Electron multiplier

Abstract: An electron multiplier according to this invention comprises dynodes DY1 ∼ DY16 arranged in multi-stages along a direction of incidence of an energy beam for, upon incidence of the energy beam, gradually multiplying secondary electrons to emit the same, a collection electrode A for receiving electrons emitted from that of the dynodes on a last stage, and resistors R1 ∼ R16 inserted between the respective dynodes and their adjacent ones, the dynodes, the collecting electrode, and the resistors being mounted between two support plates 10a, 10b disposed in parallelism with each other, the resistors being arranged in two rows which sandwich the dynodes.

Description: This invention relates to an ion (electron) multiplier for detecting or measuring energy beams of electrons, ions, charge particles, ultraviolet rays, soft X-rays, etc. As schematically shown in FIG. 1, in an electron multiplier, energy beams, as of electrons or others, impinge on dynodes DY1 ∼ DY16 of the electron multiplying unit to multiply and emit secondary electrons, and the collecting electrodes (anodes) A collect the emitted secondary electrons for detection. The electron multiplying units have various types. Commonly quarter-cylindrical dynodes DY1 ∼ DY16 are substantially alternately arranged in a direction of incidence of energy beams. The arrangement of FIG. 1 is the typical one which is the so-called box-and-grid-type. Resistors are inserted between the respective dynodes and their adjacent ones. The resistors equidivide a voltage applied between the first-stage dynode DY1 and the final-stage dynode DY16. This is the basic structure of the electron multipliers. The common assembly of the electron multipliers is shown in FIGs. 2 and 3. In the electron multiplier of FIGs. 2 and 3, respective dynodes DY are supported, enclosed by respective support frames 1. Each support frame 1 is made of a conducting material and is electrically connected to the associated dynode DY. The electron multiplier further comprises two support rods 3 which are secured to a holder 2 and are parallel with each other. These support rods 3 are inserted in holes 4 of each support frame 1 to support the dynodes by the support rods 3. A gap between each support frame 1 and its adjacent one is retained constant by spacers 5 through which the support rods 3 are inserted. In this conventional electron multiplier, resistors R are disposed in one row on one of the rows of the dynodes. Leads L of each resistor R are welded respectively to vertically adjacent ones of the support frames 1. The above-described electron multiplier includes the resistors R arranged in one row on one of the rows of dynodes. This tends to increase a total length of the electron multiplier. To maintain a total length short, it is necessary to narrow a gap between the respective resistors and their adjacent ones. But it could adversely cause contact of the leads L of the resistors R to narrow the gap. The resistors R are supported only by welds of the forward ends of the leads L, which cannot firmly secure the resistors R. It is also a problem that the resistors R totter. US-A-4668890 was cited by the European Patent Office. The citation describes an electron multiplier comprising: a sequence of dynodes; a corresponding sequence of resistors connected to the sequence of dynodes for enabling different respective voltages to be applied to individual dynodes in the sequence; a pair of insulating support plates for supporting the sequences of dynodes and resistors. Some of the dynodes and some of the resistors are supported by one supporting plate and the other dynodes and resistors are supported by the other supporting plate. SUMMARY OF THE INVENTION In view of these problems, this invention has been made with the aim of providing an electron multiplier which has a firm structure. The invention also aims to realize a compact electron multiplier by forming an electron multiplying unit with a short total length. According to the invention there is provided an electron multiplier comprising: a sequence of dynodes; a corresponding sequence of resistors connected to the sequence of dynodes for enabling different respective voltages to be applied to individual dynodes in the sequence; a pair of insulating support plates for supporting the sequences of dynodes and resistors; characterised in that dynodes and resistors in the sequences extend between the pair of insulating support plates to be supported by both support plates. It is preferable to arrange each resistance on a back side of dynodes which are faced to each other along an arrangement direction of the dynodes and in two rows. Further, the pair of supporting plates may have recesses extending from an edge of the plate to inner direction therefrom, the recesses may be disposed on a position corresponding to the position at which each resistor should be supported, and each of the resistors may be