Electron beam detection apparatus

Abstract

To provide an electron beam detection device capable of achieving high speed and high sensitivity of detection and expansion of a dynamic range.SOLUTION: An electron beam detector 1 includes a scintillation layer 8, and a CMOS (Complementary Metal Oxide Semiconductor) image sensor 2 having a light receiving region 2a including a plurality of pixels and detecting light emitted in the scintillation layer 8. The readout noise of each of the multiple pixels is not less than 0.15 [e-rms] and not more than 5 [e-rms]; and the scintillator layer 8 includes GOS: Pr.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electron beam detection device. [Background technology]

[0002] As an electron beam detection device applied to a transmission electron microscope, Patent Document 1 describes a digital camera including a scintillator, an image sensor, and an optical fiber plate disposed between the scintillator and the image sensor. The digital camera described in Patent Document 1 uses a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor as the image sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2009 / 0080799 Summary of the Invention [Problem to be solved by the invention]

[0004] In a transmission electron microscope, in order to reduce damage to a sample caused by the electron beam, it is necessary to reduce the electron beam irradiation dose and the electron beam irradiation time. To achieve these, an electron beam detection device used in a transmission electron microscope is required to achieve faster detection, higher sensitivity, and a wider dynamic range. In the digital camera described in Patent Document 1, when a CMOS image sensor is used as the image sensor, faster detection and higher sensitivity can be achieved. However, the digital camera described in Patent Document 1 still has room for improvement in terms of wider dynamic range.

[0005] An object of the present invention is to provide an electron beam detection device that can achieve faster detection, higher sensitivity, and a wider dynamic range. [Means for solving the problem]

[0006] The electron beam detection device of the present invention is [1] "an electron beam detection device comprising: a scintillator layer; and a CMOS image sensor having a light receiving area including a plurality of pixels and detecting light emitted from the scintillator layer, wherein the readout noise in each of the plurality of pixels is 0.15 [e-rms] or more and 5 [e-rms] or less, and the scintillator layer includes GOS:Pr."

[0007] The electron beam detection device uses a CMOS image sensor as the image sensor. This allows for faster detection and higher sensitivity compared to when a CCD image sensor is used as the image sensor. Furthermore, the readout noise of each of the multiple pixels of the CMOS image sensor is between 0.15 e-rms and 5 e-rms, thereby lowering the lower limit of the dynamic range of the CMOS image sensor. Furthermore, the scintillator layer contains GOS:Pr, which reduces the optical shot noise caused by afterglow emitted in the scintillator layer (e.g., suppresses it to less than the readout noise of the CMOS image sensor). This prevents the effective dynamic range of the CMOS image sensor from being narrowed due to high optical shot noise. Therefore, the electron beam detection device allows for faster detection, higher sensitivity, and an expanded dynamic range.

[0008] The electron beam detection device of the present invention may be [2] "the electron beam detection device according to the above [1], in which the readout noise in each of the plurality of pixels is 1 [e-rms] or less." With this electron beam detection device, the readout noise is further reduced, thereby further lowering the lower limit of the dynamic range. Therefore, with this electron beam detection device, it is possible to achieve a further expansion of the dynamic range.

[0009] The electron beam detection device of the present invention may be [3] "the electron beam detection device according to the above [1] or [2], further comprising a fiber optic plate that guides the light emitted in the scintillator layer to the light-receiving region." With this electron beam detection device, the light emitted in the scintillator layer can be transmitted to the light-receiving region of the CMOS image sensor with high efficiency.

[0010] The electron beam detection device of the present invention may be [4] "the electron beam detection device according to the above [3], wherein the fiber optic plate includes a first fiber optic plate arranged on the CMOS image sensor and a second fiber optic plate arranged between the first fiber optic plate and the scintillator layer, and the scintillator layer is fixed to a light input surface of the second fiber optic plate." According to this electron beam detection device, when the scintillator layer deteriorates, the scintillator layer and the second fiber optic plate can be replaced with new ones, while the CMOS image sensor remains together with the first fiber optic plate.

