Charged particle detector

Abstract

This expands the dynamic range of the charged particle detector while improving its noise characteristics and life cycle. [Solution] The charged particle detector 1 comprises a channel-type first multiplier 10 having a channel portion 13 that emits electrons in response to the incidence of charged particles P and multiplies and emits the emitted electrons, a discrete-type second multiplier 20 that multiplies the electrons emitted from the channel portion 13 of the first multiplier 10, and an anode 40 that collects the multiplied electrons. The second multiplier 20 has a reduction portion 21 formed such that in at least one cross section along the Z direction, the width W in the direction perpendicular to the Z direction decreases as it approaches the first multiplier 10, and the reduction portion 21 has a pair of surfaces 21c formed such that in the cross section, they get closer to each other as they approach the first multiplier 10, and the second multiplier 20 multiplies the electrons emitted from the channel portion 13 of the first multiplier 10 that are incident on the pair of surfaces 21c.

Description

Technical Field

[0001] The present invention relates to a charged particle detector.

Background Art

[0002] For example, Patent Document 1 describes an electron multiplier configured by forming a plurality of channels in a main body portion. In such a channel type multiplier, when electrons enter the channel, electrons are emitted in the channel and the emitted electrons are multiplied, and the multiplied electrons are emitted from the channel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is conceivable to configure a charged particle detector by collecting electrons emitted from the channel type multiplier (multiplication section) as described above with an anode. The charged particle detector may be required to increase the maximum output current to widen the dynamic range. However, when the maximum output current increases, the number of electrons taken out increases, so there is a risk that the life of the multiplication section will be shortened. Further, when the maximum output current increases, the amount of heat generated in the multiplication section increases, and there is a risk that noise caused by thermoelectrons generated by heat generation will occur and the SN ratio will decrease.

[0005] Therefore, an object of the present invention is to provide a charged particle detector capable of improving noise characteristics and life characteristics while widening the dynamic range.

Means for Solving the Problems

[0006] The charged particle detector of the present invention is a charged particle detector comprising: [1] "a channel-type first multiplier having a main body, a channel formed inside the main body that emits electrons in response to the incidence of charged particles and multiplies and emits the emitted electrons, a discrete-type second multiplier arranged to face the first multiplier in a predetermined direction and multiplies the electrons emitted from the channel of the first multiplier, and an anode that collects the multiplied electrons, wherein the second multiplier has a reduction portion formed in at least one cross section along the predetermined direction such that its width in a direction perpendicular to the predetermined direction decreases as it approaches the first multiplier, the reduction portion has a pair of surfaces formed in at least one cross section such that they approach each other as they approach the first multiplier, and the second multiplier multiplies the electrons emitted from the channel of the first multiplier and incident on the pair of surfaces."

[0007] In this charged particle detector, electrons multiplied in a channel-type first multiplier are further multiplied in a discrete-type second multiplier. By further multiplying electrons multiplied in the discrete-type second multiplier, which has a large gain per applied voltage, the maximum output current can be increased and the dynamic range can be widened. Also, because electrons are multiplied in the subsequent second multiplier, the voltage value applied to the first multiplier can be lower compared to, for example, when electrons are multiplied by the first multiplier alone, thereby reducing the amount of heat generated in the channel-type first multiplier and suppressing the generation of noise caused by thermionic electrons. Furthermore, in this charged particle detector, the second multiplier has a reduction section formed such that its width in a direction perpendicular to a predetermined direction decreases as it approaches the first multiplier, and the reduction section has a pair of surfaces formed so that they get closer to each other as they approach the first multiplier, and the second multiplier multiplies electrons emitted from the channel section of the first multiplier and incident on the pair of surfaces. By configuring the second multiplication section in this way, the region into which electrons are incident in the second multiplication section can be widened, and the number of incident electrons per unit area in that region can be reduced. As a result, degradation of the second multiplication section can be suppressed, and the life characteristics can be improved. Therefore, this charged particle detector can improve noise characteristics and life characteristics while widening the dynamic range.

[0008] The charged particle detector of the present invention may also be [2] "the charged particle detector according to [1], wherein the pair of surfaces are inclined with respect to the predetermined direction in at least one cross-section such that they approach each other as they approach the first multiplication section." In this case, the region into which electrons are incident in the second multiplication section can be made even wider, and the life characteristics can be further improved.

[0009] The charged particle detector of the present invention may also be the charged particle detector according to [1] or [2], wherein the reduction portion includes a frustoconical portion whose apex faces the first multiplication portion, and the pair of surfaces are the surfaces of the frustoconical portion. In this case, the region into which electrons are incident in the second multiplication portion can be made even wider, and the life characteristics can be further improved.

[0010] The charged particle detector of the present invention may also be the charged particle detector according to [1] or [2], wherein the reduction portion has a uniform cross-sectional shape with respect to both the predetermined direction and the direction perpendicular to both the predetermined direction and the direction perpendicular to the predetermined direction. In this case, the second multiplication portion can be easily manufactured.

[0011] The charged particle detector of the present invention may also be [5] "a charged particle detector according to any one of [1] to [4], further comprising a support portion having electrical insulating properties and supporting the second multiplier portion on the opposite side from the first multiplier portion, wherein the second multiplier portion further comprises an extending portion extending from the reduction portion on the opposite side from the first multiplier portion, and the extended portion is supported by the support portion." In this case, the provision of the extending portion makes it possible to increase the distance between the reduction portion and the support portion, thereby suppressing the occurrence of charge-up, in which electrons emitted from the reduction portion accumulate in the support portion.

