JP2009301906A - Photomultiplier tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain sensitivity by preventing the feedback of ions to the photoelectric surface. <P>SOLUTION: A photomultiplier tube 1 utilizing the electron multiplying operation of gas comprises: a photoelectric conversion part 3 arranged opposite to an incident plane plate 7 into which incident light is emitted, and having a plurality of inclined portions 9 inclined to a light incident plane 7a and arrayed along the light incident plane 7a and a reflection type photoelectric surface 10 formed on the inclined portions 9 at the side of the incident plane plate 7; and an electron multiplying part 4 arranged opposite to the incident plane plate 7 across the photoelectric conversion part 3 and having a plurality of through-holes 8 formed along the light incident plane 7a. The plurality of inclined portions 9 are arranged adjacent to each other to prevent the electron multiplying part 4 from being seen through from the side of the incident plane plate 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photomultiplier tube using electron multiplication by gas.

In recent years, development of an electronic amplifier using an electron multiplication effect in a gas has been advanced. By using gas, there are advantages such that the inside of the apparatus is at atmospheric pressure and does not require a high vacuum container, the electron multiplication structure is simplified, and it can be manufactured at low cost. As this type of electron multiplier, a multi-hole plate (electron multiplier) having a large number of through holes is built in, and electrons are incident on the through holes by applying a voltage to both ends of the through holes. Is multiplied (see Patent Documents 1 to 3 below). In addition, it has been studied to use a photomultiplier tube by combining a photocathode with such an electron multiplier structure (see Non-Patent Documents 1 and 2 below).
JP 2006-302844 A JP 2005-32634 A JP 2001-508935 A A. Breskin et al., Nuclear Instrument and Methods in Physics Research A 513 (2003) pp250-255 J. Va'vra and T. Sumiyoshi, Nuclear Instrument and Methods inPhysics Research A 535 (2004) pp334-340

  However, when the photocathode is combined with the electron multiplying structure as described above, the photocathode tends to deteriorate due to the feedback of ions accompanying the ionization of the gas in the electron multiplying portion. As a result, the sensitivity to incident light may be reduced.

  Therefore, the present invention has been made in view of such problems, and an object thereof is to provide a photomultiplier tube capable of maintaining sensitivity by preventing feedback of ions to the photocathode.

  In order to solve the above problems, the photomultiplier tube of the present invention is provided in a photomultiplier tube using an electron multiplying action by a gas so as to face a light incident surface on which incident light is incident. A plurality of inclined portions that are inclined with respect to the surface are arranged along the light incident surface, and a photoelectric conversion portion in which a reflective photoelectric surface is formed on the light incident surface side of the inclined portion, and the photoelectric conversion portion sandwiched therebetween An electron multiplying portion provided opposite to the light incident surface and having a plurality of through holes formed along the light incident surface, and the plurality of inclined portions cannot be seen from the light incident surface side. Are arranged close to each other.

  According to such a photomultiplier tube, incident light incident from the light incident surface is converted into photoelectrons by the reflective photocathode of the photoelectric conversion unit, and the photoelectrons are amplified by being incident on the through holes of the electron multiplier unit. The incident light is detected by multiplying and measuring the multiplied electrons. At this time, the reflective photocathode is formed on the light incident surface side of the inclined portion inclined with respect to the light incident surface, and the plurality of inclined portions are arranged so that the electron multiplier portion cannot be seen from the light incident surface side. . Therefore, even when the photoelectron multiplication causes ions generated in the electron multiplication part due to gas molecules to return to the photoelectric conversion part side, it does not easily collide with the photocathode. Sensitivity can be maintained.

  The arrangement pitch along the light incident surfaces of the plurality of inclined portions is preferably larger than the arrangement pitch along the light incident surfaces of the plurality of through holes. In this case, since photoelectrons emitted from the reflective photocathode are guided to a plurality of through holes, electrons and ions generated in one through hole at the time of multiplication by gas can be reduced, and noise caused by discharge in the vicinity of the through hole. Can be suppressed.

  It is also preferable to further include a control electrode for guiding photoelectrons generated from the photocathode in response to the incident light to the electron multiplier between the light incident surface and the photoelectric conversion unit. By adopting such a configuration, the photoelectrons generated in the photoelectric conversion unit can be efficiently guided to the electron multiplying unit, so that the sensitivity of incident light can be further increased.

  According to the present invention, sensitivity can be maintained by preventing feedback of ions to the photocathode.

  Hereinafter, preferred embodiments of a photomultiplier according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a vertical cross-sectional view of a photomultiplier tube 1 according to a preferred embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view showing a main part of the photomultiplier tube 1 of FIG.

