WO1992007283A1 - A method and a device for the detection of ionizing radiation - Google Patents
A method and a device for the detection of ionizing radiation Download PDFInfo
- Publication number
- WO1992007283A1 WO1992007283A1 PCT/SE1991/000691 SE9100691W WO9207283A1 WO 1992007283 A1 WO1992007283 A1 WO 1992007283A1 SE 9100691 W SE9100691 W SE 9100691W WO 9207283 A1 WO9207283 A1 WO 9207283A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- medium
- energy
- laser light
- ionizing radiation
- state
- Prior art date
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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
- G01T1/185—Measuring radiation intensity with ionisation chamber arrangements
Definitions
- the invention relates to a method and a device for the detect ion of ionizing radiation, wherein the radiation is being attenuated in a medium, so that the ionizing radiation dissipates all or a part of its radiative energy, and the medium thereby emits energy which is detected by at least one detector.
- Such devices are commonly known.
- Ionizing radiation is in general understood as radiation, either electromagnetic radiation or particle radiation, the energy of which is high enough to cause ionization of the medium while passing therethrough.
- the ionizing radiation may e.g.
- the radiation originates from a radioactive decay or it may be generated by a particle accelerator, an X-ray tube, or the like.
- the radiation is usually of the type ⁇ (electromagnetic), ⁇ (electron, positron) or ⁇ (the nucleus of a He-atom).
- the ionizing radiation may be constituted by other elementary particles, such as protons, neutrons, mesons, etc.
- ionizing radiation o.g. an ⁇ -particlo
- a gas When ionizing radiation, o.g. an ⁇ -particlo, is decelerated in a gas, the atoms of the gas are ionized and excited. In the case of excitation, the atoms and/or the molecules take up a part of the energy of the particle.
- electrons are liberated, which may be collected and detected in the form of a charge pulse, for example at an anode, which is utilized in so-called proportional counting.
- the size or the amplitude of the charge pulse which corresponds to the number of liberated electrons, is then proportional to the energy (E) of the particular radiation quantum.
- the number of liberated electrons (N) sets a limit to the resolving power, i.e. the accuracy ( ⁇ E) with which the energy of the radiation quantum may be determined.
- the energy resolving power is determined by the relation
- N E/ ⁇ (2)
- ⁇ is the average energy lost by the particle for each liberated electron, i.e. for every ionization.
- the quantity ⁇ is therefore a parameter which depends upon the medium.
- the ionizing radiation excites neutral atoms and/or molecules in the medium.
- these excited atoms may represent a greater number than the ion pairs, mainly due to the fact that less energy is required to excite an atom than to ionize it.
- the quantity ⁇ therefore has a lovter value than it would have for the detection of liberated electrons. Therefore, according to the relation (1) above, the excited atoms provide a greater number (N) of events, upon which the detection may be based. However , the excited atoms are difficult to detect.
- photomultiplier i.a. for the following reasons: a) only a fraction of the atoms de-excite radiatively; b) only a fraction of the radiative de-excitations give rise to light of wavelengths which can be detected by the photomultiplier; and c) a part of the emitted light is absorbed by the medium.
- losses occur partly as a result of light collection losses in the optical system, and partly because, at the most, about every fourth photon in the scintillation is converted into a detectable photo-electron in the photomultiplier.
- An optimized detection would require that every such excited atom could emit several photons, i.e. energy quanta of light with wavelengths in the sensitivity range of the photo- multiplier.
- the present invention aims at enabling reliable and accurate detection of ionizing radiation, especially through the use of certain auxilliary means to bring about a modification or an amplification of the effects of the interaction between the ionizing radiation and the medium, so that the energy emitted by the medium may be detected with greater reliability and accuracy.
- the stated main object of the invention is basically achieved in that, in conjunction with the deceleration of the ionizing radiation in the medium, the medium is irradiated with laser light having at least one wavelength being characteristic to the medium, so that the medium interacts with the ionizing radiation and is excited by the laser light, whereby the medium emits easily detectable energy induced by the laser light.
- Figs, 1a, 1b, 1c and 1d schematically show a number of energy transitions, utilized in carrying out the method according to the invention
- Figs.2-5 show various examples of specific energy transitions, according to fig. 1a in conjunction with figs, 1b and 1d, with neon gas as a medium for scintillation detection; and
- Figs. 6 - 8 schematically show three different embodiments of the device according to the invention.
- figs. 1a-1d illustrate a few examples of energy transitions in the medium being used when detecting ionizing radiation according to the invention.
- the ground state of the medium is denoted by G, which constituee the energy state of the medium before it is hit by any ionizing radiation.
- G constituee the energy state of the medium before it is hit by any ionizing radiation.
