Photomultiplier and electron multiplier

Abstract: The present invention relates to a linear multi-anode photomultiplier or electron multiplier on which a plurality of light beams to be measured or energy beams of electrons, ions and so force are incident one-dimensionally. The object of the present invention is to prevent crosstalk between dynode arrays caused by leaking electrons. A transmission type photomultiplier is characterized in that the direction of secondary electron emission of the first-stage dynode of each dynode array is set in the opposite direction at 180° from that of an adjacent dynode array. Then, adjacent dynode arrays will not oppose each other but are shifted from each other at a predetermined distance in the lateral direction. Accordingly, even if electrons leak from a gap between dynodes of a certain dynode array, the leaking electrons will not enter the adjacent dynode array, thereby preventing crosstalk.

Description: The invention relates to an electron multiplier and a photomultiplier. More specifically the invention relates to a so-called linear multi-anode photomultiplier and electron multiplier in which portions thereof, on which a plurality of light beams to be measured or energy beams of electrons, ions and so forth are incident, are aligned one-dimensionally. Figs. 1, 2 and 3 show an example of a conventional linear multi-anode photomultiplier. This photomultiplier is a head-on type photomultiplier in which incident window 2 for receiving light beams to be measured are formed on one end face of a glass bulb 1. Transmission type photoelectric surfaces 3 for converting the incident light to be measured to photoelectrons are formed on the inner surface of the incident window 2 in a one-dimensional array. One focusing electrode 4 is arranged inside the glass bulb 1 to be parallel to the incident window 2, and openings 5 are formed in a one-dimensional array at a portion of the focusing electrode 4 opposing the photoelectric surfaces 3. When a plurality of light beams to be measured are incident on the respective photoelectric surfaces 3 to generate photoelectrons, the photoelectrons are guided to corresponding dynode arrays 6 through the openings 5. The dynode arrays 6 of the photomultiplier shown in Fig. 1 have in-line dynode structure. The photoelectrons are multiplied by the secondary electron emission effect in each stage of dynode 7 of the respective dynode arrays 6, and the multiplied photoelectrons are finally captured by anodes 8 as output signals. In the conventional photomultiplier described above, some of leaking electrons from the gaps among the dynodes 7 of each dynode array 6 enter the gaps among the dynodes 7 of an adjacent dynode array 6 to cause so-called crosstalk. Crosstalk impairs independency of each dynode array 6 and degrades the detection precision of the light beams to be measured. The photomultiplier described above is a transmission type photomultiplier having photoelectric surfaces on the inner surface of the incident window. A reflection type photomultiplier has a similar problem of crosstalk. An electron multiplier for detecting the energy beams of electrons, ions and so forth also has a problem of crosstalk since its dynode array has a substantially same arrangement. US-A-4881008 describes a photomultiplier with plural photocathodes. Figure 1 of this document shows two separate sequences of dynodes each supplied by respective focusing electrodes. Electrons from one focusing electrode for one dynode sequence are prevented from straying to the other dynode sequence by a dividing wall formed by and between the focusing electrodes. US-A-5077504 describes a multiple section photomultiplier tube comprising several independent tube sections within a single envelope. Each tube section is mechanically separate from every other tube section and is electron-optically isolated from every other section by way of individual dividers. US-A-4117366 describes a multichannel photomultiplier tube in which light from multiple scintillators is incident on a window containing metal inserts containing a photocathode 11. For each scintillator there is a corresponding photomultiplier channel. The metal inserts ensure that light from one scintillator is directed to the portion of the photocathode corresponding to the respective photomultiplier channel and prevents light from one scintillator straying toward another photomultiplier. It is, therefore, an object of the present invention to provide a linear multi-anode type photomultiplier and electron multiplier that can reduce crosstalk between dynode arrays caused by leaking electrons. The above object and other objects will be further apparent from the following description. According to the present invention there is provided an electron multiplier comprising a plurality of electron multiplying sequences for multiplying electrons resulting from plural respective incident beams, each of the multiplying sequences comprising a first stage electrode arranged in a row along an axis (Y) for directing electrons emitted thereby toward the next electrode in the sequence, characterised in that the first stage electrode in each sequence is oriented to direct emitted electrons in a direction away from the axis (Y) of the row, and the first stage electrodes in adjacent sequences are oriented to direct emitted electrons in respective substantially opposite directions. