converted from all the radiation intensities and intensity signals measured by the photodetectors provided in the Cherenkov counter in each of the plurality of Cherenkov counters. The radiation according to any one of claims 1 to 6, wherein the influence of radiation hardening in the radiation energy distribution is estimated by comparing with radiation intensity existing in a predetermined range of the energy threshold. Energy distribution detection Law.   In detection of an energy portion of X-rays emitted from an X-ray tube, at least one of the Cherenkov counters is provided with a converter plate for converting X-rays into charged particles on the front surface on the X-ray incident side. The detection method of the energy distribution of the radiation in any one of Claims 1-7.   X-rays emitted from an X-ray tube are used as radiation, and solids used as Cherenkov radiators of the Cherenkov counter for the X-rays are high refractive index glass, cubic zirconia, diamond, strontium titanate, moissanite and rutile. The method for detecting a radiation energy distribution according to claim 8, wherein at least one selected from the group consisting of: A device for detecting energy distribution of charged particles that are radiation or electromagnetic waves converted into the charged particles,
A Cherenkov counter group in which a plurality of Cherenkov counters having different energy thresholds when Cherenkov radiation occurs with respect to the incident direction of the charged particles or electromagnetic waves are arranged in series;
Each of the plurality of Cherenkov counters includes a processing device for converting radiation intensity existing in a predetermined range of the energy threshold from light intensity measured by a photodetector provided in the Cherenkov counter. Detection device for radiation energy distribution. The Cherenkov counter has at least a refractive index corresponding to an energy threshold when the Cherenkov radiation occurs, and has an optical material used as a Cherenkov radiator, and a photodetector that detects Cherenkov light,
The processing apparatus for converting the radiation intensity existing in the predetermined range of the energy threshold calibrates the light intensity measured by the photodetector provided in the Cherenkov counter using the relationship between the known energy and the light intensity. The radiation energy distribution detection device according to claim 10, further comprising: a unit that performs the calculation or a unit that performs a simulation calculation.   The plurality of Cherenkov counters use at least two kinds of different refractive indices selected from the group consisting of gas, gel, liquid and solid as Cherenkov radiators having different densities in order to change the energy threshold when Cherenkov radiation occurs. The incident direction of the radiation consisting of charged particles in the order of the Cherenkov counter having the Cherenkov radiator having a relatively low density and a low refractive index and the Cherenkov counter having the Cherenkov radiator having a relatively high density and a high refractive index. The radiation energy distribution detection device according to claim 10, wherein the radiation energy distribution detection device is arranged in series with respect to the radiation energy distribution.   The plurality of Cherenkov counters have a low energy threshold and a relatively high refractive index when at least two solids having different refractive indexes are used as Cherenkov radiators, respectively, in order to change the energy threshold when Cherenkov radiation occurs. The Cerenkov counter having the above-mentioned Cherenkov radiator is arranged in series with respect to the incident direction of the radiation composed of charged particles in the order of the Cherenkov counter having the Cherenkov radiator having a high energy threshold and a relatively low refractive index. The radiation energy distribution detection device according to claim 10, wherein the radiation energy distribution detection device is a radiation energy distribution detection device.   A plurality of photodetectors are installed in one Cherenkov counter, and at least one of the photodetectors is shielded so that Cherenkov light does not enter, thereby shielding the photodetectors that detect the Cherenkov light and the Cherenkov light. The radiation energy distribution detection device according to claim 10, further comprising means for obtaining an intensity of the Cherenkov light from a difference of an electric signal with the photodetector.   The plurality of Cherenkov counters each have a plurality of optical fibers as means for transmitting the Cherenkov radiator or the Turenkov light to the photodetector for changing the energy threshold, and at least one of the optical fibers does not receive the Cherenkov light. And means for determining the intensity of the Cherenkov light from the difference in electrical signal between the optical fiber that detects the Cherenkov light and the optical fiber that shields the Cherenkov light. The detection apparatus of the radiation energy distribution in any one of Claims 10-14.   A main detector consisting of a scintillation counter or a semiconductor radiation detector is provided at the end of the Cherenkov counter group or in place of the Cherenkov counter arranged at the end of the Cherenkov counter group, and is used for radiation hardening in the energy distribution of the radiation. In order to estimate the effect, the total radiation intensity transmitted through the object to be measured by the main detector and the intensity signal measured by the photodetector of the Cherenkov counter at each of the plurality of Cherenkov counters are approximated. The radiation energy distribution detection device according to claim 10, wherein the radiation intensity distribution is compared with a radiation intensity existing in a predetermined range of the energy threshold.   In detection of an energy portion of X-rays emitted from an X-ray tube, at least one of the Cherenkov counters is provided with a converter plate for converting X-rays into charged particles on the front surface on the X-ray incident side. The detection apparatus of the radiation energy distribution in any one of Claims 10-16.   X-rays emitted from an X-ray tube are used as radiation, and a solid composition of a homogeneous composition used as a Cherenkov radiator of a Cherenkov counter is a high refractive index glass, cubic zirconia, diamond, strontium titanate, The apparatus for detecting a radiation energy distribution according to claim 17, wherein at least one selected from the group consisting of moissanite and rutile is used.

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