[0012] The charged particle detector of the present invention may also be [6] "a charged particle detector according to any one of [1] to [5], further comprising a discrete third multiplier positioned opposite the pair of surfaces of the reduction section and multiplying the electrons emitted from the second multiplier, wherein the anode collects the electrons multiplied in the third multiplier." In this case, by further multiplying the electrons multiplied in the second multiplier in the discrete third multiplier, the maximum output current can be further increased and the dynamic range can be further widened. Also, since the pair of surfaces of the reduction section are formed to move closer to each other as they approach the first multiplier, the electrons emitted from the pair of surfaces are dispersed (diffused) and proceed to the third multiplier. Therefore, the region in which electrons are incident in the third multiplier can be widened, and the number of incident electrons per unit area in that region can be reduced. As a result, the deterioration of the third multiplier can be suppressed and the life characteristics can be improved.

[0013] The charged particle detector of the present invention may also be the charged particle detector according to [6], wherein the anode is located between the second multiplier and the third multiplier. In this case, the charged particle detector can be made more compact.

[0014] The charged particle detector of the present invention may also be [8] "the charged particle detector according to any one of [1] to [7], wherein the anode has a mesh portion facing the pair of surfaces of the reduction portion." In this case, electrons emitted from the reduction portion can be suitably attracted toward the anode. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a charged particle detector that can improve noise characteristics and life characteristics while widening the dynamic range. [Brief explanation of the drawing]

[0016] [Figure 1] This is a perspective view of a charged particle detector according to an embodiment. [Figure 2] It is a cross-sectional perspective view along line II-II of FIG. 1. [Figure 3] It is a cross-sectional view showing a simplified cross-section along line III-III of FIG. 1. [Figure 4] It is a diagram showing an example of a circuit for applying a voltage to a charged particle detector. [Figure 5] It is a cross-sectional view for explaining the orbit of an electron. [Figure 6] (a) is a graph schematically showing the relationship between input and output. (b) is a graph for explaining the comparison result of the maximum output current in the examples and comparative examples. [Figure 7] It is a cross-sectional view of a charged particle detector according to the first modification. [Figure 8] It is a cross-sectional perspective view of a charged particle detector according to the second modification. [Figure 9] It is a cross-sectional view of a charged particle detector according to a reference example. [Mode for Carrying Out the Invention]

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted. Also, in each figure, an orthogonal coordinate system defining the X direction, Y direction, and Z direction (predetermined direction) may be shown. [Embodiment]

[0018] As shown in FIGS. 1 to 3, the charged particle detector 1 includes a channel-type first multiplier section 10, a discrete-type second multiplier section 20, a discrete-type third multiplier section 30, and an anode 40. The charged particle detector 1 is, for example, an ion detector used for ion detection in quadrupole mass spectrometry (Q-MS). The charged particle detector 1 amplifies electrons generated in response to the incidence of charged particles P (ions in this example) (for example, up to 10 8It is amplified by a factor of [amplification factor] and taken out as an electrical signal. Specifically, the first multiplier 10 emits electrons in response to the incidence of charged particles P, and the emitted electrons are multiplied in the first multiplier 10, the second multiplier 20, and the third multiplier 30 in this order, and the multiplied electrons are collected at the anode 40. The second multiplier 20 is arranged to face the first multiplier 10 in the Z direction. Hereinafter, the side where the first multiplier 10 is located with respect to the second multiplier 20 in the Z direction (the upper side in FIG. 2) is defined as the first side S1, and the side opposite to the first side S1 (the lower side in FIG. 2) is defined as the second side S2.

[0019] The first multiplier 10 is a channel type (continuous type) multiplier having a main body 11, an incident portion 12, and a plurality (12 in this example) of channel portions 13. On the surfaces of the incident portion 12 and the channel portions 13, a multiplier portion 14 that functions as a continuous dynode and includes multiplier layers 14a and 14b described later is provided. The main body 11 is formed in a rectangular parallelepiped shape having, for example, a long direction along the Z direction. The main body 11 is made of a material having electrical insulation properties, and is formed of, for example, a ceramic such as alumina.

[0020] An input electrode A is provided at the end of the main body 11 on the first side S1 in the Z direction. The input electrode A has, for example, a connection portion A1 provided on the first end surface 11a of the first side S1 of the main body 11, and a power supply portion A2 that is electrically connected to the connection portion A1 and extends in a direction orthogonal to the Z direction from the main body 11. The connection portion A1 is a member formed of a conductive material such as a metal material, and is electrically connected to the multiplier layer 14a of the incident portion 12 described later through a conductive layer 15a continuously provided on the first end surface 11a and the surface of the incident portion 12.

[0021] An output electrode B is provided at the end of the second side S2 in the Z direction of the main body 11. The output electrode B has, for example, a connecting portion B1 provided on the second end face 11b of the second side S2 of the main body 11, and a power supply portion B2 that is electrically connected to the connecting portion B1 and extends from the main body 11 in a direction perpendicular to the Z direction. The connecting portion B1 is a member formed of a conductive material such as a metal material, and is electrically connected to the multiplier layer 14b of the channel portion 13 described later via a conductive layer 15b provided on the second end face 11b.

