METHOD FOR MANUFACTURING A FLUX DETECTORE OF A FIRST AND A SECOND IONISING RADIATION

A method for manufacturing a detector of a first and a second incident ionizing radiation including determining the abscissa em of a point of intersection between a first and a second curve, with the first and second curves representing the evolution of the number of photons or electrical charges generated per second by a transducing material as a function of the total thickness of an amplifying material when the transducing material is irradiated, through this thickness of transducing material, by the first and second incident ionizing radiation, respectively; then selecting the total thickness of amplifying material between 0.9 em and 1.1 em and producing the detector with the selected thickness of amplifying material.

The invention relates to a method for manufacturing a detector for detecting the flows of a first and a second incident ionizing radiation that differ from one another only by the fact that the median energies of the ionizing particles in the first and second incident ionizing radiation are equal to a first and a second value, respectively, with the second value differing from the first value by at least 500 keV. The invention also relates to a flow measurement method using the detector manufactured by this method and the flow detector manufactured by this method.

Such detectors are used, for example, in the field of characterizing materials, such as welds, or in the medical field and, in particular, in radiotherapy in brachytherapy or in hadron therapy. For example, such detectors are used to adjust the dimensions of the field of ionizing radiation in the case of treatments of small cancerous tumors.

Such a detector is described, for example, in application JP 2011/191255 A. The detector described in JP 2011/191255 A is advantageous in that the calibration of the detector hardly varies over a wide range of possible energies for the incident ionizing radiation to be measured. In other words, the amplitude of the measured flow hardly varies as a function of the energy of the incident ionizing radiation. By virtue of this, the measurements carried out for incident ionizing radiation with different energies are directly comparable without needing to perform a complex correction of the measurements as a function of the energy of the measured incident ionizing radiation.

To this end, JP 2011/191255 A teaches superimposing stacks, on top of one another, that are each formed by one or more thicknesses of amplifying materials and by a thickness of transducing material. The amplifying material used in JP 2011/191255 A is mainly gold. When a detector is designed according to the teaching of JP 2011/191255 A to measure high-energy incident ionizing radiation, then the total thickness of heavy material traversed by the ionizing radiation to be measured is significant, i.e., typically more than several millimeters. This increases the bulk of this detector and makes it complex to manufacture.

WO 99/18130 A1, US 2017/184730 A1 and EP 0703469 A2 are also known from the prior art.

In this application, “low-energy ionizing radiation” refers to ionizing radiation with energy below 100 keV. Conversely, “high-energy ionizing radiation” refers to ionizing radiation with energy above 100 keV and, preferably, above 500 keV or 1 MeV.

The invention aims to propose a manufacturing method that allows to obtain a detector, the calibration of which hardly varies over a wide range of energies while using a thinner amplifying material than in JP 2011/191255 A. Therefore, the invention relates to a manufacturing method in accordance with claim1.

The invention also relates to a measurement method in accordance with claim6.

The invention also relates to a detector in accordance with claim8.

In these figures, the same references are used to designate the same elements. Throughout the remainder of this description, the features and functions that are well known to a person skilled in the art are not described in detail.

In this description, detailed examples of embodiments are firstly described in Chapter I with reference to the figures. Then, in Chapter II, alternative embodiments of these embodiments are presented. Finally, the advantages of the various embodiments are presented in chapter III.

Chapter I: Examples of Embodiments:

FIG.1shows a detector2, known as “fiber dosimeter”. The detector2in this case is designed to measure, with a constant calibration, high-energy incident ionizing radiation flows. The energies of the ionizing radiation to be measured are systematically included in an extended energy range [Vmin; Vmax]. An energy range is said to be “extended” in this case when the difference between the energies Vminand Vmaxis greater than 500 keV and, preferably, greater than 1 MeV or 4 MeV. The energy of ionizing radiation designates the median energy of the ionizing particles of this radiation. The median energy is expressed in electron-volts.

The ionizing radiation to be measured with the detector2are identical to each other except that they differ in terms of their energy. In this case, the incident ionizing radiation is always high-energy X-rays. In addition, this ionizing radiation propagates in the same direction of propagation parallel to a direction Z of an orthogonal XYZ coordinate system. The direction Z is vertical in this case.

Hereafter, the numerical references 3minand 3maxdenote the incident ionizing radiation with energies that are equal to Vminand Vmax, respectively. Throughout this text, the incident ionizing radiation on the detector2is also called “primary ionizing radiation”.