fixed to said supporting plate by engagement of leads each side of the resistor to the respective recess. Further, the two-rows of arranged resistors may be alternatively arranged according to the order of the application of an electrical potential difference between the dynodes. Further, the plural dynodes constructing the electron multiplying unit may be disposed in a different pattern in the upstream and in the downstream of the flow of the multiplied secondary electrons. The dynodes located on the upstream side are preferably arranged in a box-and-grid-type, and the dynodes located on the downstream side are preferably arranged in a line-focus type or linear-focus type. Further, the resistors arranged in the two lines correspondingly to the dynodes located in the downstream may be alternatively arranged according to the order of the application of potential difference to the dynodes. Further, each of said dynodes may have tabs on both edges thereof. Slots into which the tabs of the dynodes should be inserted are formed at appropriate positions in each of the supporting plates, and each of said dynodes is fixed to said pair supporting plates by engaging the tabs in the respective slots. In an embodiment of the invention, the resistors are arranged in two rows. In comparison with the arrangement of the resistors in one row, a total length of the electron multiplier is shortened. In the dynodes and the resistors are supported by two support plates. In comparison with their support by two support rods, the assembly has much improved strength. The insertion of the leads of the resistors in recesses prohibits the displacement of the leads themselves, and the resistors themselves. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings of an embodiment of the invention which is given by way of illustration only, and thus is not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating a preferred embodiment of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view explaining the principle of the electron multiplier; FIG. 2 is a side view of a conventional electron multiplier; FIG. 3 is a perspective view of the electron multiplier of FIG. 2 being assembled; FIG. 4 is a perspective view of the electron multiplier according to one embodiment of this invention; FIG. 5 is a perspective view of the electron multiplier of Fig. 4 as viewed at a different angle; FIG. 6 is a longitudinal sectional view of the electron multiplier of FIG. 4; FIGs. 7 and 8 are, respectively a perspective view of the dynodes used in the electron multiplier of FIG. 4, FIG. 7 showing the first- to the third-stage dynodes, and FIG. 8 showing the fourth- to the sixteenth-stage dynodes; and FIG. 9 is a circuit diagram of a voltage dividing circuit used in the electron multiplier of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of this invention will be explained in good detail with reference to the attached drawings hereto. In the attached FIGs., the common members are represented by common reference numerals. In the description of FIGs. 1 to 3, "vertically, or up to down", and "horizontally, or left to right" means "vertically, or up to down" and "horizontal, or left to right" as viewed in the attached FIGs.. As shown in FIGs. 4-6, the electron multiplier according to an embodiment of this invention comprises an ion multiplier having a plurality of stages (16 stages in this embodiment) of dynodes DY1 ∼ DY16 for capturing energy beams and emitting multiplied secondary electrons, a collecting electrode (anode) A for capturing electrons emitted from the final-stage DY 16. A potential difference is provided between the respective dynodes and their adjacent ones so that the respective dynodes emit secondary electrons toward their lower-stage dynodes DY. To this end, the electron multiplier uses a voltage dividing circuit of FIG. 9. Resistors R1 ∼ R15 are inserted each between the respective resistors and their adjacent ones. A resistor R16 is inserted between the dynode DY 16 and the earth or +HV. In this embodiment, the resistors R1-R16, the dynodes DY1 ∼ DY 16, and the collecting anode A are mounted between support plates 10a, 10b of an insulating materials, such as ceramics or others, which are arranged in parallelism with each other. Each support plate 10a, 10b are substantially rectangular. A block 11 is secured to one end portions of the support plates 10a, 10b between the support plates 10a, 10b by bolts 12 and nuts 13. The block 11 is secured to the central portion of a substantially square base 14 of stainless steel by screws. The support plates 10a, 10b are thus secured to the base 14 in parallelism with each other. As shown in FIG. 7, the first- to the third-stage dynodes DY1 ∼ DY3, which are located upstream side in a flow of the multiplied secondary electron, has a one-piece structure of a quarter cylindrical portion DYa and a secular end plate portions DYb. As shown in FIG. 8, the fourth-stage dynodes