[0022] The incident portion 12 includes an opening 12a that opens into the first end face 11a of the main body portion 11. A conductive layer 15a is provided on the surface of the incident portion 12, and a multiplier layer 14a is formed on the conductive layer 15a, with a resistive layer and an electron emission layer stacked in that order from the incident portion 12 side. The incident portion 12 emits electrons in response to the incidence of charged particles P. In this embodiment, the multiplier layer 14a functions as a conversion layer that converts ions into electrons. The first end S1 of the multiplier layer 14a is electrically connected to the connection portion A1 of the input electrode A via the conductive layer 15a. The channel portion 13 is a hole (cavity) formed inside the main body portion 11, extending from the incident portion 12 to the second end face 11b of the main body portion 11, and is a communication hole that opens into the second end face 11b. In this example, the channel portion 13 extends in a meandering manner along the Z direction. Multiple channel sections 13 are arranged in multiple columns (two columns in this example) along the X direction, and each column has the same number of channel sections 13 (six in this example) arranged along the Y direction. In this example, the two columns of channel sections 13 are arranged alternately so that when viewed from the X direction, the channel sections 13 of one column do not overlap with the channel sections 13 of the other column.

[0023] A multiplier layer 14b, configured similarly to the multiplier layer 14a of the incident section 12, is formed on the surface (inner wall surface) of the channel section 13. The multiplier layers 14a and 14b constitute a continuous dynode consisting of continuously formed films. The first end S1 of the multiplier layer 14b is electrically connected to the multiplier layer 14a, and the second end S2 of the multiplier layer 14b is electrically connected to the connection part B1 of the output electrode B via the conductive layer 15b. During use, a high voltage is applied to the input electrode A and the output electrode B so that the potential of the output electrode B is higher than the potential of the input electrode A, thereby providing a predetermined potential difference across both ends of the multiplier section 14.

[0024] The channel portion 13 multiplies the electrons emitted from the incident portion 12 upon incidence of charged particles P and emits them to the second side S2. Alternatively, if charged particles P are directly incident on the channel portion 13, the channel portion 13 emits electrons in response to the incidence of the charged particles P, and then multiplies and emits the emitted electrons. More specifically, as electrons travel through the channel portion 13 from the first end face 11a to the second end face 11b, the electrons repeatedly collide with the surface (inner surface) of the channel portion 13, causing repeated emission of secondary electrons and multiplication of the electrons. The multiplied electrons are emitted from the opening at the second end face 11b toward the second multiplication portion 20.

[0025] A first support portion 50 is positioned at the end of the second side S2 of the first multiplier portion 10 to support the first multiplier portion 10. The first support portion 50 is, for example, a disc-shaped member extending along a plane perpendicular to the Z direction. The first support portion 50 is formed of, for example, a material having the same electrical insulating properties as the main body portion 11 of the first multiplier portion 10 (ceramic in this example). An opening 50a is formed in the center of the first support portion 50, surrounding the first multiplier portion 10 when viewed from the Z direction, and the first multiplier portion 10 is positioned and supported within this opening 50a. The second end face 11b of the first multiplier portion 10 is exposed from the first support portion 50 at the opening 50a when viewed from the second side S2 in the Z direction.

[0026] The second multiplication unit 20 is a discrete (individually provided, discontinuous) dynode. The second multiplication unit 20 is made of a conductive material, for example, a metallic material (stainless steel in this example). The second multiplication unit 20 is positioned to face the second end face 11b of the first multiplication unit 10 in the Z direction. The second multiplication unit 20 multiplies the electrons emitted from the channel portion 13 of the first multiplication unit 10. The second multiplication unit 20 is positioned to face the opening of the channel portion 13 at the second end face 11b of the first multiplication unit 10. The second multiplication unit 20 has a reduction portion 21 facing the second end face 11b and an extension portion 22 extending from the reduction portion 21 to the second side S2 (opposite side from the first multiplication unit 10) in the Z direction.

[0027] The reduction portion 21 is formed in a solid conical shape with its apex 21a facing the first multiplier portion 10. In this example, the reduction portion 21 is not a perfect cone, but its apex 21a is curved convexly toward the first multiplier portion 10. This suppresses discharge caused by a pointed apex 21a. Thus, the reduction portion 21 is formed in a substantially conical shape. Since the reduction portion 21 is formed in a conical shape, it can be considered to include a frustoconical portion 21b whose apex faces the first multiplier portion 10.

[0028] The reduction section 21 is formed such that, in a cross-section along the Z direction (for example, a cross-section perpendicular to the Y direction shown in Figure 3), its width W in the direction perpendicular to the Z direction (the X direction in Figure 3) decreases as it approaches the first multiplication section 10. The reduction section 21 has a pair of surfaces 21c that are inclined with respect to the Z direction so that they approach each other as they approach the first multiplication section 10 in a cross-section along the Z direction. The pair of surfaces 21c are the surfaces (side surfaces) of the frustoconical portion 21b of the reduction section 21. In this example, each surface 21c is formed flat. The second multiplication section 20 multiplies electrons emitted from the channel portion 13 of the first multiplication section 10 and incident on the pair of surfaces 21c. Figure 3 shows a cross-section of the reduction section 21 perpendicular to the Y direction, but since the reduction section 21 is formed in a substantially conical shape as described above, it has the same cross-sectional shape in any cross-section along the Z direction.

