JP2015075410A - Charged particle beam distribution measurement system, and charged particle beam distribution measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charged particle beam distribution measurement system 8 and a charged particle beam distribution measurement method having resistance to a neutron beam, and capable of measuring distribution of a charged particle beam regardless of a shape of the beam.SOLUTION: A charged particle beam distribution measurement system 8 includes: a shielding film 17 in which a temperature change occurs in an irradiation region 18 when being irradiated with a charged particle beam; a cooling part 20 that cools at least a part of the shielding film 17 other than the irradiation region 18 of the shielding film 17; an infrared camera 15 that measures at least temperature distribution of the irradiation region 18 of the shielding film 17; and a computer 7 that calculates beam distribution from the temperature distribution measured by the infrared camera 15.

Description

  The present invention relates to a charged particle beam distribution measuring system and a charged particle beam distribution measuring method for measuring a charged particle beam distribution.

  2. Description of the Related Art Conventionally, a charged particle beam irradiation system that accelerates charged particles with an accelerator and irradiates a target with an accelerated charged particle beam has been provided. In such a charged particle beam irradiation system, it is desired to accurately control the shape and irradiation position of the charged particle beam. Here, the shape and irradiation position of the charged particle beam cannot be confirmed with the naked eye. For this reason, various charged particle beam distribution measuring methods have been proposed.

  For example, a beam shape monitor system that measures a beam shape using a fluorescent screen has been proposed (see Patent Document 1). This beam shape monitoring system utilizes an excitation phenomenon caused by a charged particle beam hitting a scintillator (fluorescent plate), and observes light emitted by this excitation phenomenon with a CCD element. By this method, it is supposed that the relative position of the beam with respect to the duct section and the size of the section diameter can be displayed quantitatively and easily.

However, in such a system using a scintillator, when diagnosing a large current / DC beam used for RI generation, the CCD element used for imaging is easily damaged by neutron beams, and the scintillator is dissolved by beam heating. There was a problem.
A charged particle beam measuring apparatus using a wire monitor has been proposed (see Patent Document 2). This charged particle beam measuring apparatus includes a plurality of metal wires stretched in a direction crossing the beam path. In this charged particle beam measuring apparatus, a beam hits a metal wire, and at this time, a current generated in the metal wire is extracted. It is said that the charged particle beam measuring apparatus can know the particle distribution of the charged particle beam because of the property that this current is proportional to the beam intensity.

  However, a system that measures the charged particle beam distribution by arranging a wire monitor has a problem that it cannot be accurately measured depending on the beam shape, for example, when the beam shape is hollow.

Japanese Patent Laid-Open No. 05-223934 Japanese Patent Laid-Open No. 01-257295

  In view of the above-described problems, the present invention provides a charged particle beam distribution measurement system and a charged particle beam distribution measurement method that are resistant to neutron beams and that can measure the distribution of charged particle beams regardless of the shape of the beam. The purpose is to provide.

  The present invention includes an irradiated medium in which a temperature change occurs in an irradiated part when a charged particle beam is irradiated, a cooling unit that cools at least a part of the irradiated medium other than the irradiated part, and at least the irradiated medium A charged particle beam distribution measuring system comprising a temperature distribution measuring device for measuring a temperature distribution of the irradiated portion, and a beam distribution calculating unit for calculating a beam distribution from the temperature distribution measured by the temperature distribution measuring device, and a charged particle beam It is a distribution measuring method.

  According to the present invention, it is possible to provide a charged particle beam distribution measurement system and a charged particle beam distribution measurement method that are resistant to neutron beams and that can measure the distribution of a charged particle beam regardless of the shape of the beam.

Explanatory drawing which shows schematic structure of a charged particle beam irradiation system. The disassembled perspective view which shows a shielding film periphery. The pixel map figure which shows the position of the temperature of a heat source and discrete space. The flowchart of the operation | movement which calculates beam distribution. Explanatory drawing explaining the measured beam distribution by image display.

