Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic or electromagnetic waves, or particle emission, not having a directional significance, are being received
  • G01S3/78—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic or electromagnetic waves, or particle emission, not having a directional significance, are being received using electromagnetic waves other than radio waves
  • G01S3/7806—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic or electromagnetic waves, or particle emission, not having a directional significance, are being received using electromagnetic waves other than radio waves using gamma or X-rays
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
  • G01T1/2907—Angle determination; Directional detectors; Telescopes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T7/00—Details of radiation-measuring instruments

Definitions

• the technical field of the invention relates to the estimation of a direction between a detection device and a detected irradiating source.
• the detection device forms a compass, pointing towards the irradiating source.
• Determining a position of an irradiating radioactive source in an environment can be a tedious operation. This is an operation likely to be implemented in nuclear installations, for radiation protection purposes, or in operations to control suspicious goods or waste, for example at borders.
• a first option consists in using an irradiation measuring device such as those usually used in the field of radiation protection.
• This type of device makes it possible to estimate an ambient irradiation level, without information as to the position of sources generating the irradiation.
• the localization of an irradiation source supposes a spatial scanning by carrying out regular measurements, hoping to gradually approach the source according to the successively measured irradiation levels. Such an operation is long, and therefore penalizing from the point of view of dosimetry.
• the main advantage of this approach is to use measurement means that are inexpensive, easy to use and available.
• a gamma camera is a device making it possible to form an image of an observed scene, on which the main irradiating sources can be located. This type of device has been developed since the 1990s and has reached industrial maturity. Compact and relatively light gamma cameras are currently commercially available. However, it is an expensive device, and the use of which requires a certain know-how.
• Patent US10024981B2 describes a measuring device carried by a drone, and intended to locate an irradiating source by using several detectors.
• the localization of the source is carried out by a comparison of signals simultaneously detected by several detectors. But the localization is imprecise, because it results from a simple comparison between the intensities of the measured signals.
• the inventor has designed a device, functioning like a compass, making it possible to indicate a direction pointing towards an irradiating source.
• the device is of simple design, and allows to obtain directional information. It is also an inexpensive and simple to use device.
• a first object of the invention is a device for estimating a direction pointing towards an irradiating source, the irradiating source emitting radiation composed of gamma or X particles or neutrons, the device comprising:
• each detector being configured to generate a detection signal depending on a number of particles detected by the detector; the device being such that each detector is assigned a position, the detectors being arranged around a center corresponding to an isobarycenter of each position, the device comprising a processing unit, configured to
• the device comprises at least three non-aligned detectors.
• the processing unit is configured for:
• the device may include an orientation unit, configured to estimate a variation in the position of the detectors between the first instant and the second instant.
• the device may include a display unit, connected to the processing unit, and configured to display the direction pointing towards the irradiating source.
• At least one detector or each detector may include a scintillator-type detection material.
• At least one detector or each detector may comprise an inorganic scintillator-type detection material.
• the processing unit is configured for:
• the device may include a geolocation unit, configured to measure the distance of movement of the device between the two successive measurement instants.
• a second object of the invention is a method for determining a direction pointing towards an irradiating source using a device according to the first object of the invention, the method comprising the following steps: a) measurement of signals detection by each detector; b) calculation of a barycenter of each position weighted by the detection signal measured by the detector occupying said position; c) estimation of the direction pointing towards the source according to the calculated barycenter.
• step a) comprises:
• step b) comprises taking into account a position of each detector at the first instant and at the second instant;
• step c) comprises calculation of a barycenter of the respective positions of the detectors at each instant, weighted by the detection signals measured respectively by each detector at each instant.
• the device can perform a rotation around the isobarycentre, the angle of rotation being predetermined and/or measured.
