EP4025935A1

EP4025935A1 - Dosimeter

Info

Publication number: EP4025935A1
Application number: EP20761622.8A
Authority: EP
Inventors: Sree Bash Chandra DEBNATH; Julien DARREON; Carole Fauquet; Didier Tonneau; Agnès TALLET
Original assignee: Aix Marseille Universite; Centre National de la Recherche Scientifique CNRS; Institut Jean Paoli and Irene Calmettes
Current assignee: Aix Marseille Universite; Centre National de la Recherche Scientifique CNRS; Institut Jean Paoli and Irene Calmettes
Priority date: 2019-09-02
Filing date: 2020-09-01
Publication date: 2022-07-13
Also published as: WO2021043773A1; CA3149864A1; US20220291397A1; FR3100343A1; FR3100343B1; US11914083B2

Abstract

This dosimeter comprises: - a transducer material (30) able, when it is excited by a secondary ionising radiation, to generate photons or electric charges, - an amplifying layer (34) able, in response to its excitation by primary ionising radiation, to generate the secondary ionising radiation. This amplifying layer (34) comprises a first and second amplifying sublayer stacked one on top of the other. The first and second amplifying sublayers are composed of at least 70%, by mass, of at least a first and a second material respectively, the atomic numbers of which are greater than or equal to twenty-nine. The atomic number of the first material being less than the atomic number of the second material. The first sublayer is interposed between the second sublayer and the transducer material.

Description

DOSIMETER

The invention relates to a dosimeter.

[002] Such dosimeters are used, for example, in the field of the characterization of materials, such as welds, or in the medical field and, in particular, in radiotherapy or in hadrontherapy. For example, such dosimeters are used to adjust the dimensions of ionizing radiation in the treatment of small cancerous tumors.

[003] Such a dosimeter is for example described in the following article: Zhihua XIE et Al: "Ultracompact x-ray dosimeter based on scintillators coupled to a nano-optical antenna", Opitics Letters, vol. 42, n ° 7, 04/01/2017, page 1361-1364. This article is hereinafter referred to as "Article A1" in this application.

The dosimeter described in this article A1 is particularly advantageous in that it has both:

- a very small footprint, and

- good sensitivity for low energy ionizing radiation.

[005] In this application, low-energy ionizing radiation denotes ionizing radiation whose energy is less than 100 keV. Conversely, "high energy radiation" denotes ionizing radiation with an energy greater than 100 keV and preferably greater than 1 MeV.

[006] On the other hand, the dosimeter of article A1 is not suitable for measuring high-energy ionizing radiation because it has too low a sensitivity to this type of ionizing radiation.

[007] The state of the art is also known from:

- EP0851242A2,

- EP0703469A2,

- Zhihua Xie et Al: "Ultracompact x-ray dosimeter based on scintillators coupled to a nano-optical antenna", Optics Letters, vol. 42, n ° 7, 03/28/2017,

- JP2019028034A,

- W002 / 14904A1.

The invention aims to provide a dosimeter which has improved sensitivity to ionizing radiation and, in particular, to ionizing radiation. high energy. It therefore relates to a dosimeter for measuring the intensity of a primary ionizing radiation in accordance with claim 1.

[009] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example and made with reference to the drawings in which:

- Figure 1 is a schematic illustration, partially in cross section, of a dosimeter;

- Figure 2 is a schematic illustration of an optical amplifier used in the dosimeter of Figure 1;

- Figures 3 and 4 are partial schematic illustrations, in longitudinal section, of other possible embodiments of the dosimeter of Figure 2;

- Figure 5 is a schematic illustration of a semiconductor dosimeter.

In these figures, the same references are used to designate the same elements. In the remainder of this description, the characteristics and functions well known to those skilled in the art are not described in detail.

[0011] Chapter I: Examples of embodiments:

[0012] Figure 1 shows a dosimeter 2, known by the term "fiber dosimeter", for measuring the intensity of incident ionizing radiation 3. Ionizing radiation 3 is also called "primary ionizing radiation". Here, the dosimeter 2 is described in the particular case where the ionizing radiation 3 is an X-ray of high energy. Dosimeter 2 comprises:

- an optical fiber 4,

- a part 6 sensitive to radiation 3 located at the distal end of the optical fiber 4,

- an optical amplifier 8 connected to the opposite end of fiber 4,

- a photon sensor 10 connected to an output of amplifier 8, and

- a unit 12 for processing the signals measured by the sensor 10.

Optical fiber 4 is a single-mode or multimode optical fiber capable of guiding photons along a propagation axis 12. Here, the axis 12 extends parallel to an X direction of an XYZ orthogonal coordinate system. Here, fiber 4 is a commercial fiber capable of transmitting any wavelength from near ultraviolet to infrared. The bandwidth of the fiber is chosen centered on the luminescence wavelength of the material 30 described later. For example, fiber 4 is here designed to guide light having a wavelength A _f between

1360 nm and 1625 nm. For example, in this embodiment, the wavelength A _f is equal to 1550 nm. In this description, as is customary in the technical field of optical fibers, the term “light” is used in a broad sense which designates any electromagnetic wave guided by the optical fiber. In particular, the meaning of the term "light" is not limited to visible light.

[0014] Fiber 4 comprises in order:

- a heart 14 inside which the light propagates,

- a sheath 16 which envelops the heart 14, and

- a protective coating 18 which surrounds the sheath 16.

Here, the material in which the core 14 is made is a material chosen to have low propagation loss at the wavelength A _f .