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are 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 embodiments 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 longitudinal sectional view showing a conventional transmission type linear multi-anode photomultiplier. Fig. 2 is a plan view of the photomultiplier of Fig. 1. Fig. 3 is a perspective view showing the arrangement of dynode arrays used in the photomultiplier of Fig. 1. Fig. 4 is a longitudinal sectional view showing an embodiment of a transmission type linear multi-anode photomultiplier according to the present invention. Fig. 5 is a plan view of the photomultiplier of Fig. 4. Fig. 6 is a perspective view showing the arrangement of dynode arrays used in the photomultiplier of Fig. 4. Fig. 7 is a longitudinal sectional view showing another embodiment of a transmission type linear multi-anode photomultiplier according to the present invention. Fig. 8 is a longitudinal sectional view showing still another embodiment of a transmission type linear multi-anode photomultiplier according to the present invention. Fig. 9 is a perspective view showing the arrangement of dynode arrays used in the photomultiplier of Fig. 8. Fig. 10 is a longitudinal sectional view showing an embodiment of a reflection type linear multi-anode photomultiplier according to the present invention. Fig. 11 is a longitudinal sectional view showing another embodiment of a reflection type linear multi-anode photomultiplier according to the present invention. Fig. 12 is a longitudinal sectional view showing an embodiment of a linear multi-anode electron multiplier according to the present invention. The embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same or corresponding portions as in the conventional structures described above are denoted by the same reference numerals. Embodiment 1 Figs. 4 and 5 show a transmission type linear multi-anode photomultiplier according to an embodiment of the present invention. Referring to Figs. 4 and 5, reference numeral 1 denotes a transparent sealed container, and more preferably, a glass bulb. Incident window 2 on which a plurality of light beams to be measured are incident are formed at one end face of the glass bulb 1. A plurality of transmission type photoelectric surfaces 3 are formed on the inner surface of the incident window 2 and aligned one-dimensionally, i.e., in one array. One set of a dynode array 6 for receiving photoelectrons from the corresponding photoelectric surface 3 and multiplying them by the secondary electron emission effect is provided inside the glass bulb 1 for each photoelectric surface 3. The photoelectron incident ports of first-stage dynodes 7 1 of the respective dynode arrays 6 are arranged to oppose the photoelectric surface 3 and are thus aligned in a one-dimensional array. One focusing electrode 4 is arranged between the photoelectric surfaces 3 and the dynode arrays 6, and openings 5 serving as the inlet ports of the photoelectrons are formed at portions of the focusing electrode 4 adjacent to dynodes 7 1 . An anode 8 is arranged in front of a last-stage dynode 7 L of each dynode array 6 to collect secondary electrons emitted from this last-stage dynode 7 L . In Figs. 4 and 5, reference numerals 9 denote mesh electrodes. The mesh electrodes 9 reliably guide the photoelectrons incident through the openings 5 of the focusing electrode 4 to the corresponding first-stage dynodes 7 1 without flowing them in the opposite direction. The dynode arrays 6 used in this embodiment have in-line dynode structure and all of them have the same arrangement. The dynodes 7 of each dynode array 6 are arranged in the staggered manner along the direction of the incident light beam to be measured such that the recessed surfaces (secondary electron emission surfaces) of their arcuated wall portions oppose each other. The dynodes 7 located on the same stage are supported by one conductive support plate 10 and the same voltage is applied to the dynodes 7 on the same stage by a bleeder resistor (not shown). The adjacent dynode arrays 6 are directed alternately in the opposite directions. More specifically, as shown in Fig. 6, when the direction of secondary electron emission of the first-stage dynode 7 1 of one dynode array 6a is set in the +X direction, the direction of secondary electron emission of the first-stage dynode 7 1 of a dynode array 6b adjacent to the dynode array 6a is set in an opposite direction at 180° (-X direction). Then, the dynode array 6a is arranged at a predetermined distance from the adjacent dynode array 6b in the +X direction. This arrangement applies to other dynode arrays 6. The operation of the photomultiplier having the above arrangement will be described. When a plurality of light beams to be measured are incident on the incident window 2 of the glass bulb 1, the respective light beams to be measured are converted to photoelectrons by the corresponding photoelectric surfaces 3. The photoelectrons are incident on the first-stage dynodes 7 1 of the corresponding dynode arrays 6 through the openings 5 of the focusing electrode 4, and bombarded on the secondary electron emission surfaces of the first-stage dynodes 7 1 , thereby emitting secondary electrons. The secondary electrons are further sequentially multiplied by the dynodes 7 from the second stages, finally collected by the anodes 8, and output to the outside of the photomultiplier as output signals. The dynode array 6a in Fig. 6 will be considered. While the secondary electrons are transmitted in the dynode array 6a, some of them leak from the gap among the dynodes 7 in the lateral direction (+Y direction in Fig. 6). However, the dynode array 6b adjacent to this dynode array 6a is shifted from the dynode array 6a in the -X direction, and the gaps among the dynodes 7 of the dynode array 6b are remote from those of the dynode array 6a. Therefore, the leaking electrons from the dynode array 6a will not mix in the adjacent dynode array 6b, so that occurrence of crosstalk is prevented. Accordingly, the respective dynode arrays 6 have excellent separation and independency. The detection result of the