Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/208—Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/36—Measuring spectral distribution of X-rays or of nuclear radiation spectrometry
  • G01T1/40—Stabilisation of spectrometers

Definitions

• Device and method for measuring light intensity using a photomultiplier comprising a calibration source.
• the invention relates to the measurement of light intensity using photomultipliers.
• the gain of a photomultiplier is subject to short-term fluctuations, such as those resulting from temperature variations of this photomultiplier, and to long-term fluctuations or drifts, such as those resulting from wear and age. photomultiplier.
• the invention aims to avoid this drawback.
• the subject of the invention is a device for measuring the light intensity of a radiation comprising a photomultiplier comprising a main window for entering said radiation and an input photocathode arranged in the field of said window, characterized in that it also includes a calibration source adapted to emit radiation of constant intensity directed towards said photocathode.
• the invention may also have one or more of the following characteristics: - said calibration source is a light-emitting diode.
• the wavelength of the maximum emission intensity of said diode belongs to the range of wavelengths of maximum sensitivity of said photomultiplier.
• the device comprises a scintillator element arranged across the main input window and adapted to convert the radiation to be measured into radiation of wavelength adapted to the sensitivity of said photomultiplier, the calibration source emitting directly to said photocathode without cross the scintillator.
• the calibration radiation can be applied directly to the photomultiplier without passing through the scintillator.
• the invention also relates to a device for measuring the interaction of radiation with a material comprising a main source of radiation, a device for measuring the light intensity of the radiation having interacted with said material according to the invention, and means for placing said material on the path of the radiation between said main source and said measuring device.
• Said main source of radiation may be a source of radiation
• the device according to the invention also comprises:
• a pulsed X-ray source is used to ensure the periodic extinction of said source; preferably, this pulsed source then comprises an X-ray emission tube comprising a filament, an anode and a cathode, and means for applying a high alternating voltage between said anode and said cathode.
• Such an X-ray source is robust and economical.
• the invention also relates to a method for measuring the light intensity of a radiation using the device according to the invention in which the measurement of the radiation to be measured is related to that of the radiation from the calibration source; more precisely, this process comprises the stages in which, successively:
• the calibration source being switched off or closed, using the photomultiplier, the intensity of the radiation to be measured is measured
• the radiation to be measured being extinguished or closed, using the photomultiplier maintained under the same adjustment conditions, the intensity of the radiation from the calibration source is measured, - And the final radiation intensity value is deduced by relating the measurement of the radiation to be measured to that of the radiation from the calibration source.
• the invention finally relates to the use of the device or method according to the invention for measuring the thickness of a material interacting by absorption with said radiation to be measured.
• FIG. 1 is a simplified diagram of a device for measuring thickness of material comprising the light intensity measuring device according to the invention
• - Figure 2 is a diagram of the successive measurement sequences of the method according to the invention
• - Figures 3A and 3B are simplified electrical diagrams of pulsed and continuous X-ray source respectively.
• the invention is implemented in a device for measuring the thickness of a material 3; the thickness measurement is based in a conventional manner on that of the absorption of radiation by this material.
• the thickness measurement device comprises a main source 1 of radiation, a device 2 for measuring the light intensity of the radiation which has interacted by absorption with the material 3 and means not shown for placing the material 3 on the path of the radiation. between main source 1 and measuring device 2.
• the measuring device 2 comprises a photomultiplier 4.
• the photomultiplier 4 comprises in a conventional manner a main window for entering the radiation to be measured and an input photocathode, not shown, arranged in the field of said window, according to the invention, the measuring device 2 comprises a calibration source 5 adapted to emit radiation of constant light intensity directed towards the photocathode.
• this device 2 also comprises means 6 for preamplification and coding of the signal delivered by the photomultiplier 4 and means 7 for decoding connected both to the preamplification means 6 and to the calibration source 5.