In this embodiment, the radiation 3minand 3maxrespectively corresponds to the lowest energy and highest energy radiation that the detector2must measure.

The detector2comprises:an optical fiber4;a part6sensitive to the ionizing radiation located at the distal end of the optical fiber4;an optical amplifier8connected to the proximal end of the fiber4;a photon sensor10connected to an output of the amplifier8; anda unit12for processing the signals measured by the sensor10.

The fiber4is a single-mode or multi-mode optical fiber able to guide photons along a propagation axis12. In this case, the axis12extends parallel to the direction X of the orthogonal XYZ coordinate system. For example, the fiber4is a fiber capable of transmitting any wavelength from near ultraviolet to infrared. The bandwidth of the fiber is selected so as to be centered on the luminescence wavelength of the material30described below. For example, the fiber4in this case is designed to guide light with a wavelength λfranging between 1,360 nm and 1,625 nm. In this embodiment, the wavelength λfis equal to 1,550 nm. In this description, as it is used in the technical field of optical fibers, the term “light” is used in a broad sense that designates any electromagnetic wave guided by the optical fiber. In particular, the meaning of the term “light” is not limited to visible light.

The fiber4comprises, in the following order:a core14, inside which the light propagates;a sheath16, which surrounds the core14; anda protective coating18, which surrounds the sheath16.

The material from which the core14is produced is a material that is selected in order to exhibit low propagation losses at the wavelength λf.

The spatial resolution of the measurement carried out with the detector2is also linked to the diameter D14of the core14. For example, the diameter D14is less than 110 μm or 70 μm and, in the case of a single-mode optical fiber, is often less than 10 μm. The diameter D14is generally also greater than 1 μm or 5 μm. In this case, the diameter D14is equal to 50 μm and for this reason the fiber is a multi-mode fiber.

The sheath16is made of a material for which the refractive index, relative to the refractive index of the core14, allows the light to be guided and effectively maintained inside the core14. The thickness of the sheath16is also selected to guide and maintain the light inside the core14. Thus, the light basically propagates inside the core14. The thickness of the sheath16is conventionally greater than 50 μm or 100 μm. The outer diameter D16of the sheath16usually ranges between 1.5 D14and 5 D14or between 2 D14and 3 D14. In this case, the diameter D16is equal to 125 μm.

The coating18is used to protect the sheath16and the core14. It is made of polymer, for example. The thickness of the coating18is conventionally greater than 50 μm or 100 μm. In order to obtain a limited footprint for the sensitive part6of the detector2, the outer diameter D18of the coating18is selected so as to be less than 1 mm or 500 μm. The diameter D18often ranges between 1.5 D16and 3 D16. In this case, the diameter D18is equal to 220 μm.

Typically, the length of the fiber4between its proximal and distal ends is greater than 20 cm or 50 cm and usually less than 100 m. For example, the length of the fiber4is equal to 1.50 m.

The distal end of the fiber4comprises a light inlet face20produced in the core14. In this embodiment, the face20is a flat circular face perpendicular to the direction X and with a diameter that is equal to the diameter of the core14. The face20preferably has a large number of rotational symmetries about the axis12. In this application, a large number of rotational symmetries refers to more than four, six or ten rotational symmetries and, preferably, an infinite number.

In addition to the face20, the distal end also comprises a face22that immediately surrounds the face20and that is produced in the sheath16. In this case, this face22is a flat annular face that completely surrounds the face20and that is located in the same plane as the face20. The inner and outer diameters of this face22are therefore equal to the diameters D14and D16, respectively.

The sensitive part6comprises a transducing material30that generates photons when it is excited by the primary and/or secondary ionizing radiation. In this case, this transducing material is a luminescent material. This transducing material30is entirely covered with a reflective layer32, which itself is entirely covered with an amplifying layer34.

The transducing material30in this case assumes the shape of a droplet fixed to the distal end of the fiber4. Preferably, this droplet has a large number of rotational symmetries about the axis12. The apex of this droplet, furthest from the face20, is located on the axis12.

In this case, the material30directly and entirely covers the face20and more than 50% or 70% of the surface of the face22.

In this embodiment, the transducing material30assumes the shape of part of an ellipsoid, with this part of an ellipsoid being between:a cutting plane perpendicular to its length; andits apex furthest from this cutting plane.