[0029] The extending portion 22 is formed in a cylindrical shape, for example, having a central axis along the Z direction. The length of the extending portion 22 in the Z direction is, for example, longer than half the length of the reducing portion 21 in the Z direction. A disc-shaped second support portion 60 that supports the second multiplier portion 20 is positioned at the end of the second side S2 of the extending portion 22. That is, the second multiplier portion 20 is supported by the second support portion 60 on the second side S2 of the extending portion 22. The second support portion 60 extends, for example, along a plane perpendicular to the Z direction. The second multiplier portion 20 is supported by the second support portion 60 with a portion of the extending portion 22 located within the second support portion 60. The second support portion 60 is formed of, for example, a material having the same electrical insulating properties as the main body portion 11 and the first support portion 50 of the first multiplier portion 10 (ceramic in this example).

[0030] The second multiplier section 20 further has a connecting section 23 connected to the end of the second side S2 of the extending section 22. The connecting section 23 is led out to the outside of the second support section 60. When in use, a voltage is applied to the shrinking section 21 and the extending section 22 via the connecting section 23. Specifically, a voltage is applied to the second multiplier section 20 such that it is at a higher potential than the first end face 11a of the first multiplier section 10 and at a lower potential than the third multiplier section 30 and the mesh member 33, which will be described later.

[0031] The third multiplier 30 is a discrete dynode and is formed of a conductive metallic material (stainless steel in this example), similar to the second multiplier 20. The third multiplier 30 has a cylindrical portion 31 and a top wall portion 32. The cylindrical portion 31 is formed in a cylindrical shape, for example, having a central axis along the Z direction, and is arranged to surround the second multiplier 20. The cylindrical portion 31 faces a pair of surfaces 21c of the reduction portion 21 of the second multiplier 20. In this example, the cylindrical portion 31 has a portion that overlaps with the pair of surfaces 21c of the reduction portion 21 when viewed from a direction perpendicular to the Z direction. The end of the second side S2 of the cylindrical portion 31 is in contact with the second support portion 60.

[0032] The top wall portion 32 is connected to the first side S1 of the cylindrical portion 31. The top wall portion 32 is formed in a disc shape along a plane perpendicular to the Z direction, for example. The top wall portion 32 faces, for example, a pair of surfaces 21c of the reduction portion 21 in the Z direction. In the central part of the top wall portion 32, there is a rectangular opening 32a formed so as to overlap with the first end face 11a of the first multiplication portion 10 in the Z direction. The surface of the first side S1 of the top wall portion 32 is in contact with the first support portion 50.

[0033] Inside the opening 32a, a mesh member 33 is provided, formed by a planar mesh perpendicular to the Z direction. The mesh member 33 faces the second end face 11b of the first multiplication section 10. The mesh member 33 is positioned between the first multiplication section 10 and the second multiplication section 20 in the Z direction. The mesh member 33 has a plurality of through holes opening to the first multiplication section 10 side and the second multiplication section 20 side. The mesh member 33 is made of a conductive material such as a metallic material and functions as an electrode that adjusts the trajectory of electrons emitted from the channel section 13 so that they proceed to the reduction section 21 of the second multiplication section 20. Specifically, when in use, a voltage higher than that of the output electrode B of the first multiplication section 10 is applied to the mesh member 33, thereby attracting electrons emitted from the channel section 13 to the mesh member 33. As a result, these attracted electrons pass through the through holes in the mesh member 33 and proceed to the reduction section 21 of the second multiplication section 20. In this embodiment, the mesh member 33 is electrically connected to the third multiplication unit 30 and is given the same potential as the third multiplication unit 30.

[0034] The third multiplier 30 further has a connecting portion 34 that extends outward from the top wall portion 32 in the X direction. During use, a voltage is applied to the cylindrical portion 31, the top wall portion 32, and the mesh member 33 via the connecting portion 34. Specifically, a voltage is applied to the third multiplier 30 such that it is at a higher potential than the second multiplier 20 and at a lower potential than the anode 40 described later.

[0035] The anode 40 is made of a conductive material, for example, a metallic material (stainless steel in this example). The anode 40 has a cylindrical portion 41, a fixing portion 42, and a connecting portion 43. The cylindrical portion 41 extends cylindrically in the Z direction from the second support portion 60 toward the first multiplier portion 10. The cylindrical portion 41 is positioned between the second multiplier portion 20 and the third multiplier portion 30. Specifically, when viewed from the Z direction, the cylindrical portion 41 is positioned inside the third multiplier portion 30 and surrounding the second multiplier portion 20.

[0036] The cylindrical portion 41 has a mesh portion 44 formed on the first side S1. The mesh portion 44 has a plurality of through holes that open to the second multiplication portion 20 side and the third multiplication portion 30 side. The mesh portion 44 faces the pair of surfaces 21c of the reduction portion 21 of the second multiplication portion 20. In this example, the mesh portion 44 includes a portion that overlaps with the pair of surfaces 21c of the reduction portion 21 when viewed from a direction perpendicular to the Z direction. Note that the mesh portion 44 of the anode 40 is not shown in Figure 2.