[0011] The electron beam detection device of the present invention may be [5] "the electron beam detection device according to the above [1] or [2], further comprising a lens that guides the light emitted from the scintillator layer to the light-receiving region." With this electron beam detection device, the light emitted from the scintillator layer can be transmitted to the light-receiving region of the CMOS image sensor with high efficiency. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an electron beam detection device that can achieve faster detection, higher sensitivity, and an expanded dynamic range. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an example of a transmission electron microscope. [Figure 2] FIG. 2 is a cross-sectional view of the electron beam detection device shown in FIG. [Figure 3] 10A and 10B are diagrams for explaining the operation and effect of the electron beam detection device. [Figure 4] FIG. 1 shows the light output of light emitted in a scintillator. [Figure 5] FIG. 1 shows the relative light output of the light emitted in the scintillator. [Figure 6] FIG. 10 is a diagram showing a simulation result of the dynamic range. [Figure 7] FIG. 10 is a configuration diagram of a modified example of an electron beam detection device. DETAILED DESCRIPTION OF THE INVENTION

[0014] An example of the present invention will now be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted.

[0015] As shown in FIG. 1, a transmission electron microscope 10 includes a housing 11, an electron beam source 12, a plurality of lens coils 13, a sample support 14, a plurality of lens coils 15, and an electron beam detection device 1. The electron beam source 12, the plurality of lens coils 13, the sample support 14, the plurality of lens coils 15, and the electron beam detection device 1 are arranged in this order along a direction A from one side in the direction A. The direction A is, for example, a vertical direction, and the one side in the direction A is, for example, an upper side. In the following description, the one side in the direction A (the upper side in FIG. 1) will be simply referred to as "the one side," and the other side in the direction A (the lower side in FIG. 1) will be simply referred to as "the other side."

[0016] The housing 11 houses an electron beam source 12, multiple lens coils 13, a sample support 14, multiple lens coils 15, and an electron beam detection device 1. The electron beam source 12 outputs an electron beam EB. The electron beam source 12 is, for example, an electron gun that emits the electron beam EB. The sample support 14 is disposed between the electron beam source 12 and the electron beam detection device 1. The sample support 14 supports a sample S. The sample support 14 is, for example, a sample holder that holds the sample S. The electron beam detection device 1 detects the electron beam EB that has transmitted through the sample S. The multiple lens coils 13 focus the electron beam EB output from the electron beam source 12 on a predetermined region of the sample S. The multiple lens coils 15 focus the electron beam EB that has transmitted through the sample S on a predetermined region of a scintillator layer (details will be described later) of the electron beam detection device 1. The space within the housing 11 is evacuated when an electron beam transmission image of the sample S is acquired.

[0017] As shown in FIG. 2 , the electron beam detection device 1 includes a CMOS (Complementary Metal Oxide Semiconductor) image sensor 2, an adhesive layer 3, a first FOP (first fiber optic plate) 4, an immersion oil layer 5, a second FOP (second fiber optic plate) 6, a transparent conductive film 7, and a scintillator layer 8. The electron beam detection device 1 is supported by a support member 91. The support member 91 is attached to the wall portion 111 so as to cover the opening 111a of the wall portion 111, thereby placing the electron beam detection device 1 in the space within the housing 11 via the opening 111a of the wall portion 111. The wall portion 111 is a wall portion that constitutes a part of the housing 11 of the transmission electron microscope 10. The wall portion 111 and the support member 91 are formed of, for example, metal.

[0018] The CMOS image sensor 2 is disposed on one surface 92a of the wiring substrate 92. A plurality of terminals of the CMOS image sensor 2 are electrically connected to a plurality of wires of the wiring substrate 92. The CMOS image sensor 2 and the wiring substrate 92 are housed in a ceramic package 93. The ceramic package 93 is disposed on one surface of a wiring substrate 98 fixed to a support member 91. The ceramic package 93 includes a bottom wall 94 and a side wall 95. The side wall 95 is located on one side of the bottom wall 94 and defines an opening facing the bottom wall 94 in direction A. The bottom wall 94 is formed, for example, in the shape of a rectangular plate. The side wall 95 is formed, for example, in the shape of a rectangular frame. The wiring substrate 92 is fixed to the bottom wall 94 of the ceramic package 93 while being surrounded by the side wall 95 of the ceramic package 93.