• the method may include a step of displaying the direction pointing towards the irradiating source. According to one embodiment, the method comprises the steps of:
• the method may include the steps of:
• a third object of the invention is a device for estimating a distance relative to an irradiating source, the irradiating source emitting radiation composed of gamma or X particles or neutrons, the device comprising:
• a radiation detector configured to generate a detection signal, depending on a number of particles detected by the detector; the device being such that it includes a processing unit, configured to
• a fourth object of the invention is a method for estimating a distance between an irradiating source and a device according to the third object of the invention, comprising:
• Figures IA and IB schematize a first embodiment.
• Figure IA is a perspective view and Figure IB is a top view.
• FIGS. 2A and 2B illustrate a possible implementation of the first embodiment. These two figures are top views.
• FIGS. 3A and 3B schematize a second embodiment.
• Figure 3A is a perspective view and Figure 3B is a top view.
• FIG. 4 represents an example of a portable device according to the second embodiment.
• FIG. 5 schematizes an experimental test carried out using a device according to the second embodiment.
• FIGS. 6A and 6B show the use of a device for performing three-dimensional localization of an irradiating source.
• FIG. 7 schematizes a simulation carried out using a device according to the first embodiment.
• FIG. 8 illustrates an implementation of the device for estimating a distance relative to an irradiating source whose orientation relative to the device has been previously determined.
• Figures 9A and 9B represent experimental measurements made to estimate the distance et between the device and the source.
• FIG. 10 summarizes various stages of implementation of a device forming an object of the invention.
• Figures IA and IB represent a first embodiment of a device 1 according to the invention.
• the device is intended to determine an orientation of an irradiating source S, disposed at a distance from the device, and to determine a rectilinear direction pointing towards the source, from the device.
• the irradiating source S is typically positioned a few meters from the device. It may be a source emitting photonic (X or gamma photons) and/or neutron irradiation.
• the use of the device assumes that the irradiating source is placed at a distance such that, given its activity, the radiation incident on the device is sufficient to be detected.
• the device is intended to be worn by a user, so as to indicate the direction pointing towards the source. It is therefore a device for nomadic use.
• the device can be mounted on a vehicle, in particular in the context of operations in a hostile environment.
• the device 1 comprises a support 2, on which several detectors 10i, 10 2 are placed. Each detector is configured to detect ionizing radiation, in particular neutrons or X or gamma photons.
• Each detector is formed from a detection material connected to a detection circuit. Under the effect of an interaction in the detection material, a particle forming the ionizing radiation (neutron or X or gamma photon) generates an electric pulse, the latter being detected by the detection circuit.
• the detection material is a scintillator
• the electric pulse is generated by a photodetector coupled to the detection material.
• the detection material is a semiconductor
• the electric pulse results from the collection of charge carriers created in the material under the effect of the interaction.
• the detection circuit makes it possible to establish a counting rate, which corresponds to a number of pulses detected per unit of time. For example a number of pulses per second, usually referred to as "strokes per second".
• the detection circuit makes it possible to establish a count, which corresponds to a number of pulses detected during a measurement duration.
• the detection circuit makes it possible to form a detection signal, the latter corresponding either to a counting rate, or to a counting.
• the detection signal is a count rate.
• the detection material of each detector is solid. It may in particular be a scintillator.
• inorganic scintillating materials are preferred, because of their high atomic number, which gives them a good attenuation property. Among the latter, mention may be made, without limitation, of Nal(TI), Csl(TI), GBO (Bismuth Germanate), LaBrs, YSO(Ce) (Yttrium Orthosilicate Cerium - Y 2 SiO 5 :Ce), Srl 2 (Eu).
• organic scintillator materials are preferred, due to their high content of light atoms.
• the device is dedicated to determining a source emitting gamma photons.
• the detectors are based on an inorganic scintillator type detection material.
• the device also comprises: a processing unit 20, connected to each detector.
• the processing unit may comprise a computer, for example of the FPGA type (Field Programmated Gate Array - Programmable Logic Circuit or ASIC - Application Specific Integrated Circuit - Application Specific Integrated Circuit), or a microprocessor, programmed to perform calculations using the rates respectively generated by each detector.
• the processing unit is programmed to establish a direction, pointing towards the source, from the counting rates.