The spatial resolution of the measurement performed with the dosimeter 2 is also linked to the diameter D _i4 of the heart 14. For example, for an application of the dosimeter

2 in radiotherapy, a spatial resolution of 100 µm is considered sufficient at the present time. The diameter D _i4 of the core 14 is generally less than 110 μm or 70 μm and, in the case of a single-mode optical fiber, often less than 20 μm. The diameter D _i4 is generally also greater than 1 µm or 5 µm. Here, the diameter D _i4 is equal to 50 µm and the fiber is therefore a multimode fiber.

The sheath 16 is made of a material whose refractive index, relative to the refractive index of the core 14, makes it possible to effectively guide and maintain the light inside the core 14. The thickness of the sheath 16 is also chosen to guide and maintain the light inside the core 14. Thus, the light propagates essentially inside the core 14. The thickness of the sheath 16 is conventionally greater than 50 μm or 100 pm. The outer diameter D _i6 of the sheath 16 is usually between 1.5D _M and 5D _i4 or between 2D _i4 and 3D _i4 . Here, the diameter D _i6 is equal to 125 µm.

The coating 18 serves to protect the sheath 16 and the core 14. It is for example made of polymer. The thickness of the coating 18 is conventionally greater than 50 µm or 100 µm. To obtain a small space requirement for the sensitive part 6 of the dosimeter 2, the _{outer diameter D i8} of the coating 18 is chosen to be less than 500 μm or 250 μm. The diameter D _i8 is often between 1.5D _I6 and 3D _I6 . Here, the diameter D _i8 is equal to 220 µm. The fiber 4 extends from a proximal end, attached to an input of the amplifier 8, to a distal end attached to the sensitive part 6. Typically, the length of the fiber 4 between its proximal ends and distal is greater than 20 cm or 50 cm and usually less than 10 m or 5 m. For example, the length of fiber 4 is equal to 1.50 m.

The distal end of the fiber 4 comprises a light entry face 20 formed in the heart 14. In this first embodiment, the face 20 is a planar face perpendicular to the X direction and which extends over the entire cross section of the core 14. The face 20 preferably has a large number of symmetries of revolution about the axis 12. In this application, a large number of symmetries of revolution denotes a number of symmetries. of revolution greater than 4, 6 or 10 and, preferably, an infinite number.

The face 20 is here a circular face, the diameter of which is equal to the diameter of the heart 14.

In addition to the face 20, the distal end also includes a face 22 which immediately surrounds the face 20 and which is produced in the sheath 16. Here, this face 22 is a planar annular face which completely surrounds the face 20 and which is located in the same plane as the face 20. This face 22 therefore extends over the entire cross section of the sheath 16. The inner and outer diameters of this face 22 are therefore equal, respectively, to the diameters D _i4 and D _I6 .

The sensitive part 6 comprises a transducer material which generates photons when it is excited by the primary and / or secondary ionizing radiation. Here, this transducer material is a luminescent material 30. This luminescent material 30 is entirely covered with a reflective layer 32, itself entirely covered with an amplifying layer 34.

The luminescent material 30 here has the shape of a drop fixed to the distal end of the fiber 4. Preferably, this drop has a large number of symmetries of revolution about the axis 12. The top of this drop, furthest from face 20, is located on axis 12.

Here, the luminescent material 30 directly and entirely covers the face 20. In addition, here, it also covers more than 50% or 70% of the surface of the face 22

The luminescent material 30 has, in this embodiment, the shape of a part of an ellipsoid, this ellipsoid part being between: - a section plane perpendicular to its length, and

- its vertex furthest from this section plane.

In the illustration of Figure 1, the section plane passes through the center of the ellipsoid. This section plane coincides with the plane containing the faces 20 and 22.

The maximum thickness of the luminescent material 30 corresponds here to the distance, along the axis 12, between the face 20 and the top of the drop. This maximum thickness is between 0.1D _I4 and 3D _I6 , where D _i4 and D _i6 are the diameters, respectively, of the core 14 and of the sheath 16. In this embodiment, the maximum thickness of the luminescent material 30 is for example between D _i4 and 2D _I6 . The maximum thickness of the luminescent material 30 is therefore between 50 μm and 250 μm.

[0028] Here, the luminescent material 30 is a mixture of a polymer 38 and of scintillator 40. The spatial resolution of the measurement carried out with the dosimeter 2 also depends on the size and the structure of the scintillator used. For example, here the scintillator 40 is in the form of an aggregate of scintillator grains. For example, the greatest length of one of these scintillator grains is less than 40 µm or 10 µm. Here, the average length of each scintillator grain is 10 µm.

The polymer 38 is here a polymer capable of polymerizing and thus bonding the luminescent material 30 on the distal end of the fiber 4. For example, it is the polymer PMMA (Polymethyl methacrylate), or any other resin photosensitive used in microelectronics, or a polymer glue, or cyanolite.

The scintillator 40 is chosen according to the wavelength A _f of the light that is to be generated in response to exposure to ionizing radiation 3. For example, in the case of a wavelength At _f equal to 1550 nm, the following scintillator 40 is suitable: ln _x Ga _(ix) As, where the index X is equal to 0.45. This scintillator is sensitive to X-rays and, in particular, to low-energy X-rays.