  As a result of earnest research on the method of measuring the distribution of the charged particle beam irradiated by the charged particle beam irradiation system, the present inventors measured the beam distribution with high accuracy regardless of the beam shape, which was difficult with the conventional method. A charged particle beam distribution measurement system was developed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1A is a block diagram showing a schematic configuration of the charged particle beam irradiation system 1, and FIG. 1B is a longitudinal front view showing a schematic configuration of the charged particle beam distribution measurement system 8. FIG. 2 is an exploded perspective view showing the periphery of the shielding film 17 by cutting along the AA plane of FIG.

As shown in FIG. 1A, the charged particle beam irradiation system 1 includes a charged particle generator 2, an accelerator 4, and a charged particle beam irradiation unit 6.
The charged particle generator 2 is a device that generates charged particles, and can be configured by an appropriate device such as an ion source that generates a desired ion species. The charged particles generated by the charged particle generator 2 are electrons, protons,
Deuterons, alpha particles, heavy ions, or the like can be used depending on the purpose.

  The accelerator 4 is a device for accelerating charged particles, and can be composed of, for example, a cyclotron. The accelerator 4 is not limited to a cyclotron but may be an appropriate accelerator such as a synchrotron, and is not limited to a circular accelerator as shown in the figure, but is a linear accelerator, or both a linear accelerator and a circular accelerator are used. An appropriate configuration can be adopted.

  The charged particle beam irradiation unit 6 is a device that irradiates a target with charged particles, and is provided with a computer 7. The charged particle beam irradiation unit 6 and the computer 7 constitute a charged particle beam distribution measurement system 8.

The computer 7 includes an appropriate computer including an arithmetic device, an input device, a storage device, and an output device (monitor).
The computer 7 receives temperature distribution data from an infrared camera 15 (thermographic camera, see FIG. 1B), which is a temperature distribution measuring device, by an input device, and operates a conversion program installed in a storage device by an arithmetic device. Then, the temperature distribution data is converted into beam distribution data, and the result is transmitted to a monitor which is an output device.
The computer 7 can repeatedly and continuously execute this series of operations. Therefore, the beam distribution data is constantly updated, and the position, size, and shape of the beam spot where the charged particle beam is irradiated onto the shielding film 17 (see FIG. 1B) can be displayed in real time.

The computer 7 is an FPGA (field-programmable).
gate array) and DSP (digital signal)
It may be configured as a system including a digital arithmetic unit such as a processor. Since the calculation performed in the conversion process from the temperature distribution to the beam distribution according to the present invention is simply constructed as will be described later, these digital calculation units can be processed without any problem.

As shown in FIG. 1B, the charged particle beam distribution measurement system 8 includes a charged particle beam irradiation unit 6 and a computer 7.
The charged particle beam irradiation unit 6 includes a beam transport duct 11, an observation duct 12, an infrared camera 15, a shielding film 17, a cooling unit 20, and an irradiation duct 31. A target 33 is disposed downstream of the irradiation duct 31 (downward in the figure).

  The beam transfer duct 11 is a cylindrical conduit, and the inside is kept in a vacuum. A charged particle beam passes from the accelerator 4 (see FIG. 1A) toward the target 33 in the beam transport duct 11. The end of the beam transport duct 11 on the rear stage side (beam emission side) is shielded by the shielding film 17 without any gap.

  The observation duct 12 is a cylindrical conduit connected to a position close to the shielding film 17 on the side surface of the beam transport duct 11. The observation duct 12 is disposed at an inclination of 45 degrees with respect to the beam transport duct 11, and the observation window 13 is provided on the observation side (upper left side in the drawing) opposite to the shielding film 17. The inside is vacuum sealed. The infrared camera 15 is installed on the outside (atmospheric pressure) of the observation duct 12 so as to capture the shielding film 17 through the observation window 13.