• an orientation unit 21 configured to measure an orientation of the device.It can by example this may be an inertial unit
• the orientation unit is optional a display unit 22, to display the direction pointing towards the source This may be a screen or a set
• the display unit is optional, a geolocation unit 23, configured to establish a position of the device, it can for example be a GPS type system when the device is used outdoors. It can be a system using beacons emitting a short-range electromagnetic signal (eg wifi) when the device is used indoors.
• the geolocation unit is optional.
• FIG. 1A represents a particularly simple configuration of device 1. According to this configuration, the device comprises only two detectors 10i and 10 2 . In FIG. 1B, the device and the source S have been represented, in top view.
• each detector 10j can be assigned a point position P it which corresponds to the center of the detector, i is a natural number designating each detector.
• the processing unit 20 is configured to calculate a barycenter B of the position P t of each detector 10i, weighted by the counting rate respectively measured by each detector. If P t designates a point of the support associated with each detector 10i, which can be for example the center of each detector, the barycenter B is such that:
• N corresponds to the counting rate measured by the detector 10i.
• the vector OB points towards the source S.
• the calculation of the vector OB makes it possible to estimate a direction, pointing towards the source, from the device.
• the direction pointing to the source can be displayed on the display unit 22.
• the device then operates equivalently to a compass.
• the display unit may include an arrow pointing to the source.
• detector 10i When detectors 10i, IO2 and source S are aligned, detector 10i forms a front detector and detector IO2 forms a rear detector.
• the front detector is interposed between the source and the rear detector. According to this arrangement, the radiation emitted by the source and reaching the rear detector is attenuated by the front detector.
• the detection materials composing the detectors being absorbent, in particular when it comes to inorganic detectors, the attenuation of the radiation by the front detector is significant.
• the difference between the counting rates respectively measured by each detector is maximum. This maximizes the norm
• the display unit 22 can display an arrow whose size is correlated to the norm
• FIGS. 2A and 2B illustrate a simple method for determining the position of a source relative to the device, using a device comprising at least two detectors.
• the device corresponds to that described in connection with FIG. 1A: it comprises only two detectors.
• the processing unit 20 is configured to memorize the respective counting rates at each measurement instant and to calculate a position of the barycenter B.
• Ni ⁇ tj' is the count rate of the detector 10i, occupying the position at the measurement time tj, with j varying between 1 and 2 in this example.
• FIGS. 2A and 2B the configuration of the device has been represented respectively at the first instant and at the second instant t 2 .
• the direction pointing towards the source is calculated following the second instant t 2 .
• the device comprises an orientation unit 21 as previously described.
• the orientation unit 21 can be configured to detect, during the rotation of the device, the reaching of an angle of rotation of 90° with respect to the first instant ti and to carry out the measurements directly.
• the orientation unit 21 determines a rotation angle between the first instant and the second instant. This allows a more precise calculation of the position of the barycenter B and this avoids the user having to perform a rotation according to an angle close to 90°.
• the user can activate a switch, so as to signal to the processing unit the first and second instants.
• the orientation unit determines the angle between the first instant and the second instant and supplies it to the processing unit. The real value of the angle is taken into account to calculate the barycenter.
• the rotation between the two instants can thus be different from 90°. It can be 45° or 110°. However, it is preferable that the angle of rotation be close to 90°.
• FIGS. 3A and 3B represent an embodiment in which the device comprises four detectors regularly distributed around an isobarycenter O.
• the processing unit 20 is configured to calculate the barycenter of the positions of each detector, weighted by their respective count rates. This makes it possible to obtain a direction pointing towards the irradiating source without having to perform a rotation of the device.
• Such an embodiment can operate as soon as the device comprises at least three non-aligned detectors.
• the device comprises three detectors, preferably regularly distributed around a center, with an angular difference of 120°.
• the use of detectors based on inorganic materials maximizes the absorption of a part of the radiation emitted by the source by the detectors closest to it. This makes it possible to increase the contrast between the counting rates measured by each detector.