light beam to be measured incident on each photoelectric surface 3 has high precision which is not adversely affected by other light beams to be measured. The following Table 1 indicates the rate of occurrence of crosstalk in the conventional 6-channel photomultiplier shown in Figs. 1 and 2. Table 2 indicates the rate of occurrence of crosstalk in the 6-channel photomultiplier of the same type as that shown in Figs. 4 and 5. From Tables 1 and 2, it is apparent that crosstalk is largely decreased by adopting the arrangement of the present invention. Embodiment 2 Although the dynode arrays 6 used in the photomultiplier of the above embodiment have in-line dynode structure, the present invention is not limited to them. For example, in dynode arrays 16 of a photomultiplier shown in Fig. 7, dynodes on the first and second stages use cylindrical quarter dynodes 17 1 and 17 2 , and dynodes on the third stage and so on have venetian-blind structure. Except for that, the constituent elements are the same as in the above embodiment. Thus, they are denoted by the same reference numerals, and a detailed description thereof will be omitted. As is apparent from Fig. 7, the adjacent dynode arrays 16 are shifted from each other, and leaking electrons in the horizontal direction will not mix in the adjacent dynode array 16. Embodiment 3 Fig. 8 shows a photomultiplier in which dynode arrays 26 have venetian-blind structure in all the stages. In these dynode arrays 26, unlike in the embodiment described above, even the secondary electron emission direction of second-stage dynodes 27 2 is set the same as that of first-stage dynodes 27 1 , as is clearly seen in Fig. 9. Accordingly, the distance between adjacent dynode arrays 26a and 26b is further increased, thereby further improving the effect of preventing mixing of leaking electrons. All the above various embodiments are related to transmission type photomultipliers. However, the present invention can similarly be applied to a reflection type photomultiplier. Embodiment 4 Fig. 10 shows a reflection type photomultiplier embodying the invention. Although the basic arrangement of this photomultiplier is close to that of the transmission type photomultiplier, this photomultiplier has neither photoelectric surfaces on the inner surface of incident window 2 of its glass bulb 1 nor a focusing electrode. Referring to Fig. 10, reference numerals 30 denote cylindrical quarter photocathodes. Reflection type photoelectric surfaces 31 are formed on the recessed surfaces of the photocathodes 30. Light beams to be measured incident through the incident window 2 passes through a mesh electrode 9 and are bombarded on the photoelectric surfaces 31 of the photocathodes 30 to generate photoelectrons. The photoelectrons are guided to dynode arrays 36 having proximity mesh dynode structure, multiplied by the secondary electron emission effect, and captured by anodes 8. Although the light beam incident ports of the photoelectric surfaces 31 are aligned one-dimensionally, the photoelectron emission directions of the adjacent light beam incident ports are set in opposite directions at 180° from each other. Accordingly, a dynode array 36 connected to a certain photocathode 30 is set in the opposite direction alternately from the adjacent dynode array 36, so that crosstalk between the dynode arrays 36 is prevented in the same manner as in the above transmission type photomultiplier. Embodiment 5 This reflection type photomultiplier has various types, and Fig. 11 shows an example. In a reflection type photomultiplier shown in Fig. 11, photocathodes 40 having reflection type photoelectric surfaces 41 and first-stage dynodes 47 1 of dynode arrays 46 have venetian-blind structure, and the dynodes from the second stage of the dynode arrays 46 have proximity mesh dynode structure. The photoelectron emission direction of the photoelectric surface 41 of one photocathode 40 is set in the opposite direction at 180° from that of the adjacent one, and the positions of the adjacent dynode arrays 46 are shifted from each other, which will be readily understood from Fig. 11. Embodiment 6 Fig. 12 shows a linear multi-anode electron multiplier for detecting the energy beams of electrons, ions and so forth The electron multiplier corresponds to an arrangement obtained by removing a glass bulb, photoelectric surfaces, and a focusing electrode 4 from a transmission type photomultiplier. The electron multiplier of the embodiment shown in Fig. 12 has a plurality dynode arrays 56 having box-and-grid dynode structure, and the energy beam incident ports of first-stage dynodes 57 1 of the dynode arrays 56 are aligned one-dimensionally. The present invention is applicable to this electron photomultiplier as well. The direction of secondary electron emission of the first-stage dynode 57 1 of each dynode array 56 is set in the opposite direction at 180° from that of first-stage dynode 57 1 of an adjacent dynode array 56. Accordingly, when the energy beams of electrons are incident on the energy beam incident ports of the first-stage dynodes 57 1 , the electrons leaking from the gaps among dynodes 57 will not mix in the adjacent dynode array 56 in completely the same manner as in the function at the diode arrays 6 of the above-mentioned photomultiplier. The electrons multiplied in the dynode arrays 56 are finally captured by anodes 8. In Fig. 12, reference numerals 60 denote bleeder resistors. More details of photomultiplier itself and the dynode suructure used therefor are disclosed in Photomultiplier Handbook by RCA Corporation printed in USA. From the embodiments thus described, it will be obvious that the invention may be varied in many ways, without departing from the scope of the invention as defined in the following claims.