[0037] The anode 40 collects electrons multiplied in the third multiplication section 30. Specifically, the anode 40 attracts electrons emitted from the reduction section 21 of the second multiplication section 20 towards the anode 40 in the mesh section 44, and allows these electrons to pass through and enter the third multiplication section 30, where the electrons multiplied are collected. For example, electrons emitted from a pair of surfaces 21c of the reduction section 21 pass through the opening 44a of the mesh section 44 and enter the third multiplication section 30. The electrons multiplied in the third multiplication section 30 are then entered into the anode 40 and collected. Furthermore, the anode 40 collects not only electrons that enter the anode 40 from the third multiplication section 30, but also electrons that enter the anode 40 from the second multiplication section 20 without passing through the third multiplication section 30. The anode 40 is at a higher potential than the third multiplication section 30 when in use.

[0038] The fixing portion 42 is formed in the shape of an annular plate along the outer edge of the end of the second side S2 of the cylindrical portion 41 and is connected to the cylindrical portion 41. The fixing portion 42 is formed inside the second support portion 60 and is connected to the connecting portion 43. The connecting portion 43 extends in a direction perpendicular to the Z direction and is drawn out to the outside of the second support portion 60. The connecting portion 43 is grounded, for example, so that the anode 40 is at ground potential.

[0039] When the charged particle detector 1 is in use, voltages are applied to each of these components such that the potential increases in the following order: the first end face 11a of the first multiplier unit 10, the second end face 11b of the first multiplier unit 10, the second multiplier unit 20, the third multiplier unit 30 and the mesh member 33, and the anode 40.

[0040] Next, the circuit configuration of the charged particle detector 1 will be explained with reference to Figure 4. As shown in Figure 4, in the circuit 100 that constitutes the charged particle detector 1, the power supply PW, the external resistor R, and the diodes D1 to D3 are connected in series in this order. The power supply PW applies a voltage of, for example, -2600V to the input electrode A of the first multiplier unit 10. The external resistor R is an external resistor connected in parallel with the first multiplier unit 10, and is provided, for example, to increase the current flowing from the first multiplier unit 10 onward. The resistance value of the external resistor R is, for example, about 5MΩ to 20MΩ.

[0041] Diodes D1 to D3 are, for example, Zener diodes, and generate potential differences of 300V, 200V, and 100V, respectively. Diode D1 is connected between the output electrode B of the first multiplier unit 10 and the second multiplier unit 20. Diode D2 is connected between the second multiplier unit 20 and the third multiplier unit 30. One terminal of diode D3 is connected to the third multiplier unit 30, and the other terminal is grounded. With this configuration, -2600V, -600V, -300V, and -100V are applied to the input electrode A, output electrode B, second multiplier unit 20, and third multiplier unit 30, respectively. As described above, the anode 40 is grounded.

[0042] Next, the operation of the charged particle detector 1 will be explained with reference to Figure 5. Figure 5 shows the electron orbits in the charged particle detector 1 in Figure 3, indicated by dashed arrows E1, E21, E22, E23, and E3, and the equipotential lines indicated by dashed lines.

[0043] During use, the above-mentioned voltages are applied to the first multiplier unit 10, the second multiplier unit 20, the third multiplier unit 30, and the anode 40, creating an electric field as shown by equipotential lines in Figure 5, for example. As a result, electrons emitted from the channel unit 13 of the first multiplier unit 10 travel along the trajectories indicated by arrows E1, E21~E23, and E3. In other words, an electric field that causes electrons to travel along the trajectories indicated by arrows E1, E21~E23, and E3 is created by the voltages applied to the input electrode A, the output electrode B, the second multiplier unit 20, the third multiplier unit 30, and the anode 40.

[0044] For example, when a charged particle P is incident on the incident portion 12 of the first multiplication portion 10, electrons are emitted in the incident portion 12, and the emitted electrons are secondary electron multiplied in the channel portion 13. The electrons multiplied in the channel portion 13 are emitted from the opening of the channel portion 13 at the second end face 11b and are attracted to the mesh member 33, so they travel toward the pair of surfaces 21c of the reduction portion 21 of the second multiplication portion 20 (arrow E1). Of these electrons, those incident on the pair of surfaces 21c are secondary electron multiplied and emitted on the pair of surfaces 21c, and travel toward the third multiplication portion 30 (arrows E21~E23). Of these electrons, those incident on the third multiplication portion 30 are secondary electron multiplied and emitted in the third multiplication portion 30, and are collected in the anode 40 (arrow E3). The electrons collected in the anode 40 are finally output as a current output via the connection portion 43. More specifically, electrons emitted from the pair of surfaces 21c can pass through the opening 44a of the mesh portion 44 of the anode 40 and be incident on the inner surface 31a of the cylindrical portion 31 of the third multiplication portion 30 (arrow E21), be incident on the inner surface 32b of the top wall portion 32 of the third multiplication portion (arrow E22), or be incident on the anode 40 without passing through the third multiplication portion (arrow E23). As shown in Figure 5, the pair of surfaces 21c of the reduction portion 21 are formed inclined with respect to the Z direction so that they get closer to each other as they approach the first multiplication portion 10. Therefore, electrons emitted from the pair of surfaces 21c are dispersed (diffused) and proceed to the third multiplication portion 30. [Mechanism of Action and Effects]