- the state or states A may consist of a single state or a group or a band of energy states.
- the states A and the ground energy state G of the medium lie so far apart that each state A, without the influence of the ionizing radiation, is unpopulated, i.e. practically none of the atoms of the medium can be excited into such states, for example through the thermal motion of the medium.
- the atoms of each energy state A are excited to another one or a band of higher energy states B. Then, the wavelengths of the laser radiation have been selected so that the transition from the state A to the state B has the highest probabiity.
- the atoms of the state B may dissipate their energy through different
- the state D may then be an energy state in an atom, a molecule or a material of different kind than those to which the states A, B and C belong. This transition from the state B may arise e.g. from collisions, where the liberated energy is transferred into kinetic energy.
- Atoms in the state D thereupon dissipate their energy by radiation in a similar manner as the atoms in the state B in the processes according to fig. 1b and/or 1c. While emitting their energy, the atoms in the state D transcend into a state E; - the atoms dissipate their energy in any one of the processes according to figs, 1b, 1c, 1d, the only difference being that the state C or E forms or is transferred into the initial energy state A, which enables a repetition of the whole process including laser excitation and subsequent detection. This repetition of the process is signified by a multiplied amplification, here called multiplying effect.
- Figs. 2 - 5 illustrate four specific processes corresponding to figs, 1b and 1d for neon gas,
- the lower excited states A are composed of the four 3s-states, which are populated under the influence of the ionizing radiation. These states are brought to interact with the laser light, which in this case contains four wavelengths, namely 7032 A, 7245 A, 7439 A, and 8082 A.
- the atoms are excited resonantly to the state B, which in this example is composed of the lowest of the 3p-states.
- the state B which in this example is composed of the lowest of the 3p-states.
- the process may be repeated a number of times, a photon being obtained each time. Almost every atom in any 3s-state A may therefore be measured selectively in the wavelength of the laser with such a high amplification that the losses in collecting the emitted light are compensated. These losses involve e.g. the limited solid angle covered by the detector because the incoming laser light must be screened from the detector.
- the invention enables the detection of approximately every atom being excited to said 3s-state through the influence of the ionizing radiation.
- the wavelength of the laser light has been selected to 6402 A, which is tuned such that an atom in the lower, excited state A is excited resonantly to the state B.
- This state has no so-called "allowed" transition to the 3s-states other than the one corresponding to the laser excitation. Atoms, which have been excited to the state A by the ionizing radiation, will therefore, if the intensity of the laser light is sufficiently high, occupy the state B during a large part of the time.
- Ne-atoms Ne-atoms.
- the difference in excitation energy between the states B and D is normally normally converted to kinetic energy that the atoms receive.
- the atoms in said state have only a small possibility to dissipate additional parts of their
- the state D also has "allowed" radiative transitions to the other 3s-states, while emitting light with wavelengths 7245 A, 7439 A and 8002 A. These wavelengths are also selected by said filter and are detected by the detector. The process cannot be repeated directly, when the transitions last mentioned occur. However, it is known that transfer reactions similar to those described above also occur between the 3s-states, the occupancy of the lowest 3s-state A being preferred. Through these
- FIG. 5 Another example of laser light induced detection of ionizing radiation, through the use of neon gas, is shown in fig. 5. Like in fig. 2, laser light containing four wavelengths is used.
- These wavelengths are selected so that atoms, which have been excited to one of the four 3s-states by the influence of the ionizing radiation, are excited resonantly from each one of these 3s-states to one or more preselected 3p-states.
- the process may in principle be continued for a long time and be stopped when desired, as will be described below.
- the process according to fig. 5 is effective enough to enable imaging of the path of an ionizing radiation quantum in the gas volume.
- the imaging can easily be accomplished through the use of conventional optics, such as e.g. lenses.
- the inert gases may also be present in a liquid state or in a solid state. In such a case, the mechanisms shown in the
- the invention is not limited to inert gases as a medium. Accordingly, other gases as well as other liquid and solid materials may be used within the concept of the invention.
- the invention limited to the feature that the state (B), being populated by laser excitation, dissipates its energy through detectable electromagnetic radiation. This energy may also be dissipated through liberation of charges, especially electrons from another atom or molecule in the medium, which charges are detected e.g. with an anode in the medium.
- the laser irradiation can also be made in a broad band, i.e.
- the laser light may contain one or several bands of wavelengths. Further, the laser light may be interrupted for example by a so-called optical modulator, wherein the repeated excitation process, described in figs. 1 - 4, may be stopped when desired so as to restore the medium in the sense that the excited atoms and molecules return to their ground energy states. Thereafter, the medium is ready again for the detection of ionizing radiation.