  The observation window 13 is a plate-like member formed of a material (infrared transmitting member) that transmits infrared rays, such as glass of barium fluoride (BaF2) or glass of calcium fluoride (CaF2). The observation window 13 also functions as an attachment portion to which the lens 15a side of the infrared camera 15 is attached. The mounting portion is configured to be fixed by directly attaching the infrared camera 15 to the observation window 13 or by fixing the infrared camera 15 to another part such as the beam carrying duct 11 so that the lens 15a faces the observation window 13. For example, an appropriate configuration may be adopted.

  The infrared camera 15 is a thermography that measures the temperature distribution by measuring infrared rays. The infrared camera 15 uses the observation window 13 and the observation duct 12 to photograph at least the entire charged particle beam irradiation range of the shielding film 17 in the confirmation direction Y2 that is an angle of 45 degrees with respect to the irradiation direction Y1 of the charged particle beam. It is arranged to be able to. This infrared camera 15 can be constituted by an appropriate camera capable of photographing an infrared region, and among them, a camera that is resistant to neutron rays is preferable. In this embodiment, an infrared camera 15 that uses an uncooled microbolometer or the like that is resistant to neutron rays as an image sensor is used.

  The shielding film 17 is a disk-shaped and constant-thickness film for maintaining a vacuum, and is formed of a material through which a charged particle beam is transmitted and a temperature change is caused by the transmission. The shielding film 17 has an area larger than the irradiation range of the charged particle beam, and the plane (surface) is perpendicular to the transmission direction of the charged particle beam, in other words, the width direction of the charged particle beam is the plane direction. Are arranged as follows. The shielding film 17 has a function of maintaining a pressure difference between the beam transport line (beam transport duct 11 side) and the irradiation target portion (irradiation duct 31 side). The shielding film 17 also functions as a medium to be irradiated with a charged particle beam, and also functions as an object to be imaged by the infrared camera 15 in order to measure the beam distribution. For this reason, the shielding film 17 is made of a material whose temperature changes even slightly by irradiation with a charged particle beam. Specifically, the shielding film 17 can be made of a material such as niobium, graphite, aluminum, or copper.

  The cooling unit 20 is a cooling device that cools the shielding film 17 from the outside. As shown in FIG. 2, the cooling unit 20 includes a ring-shaped portion 21 formed in a ring shape, and a refrigerant inlet 23 and a refrigerant discharge port 24 that are arranged close to each other on the side surface of the ring-shaped portion 21. ing. The refrigerant inlet 23 and the refrigerant outlet 24 are connected to a cooling device 35 that circulates the refrigerant. The refrigerant 22 supplied from the cooling device 35 and flowing in from the refrigerant inlet 23 circulates in the ring-shaped part 21 and is discharged from the refrigerant outlet 24. Note that FIG. 2 is illustrated by partially cutting the vicinity of the refrigerant inlet 23 of the cooling unit 20 having a bilaterally symmetric shape in order to make the flow path of the refrigerant 22 easier to understand.

  Further, the ring-shaped portion 21 of the cooling unit 20 is formed in a ring shape having the same size as the disk-shaped outer peripheral portion of the shielding film 17. In particular, in order not to disturb the charged particle beam, the entire irradiation region 18 where the charged particle beam is irradiated onto the shielding film 17 is configured to be a hollow portion generated inside the ring-shaped portion 21. Thereby, the cooling unit 20 can cool the shielding film 17 from the outer peripheral portion without hindering the passage of the charged particle beam.

The irradiation region 18 refers to a region (irradiation portion) where the charged particle beam is mainly irradiated, and a very small amount of the charged particle beam that slightly deviates from the beam path is irradiated to the outside of the irradiation region 18. The case is not excluded.
Moreover, the refrigerant | coolant 22 can be made into the liquid or gas for cooling, and can be used as appropriate media, such as liquid nitrogen, water, and air.