[0045] As explained above, in the charged particle detector 1, electrons multiplied in the channel-type first multiplier unit 10 are further multiplied in the discrete-type second multiplier unit 20. By further multiplying the electrons multiplied in the channel-type first multiplier unit 10, which has a large gain per applied voltage, in the discrete-type second multiplier unit 20, the maximum output current can be increased and the dynamic range can be widened. In addition, since electrons are multiplied in the subsequent second multiplier unit 20, the voltage value applied to the first multiplier unit 10 can be lowered compared to, for example, the case where electrons are multiplied by the first multiplier unit 10 alone, thereby reducing the amount of heat generated in the channel-type first multiplier unit 10 and suppressing the generation of noise (dark) caused by thermionic electrons. Furthermore, in the charged particle detector 1, the second multiplication unit 20 has a reduction unit 21 formed such that its width W in the direction perpendicular to the Z direction decreases as it approaches the first multiplication unit 10, and the reduction unit 21 has a pair of surfaces 21c formed so that they get closer to each other as they approach the first multiplication unit 10, and the second multiplication unit 20 multiplies electrons emitted from the channel unit 13 of the first multiplication unit 10 and incident on the pair of surfaces 21c. By configuring the second multiplication unit 20 in this way, the region in which electrons are incident in the second multiplication unit 20 can be widened, and the number of incident electrons per unit area in that region can be reduced. As a result, the degradation of the second multiplication unit 20 can be suppressed, and the life characteristics can be improved. Thus, the charged particle detector 1 can widen the dynamic range while improving noise characteristics and life characteristics.

[0046] The pair of surfaces 21c are inclined with respect to the Z direction such that they move closer to each other as they approach the first multiplication section 10. This makes it possible to further widen the region in which electrons are incident in the second multiplication section 20.

[0047] The pair of surfaces 21c are the sides of the frustoconical portion 21b of the reduced portion 21. This allows for an even wider region to which electrons are incident in the second multiplication portion, thereby further improving the life characteristics.

[0048] The second support portion 60 has electrical insulating properties, and the second multiplier portion 20 is supported by the second support portion 60 in the extension portion 22. As a result, the distance between the shrinking portion 21 and the second support portion 60 can be increased by providing the extension portion 22, thereby suppressing the occurrence of charge-up, where electrons emitted from the shrinking portion 21 accumulate in the second support portion 60.

[0049] The third multiplier section 30 multiplies the electrons emitted from the second multiplier section 20, and the anode 40 collects the electrons multiplied in the third multiplier section 30. As a result, the maximum output current can be further increased and the dynamic range can be further widened by further multiplying the electrons multiplied in the second multiplier section 20 in the third multiplier section 30. In addition, since the pair of surfaces 21c of the reduction section 21 are formed to move closer to each other as they approach the first multiplier section 10, the electrons emitted from the pair of surfaces 21c are dispersed (diffused) and proceed to the third multiplier section 30. Therefore, the region in which electrons are incident in the third multiplier section 30 can be widened, and the number of incident electrons per unit area in that region can be reduced. As a result, the degradation of the third multiplier section 30 can be suppressed and the life characteristics can be improved.

[0050] The cylindrical portion 41 of the anode 40 is positioned between the second multiplication section 20 and the third multiplication section 30. This makes the charged particle detector 1 more compact. For example, the length in the Z direction can be shortened compared to the case where the first multiplication section 10, the second multiplication section 20, the third multiplication section 30 and the anode 40 are arranged in this order along the Z direction. Also, for example, when viewed from the Z direction, the length in the direction perpendicular to the Z direction can be shortened compared to the case where the third multiplication section 30 and the anode 40 are arranged in this order toward the outside of the second multiplication section 20.

[0051] The anode 40 has a mesh portion 44 that faces a pair of surfaces 21c of the reduction portion 21. This allows electrons emitted from the reduction portion 21 to be suitably attracted toward the anode 40.

[0052] The above operation and effects will be explained with reference to Figure 6. Figure 6(a) is a schematic graph showing the relationship between input and output in the charged particle detector 1. The horizontal axis is the input (input of charged particles P in this example), and the vertical axis is the output (output current in this example). As the input increases, the output also increases linearly, but in a certain region the charged particle detector 1 begins to saturate, and the increase in output slows down and the linearity of the output decreases. For example, as shown in Figure 6(a), before saturation of the charged particle detector 1, an increase of 1 in the input of charged particles P results in an increase of 1 in the output, but after saturation, even if the input increases by 1, the output may only increase up to 0.8. In this case, the slope of the output current (the ratio of the increase in output current to the increase in the input of charged particles P) decreases from 1 to 0.8, and the rate of change of the slope of the output current is -20%.

[0053] Figure 6(b) is a graph illustrating the comparison results of the maximum output current in the example and comparative example. The maximum output current was defined as the output current at which the rate of change of the slope of the output current was -10%. The example corresponds to the charged particle detector 1 described above. Comparative example 1 corresponds to a charged particle detector that does not have discrete type second multipliers 20 and third multipliers 30, and is composed only of a channel type first multiplier 10. In Figure 6(b), the horizontal axis is the output current (A), and the vertical axis is the rate of change of the slope of the output current (%). The gain (amplification factor) in the example and comparative example is 8 × 10⁻¹⁰. 6 That is the case.