• main source 1 if the material 3 is opaque to visible radiation, an X-ray source is used which emits in a wavelength range suitable for measuring the thickness of this material; as the photomultipliers are generally not very sensitive for the detection of X-ray radiation, the photomultiplier 4 is provided with a scintillator element 8 arranged across its main input window and adapted to convert the radiation to be measured into radiation of length d wave adapted to the sensitivity of the photomultiplier.
• the calibration source is arranged so as to emit directly to the photocathode of the photomultiplier 4, without passing through the scintillator 8.
• a pulsed X-ray source which comprises an X-ray emission tube 1 - or tube "X" - comprising a filament, an anode and a cathode , and means for applying an alternating high voltage between said anode and said cathode:
• FIG. 3A represents the diagram of such a pulsed source, without rectifier on the high voltage circuit, as opposed to the diagram of a so-called continuous source represented in FIG. 3B, which includes a rectifier on the high voltage circuit.
• the pulsed emission mode of this source advantageously forms means for periodically switching off the main source 1 of radiation.
• a light-emitting diode is preferably used as the calibration source 5.
• the measuring device 2 finally comprises means for activating the calibration source 5 only during the periods of extinction of the radiation source 1 and the decoding means 7 are adapted to report the measurement carried out by the photomultiplier 4 subjected to the radiation at measure during an emission pulse from the source main 1 to the measurement made by the photomultiplier 4 under the same conditions during a period of emission from the calibration source 5.
• the calibration source 5 does not emit and is switched off , and, using the photomultiplier, the intensity of the radiation coming from this source 1 is measured through the material 3,
• the calibration source 5 emits (“on” mode) and, using the photomultiplier maintained under the same adjustment conditions, the intensity of the radiation from the calibration source 5 is measured.
• the decoding means 7 are adapted to separate the signals delivered by the photomultiplier during the phases B (actual measurement) and the signals delivered by the photomultiplier during the phases C
• the final radiation intensity values are deduced by relating the radiation measurements carried out during phases B to those carried out during phases C.
• the values obtained are then independent of the fluctuations or drifts of the photomultiplier.
• the temperature of the light-emitting diode is stabilized in a temperature range where its emissivity is the most stable and the most independent of the temperature.
• the thickness of the material 3 is then deduced in a manner known per se from the radiation intensity values obtained.
• the radiation measuring device according to the invention can be used for a wide variety of applications which go far beyond the field of measurement of material thickness or the wavelength range of X-rays.
• the radiation intensity measurement device makes it possible to know the influence of spurious signals on the measurement delivered by the photomultiplier.
• the device and method according to the invention thus make it possible to control the “reception” section independently of the “transmission” section of an installation.
• many devices use photomultiplier type detectors equipped with scintillators, in particular conventional “X” ray gauges; with reference to FIGS. 3A and 3B, the invention makes it possible, without interrupting the measurement of light intensity, to take special advantage of the pulsed emission gauges which remain by far the most reliable due to the rusticity of their X-ray source. »Which is only composed (fig. 3A) of a filament heating transformer, a high voltage transformer direct supply of the tube between anode and cathode and of the tube" X "itself.
• a continuous source comprising a possible rectification and filtering by capacitor (FIG. 3B) would not have made it possible to implement the invention so simply and economically and the device obtained would have been less reliable.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• High Energy & Nuclear Physics (AREA)
• Molecular Biology (AREA)
• Length-Measuring Devices Using Wave Or Particle Radiation (AREA)
• Analysing Materials By The Use Of Radiation (AREA)
• Measurement Of Radiation (AREA)

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• 1999
  • 1999-08-26 FR FR9910833A patent/FR2797961B1/fr not_active Expired - Fee Related
• 2000
  • 2000-08-25 EP EP00958735A patent/EP1236055A1/de not_active Withdrawn
  • 2000-08-25 WO PCT/FR2000/002370 patent/WO2001014909A1/fr not_active Ceased
  • 2000-08-25 AU AU70162/00A patent/AU7016200A/en not_active Abandoned
  • 2000-08-25 CN CNB00813393XA patent/CN1187624C/zh not_active Expired - Fee Related

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