The irradiation duct 31 is a cylindrical duct and covers the passage to the target 33.
The target 33 is an object that irradiates a charged particle beam. The target 33 can be appropriately selected according to the purpose of using the charged particle beam irradiation system 1.

  FIG. 3 is a pixel map diagram showing the positions of the heat source and the temperature of the discrete space. Here, the concept of the conversion processing method from the temperature distribution to the beam distribution executed by the charged particle beam distribution measurement program will be described.

  When the energy loss ΔE of each incident ion in the shielding film 17 is uniform in the z-axis direction (beam traveling direction) of the shielding film 17, the temperature distribution T (x, y) and the heat source S ( The relationship of x, y) is determined by the two-dimensional steady heat conduction equation shown in the following [Equation 1].

* Λ (T): Thermal conductivity depending on temperature.

  Applying the central difference method to the second order differential term of [Equation 1] and solving for Si, j yields [Equation 2] below.

* I, j: x, y coordinates in discrete space.
Δx, Δy: The length of one side in the x, y direction of a cell divided in a discrete space.
Ti, j: temperature on the cell at point (i, j).
Si, j: Heat source on the cell at point (i, j).

  [Equation 2] shows that the heat source of the point (i, j) is obtained from the temperature of the point and the surrounding four points. That is, as shown in the pixel map diagram of FIG. 3, the heat source 50 includes the temperature of the target pixel 40 and four adjacent pixels 41 to 44 adjacent to each side of the target pixel 40 (that is, colored 5 in the drawing). Temperature of one pixel).

  Here, although the shielding film 17 has a thickness and heat propagates in the three-dimensional directions of x, y, and z, the two-dimensional calculation is effective in this way. Is due to. That is, the cooling unit 20 is provided around the shielding film 17 and is not provided on the beam path. For this reason, when the charged particle beam passes through the shielding film 17 and heat is generated, this heat propagates in the direction in which the cooling unit 20 exists, that is, in the width direction (x, y direction) of the charged particle beam. Since the cooling unit 20 does not exist in the traveling direction (z direction) of the charged particle beam, there is no temperature gradient in the thickness direction (z direction) of the shielding film 17. Therefore, by restricting the heat propagation direction to two dimensions, the term in the z direction can be ignored from the differential equation. As shown in the pixel map diagram of FIG. These four points (adjacent pixels 41 to 44) can be expressed by a two-dimensional calculation formula that considers the temperature.

  Using the above relationship, conversion from the heat source to the beam distribution is performed using the following [Equation 3].

* Q: Ion charge. lz: thickness of the shielding film 17.
ΔE: Energy loss in the shielding film 17 of individual ions forming the beam.

  A charged particle beam distribution measurement program combines the above-described conversion method from temperature distribution to beam distribution and the averaging and filtering method for removing noise on the two-dimensional temperature data measured by the infrared camera 15. A conversion algorithm to be executed is configured.

  FIG. 4 is a flowchart showing an algorithm executed by the computer 7 in accordance with the charged particle beam distribution measurement program. The computer 7 that executes this flowchart functions as a beam distribution calculation unit.

  First, the computer 7 initializes the variable N by substituting “0” (step S1), and collects two-dimensional temperature data photographed by the infrared camera 15 (step S2). At this time, the infrared camera 15 acquires temperature data for each pixel of the two-dimensional image of the x and y coordinates, and the computer 7 acquires the temperature data of each pixel.

  The computer 7 adds 1 to the variable N (step S3), and if the predetermined number of repetitions for average value calculation has not been reached (step S4: No), the process returns to step S2 to perform two-dimensional processing. Repeat temperature data collection.

  If the number of collections of the two-dimensional temperature data has reached the number of repetitions for calculating the average value (step S4: Yes), the computer 7 executes an averaging process (step S5). This averaging process is a process of calculating an average value from Nave temperature data for each pixel unit.

  The computer 7 assigns “0” to the variable N and initializes it (step S6), and determines whether the number of times assigned to the variable N has reached a predetermined number of times of filtering (step S7). The number of times of filtering can be set to an appropriate number of times, for example, once or a plurality of times.