Layer 32 is able to reflect the light emitted by the luminescent material 30 to return it, as much as possible, to the face 20. For this purpose, the layer 32 is made of a material reflecting the light generated by the material. luminescent 30. Here, by "· reflecting the light" is meant the fact that the layer in question reflects at least Z% of the light at the wavelength A _f , where Z is a number greater than 50 and, of preferably greater than or equal to 90 or 95. In addition, the layer 32 is made of a material transparent to radiation. ionizer which excites the luminescent material. Here, the term “transparent to ionizing radiation” denotes the fact that the layer in question allows at least Y% of the incident ionizing radiation to pass through, where Y is a number strictly greater than 50 and, preferably, greater than or equal to 80, 90. or 95. For example, the layer 32 is made of aluminum.

The thickness of the layer 32 is small, that is to say less than 10 µm and, preferably, less than 1 µm or 300 nm. The thickness of layer 32 is also generally greater than 20nm or 50nm. Here, the thickness of the layer 32 is between 100nm and 300nm. For example, the thickness of the layer 32 is equal to 150 nm.

The layer 32 is deposited on the luminescent material 30 by a conventional deposition process such as by spraying or by evaporation. Depending on the deposition process used, a very thin bond layer is first deposited on the luminescent material 30. This bond layer is generally less than 20 nm thick. For example, the grip layer is made of titanium or chrome. Such a tie layer has not been shown in the figures to simplify them.

Layer 34 is able to interact with the primary ionizing radiation 3 to, in response, generate secondary ionizing radiation of lower energy. If the primary radiation 3 is of high energy, the secondary ionizing radiation is composed mainly of electron-positron pairs or of high energy X-rays emitted by the Compton effect. In the case where the secondary radiation is an X-ray, this phenomenon is known as X-ray fluorescence and even better known by the acronym XRF ("X-Ray Fluorescence"). Because of the presence of the layer 34, the luminescent material 30 is exposed, in addition to the ionizing radiation 3, to the secondary ionizing radiation generated by the layer 34. Thus, in response to the same intensity of the ionizing radiation 3, luminescent material 30 generates more photons than if layer 34 were omitted. Layer 34 therefore amplifies the number of photons generated, which increases the sensitivity of dosimeter 2.

It is accepted that the secondary ionizing radiation generated by the layer 34 increases:

- according to the atomic number of the atoms of the material which composes it, and

- the thickness e ₃ of this layer 34. To significantly increase the number of photons generated by the luminescent material 30, it has been determined that the thickness e ₃ 4 must be greater than 15 μm and, preferably, greater than 30 μm or 50 μm.

Furthermore, in this embodiment, to minimize the size of the sensitive part 6, the thickness e ₃ 4 is chosen so that the outer diameter of the sensitive part 6 in any plane perpendicular to the axis 12 does not much exceed the diameter D _I8 . Thus, the thickness e ₃₄ is here chosen less than (Dis - D _I4 ) / 2. For example, the thickness of the layer 34 is therefore chosen in this embodiment to be less than 85 μm. Here, the thickness e ₃₄ is chosen to be less than 60 μm. In the figures, to improve their readability, the thicknesses of the different layers have not been shown to scale.

[0039] It was also determined that the atomic number from which the increase in the number of photons generated by the luminescent and significant material, is No. 29, that is, the one corresponding to copper. Hereinafter, the term "heavy" denotes any material whose atomic number is greater than or equal to 29. Here, since the phenomenon of fluorescence by X-ray is generally greater in heavy materials than in other materials, the atomic number of the material which makes up the layer 34 is preferably greater than or equal to 79, that is to say to that corresponding to gold.

Finally, preferably, the material chosen to make the layer 34 should allow deposition in the form of a layer as simple as possible to achieve.

For example, copper, silver, gold and lead are metals which satisfy the various constraints set out above. Here, by way of illustration, the layer 34 is therefore made of gold or of lead or of silver or of an alloy of these metals. In this description, the expression “an element made of material X” means that material X represents at least 70% or 90% or 95% of the mass of this element. Thus at least 70% and, preferably at least 90% or 95%, of the mass of the layer 34 is formed from these heavy materials. Here the layer 34 is made of gold and its thickness e ₃₄ is equal to 50 μm.

Layer 34 is deposited directly on layer 32, for example, by the same deposition methods as those described in the particular case of layer 32. It can also be deposited by other faster deposition methods and less expensive like electrolysis or an "electroless" deposit. So, possibly, a very thin bond layer, less than 20 nm thick, is interposed between layer 32 and layer 34.

Here, the wavelength A _f used corresponds to a wavelength conventionally used in the telecommunications industry. Thus, the amplifier 8 is preferably an optical amplifier conventionally used in the telecommunications industry to amplify and repeat the light which propagates inside the optical fibers without having for this to transform the light to be amplified into a electrical signal. An exemplary embodiment of such an amplifier is illustrated in FIG. 2.

The amplified optical signal is sent to the sensor 10 via an optical fiber 40. The sensor 10 is able to transform the light intensity received into an electrical signal processed by the processing unit 12. The sensor 10 is for example a photodiode or a photon sensor.

Unit 12 receives the electrical signal generated by sensor 10 and, in response, controls one or more electrical devices. For example, the controlled electrical device is a screen which displays the intensity of the ionizing radiation 3 measured by the dosimeter 2. The controlled electrical device can also be the source of the ionizing radiation 3, which makes it possible, for example, to slaving the intensity of this ionizing radiation 3 to an intensity setpoint recorded in the unit 12. FIG. 2 represents an exemplary embodiment of the optical amplifier 8. In this embodiment, the amplifier 8 is an erbium doped fiber amplifier. Such an amplifier performs optical pump amplification using EDFA ("Erbium Doped Fiber Amplifier") technology. For this, amplifier 8 includes:

an input port 50 connected to a laser source which generates an optical pumping signal at a wavelength A _e equal, here, to 980 nm,

- an input port 52 connected to the proximal end of fiber 4 to receive the light to be amplified,

- an output port 54 through which the pump signal is discharged, and

- an output port 56 directly connected to the input of sensor 10.