In the illustration ofFIG.1, the cutting plane coincides with the plane containing the faces20and22.

The maximum length of the transducing material30in this case corresponds to the distance, along the axis12, between the face20and the apex of the droplet. This maximum length ranges between 0.1 D14and 3 D16. In this embodiment, the maximum length of the transducing material30ranges, for example, between D14and 2 D16. The maximum length of the transducing material30therefore ranges between 50 μm and 250 μm.

In this case, the transducing material30is a mixture of a polymer38and of a scintillator40. The spatial resolution of the measurement carried out with the detector2also depends on the size and the structure of the scintillator that is used. For example, the scintillator40is 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. In this case, the average length of each scintillator grain is equal to 10 μm.

The polymer38in this case is a polymer capable of polymerizing and thus bonding the transducing material30on the distal end of the fiber4. For example, it is PMMA (polymethyl methacrylate) polymer, or any other photosensitive resin used in microelectronics, or a polymer adhesive, or cyanolite.

The scintillator40is selected as a function of the wavelength λfof the light intended to be generated in response to exposure to the ionizing radiation to be measured. In the case of a wavelength λfequal to 1,550 nm, for example, the following scintillator40is suitable: InxGa(1-x)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.

The layer32reflects the light emitted by the transducing material30in order to return it, as far as possible, toward the face20. “Reflecting light” refers to the fact that the layer32reflects at least Z % of the light at the wavelength λf, where Z is a number greater than 50 and, preferably, greater than or equal to 90 or 95. Moreover, in this case, the layer32is made of a material transparent to ionizing radiation that excites the transducing material30. In this case, “transparent to ionizing radiation” refers to the fact that the layer32allows through at least Y % of the incident ionizing radiation, where Y is a number strictly greater than 50 and, preferably, greater than or equal to 80, 90 or 95. For example, the layer32is made of aluminum.

The thickness of the layer32is low, i.e., less than 10 μm and, preferably, less than 1 μm or 300 nm. The thickness of the layer32is also generally greater than 20 nm or 50 nm. In this case, the thickness of the layer32ranges between 100 nm and 300 nm. For example, the thickness of the layer32is equal to 150 nm.

The layer34interacts with the primary ionizing radiation in order to generate a lower energy secondary ionizing radiation in response. This secondary radiation is, for example, made up of lower energy X-rays and/or lower energy ionizing particles. The secondary radiation re-emitted by the layer34depends on the material used to manufacture the layer34and on the energy of the incident primary radiation. By way of an indication, if the layer34is made of lead (atomic number82), if the energy of the primary ionizing radiation is greater than 6 MeV, the secondary ionizing radiation is mainly made up of electron-positron pairs. If the primary ionizing radiation ranges between 1 MeV and 6 MeV, the secondary ionizing radiation is mainly made up of electrons and high-energy X-rays emitted by the Compton effect. If the primary ionizing radiation ranges between 10 keV and 1 MeV, the secondary ionizing radiation is mainly made up of high-energy X-rays emitted by the photoelectric effect. In this latter case, the phenomenon is known as “X-ray fluorescence” and is even more widely known using the acronym XRF.

Due to the presence of the layer34, the transducing material30is exposed, in addition to the primary ionizing radiation, to the secondary ionizing radiation generated by the layer34. In addition, the energy of the secondary radiation is lower than the incident ionizing radiation and is therefore absorbed more by the transducing material30, which also increases its emission. Thus, in response to the same intensity of the primary ionizing radiation, the transducing material30generates more photons than if the layer34was omitted. The layer34therefore amplifies the number of photons generated, which enhances the sensitivity of the detector2.

It is acknowledged that the flow of the secondary ionizing radiation generated by the layer34increases:as a function of the atomic number of the atoms of the material it is made up of; andof the thickness e34of this layer34.

In this embodiment, the layer34is traversed twice by the primary ionizing radiation that propagates parallel to the direction Z. Under these conditions, the total thickness eTof amplifying material traversed by the primary ionizing radiation is equal to 2e34.

In order to significantly increase the number of photons generated by the transducing material30, it has been determined that the thickness eTmust be greater than 15 μm and, preferably, greater than 30 μm or 50 μm.

Moreover, in this embodiment, in order to minimize the bulk of the sensitive part6, the thickness eTis also preferably less than 1.5 mm or 1 mm. In addition, as explained in detail hereafter, the thickness eTis selected so that the calibration of the detector2is the same when the radiation 3minis measured as when the radiation 3maxis measured. InFIG.1, the thicknesses of the various layers have not been shown to scale.