  If the number of times of filtering has not been reached (step S7: No), the computer 7 executes the filtering process (step S8), adds 1 to the value of the variable N (step S9), and returns to step S7 to repeat the process. . This filtering process is a process of smoothing two-dimensional temperature data with a smoothing filter such as a Gaussian filter.

  If the number of times of filtering has been reached (step S7: Yes), the computer 7 executes the conversion processing method from the temperature distribution to the beam distribution (step S10). This temperature distribution to beam distribution conversion processing method uses two-dimensional temperature data for the temperature data that has undergone the averaging process (step S5) and the filtering process (step S8) according to the above-described equation [2]. Is converted to a two-dimensional heat source distribution, and further converted from a two-dimensional heat source distribution to a two-dimensional beam distribution by the equation [3].

With the above configuration and algorithm, the distribution of the charged particle beam can be accurately measured.
In order to confirm the effect of the calculation performed by the temperature distribution to beam distribution conversion processing method, the two-dimensional temperature data of the shielding film 17 obtained by the infrared camera 15 during beam irradiation is simulated by simulation including noise. Applying this algorithm to the results, the two-dimensional beam distribution was obtained.
The simulation of the two-dimensional temperature data of the shielding film 17 obtained by the infrared camera 15 was performed by the following procedures (1) and (2).
(1) The beam parameters (energy, current, beam width), the thickness and material of the shielding film 17 are determined, and the temperature distribution generated under these conditions is obtained from the two-dimensional steady heat conduction equation.
The region of φ100 mm is discretized with a 200 × 200 cell, and the two-dimensional steady heat conduction equation is solved by the finite difference method.
(2) Assuming that the amplitude of the noise is a normal distribution, the noise is determined using a pseudo random number so that 2σ = ΔT _NETD . The obtained noise is added to the temperature distribution not including the noise calculated in (1).

This ΔT _NETD (NETD: noise equivalent temperature difference) indicates a temperature spread corresponding to the amplitude of noise and depends on the performance of the infrared camera 15.

In this analysis, ΔT _NETD = 0.3K, assuming the use of a general-purpose infrared camera 15 with relatively large noise.

  The temperature distribution obtained by the above simulation was converted into a beam distribution by using an algorithm of a conversion processing method from the temperature distribution to the beam distribution. The result of comparing the result with a predetermined exact solution is shown in FIGS. 5 (A) to 5 (F).

  FIG. 5A and FIG. 5B show beam profiles derived using only the conversion processing method from the temperature distribution to the beam distribution without performing averaging and filtering. FIG. 5A is an image diagram showing the two-dimensional distribution in the x and y directions by color shading, and FIG. 5B is a measurement of the original beam distribution in the x direction (black broken line) and calculation. It is a graph which shows beam distribution (gray solid line). The incident beam was a proton beam with 20 MeV, 20 μA, and beam diameter 2σ = 10 mm. The shielding film 17 was a copper foil having a thickness of 100 μm.

  As can be seen from the two-dimensional distribution in FIG. 5A, it is possible to determine a certain beam shape, but noise is conspicuous. This noise is generated by propagating from the temperature distribution before conversion. As shown in FIG. 5B, the noise amplitude and the beam distribution intensity are approximately the same. Therefore, in order to accurately measure the beam distribution, it is necessary to remove the noise on the temperature distribution from here.

  FIG. 5C and FIG. 5D show beam distributions derived using the conversion method after averaging using the temperature distributions for 10 sheets. FIG. 5C is an image diagram showing the two-dimensional distribution in the x and y directions by color shading, and FIG. 5D is measured by calculation with the original beam distribution in the x direction (black broken line). It is a graph which shows beam distribution (gray solid line). Thus, it can be seen that the noise is reduced by performing the averaging process.