• the barycenter B is thus all the further from the isobarycenter O, which increases the accuracy of the direction estimated by the device. So that the absorption resulting from one detector can significantly influence the count rate of another detector, the distance between the detectors is preferably less than 30 or 40 cm. In order for the effect of absorption to be more significant, it is preferable that the distance between the detectors be less than 20 cm.
• FIG. 4 schematizes an embodiment similar to that of FIGS. 3A and 3B, based on four detectors extending around a center. The respective positions of each detector form a cross, the center of which corresponds to the isobarycenter O. On the device represented in FIG. 4, the device comprises handles 25, facilitating gripping of the device.
• the inventor carried out an experimental test by arranging four detectors in the same horizontal plane, according to a configuration similar to that represented in FIGS. 3A and 3B.
• Each detector was made of Na I (Tl) scintillator material 50.8 mm in diameter and 25.4 mm in height, ie 2 inches in diameter and 1 inch in height.
• the positions of each detector formed a square with a diagonal of 20 cm. See figure 5.
• a source of 137 Cs of 500 kBq activity was placed at a distance of 5 cm from the nearest detector. The following count rates were measured: detector 10i: 800 cps (counts per second); IO2 detector: 150 cps; IO3 detector: 240 cps; detector 10 4 : 250 cps;
• the difference between the different counting rates made it possible to easily determine the direction pointing towards the source.
• each detector being a detector of the YSO type, of dimensions 7.11 mm ⁇ 7.11 mm ⁇ 21.08 mm.
• the distance between two opposite detectors was 20 cm.
• a source of 137 Cs with an activity of 2.9 10 9 Bq placed at different distances from the device was simulated. The source was centered with respect to the device, in the XY plane. The distance between the 137 Cs source and the device was varied.
• Table 1 shows the simulated count rates (counts per second) resulting from each detector, as a function of distance. [Table 1]
• each detector was cylindrical in size, with a diameter and height equal to 25.4 mm.
• Table 2 shows the estimated count rates for each detector as a function of the detection materials, the latter being Nal(TI), BGO, LaBr 3 (Ce), Srh(Eu). [Table 2]
• Figures 6A and 6B illustrate two possible uses of the device.
• the device is arranged horizontally, parallel to the ground, so as to be able to estimate a direction pointing towards the source in the horizontal plane.
• the device is arranged vertically, for example parallel to a wall, so as to be able to estimate a direction pointing to the source in the vertical plane.
• FIGS. 2A and 2B The operation of the device according to the embodiment described in connection with FIGS. 2A and 2B has been simulated.
• a source has been randomly positioned in a plan. An initial position was randomly assigned to the device. A progression of the device in the plane, between different measurement points, was simulated. At each measurement point: a barycentric calculation was performed after rotating the detector, so as to have 4 measurements in 4 different positions. from the barycentric calculation, a direction pointing towards the source was determined at each measurement point. the device was moved by a predetermined spatial step according to the determined direction.
• Figure 7 illustrates the progress from the device to the source. The source is considered to have been reached when the direction pointing towards the source varies greatly under the effect of a small displacement of the device.
• the previously described embodiments make it possible to determine a direction pointing towards an irradiating source.
• the directional information can then be used to estimate a distance between the device and the source.
• the intensity of the radiation decreases proportionally to the inverse square of the distance. If r designates a distance between an irradiating source and the device, the intensity of the radiation, between the device and the source, varies in ;. Intensity can correspond to a flux (number of particles per unit time) or to a fluence rate (number of particles per unit time and area). The count rate of each detector varies linearly with the intensity of the radiation emitted by the source. Knowing the direction in which the source is located, by implementing one of the embodiments described above, it is possible to estimate a distance between the device and the source, by moving, a known distance, relative to the source, and by measuring the variation of the counting rate of at least one detector. The movement relative to the source is performed in the direction pointing to the source. The knowledge of the distance traveled, combined with the measurement of the counting rates before and after the displacement, makes it possible to evaluate the distance between the device and the source.
• d can be predetermined or measured.