The amplifier 8 also comprises an optical coupler 58 comprising an input 60 connected to the port 50, an input 62 connected to the port 52 and an output 64 connected to a first end of a fiber 66 doped with erbium. The coupler 58 combines the optical signals received on its inputs 60 and 62 and restores, on the output 64, an optical signal combining the two optical signals received at its inputs.

The second end of the fiber 66 is connected to an input 68 of an optical divider 70 which restores on an output 72 the optical pumping signal and on an output 74 the amplified optical signal. The outputs 72 and 74 are connected, respectively, to the output ports 54 and 56.

FIG. 3 represents an optical fiber 80 and a sensitive part 82 which can be used instead, respectively, of the optical fiber 4 and of the sensitive part 6. The optical fiber 80 is identical to the fiber 4 except that the entry face 20 is replaced by a conical entry face 84 and the face 22 is replaced by a frustoconical face 86.

The face 84 is, in this embodiment, identical to the face 20 except that it has the shape of a cone of revolution, the base of which is circular and the top is centered on the axis 12. The face 84 therefore always has a very large number of symmetries of revolution around axis 12.

The distance along the axis 12 between the base of the cone and its apex is typically greater than or equal to 0.5D _I4 or greater than or equal to D _i4 or greater than or equal to 2D _i4 . This distance is also typically less than 5D _M OR 10D _I4 . Here, this distance is equal to 150 µm.

The frustoconical face 86 is typically located in the extension, in a straight line, of the face 84 going in the X direction. Here, the face 86 therefore extends, by widening gradually, from the base of the cone. from the face 84 to the interface between the sheath 16 and the coating 18.

To manufacture the face 84, the heart 14 and at least part of the sheath 16 are cut to form a point. Such a tip shape is for example obtained by chemical attack. For example, to obtain such a tip, the end of the fiber 80 is dipped in a first bath, for example of sulfuric acid, which removes the coating 18 and bares the sheath 16. Then, the end exposed. bare of the sheath 16 is dipped in a second bath which dissolves the sheath 16 and the core 14 then gradually withdrawn from this second bath to obtain the desired tip shape.

The sensitive part 82 is identical to the sensitive part 6 except that the luminescent material 30, the reflective layer 32 and the amplifying layer 34 are replaced, respectively, by a luminescent material 90, a reflective layer 92 and an amplifying layer 94. The luminescent material 90 is identical to the luminescent material 30 except that it covers the whole of the entry face 84 and, a part, of the frustoconical face 86. Here, the part of the frustoconical face 86 covered by the luminescent material 90 may represent less than 50% or less than 70% of the surface of the frustoconical face 86.

The reflective layer 92 is identical to the reflective layer 32 except that the latter completely covers the luminescent material 90. Here, the layer 92 also covers the portion of the frustoconical face 86 which is not covered by the luminescent material 90.

The amplifying layer 94 is identical to the amplifying layer 34 except that it completely covers the reflective layer 92 and not the reflective layer 32. In addition, in this embodiment, its thickness e ₉₄ is adjusted so that, at the level of the distal end of the fiber 80, the outside diameter of the sensitive part 82 is equal to the diameter D _i8 of the coating 18.

FIG. 4 shows an optical fiber 100 and a sensitive part 102 that can be used instead, respectively, of the optical fiber 4 and of the sensitive part 6. The optical fiber 100 is identical to the fiber 4 except that the entry face 20 and the face 22 are replaced, respectively, by an entry face 104 and a face 106.

In this embodiment, the sensitive part 102 is not located at the level of the distal end of the fiber 100 but at a non-zero distance from this end in the X direction. For example, this distance is included between 1 mm and 10 cm from the distal end. For this, a trench is dug in the outer periphery of the fiber 100. The bottom of this trench opens out inside the core 14 of the fiber 100 and forms the inlet face 104. The cross section of the bottom of this trench , in a plane containing the axis 12 and parallel to the X and Z directions, has a triangular profile. The vertex of this triangle is the point of the bottom of the trench closest to the axis 12. The sides of this triangle located to the right and to the left of the vertex form inclined faces which extend to the interface between the sheath 16 and coating 18.

The sensitive part 102 is identical to the sensitive part 6 except that the luminescent material 30, the reflective layer 32 and the amplifying layer 34 are replaced, respectively, by a luminescent material 110, a reflective layer 112 and an amplifying layer 114 . The luminescent material 110 is identical to the luminescent material 30 except that it completely covers the entry face 104. In addition, here, the luminescent material 110 fills the bottom of the trench up to the level of the interface between the sheath 16 and the coating 18.

The reflective layer 112 and the amplifying layer 114 are identical, respectively, to the reflective layer 32 and to the amplifying layer 34 except that they cover, respectively, the luminescent material 110 and the reflective layer 112. Here, the thickness of the amplifying layer 114 is adjusted so that on the side opposite to the axis 12, it is flush with the outer periphery of the coating 18.