  FIG. 5E and FIG. 5F are beam distributions derived using the conversion method after averaging using the temperature distribution for 10 sheets and further performing filtering once. FIG. 5 (E) is an image diagram showing the two-dimensional distribution in the x and y directions by color shading, and FIG. 5 (F) was measured by calculation with the original beam distribution (black broken line) in the x direction. It is a graph which shows beam distribution (gray solid line). In this way, noise that remains a little by averaging alone can be effectively removed by filtering. In addition, it can be confirmed that the converted beam distribution sufficiently reproduces the exact solution indicated by the broken line. For the 2σ = 10 mm beam considered here, the width of the temperature distribution on the thin film was 2σ≈30 mm, and a distribution spreading about 3 times was observed. Therefore, the algorithm developed this time is very useful for correctly verifying the beam distribution correctly.

  Next, with FIGS. 5G to 5I, even with a beam shape that cannot be accurately detected by the temperature distribution, the accuracy is improved by the above-described conversion processing method from the temperature distribution to the beam distribution of the present invention. Explain that the beam distribution can be obtained.

  FIG. 5G is an image diagram showing a temperature distribution. As shown in the figure, it can be seen that a wide portion at the center is bright, and one large circle is bright toward the center (temperature is high).

  FIG. 5H is an image diagram of the beam distribution obtained from the temperature distribution by the conversion processing method from the temperature distribution to the beam distribution according to the present invention. As shown in the figure, it can be seen that two elliptical beams that are elongated in the vertical direction in the figure are actually irradiated side by side in the horizontal direction in the figure. In this way, even if the temperature distribution is such that heat from the two beams is mixed and cannot be identified, and it looks like one large beam, by performing the conversion processing method from the temperature distribution to the beam distribution of the present invention, It can be accurately confirmed that there are two elliptical beams.

  FIG. 5I is a graph showing the temperature distribution and the beam distribution in the x direction. The original beam distribution (black broken line) is so high that it protrudes in two places near the center, while the temperature distribution (gray broken line) is a mountain shape with these two vertices as one large vertex. become. On the other hand, the beam distribution (gray solid line) obtained by the temperature distribution to beam distribution conversion processing method of the present invention has substantially the same shape as the original beam distribution, and is so high that it protrudes at two locations near the center. It has become.

  As described above, the charged particle beam distribution measurement system 8 can accurately measure the beam distribution regardless of the beam shape.

  Since the camera used for imaging is the infrared camera 15 using a microbolometer or the like as an image sensor, it is resistant to neutrons and can withstand repeated use.

  In addition, since the cooling unit 20 is structured to cool from the periphery of the shielding film 17, heat propagation in the shielding film 17 can be made two-dimensional in the x and y directions that are the beam width direction.

  Also, by making this heat propagation two-dimensional, the z-axis term can be reduced from the differential equation, making it possible to perform a two-dimensional calculation, and the equation for obtaining the beam distribution from the temperature distribution can be simplified.

  In addition, since the calculation can be performed with a simple expression, it can be realized using an FPGA, a DSP, or the like without using a high-performance computer.

  Further, according to the present invention, even when a relatively noisy infrared camera 15 (ΔTNETD≈0.3K) is used, a proton beam of about 0.1 μA to several tens of μA can be sufficiently accurately obtained by using a niobium thin film. It was confirmed by calculation that the beam distribution could be measured.

  In addition, in the averaging process, since the averaging is performed for each pixel using the temperature acquired a plurality of times, variations in measurement results in all the pixels can be eliminated and the accuracy can be improved.

  Further, in the filtering process, since the difference between adjacent pixels is smoothed, the accuracy and accuracy can be improved by eliminating variations and errors between pixels.

  In this way, by performing both the averaging process for eliminating the error in the pixel and the filtering process for eliminating the error between the pixels, the radionuclide of the charged particle beam is stochastically heated in the shielding film 17. The noise generated by generating can be eliminated with high accuracy, and the measurement result of the beam distribution can be brought close to the true beam distribution with high accuracy.