- pulsed laser light can be used within the scope of the invention. Likewise, other laser techniques may be used to achieve an optimal result in each individual case.
- the laser light from one or several lasers is expanded so as to irradiate, via a lens 1, a chamber 2 containing a medium, for example neon gas.
- Ionizing radiation for example K-radiation, from a sample 3 or some other radiation source located within or outside the chamber, is detected in a detector 4 by way of the light
- the chamber must be designed in such a way, that the laser light does not generate scattered light which disturbs the detection of the emission from the medium as generated according to the invention.
- the processes according to figs. 3, 4 and 5 are used, the laser light can be eliminated from the detector in a familiar way, with the aid of e.g. optical filters 5 located between the chamber 2 and the detector 4, These filters are transparent to the emission from the medium as generated according to the invention.
- the device in another embodiment according to the invention (fig. 7), includes two detector units 4a, 4b, each comprising a lens 6a, 6b and an electronic image detector 7a, 7b.
- the detector units are oriented in such a way that the image recordings in the two units are carried out. in two mutually perpendicular directions.
- the filters 5a, 5b are inserted between the chamber 2 and each corresponding detector unit 4a, 4b.
- the lenses 6a, 6b the image of the chamber 2 is reproduced in each detector unit, which detects the path of the ⁇ -particles in the detector medium.
- the invention is thus used for track detection of charged particles.
- the paths of the particles are then imaged in the light, which is emitted by the excited atoms while using any of the processes according to figs. 2-5.
- the intensity of this light along the track is then a measure of the specific energy loss dE/dx, (if the intensity of the laser light is taken into consideration).
- FIG. 8 Another realization of the device is shown in fig. 8.
- a cylindrical chamber 2' the walls of which are made of an electrically conducting material and which contains a gas medium, for example an inert gas, such as Ne, is provided with a thin wire 8
- the wire serving as an anode or which, accordingly, a positive electrical voltage is applied in relation to the walls of the chamber 2',
- the laser light which in this case is further focused through the lens 1', is brought to graze along the wire 8, which is thus located in the center of the beam of the laser light.
- the inert gas in the chamber 2' is ionized, and electrons, so-called secondary electrons, are liberated and collected by the anode 8.
- the electrons In proximity to the anode 8 the electrons reach such a high energy that, when colliding with the inert gas atoms, they are able to excite the latter into their s-states.
- This light emission upon passing through a filter 5', is registered by the detector 4'.
- the light is constituted by laser induced, proportional scintillations, which also have wavelengths deviating from the wavelengths which the scintillations would have without laser light excitation.
- the invention is used in amplifying the scintillations and simultaneously change their wavelengths.
- the amplified signal then provides better energy resolving power, as discussed above, and the change in wavelength of the scintillations may be optimized for reliable and accurate detection of the same.
- the amplification factor at certain energy transitions in inert gases may amount to about 1.5-5 and in exceptionally cases yet higher, namely about 9 for the transition mentioned in connection with fig. 3, the transition corresponding to a laser light wavelength of 6402 A in neon.
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- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- High Energy & Nuclear Physics (AREA)
- Molecular Biology (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
Description
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Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE9003293A SE9003293L (en) | 1990-10-15 | 1990-10-15 | SET TO DETECT IONIZING RADIATION AND DEVICE FOR EXERCISE OF THE SET |
SE9003293-9 | 1990-10-15 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1992007283A1 true WO1992007283A1 (en) | 1992-04-30 |
Family
ID=20380652
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/SE1991/000691 WO1992007283A1 (en) | 1990-10-15 | 1991-10-15 | A method and a device for the detection of ionizing radiation |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0510142A1 (en) |
SE (1) | SE9003293L (en) |
WO (1) | WO1992007283A1 (en) |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0174691A1 (en) * | 1984-09-10 | 1986-03-19 | Philips Electronics Uk Limited | Ionisation chamber |
-
1990
- 1990-10-15 SE SE9003293A patent/SE9003293L/en not_active IP Right Cessation
-
1991
- 1991-10-15 WO PCT/SE1991/000691 patent/WO1992007283A1/en not_active Application Discontinuation
- 1991-10-15 EP EP19910918859 patent/EP0510142A1/en not_active Withdrawn
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0174691A1 (en) * | 1984-09-10 | 1986-03-19 | Philips Electronics Uk Limited | Ionisation chamber |
Also Published As
Publication number | Publication date |
---|---|
SE9003293D0 (en) | 1990-10-15 |
SE466121B (en) | 1991-12-16 |
EP0510142A1 (en) | 1992-10-28 |
SE9003293L (en) | 1991-12-16 |
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