[0019] The ceramic package 93 is provided with a plurality of lead pins 96. Each lead pin 96 extends from the bottom wall 94 to the other side. The plurality of lead pins 96 are terminal portions of a plurality of wires provided in the ceramic package 93, and are electrically connected to a plurality of wires on a wiring board 98. The CMOS image sensor 2 is electrically connected to external wiring via the plurality of wires on the wiring board 92, the plurality of wires (including the plurality of lead pins 96 which are terminal portions) provided in the ceramic package 93, and the plurality of wires on the wiring board 98. This enables input and output of signals to and from the CMOS image sensor 2.

[0020] The CMOS image sensor 2 detects light emitted from the scintillator layer 8. The CMOS image sensor 2 has a light receiving area 2a. The light receiving area 2a includes a plurality of pixels arranged two-dimensionally along a plane perpendicular to direction A. The CMOS image sensor 2 is formed, for example, in the shape of a rectangular plate. The shape of the light receiving area 2a when viewed from direction A is, for example, rectangular. The CMOS image sensor 2 is, for example, a back-illuminated CMOS image sensor. The CMOS image sensor 2 may also be, for example, a front-illuminated CMOS image sensor. The CMOS image sensor 2 may also be, for example, a CMOS area sensor or a CMOS line sensor.

[0021] The readout noise of each of the plurality of pixels is 0.15 e-rms or more and 5 e-rms or less. The readout noise of each of the plurality of pixels may be 0.15 e-rms or more and 1 e-rms or less. The readout noise is a statistical expression of the variation in the electronic circuit when the photoelectron signal of each pixel is converted into a digital value. For example, if each pixel has a photodiode (photoelectric conversion element) and an amplifier, the readout noise is random noise generated in the amplifier when the voltage amplified by the amplifier is read out.

[0022] A Peltier element 97 is disposed between the support member 91 and the wiring board 92, penetrating the bottom wall 94 and the wiring board 98. A heat absorbing portion of the Peltier element 97 is connected to the wiring board 92. A heat generating portion of the Peltier element 97 is connected to the support member 91. When the transmission electron microscope 10 is in operation, heat generated in the CMOS image sensor 2 is released to the support member 91 via the Peltier element 97, and the temperature of the CMOS image sensor 2 is maintained within a constant range.

[0023] The wall portion 111 includes an inward-facing flange portion 112. The flange portion 112 extends along the inner surface of the opening 111a. A groove 112a is formed in the flange portion 112. The groove 112a opens to the other side and extends along the flange portion 112. The flange portion 112 is formed, for example, in the shape of a rectangular frame. The groove 112a extends, for example, in a rectangular shape when viewed from direction A. The groove 112a faces a surface 95a on one side of the side wall 95 in direction A. An O-ring 113 is arranged between the surface 95a of the side wall 95 and the bottom surface of the groove 112a.

[0024] In the transmission electron microscope 10, when the support member 91 is attached to the wall portion 111 by, for example, bolts, the side wall 95 of the ceramic package 93 fixed to the support member 91 approaches the flange portion 112. At this time, the O-ring 113 is crushed between the surface 95a of the side wall 95 and the bottom surface of the groove 112a, thereby ensuring airtightness of the space within the housing 11 and enabling the space within the housing 11 to be evacuated.

[0025] The first FOP4 is disposed on the CMOS image sensor 2. The first FOP4 is composed of a bundle of multiple optical fibers. The first FOP4 has a light input surface 4a and a light output surface 4b. The light input surface 4a is the surface on one side of the first FOP4 and is composed of multiple light input end faces of multiple optical fibers. The light output surface 4b is the surface on the other side of the first FOP4 and is composed of multiple light output end faces of multiple optical fibers. The light output surface 4b faces the light receiving region 2a of the CMOS image sensor 2 in direction A. The first FOP4 is formed, for example, in the shape of a quadrangular prism or a cylinder with a center line parallel to direction A.

[0026] The second FOP6 is disposed on the first FOP4. The second FOP6 is disposed between the first FOP4 and the scintillator layer 8. The second FOP6 guides light emitted from the scintillator layer 8 to the first FOP4. The first FOP4 guides light transmitted through the second FOP6 to the light-receiving region 2a. In other words, the first FOP4 and the second FOP6 guide light emitted from the scintillator layer 8 to the light-receiving region 2a. The second FOP6 is formed by a bundle of multiple optical fibers. The second FOP6 has a light input surface 6a and a light output surface 6b. The light input surface 6a is a surface on one side of the second FOP6 and is formed by multiple light input end faces of multiple optical fibers. The light output surface 6b is a surface on the other side of the second FOP6 and is formed by multiple light output end faces of multiple optical fibers. The light output surface 6b faces the light input surface 4a of the first FOP 4 in the direction A. The second FOP 6 is formed in the shape of a cylinder having a center line parallel to the direction A, for example.