The teaching given in the previous embodiments can also be applied to dosimeters in which the sensitive part comprises a transducer material which generates electric charges when it is excited by the secondary ionizing radiation instead of photons. Such dosimeters are referred to herein as "semiconductor dosimeters". They are also known by the term “electronic sensor” or “electronic detector” of the PIN or transistor or Schottky junction type. By way of illustration, FIG. 5 represents a possible example of an arrangement of such a dosimeter 160. In this exemplary embodiment, the architecture of the dosimeter 160 differs from that described with reference to FIG. 2 of application WO2017198630. mainly by the fact that it additionally comprises an amplifying layer. Thus, for more details on the architecture of the dosimeter 160 or the various variants of such an architecture, the reader can consult this request.

The dosimeter 160 is a semiconductor sensor. More precisely, the dosimeter 160 comprises a sensitive part 170 situated on an axis 171 along which the primary ionizing radiation propagates. Here, it is centered on the axis 171. More precisely, in this embodiment, the sensitive part 170 is a cylinder of revolution whose axis of revolution coincides with the axis 171.

The sensitive part 170 has an input face 172 located in a vertical plane parallel to the X and Y directions of an orthogonal reference mark XYZ, where the Z direction is parallel to the axis 171. The face 172 is directly exposed to primary ionizing radiation 166 incident. The sensitive part 170 also comprises an exit face 174 situated in another vertical plane perpendicular to the axis 171. The portion of the beam 166 which has not interacted with the sensitive part 170, emerges from the dosimeter 160 via the face 174 and forms a beam 168.

The sensitive part 170 comprises a transducer material capable of generating electrical charges when it is traversed by the primary ionizing radiation. In this embodiment, the transducer material is a depletion region 176 also referred to as a "space charge zone". This region 176 produces charge carriers of a first type and charge carriers of a second type when it is crossed by the ionizing radiation 166. This region 176 is located between the face 172 and a boundary represented by a line. dotted line parallel to the Y direction in Figure 5.

In this example, the region 176 comprises a semiconductor layer 178 and a conductive layer 180 deposited directly on the face of the layer 178 facing the incident ionizing radiation 166. The face 172 is here formed by the outer face of the layer 180 facing the incident ionizing radiation 166. The face 174 of the sensitive part 170 is formed by the face of the layer 178 turned on the side opposite to the face 172.

[0067] Region 176 is located in the region of layer 178 in contact with conductive layer 180. The combination of layers 178 and 180 forms a rectifying junction and more specifically a Schottky diode in this embodiment.

The semiconductor material used to make the layer 178 comprises two energy bands known by the terms, respectively, of "valence band" and "conduction band". In the case of semiconductor materials, these two energy bands are separated from each other by a forbidden band better known as the "gap". Preferably, the semiconductor material used to produce the layer 178 is a large-gap semiconductor material, that is to say a semiconductor material having a gap whose value is at least twice greater than the silicon gap value. Typically, the gap of the semiconductor material used for the layer 178 is therefore greater than 2.3 eV.

Here, the layer 178 is made of silicon carbide SiC-4H. Here, the semiconductor layer 178 is additionally doped. For example, when the semiconductor layer 178 is made of silicon carbide, a P doping can be obtained. by implantation of boron atoms and, alternatively, an N doping can be obtained by implantation of nitrogen atoms.

In this embodiment, the layers 178 and 180 extend transversely beyond the sensitive part 170 to form a peripheral part 184 which completely surrounds the sensitive part 170. Unlike the sensitive part 170, the peripheral part 184 is not crossed by the primary radiation 166. The portion 186 of the conductive layer 180 which extends beyond the sensitive part 170 forms a first electrode which collects the charge carriers of the first type produced by the region 176. .

Here, the thickness of the semiconductor layer 178 in the peripheral part forms the side walls of a blind hole 188, the bottom of which coincides with the face 174.

Finally, only in the peripheral part 184, the face of the semiconductor layer 178 located on the side opposite to the face 172 is covered with a conductive layer 190. The conductive layer 190 forms a second electrode which collects the carriers. charge of the second type produced by region 176.

In this embodiment, the conductive layer 180 also acts as an amplifying layer. For this purpose, it is composed of at least 70%, by mass, of conductive material whose atomic number is greater than or equal to twenty nine and its thickness is greater than 15 μm and, preferably, greater than 30 μm or 50. pm. The conductive layer 180 is for example made of metal such as copper, zinc or gold. Its operation and design can be deduced from the explanations given in the previous embodiments.

In addition, in this embodiment, the layer 180 is formed by stacking one on top of the other of several sub-layers each made of a different heavy material. The thickness of each of these sublayers is, for example, greater than 15 µm or 30 µm or 50 µm. In this case, preferably, the sublayers are stacked on top of each other in increasing order of the atomic numbers of the heavy materials of which they are made. The sublayer composed of the heavy material with the lowest atomic number is closest to the transducer material. For example, the amplifying layer 180 comprises, in order, a sublayer 200 of gold then a sublayer 202 of copper. In this case, when the primary ionizing radiation arrives on the outer sublayer 200, this sublayer 200 absorbs the primary ionizing radiation and re-emits a secondary ionizing radiation of lower energy than primary ionizing radiation. This secondary radiation is better suited to excite the next sublayer 202. When the next sublayer 202 is energized, it in turn generates secondary ionizing radiation of even lower energy. The energy of the secondary ionizing radiation and thus gradually reduced before reaching the transducer material. This makes it possible to increase the sensitivity of the dosimeter to the incident primary radiation 166.