[0054] As shown in Figure 6(b), the output current (i.e., maximum output current) when the rate of change of the slope of the output current is -10% was approximately 20 μA in the comparative example and approximately 157 μA in the example. Therefore, it can be seen that the maximum output current was increased in the example compared to the comparative example. Consequently, the example can detect a larger amount of charged particles P compared to the comparative example. For this reason, even with high concentrations of charged particles P, which may cause the output current to exceed the maximum output current and saturate in the comparative example's charged particle detector, the example's charged particle detector can detect them without the output current exceeding the maximum output current. In other words, the example's charged particle detector can widen the dynamic range compared to the comparative example's charged particle detector. [First variation]

[0055] The charged particle detector 1A according to the first modified example shown in Figure 7 differs from the charged particle detector 1 according to the embodiment in that the second multiplier 20A, the third multiplier 30A, and the anode 40A are formed from plate members.

[0056] The second multiplier section 20A has a reduction section 21A and an extension section 22A. The reduction section 21A has a uniform cross-sectional shape with respect to the Y direction (a direction perpendicular to both the Z and X directions). The reduction section 21A includes a pair of flat, inclined sections 24 that are inclined with respect to the Z direction so that they get closer to each other as they approach the first multiplier section 10 in a cross-section perpendicular to the Y direction. The pair of inclined sections 24 face each other in the X direction, and the ends of the pair of inclined sections 24 on the first side S1 (the side of the first multiplier section 10) are connected to each other. Alternatively, the reduction section 21A is formed in a triangular shape by the pair of inclined sections 24, with its apex facing the first multiplier section 10. The pair of surfaces 21c are formed on the surfaces of each inclined section 24 that face the first multiplier section 10.

[0057] The extending portion 22A includes a pair of flat plate-like portions 25 facing each other in the X direction. The pair of plate-like portions 25 extend from the end of the second side S2 of each inclined portion 24 toward the second side S2. The third multiplier portion 30A includes a pair of flat plate-like portions 31A facing each other in the X direction with the second multiplier portion 20A in between, and a pair of top wall portions 32A that extend in a flat manner from the end of the first side S1 of each plate-like portion 31A toward each other along the X direction. The pair of plate-like portions 31A extend along a plane perpendicular to the X direction and face a pair of surfaces 21c of the shrinking portion 21A in the X direction.

[0058] The anode 40A has a pair of flat plate-like portions 41A that face each other in the X direction, with the second multiplication portion 20A in between. The pair of plate-like portions 41A extend along a plane perpendicular to the X direction and face a pair of surfaces 21c of the reduction portion 21A in the X direction. Each plate-like portion 41A is positioned in the X direction between the second multiplication portion 20A and each plate-like portion 31A of the third multiplication portion 30A. Note that in Figure 7, the mesh portion 44 of the anode 40A is omitted.

[0059] The charged particle detector 1A according to the first modification also improves noise characteristics and life characteristics while widening the dynamic range, similar to the charged particle detector 1 according to the above embodiment. Furthermore, in the first modification, the reduction section 21A has a uniform cross-sectional shape with respect to the Y direction. This makes it easier to manufacture the second multiplier section 20A compared to, for example, the case where the reduction section of the second multiplier section is formed in a frustoconical shape. [Second variation]

[0060] The charged particle detector 1B according to the second modified example shown in Figure 8 differs from the charged particle detector 1 according to the embodiment in that it does not have a third multiplier 30, and the anode 40B collects electrons multiplied by the second multiplier 20. In this charged particle detector 1B, the cylindrical portion 41, fixed portion 42, and connecting portion 43 of the anode 40 according to the embodiment are omitted, and the configuration of the third multiplier 30 according to the embodiment functions as the anode 40B. That is, the anode 40B has a cylindrical portion 45, a top wall portion 46, and a connecting portion 47, and these configurations correspond to the cylindrical portion 31, top wall portion 32, and connecting portion 34 of the third multiplier 30 according to the embodiment, respectively. The cylindrical portion 45 and top wall portion 46 of the anode 40B are grounded, for example, via the connecting portion 47. The anode 40B collects electrons multiplied in the second multiplier 20 at the cylindrical portion 45 and top wall portion 46.

[0061] The charged particle detector 1B according to the second modified example also improves noise characteristics and life characteristics while widening the dynamic range, similar to the charged particle detector 1 according to the above embodiment. [Reference example]

[0062] The charged particle detector 200, a reference example shown in Figure 9, differs from the charged particle detector 1 according to the embodiment in that the reduction portion 21 of the second multiplication portion 20 does not have a pair of surfaces 21c, but has a single inclined surface 21d that is inclined to only one side, and that the anode 40 is not formed on both sides in the X direction of the second multiplication portion 20 in a cross section perpendicular to the Y direction, but is formed on only one side. The inclined surface 21d is inclined with respect to the Z direction so as to face the mesh member 33 of the third multiplication portion 30 and the mesh portion 44 of the anode 40 in a cross section perpendicular to the Y direction. The inclined surface 21d multiplies electrons emitted from the channel portion 13 of the first multiplication portion 10 and incident on the inclined surface 21d. The reduction portion 21 is formed in a triangular shape with its apex facing the first side S1 in a cross section perpendicular to the Y direction.