DY4 and the following dynodes DY5 ∼ DY 16, which are located downstream side in the flow, have a one-piece structure of a quarter cylindrical portion DYa' as do the dynodes DY1 ∼ DY 3, and arc-shaped end plate portions DYb'. In the inner surfaces of the quarter cylindrical portions DYa, DYa', a secondary electron emission surface formed of Cu-BeO is formed, and emit secondary electrons upon incidence of electrons or ions or energy beams. Each dynode has tabs DYc, DYc' projected from the end plate portions DYb, DYb' and bent. The tabs DYc, DYc' are inserted into slots formed in the support plates 10a, 10b, and the end portions of the tabs DYc, DYc' projected out of the slots are bent. Thus the dynodes DY1 ∼ DY 16 are secured to set positions. As shown in FIG. 6, the dynodes DY1 ∼ DY16 are arranged substantially alternately in the longitudinal direction of the support plates 10a, 10b. The relatively larger first-to the third-stage dynodes DY1 ∼ DY3, which is located the upstream of the flow, are disposed in the so-called box-and grid-type arrangement. The other smaller dynodes DY 4 ∼ DY16 are disposed in the so-called line focus-type or the linear focus-type arrangement. In this arrangement, energy beams enter along the longitudinal axis C of the support plates 10a, 10b and impinge on the quater clindrical portion DYa of the first-stage dynode DY 1. A secondary electron emission takes place, and electrons are multiplied. The multiplied secondary electrons are led to the quater clindrical portion DYa of the second-stage dynode DY2. In this way, the secondary electrons are led subsequently to a next dynode to finally arrive at the final-stage dynode DY16, which is nearest to the base 14. Reference numeral 15 represents mesh wires disposed on the entrance surface of the respective dynodes DY 1 ∼ DY3. The mesh lines prevent the polarization of the electrons or the energy bemas surely to lead without failure the secondary electrons to the concave surface of a next dynode DY. The collecting electrode A is disposed at a position suitable to receive the electrons emitted from the final-stage dynode DY16. Both ends of the final-stage dynodes are inserted in the slots to be positioned. The collecting electrode A is surrounded by a shield SH of U-shaped section mounted between the support plates 10a, 10b. The shield SH has the same potential as the final-stage dynode DY16 to prevent the entrance of noises into the collecting electrode A. A plurality of recesses are formed in the longitudinal edges of each support plate 10a, 10b. In the two support plates 10a, 10b fixed to the base 14, the recesses 16 in the respective edges are on the same height as those 16 in their adjacent edges. Resistors R1 ∼ R16 of a voltage dividing circuit are mounted between he support plates 10a, 10b by means of the recesses 16. That is, each resistor is positioned between one pair of the recesses 16 on the same height with the leads inserted into the associated recesses 16, and are secured by bending the leads L toward the center of the support plates 10a, 10b and welding the forward ends of the leads to the forward ends of the tabs of the associated dynodes DY. Thus, the respective resistors R1 ∼ R16 are disposed horizontal on both sides of the gap between the support plates 10a, 10b. The resistors R1 ∼ R16 are arranged accordingly in the longitudinal direction and bewteen the support plates 10a, 10b at a certain interval. In this embodiment, nine resistors R are disposed on a back side of diodes arranged in one row of two rows arranged diodes, and seven register R are disposed on a back side of diodes arranged in the other row on the other side seven resistors R are disposed. One of the leads L of the uppermost-stage resistor R1 is welded to one of the tabs DYc of the first-stage dynode DY1 on the support plate 10a (FIG. 4), and the other lead L is welded to the tab DYc of the second-stage dynode DY2 on the support plate 10b (FIG. 5). The other tab DYc of the second-stage dynode DY2 on the support plate 10a is connected to one lead L of the second-stage resistor R2 (FIG. 1). In this way, the leads of the resistors R are connected to the tabs DYc of the associated dynodes DY. The lowermost resistor R16 is inserted between the tab of the shield SH which (tab) is connected to one tab DYc of the lowermost-stage dynode DY 16, and a hermetic terminal 17 on the side of the earth or +HV which is formed through the base 14. In this embodiment, a metal plate 18 is mounted at the upper end of the gap between the support plates 10a, 10b. The metal plate 18 has an opening 19 formed at a position opposed to an entrance for energy beams. The metal plate 18 is connected to the first-stage dynode DY1 by a conductor 20 and is maintained at the same potential, so that the metal plate functions as a shield and also as a reinforcement of the electron multiplier assembly. On the base 14 there are provided three hermetic terminals 21, 22, 