[0075] Chapter II: Variants:

[0076] Variants of the optical fiber:

Other shapes are possible for the entry face. For example, the entry face can be frustoconical. The entry face is not necessarily a cone of revolution either. For example, as a variant, the entry face is a pyramidal cone. The entry face can also have other shapes than a conical or frustoconical shape. For example, the entry face may have the shape of a cylinder of revolution, the end of which is intersected by a plane inclined with respect to the axis 12. Preferably, in this case, the axis of the cylinder of revolution. coincides with the axis 12. Other embodiments for the coating 18 are possible. In particular, it will be noted that the smaller the diameter D _i8 , the more it is possible to reduce the size of the sensitive part. Thus, alternatively, the outer diameter of the coating 18 is less than 100 µm or 80 µm or 60 µm. In this case, the shape of the entry face and the thicknesses of the luminescent material, of the reflecting layer and of the amplifying layer are adapted so that the maximum outside diameter of the sensitive part remains less than or close to the diameter Dis.

What has been described here makes it possible to manufacture dosimeters having a spatial resolution ranging from 50 nm to 300 μm. For example, for applications where the space constraints are relaxed, it is possible to use optical fibers, in which the outer diameter of the cladding 18 is greater than 250 µm or 500 µm. Similarly, for those applications where the constraints in terms of size are relaxed, the diameter of the core 14 can be increased and, for example, be greater than 120 μm or 150 μm.

Variants of the sensitive part:

In this chapter, the variants are mainly described in the particular case of a fiber dosimeter. However, the lessons given in this case particular are transposable without particular difficulty to the case of a semiconductor dosimeter.

In variants, the luminescent material also covers part of the sheath 16.

In variants, the luminescent material covers only part of the light entry face. For example, the luminescent material is a graft of luminescent material only deposited on the tip of the entry face 84 as described, for example, in article A1. Thus, in this embodiment, the luminescent material does not cover the entire face 82 and does not cover the sheath 16. It is possible to use other luminescent materials generating light at wavelengths A _{f other} than those between 1360 nm and 1625 nm. In this case, the optical fiber must be adapted to have propagation losses that are as low as possible at the chosen _{wavelength A f.} For example, what has been described in this application can be applied to the case of luminescent materials generating light at a wavelength between 350 nm and 2000 nm or even outside this range of wavelengths. Other shapes are possible for the luminescent material 30. For example, in the embodiment of Figure 1, the shape of the luminescent material is a hemisphere centered on the axis 12. In another embodiment embodiment, the maximum thickness of the luminescent material 30, in the embodiment of FIG. 1, is between D _i4 and D _I6 . In another embodiment, the maximum thickness of the luminescent material 30 is less than diameter D _i4 and greater than 1 µm.

Other scintillators 40 are known and can be used in place of scintillator 40. The scintillator chosen depends in particular on the desired _{wavelength A f.} By way of example, other scintillators which can be used with X-rays include barium platinocyanide, ZnS alloy doped with silver (Ag), Ag ₂ S alloy doped with Europium (Eu ), the Gd ₂ 0 ₂ S alloy doped with Europium (Eu), the ZnWOs alloy, the Csl alloy doped with Europium (Eu), quantum dots ... etc.

In a particular embodiment, the luminescent material is integrated inside the heart 14 of the optical fiber. For example, the distal end of the core 14 of the optical fiber is doped with a dopant which converts secondary ionizing radiation into light. For example, this dopant is Erbium. In this embodiment, the reflective layer is directly deposited on this distal end doped and the amplifying layer is deposited on the reflective layer. For example, for this, the outer face of the doped distal end of the core 14 is exposed and the reflecting and amplifying layers are deposited on this exposed face. In this case, the optical fiber does not have a light entry face since the light is directly generated by the dopant inside the core of the optical fiber. The dosimeter thus obtained maintains excellent spatial resolution along the X and Y directions perpendicular to the incident ionizing radiation 3. It will be noted that what has been described above concerning the amplification using layer 34 remains valid. . The addition of the amplifying layer increases the signal emitted by the doped end of the optical fiber. In another embodiment, the entire core 14 is doped with a dopant such as Erbium. Such a fiber is then known by the term “doped fiber”. In this configuration, the reflecting and amplifying layers are deposited, for example, on a portion of the doped core 14. For example, this portion corresponds to the distal end of the heart 14. This latter embodiment makes it possible to obtain excellent spatial resolution but mainly in the Y direction.

Other materials can be used to make the reflective layer 32. For example, the layer 32 can also be made from another metal or even using a stack of thin dielectric layers sized to reflect light.

When the amplifying layer is sufficient on its own to cause the generation of a sufficient quantity of photons which penetrate inside the core 14, then the reflective layer 32 is omitted. For example, as a variant, the dosimeter comprises only an amplifying layer of lead or gold or copper or silver with a thickness greater than 15 µm.

In another embodiment, when the amplifying layer sufficiently reflects the light generated by the luminescent material, then in this case too, the reflective layer can be omitted. This is for example the case when the amplifying layer is made of metal. For example, in a simplified embodiment, a single layer of gold, silver or copper, with a thickness greater than 15 μm, fulfills both the functions of the amplifier and reflector layers.

The amplifying layer can be formed from other heavy materials than gold and lead. For example, the amplifying layer is made by a heavy metal selected from the group consisting of silver (Ag), tungsten (W), titanium (Ti), cobalt (Co), chromium (Cr), gold (Gold) and lead (Pb) . The amplifying layer can also be made from any other heavy material commonly deposited in the electronics industry even if it is not a metal.

In another embodiment, the amplifying layer is made from an alloy of several heavy materials and, for example, from an alloy of several heavy metals.