  The photomultiplier tube 1 shown in FIGS. 1 and 2 includes a photoelectric conversion unit 3 and an electron multiplier 3 in a housing 2 in which a rare gas such as argon or xenon or a mixed gas of a rare gas and a quenching gas is enclosed. The multiplier 4, the anode 5, and the control electrode 6 are accommodated. The photomultiplier tube 1 converts incident light incident from an incident surface plate 7 provided on one end face of the housing 2 into photoelectrons, and amplifies the photoelectrons by an electron multiplying action by a rare gas to thereby convert the incident light. To detect.

  The electron multiplier 4 is a flat plate member made of glass provided to face the incident surface plate 7, and both surfaces thereof are formed by a metal film such as Al or Ni. Furthermore, a plurality of through holes 8 arranged along the direction parallel to the light incident surface 7a of the incident surface plate 7 are formed in the electron multiplier 4 so as to penetrate in a direction substantially perpendicular to the light incident surface 7a. Has been. The thickness of the electron multiplying portion 4 is set to, for example, 300 μm, and the through holes 8 have a diameter of about several tens to several hundreds of μm and an arrangement pitch of 25 μm to 800 μm by laser processing, plasma etching, or microblast processing. It is formed as follows.

  The photoelectric conversion unit 3 is disposed at a position sandwiched between the incident surface plate 7 and the electron multiplying unit 4 so as to face the incident surface plate 7, and a plurality of inclined portions 9 are formed on a part of a metal plate such as Ni. Are provided close to each other. Specifically, the plurality of inclined portions 9 are formed by pressing or the like so as to be arranged at a constant pitch along the light incident surface 7a, and are inclined along the arrangement direction with respect to the light incident surface 7a. Yes. Further, two adjacent inclined portions 9 are separated in a slit shape, so that photoelectrons emitted from the surface on the incident surface plate 7 side of the inclined portion 9 can pass to the electron multiplying portion 4 side. A reflection type photoelectric surface 10 for converting incident light into photoelectrons is formed on the surface of the inclined portion 9 on the incident surface plate 7 side, and this photoelectric surface 10 is substantially equal to the incident angle of incident light from the incident surface plate 7 side. Photoelectrons are emitted in the direction of reflection. The surface of the incident inclined portion 9 opposite to the photocathode 10 is covered with an oxide such as ZnO or SnO that suppresses the emission of secondary electrons.

Here, the inclination angle θ _{1 of} the inclined portion 9 with respect to the incident surface plate 7 in the photoelectric conversion unit 3 and the pitch P ₁ along the light incident surface 7 a of the inclined portion 9 are directions perpendicular to the light incident surface 7 a from the incident surface plate 7. Is set to such a value that the electron multiplier section 4 is covered by the photoelectric conversion section 3 and cannot be seen through (see FIG. 2). That is, processing is performed such that the inclination angle θ _{1 of the} inclined portion is equal to or smaller than a predetermined angle with respect to the pitch P ₁ of the inclined portion 9. Furthermore, the pitch P ₁ of the inclined portion 9 is set to be larger than the pitch P ₂ along the light incident surface 7 a of the through hole 8 of the electron multiplying portion 4.

Between the photoelectric conversion unit 3 and the incident surface plate 7, a mesh-like control electrode 6 is provided along the light incident surface 7a. The control electrode 6 generates an electric field for guiding photoelectrons generated from the photocathode 10 to the electron multiplier 4. That is, the control electrode 6 is applied with a lower potential than the photoelectric conversion unit 3 that reflects the photoelectrons emitted from the photocathode 10 to the electron multiplying unit 4 side. The mesh-shaped control electrode 6 is formed such that the pitch P ₃ along the light incident surface 7 a is sufficiently smaller than the pitch P ₁ of the inclined portion 9.

In such a photomultiplier tube 1, incident light L incident from the light incident surface 7 a is converted into photoelectrons E ₁ by the reflective photocathode 10 of the photoelectric conversion unit 3, and the photoelectrons E ₁ are amplified from the photocathode 10. The light enters the through hole 8 of the multiplication unit 4. An electric field is applied to the electron multiplier 4 between the openings of the through hole 8, and the photoelectron E ₁ receives energy from this electric field, and as a result, collides with gas molecules inside the through hole 8 to cause ionization and collision. Repeatedly avalanche multiplication. Thereafter, it multiplied electrons E ₂ is the incident light is detected by being taken out by the anode 5. At this time, ions I ₁ are generated inside the through-holes 8 due to ionization of gas molecules, and the ions I ₁ return to the photoelectric conversion unit 3, but most of them are on the surface of the inclined portion 9 opposite to the photoelectric surface 10. Since it is absorbed, deterioration due to ion collision on the photocathode 10 is extremely reduced. In particular, when an alkali metal such as a bialkali is used as the material of the photocathode 10, the influence of deterioration due to ion feedback is large. However, when such a photocathode is combined with the electron multiplier 4, the deterioration is prevented. This increases the degree of freedom in selecting the material of the photocathode 10. As a result, the detection sensitivity of incident light in various wavelength bands can be stably maintained. Furthermore, since the surface of the inclined portion 9 opposite to the photocathode 10 is covered with a material that suppresses the emission of secondary electrons, the generation of noise due to the incidence of ions is also prevented.