23 in addition to the hermetic terminal 17 on the side of the earth or +HV. The terminal 21 is connected to the tab DYc of the first-stage dynode DY1 on the support plate 10b by a ceramic piped conductor 24. The terminal 22 is connected to the collecting electrode A by a ceramic piped conductor 25. In this embodiment, the resistors R1 ∼ R16 are divided in two rows. In comparison with an electron multiplier with the resistors R1 ∼ R16 arranged in one row, a length of the electron multiplier according to this embodiment can be reduced to a half. The leads L of the resistors R1 ∼ R16 are held at the proximal ends by the support plates 10a, 10b, and the resistors R1 ∼ R16 do not substantially totter. In the above-described embodiment, the resistors R are divided in two rows, one row including of 9 resistors, the other row including 7 resistors. But this invention is not limited to this embodiment. The arrangement of the dynodes and the stage number thereof are not limited to the described above types and stage number. As described above, according to this embodiment resistors in the voltage dividing circuit is arranged in two rows. Accordingly a total length of an electron multiplier restricted by the resistors can be reduced to substantially a half. The electron multiplier can be accordingly small-sized and can be installed at relatively small spaces. Two sheets of plates hold resistors, dynodes and a collecting electrode therebetween. Accordingly the electron multiplier can have a strong structure and can be strong against impacts. Furthermore, according to this embodiment, recesses are formed in the support plates, and leads of resistors are inserted in the recesses to position the resistors. Accordingly, the resistors can be positioned stationary, so that adjacent resistors are prohibited from interfering with each other, and adjacent leads are prohibited from interfering with each other. Stationary positioning of the resistors contributes to the improvement of noise characteristics. Such secured positioning of the resistors allows a gap between adjacent ones of the resistors to be reduced, so that a total length of an electron multiplier can be reduced. From the embodiment thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the invention as defined by the following claims.

Claims: An electron multiplier comprising: a sequence of dynodes (DY1 to DY16); a corresponding sequence of resistors (R1 to R16) connected to the sequence of dynodes for enabling different respective voltages to be applied to individual dynodes in the sequence; a pair of insulating support plates (10a, 10b) for supporting the sequences of dynodes (DY1 to DY16) and resistors (R1 to R16); characterised in that dynodes (DY1 to DY16) and resistors (R1 to R16) in the sequences extend between the pair of insulating support plates to be supported by both support plates. An electron multiplier as claimed in claim 1, wherein resistors in said sequence are arranged in two groups along two respective opposed sides of the multiplier. An electron multiplier as claimed in claim 1 or 2, wherein each of said support plates (10a, 10b) have formed therein recesses (16) for receiving leads (L) of, and thereby supporting, resistors extending therebetween. An electron multiplier as claimed in any preceding claim, wherein each of said support plates (10a, 10b) have formed therein slots for receiving tabs (DYc) of, and thereby supporting, dynodes extending therebetween. An electron multiplier as claimed in claim 4 as dependent on claim 3, wherein the resistors (R1 to R16) are connected to the dynodes (DY1 to DY16) by the leads (L) being welded to respective tabs (DYc). An electron multiplier as claimed in any preceding claim, wherein the dynode sequence is arranged such that each dynode (DY1 to DY15) faces the next dynode (DY2 to DY16) in the sequence and the resistors (R1 to R16) are positioned behind the dynodes. An electron multiplier as claimed in claim 6, wherein some of the dynodes (DY1 to DY3) at the beginning of the sequence are formed as relatively large stages in a box and grid type arrangement and the other dynodes (DY4 to DY16) in the sequence are formed as relatively small stages in a linear- or line- focus type arrangement. An electron multiplier as claimed in claim 7, further comprising a metal plate (18) extending between and supported by the supporting plates (10a, 10b), the metal plate defining an opening (19) through which electrons can pass to the sequence of dynodes (DY1 to DY16). An electron multiplier as claimed in any preceding claim, further comprising a collecting electrode (A) extending between the two support plates (10a, 10b).

Inventors: NAKAMURA MAKOTO, OKAMOTO TAKEHISA, SAKAI SHIRO, YAMAGUCHI HARUHISA, NAKAMURA, MAKOTO, OKAMOTO, TAKEHISA, SAKAI, SHIRO, YAMAGUCHI, HARUHISA
Applicants: HAMAMATSU PHOTONICS KK, HAMAMATSU PHOTONICS K.K.
Application year: 1993
Main classification: H01J43
IPC codes: H01J43