As illustrated in the particular case of the embodiment of FIG. 5, the amplifying layer is not necessarily formed from a single layer of heavy material. This also applies to the case of fiber dosimeters. Preferably, in the case of fiber dosimeters, the heavy metal of the sublayer closest to the scintillator comprises an element of the scintillator. For example, if the scintillator is ZnS, then the sublayer closest to this scintillator is made of Zinc. This allows the ultimate metallic layer closest to the scintillator to generate X photons that resonate with the scintillator's absorption.

Layer 34 is mainly made of heavy materials, that is to say that at least 70% and, preferably, at least 80% or 90% or 95%, of the mass of this layer 34 is formed of heavy materials. The remaining proportion of layer 34 may, however, be formed by other materials with atomic number less than 29.

If there is no particular size constraint, the thickness e ₃ 4 of the amplifying layer 34 can be chosen to be much greater than the limit (D _I8 - D _I4 ) / 2. For example, the thickness e ₃₄ can be chosen to be greater than 250 μm or 500 μm or 1 millimeter.

In another embodiment, the amplifying layer covers only a part of the reflective layer 32. For example, the amplifying layer covers only the tip of the layer 32.

What has been described in the particular case where the ionizing radiation 3 is an X-ray, applies to any type of ionizing radiation. For example, what has been described here can be adapted to the gamma ray or to charged particle radiation. Radiation from charged particles is, for example, radiation from alpha, beta +, beta particles, carbon ions or protons. In these cases, the material of the amplifying layer 34 and / or the luminescent material 30 must be adapted to the incident ionizing radiation. More precisely, the material of the layer 34 must generate, in response to the incident ionizing radiation, a secondary radiation capable of exciting the luminescent material. Thus, it is not necessary for the luminescent material itself to be directly excitable by the incident ionizing radiation. In fact, it suffices for it to be sensitive to the secondary ionizing radiation generated by the amplifying layer 34. By way of illustration, in the case where the incident ionizing radiation is a gamma ray of high energy, it is possible to choose a material. Luminescent only sensitive to X-rays. In this case, the material of the layer 34 is a material which generates lower energy rays when exposed to the high energy gamma ray. This latter embodiment is even advantageous in the case where several sensitive parts of several dosimeters are located next to each other because it limits the interference between these different sensitive parts.

[0098] Other variants:

Many other embodiments of the dosimeter 160 are possible. For example, the depletion region 176 can also be formed as a PN diode or a PiN diode or by the depletion region of a field effect transistor. In particular, the addition of an amplifying layer in a semiconductor dosimeter applies to the different architectures of such a semiconductor dosimeter described in application WO2017198630A1.

What has been described here also applies to the case where the primary ionizing radiation is ionizing radiation of low energy, In the latter case, the secondary ionizing radiation is generally an X-ray of lower energy, such as a low energy x-ray.

[00101] Other embodiments of amplifier 8 are possible. For example, alternatively amplifier 8 is an SOA ("Semiconductor Optical Amplifer") amplifier.

[00102] Alternatively, measuring the intensity of ionizing radiation simply consists of detecting that the intensity of the ionizing radiation exceeds a predetermined threshold.

In a particular embodiment, the sensitive parts of several identical dosimeters are grouped together in rows and columns to form a matrix of several sensitive parts. In this case, each sensitive part measures the intensity of a pixel of an image of the spatial distribution of the intensity of the primary ionizing radiation. In a particular embodiment, the amplifying layer of the semiconductor dosimeter comprises a single amplifying layer. In this case, the amplifying layer of the semiconductor dosimeter does not include a stack of several amplifying sublayers.

Chapter III: Advantages of the embodiments described:

[00106] Incident ionizing radiation, especially when it is of high energy, reacts with the atoms of the material of the amplifying layer 34 to generate secondary ionizing radiation of lower energy. The secondary ionizing radiation then in turn reacts with the transducer material to generate light or electrical charges. Thus, due to the presence of the amplifying layer, the transducer material is exposed to a greater amount of low energy ionizing radiation than in the absence of the amplifying layer. It therefore produces a greater quantity of light or electric charges for the same intensity of the incident ionizing radiation than in the absence of this amplifying layer. The sensitivity of the dosimeter is therefore increased.

The fact that the amplifying layer is itself formed by a stack of several amplifying sublayers of decreasing atomic numbers as one gets closer to the transducer material makes it possible to further increase the sensitivity of the dosimeter compared to the case of a single-layer amplifying layer.

The principle of the amplifying layer is to adapt the primary ionizing radiation by transforming it into secondary ionizing radiation of lower energy which is more absorbed by the transducer material. The dosimeter thus provides a stronger signal. This principle of amplification using an amplifying layer made of heavy materials can therefore be used to increase the signal of any type of dosimeter sensitive to ionizing radiation such as a beam of electrons, positrons, X photons of high or low energy.

The combination of the amplifying layer with a reflective layer makes it possible to further increase the sensitivity of the dosimeter.

[00110] The fact of using an aluminum layer less than 300 nm thick as a reflective layer makes it possible to substantially increase the sensitivity of the dosimeter without substantially increasing the size of its sensitive part. [00111] The fact that the thickness of the amplifying layer is less than 50 μm or 100 μm makes it possible to keep a very small space requirement for the fiber dosimeter. Under these conditions, in particular, the dimensions of the sensitive part remain compatible with endoscopy techniques. For example, it is then possible to place the sensitive part of the fiber dosimeter directly inside the tumor to be irradiated. This therefore makes it possible to better control the doses of radiation applied to the tumor. In addition, the sensitive part of the dosimeter practically does not attenuate the ionizing radiation which must touch the tumor to be irradiated. Thus, such a small size of the sensitive part and of the distal end of the optical fiber makes it possible to practically not disturb the treatment.