[0027] The thickness of the second FOP6 (i.e., the distance between the light input surface 6a and the light output surface 6b) is greater than the thickness of the first FOP4 (i.e., the distance between the light input surface 4a and the light output surface 4b). The thickness of the first FOP4 is, for example, about 10 mm. The thickness of the second FOP6 is, for example, about 20 mm. When viewed from direction A, the outer edge of the first FOP4 is located outside the outer edge of the light receiving region 2a and inside the outer edge of the CMOS image sensor 2. When viewed from direction A, the outer edge of the second FOP6 is located outside the outer edges of the first FOP4, the CMOS image sensor 2, and the wiring substrate 92.

[0028] The adhesive layer 3 is disposed between the CMOS image sensor 2 and the light output surface 4b of the first FOP4. In other words, the adhesive layer 3 is disposed between the CMOS image sensor 2 and the first FOP4. The adhesive layer 3 is optically transparent. The first FOP4 is adhered to the CMOS image sensor 2 by the adhesive layer 3. The thickness of the adhesive layer 3 is, for example, about 10 μm. The material of the adhesive layer 3 is, for example, an optically transparent epoxy resin.

[0029] The immersion oil layer 5 is disposed between the light input surface 4a of the first FOP 4 and the light output surface 6b of the second FOP 6. In other words, the immersion oil layer 5 is disposed between the first FOP 4 and the second FOP 6. The immersion oil layer 5 is in contact with the light output surface 6b and the light input surface 4a. The immersion oil layer 5 is filled between the light output surface 6b and the light input surface 4a. The thickness of the immersion oil layer is 3 μm or less.

[0030] The immersion oil layer 5 is a layer formed from oil (liquid) that is transparent to light emitted from the scintillator layer 8 in response to the incidence of the electron beam EB and has a refractive index of 1.4 or more and 1.9 or less. Examples of oil that can be used to form the immersion oil layer 5 include "Immersion Oil F30cc (MXA22168)" manufactured by Nikon Solutions Corporation and "MOIL-30" manufactured by Evident Co., Ltd.

[0031] The transparent conductive film 7 is disposed between the light input surface 6a of the second FOP 6 and the scintillator layer 8. That is, the transparent conductive film 7 is disposed between the second FOP 6 and the scintillator layer 8. The transparent conductive film 7 is a film formed on the light input surface 6a by, for example, a vapor deposition method. The transparent conductive film 7 has a thickness of, for example, about 20 nm. The transparent conductive film 7 is made of, for example, ITO. When viewed from direction A, the shape of the transparent conductive film 7 is, for example, circular. When viewed from direction A, the outer edge of the transparent conductive film 7 coincides with the outer edge of the light input surface 6a.

[0032] The scintillator layer 8 is disposed on the transparent conductive film 7. That is, the scintillator layer 8 is disposed on the second FOP 6 via the transparent conductive film 7. The scintillator layer 8 and the transparent conductive film 7 are in contact with each other. The scintillator layer 8 is a layer whose thickness direction is in the direction A and contains GOS:Pr. The scintillator layer 8 is a layer formed on the transparent conductive film 7 by, for example, a precipitation method. The scintillator layer 8 is fixed to the light input surface 6a of the second FOP 6 via the transparent conductive film 7. The thickness of the scintillator layer 8 is, for example, approximately 10 μm. When viewed from the direction A, the shape of the scintillator layer 8 is, for example, circular. When viewed from the direction A, the outer edge of the scintillator layer 8 is located inside the outer edge of the transparent conductive film 7. In other words, when viewed from the direction A, the outer edge of the transparent conductive film 7 is located outside the outer edge of the scintillator layer 8.