• the user wearing the device moves, along the direction pointing towards the source, a predetermined distance, for example 50 or 60 cm, which corresponds to one step.
• the device is equipped with a geolocation unit 23, allowing a measurement of the distance d traveled between the positions r 2 and r .
• the processing unit 20 is programmed to estimate r ⁇ by solving (4).
• Curve c) represents the evolution of the statistical threshold as a function of the distance.
• the difference in counting rates N 2 —N ⁇ can be considered as statistically representative when N 2 —N 1 >(1 —a)/2/V 2 .
• N 2 crosses the statistical threshold at a threshold distance d s of 6.5 m from the source.
• the differential measure N 2 allows an estimation of the distance between the detector and the source over a distance range between 0 and 6.5 m, that is to say up to the threshold distance. This corresponds to a relative difference of about 6%.
• Figure 9B represents the relative deviation (gray levels) as a function of the variation of distance — r 2 (axis of abscissas - unit meter - r 2 ⁇ r ), and this for different distances from the source (axis of ordinates - unit meter). The more increases, the greater the variation in distance — r 2 must be high to observe a relative difference greater than the statistical fluctuations.
• This figure shows that the distance r ⁇ - r 2 is preferably greater than 20 cm to obtain a relative deviation greater than 6%, the latter corresponding to the statistical threshold: cf.
• Figure 9A Figure 9A.
• Figures 9A and 9B show that beyond a certain threshold distance, the estimated distance should not be considered valid due to the associated uncertainty.
• the threshold distance depends on the detector, in particular the sensitivity, and can be determined experimentally as described in connection with FIG. 9A.
• the processing unit can be programmed to invalidate the estimated distance if the latter is greater than the predetermined threshold distance .
• the detector closest to the source will preferably be used, the latter not being subjected to the attenuation of the radiation emitted by the source due to the other detectors.
• FIG. 10 schematizes the main steps of a method for determining a direction between a measuring device and a source, as well as possibly an estimation of the distance between the source and the device.
• Step 100 measurement of the counting rates of the detectors forming the device.
• step 120 can be implemented directly.
• Step 110 this step is notably implemented when the device comprises only 2 detectors.
• the device undergoes a rotation around the isobarycentre O and perpendicular to the support. A measurement of the counting rate of each detector is carried out.
• Step 120 Depending on the measurements performed during step 100 and any step 110, calculation of the barycenter of the positions of each detector weighted by the counting rates respectively measured by each detector.
• Step 130 Depending on the position of the barycenter resulting from step 120, determination of a direction pointing towards the source.
• Step 140 displacement of the device in the direction resulting from step 130 by a predetermined distance or any distance.
• Step 150 when the displacement distance of step 140 is arbitrary, estimation of the distance by the geolocation unit or using the inertial navigation unit, from a starting position.
• Step 160 measurement of the count rate of a detector of the device.
• Step 170 from the measurement resulting from step 160 and from the measurement of the detector performed before the displacement, for example during step 100 (or 110), estimation of a distance between the source and the device.
• Step 180 comparison of the estimated distance with the threshold distance d s , so as to validate or invalidate the measurement.
• the threshold distance has been previously determined.
• the device described above can be used while being worn by a user. It can also be mounted on an autonomous vehicle. In this case, the direction determined by the device is transmitted to a control unit of the vehicle, so that the vehicle can be directed according to this direction.
• the use of a vehicle is suitable for hostile environments, for example in the presence of contamination or high irradiation.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Life Sciences & Earth Sciences (AREA)
• High Energy & Nuclear Physics (AREA)
• Molecular Biology (AREA)
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• Electromagnetism (AREA)
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• 2021
  • 2021-12-27 FR FR2114564A patent/FR3131391B1/fr active Active
• 2022
  • 2022-12-25 WO PCT/EP2022/087838 patent/WO2023126381A1/fr not_active Ceased
  • 2022-12-25 EP EP22839379.9A patent/EP4457531A1/de active Pending
  • 2022-12-25 US US18/724,956 patent/US20250102610A1/en active Pending

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