Claims: An electron multiplier comprising a plurality of electron multiplying sequences (6, 16, 26, 36, 46, 56) for multiplying electrons resulting from plural respective incident beams, each of the multiplying sequences comprising a first stage electrode (7 1 , 17 1 , 27 1 , 30, 40, 57 1 ) arranged in a row along an axis (Y) for directing electrons emitted thereby toward the next electrode in the sequence, characterised in that the first stage electrode (7 1 , 17 1 , 27 1 , 30, 40, 57 1 ) in each sequence is oriented to direct emitted electrons in a direction away from the axis (Y) of the row, and the first stage electrodes in adjacent sequences (6a, 6b, 26a, 26b) are oriented to direct emitted electrons in respective substantially opposite directions (+X, -X). An electron multiplier as claimed in claim 1, wherein the first stage electrode (7 1 , 17 1 , 27 1 , 57 1 ) in each sequence is oriented to direct incident electrons in a direction (+X, -X) substantially perpendicular to the row. An electron multiplier as claimed in claim 1 or 2, wherein the first stage electrodes in adjacent sequences (6a, 6b, 26a, 26b) are oriented to direct electrons in respective directions differing by 180°. An electron multiplier as claimed in any of claims 1 to 3, wherein the first two electrodes in each sequence are cylindrical quarter dynodes (7 1 , 17 1 , 17 2 , 30, 57). An electron multiplier as claimed in any of claims 1 to 4, wherein electrodes in each sequence (6) have an in-line structure. An electron multiplier as claimed in any of claims 1 to 4, wherein electrodes in each sequence (56) have a box-and-grid structure. A photomultiplier comprising an electron multiplier as claimed in any preceding claim, and further comprising: a window (2) on which a beam to be measured in incident; and a photoelectric surface (3) for emitting electrons in response to the incidence of a beam thereon. A photomultiplier as claimed in claim 7, wherein the photoelectric surface is a transmission type surface (3) formed behind said window (2). A photomultiplier as claimed in claim 8, further comprising a focusing electrode (4) between the photoelectric surface (3) and the sequences (6, 16, 26), the focusing electrode defining a plurality of openings (5) to enable each sequence to receive electrons from respective portions of the photoelectric surface. An electron multiplier as claimed in any of claims 1 to 4, wherein electrodes in each sequence (16, 26) have a venetian blind structure. An electron multiplier as claimed in any of claims 1 to 4, wherein electrodes in each sequence (36, 46) have a proximity mesh structure. A photomultiplier comprising an electron multiplier as claimed in claim 10 or 11, and further comprising: a window (2) on which a beam to be measured in incident; and a photoelectric surface (31, 41) for emitting electrons in response to the incidence of a beam thereon. A photomultiplier as claimed in claim 12, wherein the photoelectric surface is a reflection type surface formed on the first stage electrode (30, 40) behind said window. A photomultiplier as claimed in claim 13, wherein the first stage electrode (30) has a cylindrical-quarter structure. A photomultiplier as claimed in claim 13, wherein the first stage electrode (40) has a venetian-blind structure.

Inventors: KATO HISAKI, KIMURA SUENORI, NAKATSUGAWA KIYOSHI, ONDA HIROYUKI, OZAWA ITSUO, UCHINO TSUGUO, KATO, HISAKI, KIMURA, SUENORI, NAKATSUGAWA, KIYOSHI, ONDA, HIROYUKI, OZAWA, ITSUO, UCHINO, TSUGUO, KATO, HISAKI, C/O HAMAMATSU PHOTONICS K.K., KIMURA, SUENORI, C/O HAMAMATSU PHOTONICS K.K., NAKATSUGAWA, KIYOSHI, C/O HAMAMATSU PHOTONICS K.K., ONDA, HIROYUKI, C/O HAMAMATSU PHOTONICS K.K., OZAWA, ITSUO, C/O HAMAMATSU PHOTONICS K.K., UCHINO, TSUGUO, C/O HAMAMATSU PHOTONICS K.K.
Applicants: HAMAMATSU PHOTONICS KK, HAMAMATSU PHOTONICS K.K.
Application year: 1993
Main classification: H01J43
IPC codes: H01J43