[0033] The unitized second FOP 6, transparent conductive film 7, and scintillator layer 8 are held down by a holding member 114 relative to the unitized CMOS image sensor 2, adhesive layer 3, and first FOP 4. The holding member 114 includes a cylindrical main body 115, an inward flange 116, and an outward flange 117. The main body 115 is formed, for example, in the shape of a cylinder having a center line parallel to direction A. The holding member 114 is formed, for example, from metal. An inner side surface 115a of the main body 115 contacts the outer edge of the transparent conductive film 7 and the side surface of the second FOP 6. A surface 116a on the other side of the flange 116 contacts a surface 7a on one side of the transparent conductive film 7.

[0034] A plurality of spacers 118 are disposed between the wall portion 111 and the flange portion 117 of the holding member 114. The flange portion 117 of the holding member 114 is fixed to the wall portion 111 via the plurality of spacers 118, for example, with bolts or the like, thereby holding down the unitized second FOP 6, transparent conductive film 7, and scintillator layer 8 relative to the unitized CMOS image sensor 2, adhesive layer 3, and first FOP 4. In the electron beam detection device 1, the transparent conductive film 7 is electrically connected to the wall portion 111 via the holding member 114 and the plurality of spacers 118, and the transparent conductive film 7 is grounded. For example, a single cylindrical spacer 118 may be disposed between the wall portion 111 and the flange portion 117 of the holding member 114. [Action and effect]

[0035] As described above, the electron beam detection device 1 uses the CMOS image sensor 2 as an image sensor. This allows for faster detection and higher sensitivity compared to when a CCD (Charge Coupled Device) image sensor is used as the image sensor. Furthermore, the readout noise of each of the multiple pixels of the CMOS image sensor 2 is 0.15 e-rms or more and 5 e-rms or less, thereby lowering the lower limit of the dynamic range of the CMOS image sensor 2. Furthermore, the scintillator layer 8 contains GOS:Pr, which reduces the optical shot noise caused by afterglow emitted in the scintillator layer 8 (for example, suppressing it to below the readout noise that determines the lower limit of the dynamic range of the CMOS image sensor 2). This prevents the effective dynamic range of the CMOS image sensor 2 from being narrowed due to high optical shot noise. Therefore, the electron beam detection device 1 allows for faster detection, higher sensitivity, and an expanded dynamic range.

[0036] The above-mentioned functions and effects will be further explained with reference to Figures 3(a) and 3(b). Figures 3(a) and 3(b) show the value obtained by subtracting the dark offset value from the digital count value for each of the multiple pixels of the image sensor, the saturation charge calculated from the conversion coefficient, the readout noise specific to the image sensor, and the optical shot noise due to afterglow generated in the scintillator layer. Figure 3(a) corresponds to the electron beam detection device of the reference example, and Figure 3(b) corresponds to the electron beam detection device 1. The scintillator layer emits light the instant it is irradiated with radiation, but may continue to emit light even after the radiation irradiation is stopped. This light is called afterglow. Optical shot noise refers to noise caused by the number of photons incident on the image sensor per unit time being nonuniform according to a Poisson distribution. The effective dynamic range ("DR" in Figures 3(a) and 3(b)) of each of the multiple pixels is expressed as the ratio of the saturation charge to the square root of the sum of the squares of all added noise components. It should be noted that the ranges of the dynamic range (DR) shown in Figures 3(a) and (b) are for convenience only and do not mean that the "optical shot noise due to afterglow" and the "CMOS readout noise" are the lower limits of the dynamic range.

[0037] The scintillator layer of the electron beam detection device according to the reference example shown in FIG. 3(a) is a layer containing a scintillator material other than GOS:Pr (e.g., P43). In order to expand the effective dynamic range in the example of FIG. 3(a), it is conceivable to reduce the readout noise of the CCD image sensor. However, even if the readout noise is reduced by using a CMOS image sensor instead of a CCD image sensor, if the optical shot noise due to afterglow generated in the scintillator layer (e.g., the layer containing P43) is relatively large, it may not be possible to sufficiently expand the effective dynamic range of each of the multiple pixels.

[0038] In contrast, in the electron beam detection device 1 shown in FIG. 3(b), the scintillator layer 8 contains GOS:Pr, which makes the optical output of the afterglow emitted in the scintillator layer 8 relatively small, as shown in the experimental results described below. This makes it possible to suppress, for example, the optical shot noise due to the afterglow emitted in the scintillator layer 8 to less than the readout noise of the CMOS image sensor 2. In this case, the effective dynamic range of each of the multiple pixels can be sufficiently expanded. Therefore, in the example of FIG. 3(b), it is possible to avoid a narrowing of the effective dynamic range of the CMOS image sensor 2 caused by the optical shot noise exceeding the readout noise.