  Further, although the electron multiplier 4 may emit light due to recombination of electrons and ions, the electron multiplier 4 is structured so that the electron multiplier 4 cannot be seen from the photocathode 10, so that noise is generated due to photon feedback. Will also be reduced.

Further, since the arrangement pitch P ₁ along the light incident surface 7 a of the inclined portion 9 is larger than the arrangement pitch P ₂ along the light incident surface 7 a of the through hole 8, a plurality of photoelectrons E ₁ emitted from the photocathode 10 are present. Therefore, the number of electron-ion pairs generated in one through-hole 8 during electron multiplication can be reduced, and the generation of noise due to discharge in the vicinity of the through-hole 8 can be suppressed.

In addition, since the control electrode 6 is provided between the incident face plate 7 and the photoelectric conversion unit 3, the photoelectrons generated in the photoelectric conversion unit 3 can be efficiently guided to the electron multiplication unit 4. The sensitivity can be further increased. Furthermore, by making the pitch P ₃ of the control electrode 6 sufficiently smaller than the pitch P ₁ of the inclined portion 9, it is possible to guide photoelectrons to the electron multiplying portion 4 more efficiently.

  FIG. 3 is a graph showing a change in relative detection efficiency of incident light with respect to a potential difference [V] between the control electrode 6 and the photoelectric conversion unit 3. In this case, the distance between the control electrode 6 and the photocathode 10 is 0.5 mm. As shown in the figure, in the range where the potential difference between the control electrode 6 and the photoelectric conversion unit 3 is larger than 0 to about 8 V, the detection efficiency is improved as compared with the case where no potential difference is applied. I understand.

  In addition, this invention is not limited to embodiment mentioned above. For example, a resin sheet such as a polyimide film may be used as the material of the electron multiplying unit 4 in addition to a glass substrate, and Cu or the like may be used as a metal thin film formed on both surfaces.

  Further, as for the control electrode 6, as in the photomultiplier tube 101 which is a modification of the present invention shown in FIG. May be. As such a conductive film 106, a transparent conductive film such as ITO (Indium Tin Oxide), a metal thin film such as Cr or Au, or the like is used.

1 is a longitudinal sectional view of a photomultiplier tube according to a preferred embodiment of the present invention. It is sectional drawing which expands and shows the principal part of the photomultiplier tube 1 of FIG. It is a graph which shows the change of the relative detection efficiency of incident light with respect to the electric potential difference between the control electrode of FIG. 1, and a photoelectric conversion part. It is a longitudinal cross-sectional view of the photomultiplier tube which concerns on the modification of this invention.

Explanation of symbols

E ₁ ... Photoelectrons, L ... Incident light, P _1, P ₂ ... Arrangement pitch, _1, 101 ... Photomultiplier tube, 3 ... Photoelectric converter, 4 ... Electron multiplier, 6, 106 ... Control electrode, 7 ... Incident surface plate, 7a ... light incident surface, 8 ... through hole, 9 ... inclined portion, 10 ... photoelectric surface.

Claims (3)

In photomultiplier tubes using electron multiplication by gas,
A plurality of inclined portions that are provided to face the light incident surface on which incident light is incident and are inclined with respect to the light incident surface are arranged along the light incident surface, and the light incident surface of the inclined portion A photoelectric conversion part having a reflective photoelectric surface formed on the side;
An electron multiplier section provided opposite to the light incident surface across the photoelectric conversion portion, and having a plurality of through holes formed along the light incident surface;
The plurality of inclined portions are arranged close to each other so that the electron multiplying portion cannot be seen from the light incident surface side.
A photomultiplier tube characterized by that. The arrangement pitch along the light incident surface of the plurality of inclined portions is larger than the arrangement pitch along the light incident surface of the plurality of through holes.
The photomultiplier tube according to claim 1. A control electrode for guiding photoelectrons generated from the photoelectric surface in response to the incident light to the electron multiplying unit is further provided between the light incident surface and the photoelectric conversion unit.
The photomultiplier tube according to claim 1 or 2, wherein

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