[0063] The charged particle detector 200 according to the reference example can also improve noise characteristics while widening the dynamic range, similar to the charged particle detector 1 according to the above embodiment. Furthermore, since the inclined surface 21d is inclined with respect to the Z direction so as to face the mesh member 33 and the mesh portion 44 of the anode 40, the region in which electrons are incident in the second multiplier 20 can be widened compared to, for example, the case where the inclined surface 21d is perpendicular to the Z direction, and the number of incident electrons per unit area in that region can be reduced. As a result, the degradation of the second multiplier 20 can be suppressed, and the life characteristics can be improved. In addition, because the inclined surface 21d is inclined with respect to the Z direction, electrons emitted from the inclined surface 21d are dispersed (diffused) and proceed to the third multiplier 30. Therefore, the region in which electrons are incident in the third multiplier 30 can be widened, and the number of incident electrons per unit area in that region can be reduced. As a result, the degradation of the third multiplier 30 can be suppressed, and the life characteristics can be improved.

[0064] The present invention is not limited to the embodiments and modifications described above. For example, the materials and shapes of each component are not limited to those described above, but can be made from a variety of materials and shapes. The charged particle detector 1 may be used in applications or devices other than quadrupole mass spectrometry. The charged particles P detected by the charged particle detector 1 may be charged particles other than ions (e.g., electrons). In the embodiments described above, the pair of surfaces 21c were flat, but each surface 21c may be curved. For example, each surface 21c may be curved so as to be convex toward the first side S1 in the Z direction. The second multiplier 20 does not have to have an extended portion 22, and may be supported by the second support portion 60 in the reduction portion 21.

[0065] In the above embodiment, the reducing portion 21 was formed such that the width W in the direction perpendicular to the Z direction decreases as it approaches the first multiplier portion 10 in any cross-section along the Z direction. However, the reducing portion 21 may be formed such that the width W decreases in only one cross-section along the Z direction (for example, a cross-section perpendicular to the Y direction), as in the reducing portion 21A of the first modified example above. The reducing portion 21 only needs to be formed such that the width W in the direction perpendicular to the Z direction decreases as it approaches the first multiplier portion 10 in at least one cross-section along the Z direction.

[0066] In the above embodiment, the reduced portion 21 was formed solidly, but the reduced portion 21 may be hollow. The entire reduced portion 21 may be formed in the shape of a frustocone. That is, the apex 21a of the reduced portion 21 may be a flat surface perpendicular to the Z direction. The reduced portion 21 may also be a perfect cone. [Explanation of symbols]

[0067] 1,1A,1B...Charged particle detector, 10...First multiplication section, 11...Main body section, 13...Channel section, 20,20A...Second multiplication section, 21,21A...Reduction section, 21a...Top section, 21b...Part, 21c...Pair of surfaces, 22,22A...Extending section, 30,30A...Third multiplication section, 40,40A,40B...Anode, 44...Mesh section, 60...Second support section, P...Charged particle.

Claims

1. A channel-type first multiplier having a main body and a channel formed inside the main body that emits electrons in response to the incidence of charged particles and emits the emitted electrons after multiplying them, A discrete type second multiplier is arranged to face the first multiplier in a predetermined direction and multiplies the electrons emitted from the channel portion of the first multiplier, The device comprises an anode for collecting the multiplied electrons, The second multiplier portion has a reduction portion formed such that, in at least one cross-section along the predetermined direction, the width in a direction perpendicular to the predetermined direction decreases as it approaches the first multiplier portion. The reduced portion has a pair of surfaces formed such that they approach each other as they get closer to the first multiplier portion in at least one cross-section. The second multiplier is a charged particle detector that multiplies the electrons emitted from the channel portion of the first multiplier and incident on the pair of surfaces.

2. The charged particle detector according to claim 1, wherein the pair of surfaces are inclined with respect to the predetermined direction such that they approach each other as they approach the first multiplication portion in at least one cross-section.

3. The charged particle detector according to claim 1, wherein the reduction portion includes a frustoconical portion whose apex faces the first multiplication portion, and the pair of surfaces are the surfaces of the frustoconical portion.

4. The reduced portion has a uniform cross-sectional shape with respect to the predetermined direction and the direction perpendicular to both the predetermined direction and the direction perpendicular to that direction. The charged particle detector according to claim 1.

5. The device further comprises a support portion that has electrical insulating properties and supports the second multiplier portion on the opposite side from the first multiplier portion, The charged particle detector according to claim 1, wherein the second amplification portion further has an extension portion that extends from the reduction portion to the side opposite to the first amplification portion, and the extension portion is supported by the support portion.

6. The system further comprises a discrete third multiplier, which is positioned opposite the pair of surfaces of the reduction portion and multiplies the electrons emitted from the second multiplier, The charged particle detector according to any one of claims 1 to 5, wherein the anode collects the electrons multiplied in the third multiplication unit.

7. The charged particle detector according to claim 6, wherein the anode is disposed between the second multiplication unit and the third multiplication unit.

8. The charged particle detector according to any one of claims 1 to 5, wherein the anode has a mesh portion facing the pair of surfaces of the reduced portion.

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