[0039] In the electron beam detection device 1, the readout noise in each of the multiple pixels may be 1 [e-rms] or less. In this case, the readout noise becomes even smaller, and the lower limit of the dynamic range can be further lowered. Therefore, the electron beam detection device 1 can achieve a further expansion of the dynamic range.

[0040] The electron beam detection device 1 includes a first FOP4 and a second FOP6 that guide the light emitted in the scintillator layer 8 to the light-receiving region 2a. This allows the light emitted in the scintillator layer 8 to be transmitted with high efficiency to the light-receiving region 2a of the CMOS image sensor 2. Furthermore, even if characteristic X-rays are emitted in the scintillator layer 8, the first FOP4 and the second FOP6 can reduce damage to the CMOS image sensor 2 caused by the characteristic X-rays.

[0041] The electron beam detection device 1 includes a first FOP4 disposed on the CMOS image sensor 2 and a second FOP6 disposed between the first FOP4 and a scintillator layer 8, with the scintillator layer 8 fixed to a light input surface 6a of the second FOP6. When characteristic X-rays are emitted from the scintillator layer 8, the second FOP6 tends to be easily deteriorated by the characteristic X-rays. According to the electron beam detection device 1, when the second FOP6 deteriorates, the second FOP6 can be replaced with a new one while the CMOS image sensor 2 remains together with the first FOP4. [Experimental Results]

[0042] Six types of scintillators were prepared, each containing P43 (GOS:Tb), P46 (YAG:Ce), GOS:Pr, YAP:Ce, LuAG:Pr, and BFCl:Eu. Three types of scintillators were placed on a line sensor, and the light output of each scintillator was measured at 0.5-second intervals using an electron beam detector. The three combinations of scintillators placed on the line sensor were: "three types of scintillators containing P43, GOS:Pr, and P46," "three types of scintillators containing GOS:Pr, LuAG:Pr, and P46," and "three types of scintillators containing BFCl:Eu, GOS:Pr, and P46."

[0043] After placing the three types of scintillators on the line sensor, dark images were acquired at 0.5-second intervals. Next, X-rays output from the X-ray source were irradiated onto the three types of scintillators. The X-ray source tube voltage was 90 kV and the tube current was 5 mA. After irradiating the scintillators with X-rays for one hour, measurements were started using the electron beam detector at 0.5-second intervals. After a certain amount of time had passed since the start of measurements using the electron beam detector, a lead shield was placed between the X-ray source and the scintillators to block the X-rays. After a certain amount of time had passed since the lead shield was placed, the output of the X-ray source was turned off. The results of this experiment correlate with those obtained when irradiating a scintillator with electron beams.

[0044] The vertical axis of the graph in Figure 4 shows the light output of the light (afterglow) emitted by the scintillator as the number of photoelectrons [e] counted by the electron beam detector. For each of the six scintillators, the output of the X-ray source was switched off at the 3.5-second exposure time in the graph shown in Figure 4. Note that the light output of the scintillator containing LuAG:Pr is very high and falls outside the range of the graph in Figure 4.

[0045] As shown in Figure 4, the light output of the afterglow emitted from the scintillator 1 second after the X-ray source output was switched off (exposure time: 4.5 seconds) increased in the following order: GOS:Pr, YAP:Ce, BFCl:Eu, P46, P43, and LuAG:Pr. In other words, 1 second after the X-ray source output was switched off, the light output of the afterglow emitted from GOS:Pr was the smallest.

[0046] The vertical axis of the graph shown in Figure 5 indicates the relative light output of the light emitted by the scintillator. The relative light output was calculated by "light output when X-rays are blocked / light output when X-rays are irradiated × 100 [%]". The relative light output of each of the six types of scintillators decreased when the X-rays were blocked, and further decreased when the output of the X-ray source was switched off. Note that the relative light output of the scintillator containing LuAG:Pr was very large and was located outside the range of the graph in Figure 5.