  The cooling unit 20 has a structure that cools the entire periphery of the shielding film 17, but is not limited thereto, and may have an appropriate structure such as a structure that cools a plurality of locations around the shielding film 17. . Even in such a case, if the cooling unit 20 is arranged at a certain distance around the shielding film 17, the temperature can be propagated uniformly in the x and y directions, and the same effect as the above-described embodiment can be obtained. Can do.

  The cooling unit 20 is disposed outside the beam transport duct 11, but is not limited thereto, and may be disposed inside the beam transport duct 11. In this case, the cooling unit 20 is disposed in a peripheral portion of the shielding film 17 where the charged particle beam is not irradiated, and the charged particle beam is configured not to pass through the portion cooled by the cooling unit 20. Also in this case, the same effect as the above-described embodiment can be obtained.

  The shielding film 17 is a film for maintaining a pressure difference between the beam transport line (on the beam transport duct 11 side) and the irradiation target part (on the irradiation duct 31 side). In addition to the film, a measurement film for measuring the beam distribution from the temperature distribution may be provided. In this case, the infrared camera 15 may be configured to image a measurement film, not a film for maintaining a pressure difference. In this case, the cooling unit 20 may be configured to cool the measurement film from the surroundings. Also in this case, the beam distribution can be measured with high accuracy, and the same effect as the above-described embodiment can be obtained. In this case, the target 33 itself may be used as a measurement film, and the cooling unit 20 may be provided around the target 33.

  In addition, the cooling unit 20 is structured to be cooled by the refrigerant 22, but is not limited thereto, and has an appropriate structure for cooling the peripheral part of the shielding film 17, such as a heat sink provided in the peripheral part of the shielding film 17. be able to.

  The present invention can be used in an appropriate apparatus for irradiating a charged particle beam. For example, various irradiating charged particle beams such as RI production line for PET, neutron generation system used for BNCT treatment, proton beam therapy system, accelerator experiment, material irradiation, radiation incident electron, particle beam therapy, electron beam sterilization, etc. Can be used for various purposes.

7 ... Computer
8 ... charged particle beam distribution measurement system 15 ... infrared camera 17 ... shielding film 18 ... irradiation region 20 ... cooling unit 40 ... target pixels 41-44 ... adjacent pixels

Claims (5)

An irradiated medium in which a temperature change occurs in the irradiated portion when the charged particle beam is irradiated;
A cooling unit for cooling at least a part of the irradiated medium other than the irradiated part;
A temperature distribution measuring device for measuring a temperature distribution of at least the irradiated portion of the irradiated medium;
A charged particle beam distribution measuring system comprising: a beam distribution calculating unit that calculates a beam distribution from the temperature distribution measured by the temperature distribution measuring device. The temperature distribution measuring device is configured to measure the temperature distribution by measuring the temperature for each pixel arranged in a grid pattern,
The beam distribution calculator is
The heat source for each pixel in the temperature distribution is calculated based on the temperature of the target pixel and the temperatures of four adjacent pixels adjacent to the target pixel, and the beam distribution is calculated using the heat source. Charged particle beam distribution measurement system. The beam distribution calculator is
Calculate the average value for each pixel for the temperature distribution measured multiple times by the temperature distribution measuring device,
The charged particle beam measurement system according to claim 2, wherein the beam distribution is calculated based on an average temperature distribution that is a distribution of the average value. The beam distribution calculator is
The charged particle beam measurement system according to claim 2 or 3, wherein the temperature distribution is smoothed. When the charged particle beam is irradiated, the cooling unit cools at least a part other than the irradiated part with respect to the irradiated medium in which a temperature change occurs in the irradiated part,
A temperature distribution measuring device measures the temperature distribution of at least the irradiated portion of the irradiated medium,
A charged particle beam distribution measuring method in which a beam distribution calculating unit calculates a beam distribution from a temperature distribution measured by the temperature distribution measuring apparatus.