[00112] The use of gold or lead to make the amplifying layer simplifies the manufacture of the dosimeter because these two metals can easily be deposited in successive layers by conventional manufacturing methods. [00113] The fact that the luminescent material covers the entire entry face increases the sensitivity of the fiber dosimeter.

[00114] The fact that the entry face extends over more than 20 µm or 100 µm in the X direction also makes it possible to increase the sensitivity of the fiber dosimeter.

[00115] The fact of shaping the entry face so that at least 50% of the photons generated by the luminescent material penetrate inside the core of the optical fiber further increases the sensitivity of the fiber dosimeter. The fact that the input face adopts the shape of a cone or a truncated cone increases the proportion of photons which penetrate into the heart of the optical fiber relative to the quantity of photons generated by the material luminescent. In addition, since it is a cone or a truncated cone having a large number of symmetry of revolution, the sensitivity of the fiber dosimeter is practically independent of the angular position of its sensitive part around the axis. 12.

The fact that the luminescent material is uniformly distributed around the axis 12 of the optical fiber makes it possible to obtain a fiber dosimeter which is not very sensitive to the angular position of its sensitive part around this axis 12.

Claims

1. Dosimeter for measuring the intensity of primary ionizing radiation, this dosimeter comprising:

- a transducer material (30; 90; 110; 176) capable, when it is excited by secondary ionizing radiation, to generate photons or electric charges, the number of photons or charges generated being representative of the intensity primary radiation,

- an amplifying layer (34; 94; 114; 180) capable, in response to its excitation by the primary ionizing radiation, to generate the secondary ionizing radiation which excites the transducer material, this amplifying layer:

- being deposited on the transducer material,

- being composed of at least 70%, by mass, of material with an atomic number greater than or equal to twenty nine, characterized in that:

- the thickness of this amplifying layer is greater than 15 μm,

- the amplifying layer comprises at least a first and a second amplifying sublayers stacked one on the other,

- the first and second amplifying sublayers are composed of at least 70%, by mass, respectively, of at least a first and a second material whose atomic numbers are greater than or equal to twenty nine, the atomic number of first material being less than the atomic number of the second material, and

- the first sublayer is interposed between the second sublayer and the transducer material.

2. Dosimeter according to claim 1, wherein the dosimeter comprises:

- an optical fiber (4; 80; 100) comprising a core (14) capable of guiding light, and

- The transducer material is a luminescent material (30; 90; 110) capable, when it is excited by the secondary ionizing radiation, to generate the light guided by the core of the optical fiber.

3. Dosimeter according to claim 2, wherein the dosimeter comprises a reflective layer (32; 92; 112) interposed between the luminescent material and the amplifying layer, this reflective layer:

- covering the luminescent material,

- being made of a material whose atomic number is lower than the atomic number of the material used to make the amplifying layer,

- being able to reflect the light generated by the luminescent material towards the core of the optical fiber, and

- being transparent to secondary ionizing radiation.

4. Dosimeter according to claim 3, wherein the reflective layer is made of aluminum and its maximum thickness is less than 300 nm.

5. Dosimeter according to any one of the preceding claims, wherein the thickness of the amplifying layer (34; 94; 114) is less than 100 µm or 50 µm.

6. Dosimeter according to any one of the preceding claims, in which the second amplifying sublayer (34; 94; 114) is made of gold or of lead or of an alloy composed of more than 90%, by mass, by these two metals.

7. Dosimeter according to claim 2, wherein the optical fiber has a light input face (20; 84; 104) inside the core (14) of this optical fiber and the luminescent material (30; 90; 110) covers at least part of this entry face.

8. The dosimeter of claim 7, wherein the luminescent material (30; 90; 110) covers the entire light entry face.

9. The dosimeter of claim 8, wherein the inlet face (80; 100) extends, in a direction parallel to the axis of the optical fiber, over a distance greater than 20 µm or 100 µm.

10. Dosimeter according to any one of claims 7 to 9, wherein the inlet face (80; 100) is shaped so that more than 50% of the photons generated by the luminescent material penetrate into the heart of the optical fiber.

11. Dosimeter according to claim 10, wherein the entry face (80) of the light comprises a conical or frustoconical face having at least four symmetries of revolution around the axis of the optical fiber and located in the extension of the heart. of optical fiber.

12. Dosimeter according to any one of claims 7 to 11, wherein the luminescent material (30; 90; 110) has more than ten symmetries of revolution about the axis of the optical fiber.

13. Dosimeter according to any one of claims 7 to 12, wherein the outer diameter of the optical fiber is less than 500 µm.

14. Dosimeter according to any one of claims 7 to 13, wherein the dosimeter comprises an optical amplifier (8) connected to one end of the optical fiber (4) and capable of amplifying the light generated by the luminescent material.

15. The dosimeter of claim 1, wherein:

- the transducer material is a semiconductor material (176) capable, when excited by the secondary ionizing radiation, to generate electric charges, and

- The dosimeter comprises electrodes (186, 190) for picking up the electric charges produced by the semiconductor material, the intensity of the current between these electrodes being representative of the intensity of the primary ionizing radiation which passes through this semiconductor material.