[0047] One second after the X-ray source was turned off, the relative light output was 0.02% for the scintillator containing P43, 0.07% for the scintillator containing P46, 0.002% for the scintillator containing GOS:Pr, 0.21% for the scintillator containing YAP:Ce, 9.87% for the scintillator containing LuAG:Pr, and 0.08% for the scintillator containing BFCl:Eu. That is, one second after the X-ray source was turned off, the relative light output increased in the following order: GOS:Pr, P43, P46, BFCl:Eu, YAP:Ce, and LuAG:Pr. In other words, one second after the X-ray source was turned off, the relative light output of GOS:Pr was the smallest.

[0048] As shown by the above experimental results, the light output of the afterglow emitted from the scintillator containing GOS:Pr tends to be the smallest among the six types of scintillators. From these experimental results, it can be said that the optical shot noise due to the afterglow emitted from the scintillator containing GOS:Pr tends to be the smallest among the six types of scintillators. If an electron beam detection device includes a scintillator having afterglow characteristics equivalent to those of a scintillator containing GOS:Pr, the optical shot noise due to the afterglow emitted in the scintillator can be sufficiently reduced, and the same effects and advantages as those of the above-mentioned electron beam detection device 1 can be achieved. "Afterglow characteristics equivalent to those of a scintillator containing GOS:Pr" means, for example, that the relative light output one second after the output of the X-ray source is switched off is less than 0.02% (less than the relative light output of a scintillator containing P43). [Simulation Results]

[0049] Figure 6 shows the results of a simulation of the dynamic range of a CMOS image sensor in an electron beam detector equipped with a scintillator containing GOS:Pr and a CMOS image sensor. This simulation assumes that afterglow emitted from the scintillator is incident on each pixel of the CMOS image sensor when the CMOS image sensor detects the light (main signal) emitted from the scintillator. The simulation simulates the dynamic range of the CMOS image sensor at an exposure time of 2.5 milliseconds. In this simulation, the optical output of the afterglow (the number of photoelectrons counted by the electron beam detector) is set to 1 e. The vertical axis on the left side of the graph in Figure 6 represents the squared value of each noise (bar graph value), and the vertical axis on the right side represents the dynamic range (line graph value). As shown in Figure 6, the dynamic range expands as the readout noise of the CMOS image sensor decreases within the range of 0.15 e-rms to 5 e-rms. The lower limit of the dynamic range is calculated as the square root of the sum of the squares of the readout noise and the optical shot noise due to afterglow, and therefore the value of the dynamic range increases as the readout noise decreases. [Variations]

[0050] The present invention is not limited to the above-described example. For example, while the electron beam detection device 1 shown in FIG. 2 includes the first FOP 4 and the second FOP 6, as shown in FIG. 7, the electron beam detection device 1 may include a prism 30 and two lenses 31 and 32 instead of the first FOP 4 and the second FOP 6. In the example shown in FIG. 7, the scintillator layer 8 is fixed to the light input surface 30a of the prism 30. The two lenses 31 and 32 are disposed between the light output surface 30b of the prism 30 and the CMOS image sensor 2. Light L emitted from the scintillator layer 8 enters the prism 30 from the light input surface 30a and is reflected by the reflecting surface 30c of the prism 30 toward the light output surface 30b. The light L output from the light output surface 30b of the prism 30 is guided (focused) to the light receiving region 2a of the CMOS image sensor 2 by the lenses 31 and 32. 7 also allows light emitted from the scintillator layer 8 to be transmitted with high efficiency to the light receiving region 2a of the CMOS image sensor 2. Note that the electron beam detection device 1 shown in FIG. 7 may include one lens instead of the two lenses 31 and 32.

[0051] Although the electron beam detection device 1 includes the first FOP 4 and the second FOP 6, the electron beam detection device 1 may include a single FOP instead of the first FOP 4 and the second FOP 6. [Explanation of symbols]

[0052] 1...electron beam detection device, 2...CMOS image sensor, 2a...light receiving area, 4...first FOP (first fiber optic plate), 6...second FOP (second fiber optic plate), 6a...light input surface, 8...scintillator layer, 31, 32...lenses.

Claims

[Claim 1] a scintillator layer; a CMOS image sensor having a light receiving region including a plurality of pixels and configured to detect light emitted from the scintillator layer; readout noise in each of the plurality of pixels is equal to or greater than 0.15 [er-rms] and equal to or less than 5 [er-rms]; The electron beam detection device, wherein the scintillator layer contains GOS:Pr.

Images