It has also been determined that the atomic number at which point the increase in the number of photons generated by the transducing material is significant, is No. 29, i.e., that corresponding to copper. Hereafter, the term “heavy” refers to any material with an atomic number that is greater than or equal to 29. In addition, in this embodiment, in order for the thickness eTto remain less than 1 mm, the layer34is mainly made of a heavy material, the atomic number of which is greater than or equal to 74 (tungsten) and, preferably, greater than or equal to 79, i.e., to that corresponding to gold.

In this description, the expression “an element mainly made of material X” means that the material X represents at least 70% or 90% or 95% of the mass of this element.

Finally, preferably, the material selected to produce the layer34must allow a deposit to be implemented in the form of a layer that is as easy to produce as possible. For example, gold and lead are metals that meet the various constraints set forth above. In this case, by way of an illustration, the layer34is entirely made of lead.

In this case, the wavelength λfthat is used corresponds to a wavelength conventionally used in the telecommunications industry. Thus, the amplifier8is, preferably, an optical amplifier conventionally used in the telecommunications industry for amplifying and repeating the light that propagates inside optical fibers, yet without having to convert the light to be amplified into an electrical signal. An embodiment of such an amplifier is illustrated inFIG.2of the application filed on Jan. 9, 2020 under the number PCT/EP 2020/074364.

The amplified optical signal is sent to the sensor10via an optical fiber40. The sensor10measures a physical quantity proportional to the number of photons received per second. This number of photons received per second constitutes a measurement proportional to the flow of ionizing particles of the primary ionizing radiation. To this end, in this case, the sensor10converts the received light intensity into an electrical signal processed by the processing unit12. The received light intensity is proportional to the number of photons received per second. The sensor10is a photodiode or a photon counter, for example.

The unit12receives the electrical signal generated by the sensor10and, in response, controls one or more electrical appliances. For example, the controlled electrical appliance is a screen that displays the intensity of the primary ionizing radiation measured by the detector2. The controlled electrical appliance also can be the source of the primary ionizing radiation, which allows, for example, the intensity of this primary ionizing radiation to be set to an intensity setpoint recorded in the unit12.

FIG.2shows a method for manufacturing and using the detector2in the particular case where the values Vminand Vmaxare equal to 2 MeV and 4.5 MeV, respectively.

The method begins with a phase50of designing the detector2.

During a step52, values V1and V2are acquired. These values V1and V2define the range over which the calibration of the detector2hardly varies as a function of the energy of the primary ionizing radiation to be measured. In order to produce the detector2, the values V1and V2must be close to the values Vminand Vmax, respectively. For example, in this case, the value V1is selected in the range [0.7 Vmin; 1.1 Vmin] and the value V2is selected in the range [0.9 Vmax; 1.3 Vmax]. Preferably, the values V1and V2are selected to be equal to the values Vminand Vmax, respectively. In this case, the values V1and V2are therefore equal to 2 MeV and 4.5 MeV, respectively.

Then, during a step53, the amplifying material to be used to produce the layer34is selected. In this case, lead is selected.

During a step54, the curve60(FIG.3) is acquired. The curve60shows the evolution of the number of photons generated per second by the transducing material30as a function of the thickness eTof amplifying material traversed by the radiation 3min. InFIG.3, the abscissa axis is graduated in millimeters and the ordinate axis is graduated by the number of photons per second, denoted “p/s”.

In this case, the curve60is acquired experimentally. To this end, the measurement test bench70shown inFIG.4is used. This test bench70comprises:a detector72for detecting the flow of the primary ionizing radiation that is identical to the detector2except that the sensitive part6is replaced by a sensitive part78;a source74able to alternately emit the radiation 3minand 3maxto be measured by the detector72;a support76that supports the sensitive part78of the detector72;a protective wall80for dividing the test bench70into two distinct zones, namely a zone exposed to the radiation 3minand 3maxand in which the source74and the sensitive part78are located, and a zone protected from the ionizing radiation, in which the amplifier8, the sensor10and the processing unit12of the detector72are located.

The source74is, for example, a Linear Particle Accelerator (LINAC).

The sensitive part78is identical to the sensitive part6except that the amplifying layer34is omitted.

Finally, this measurement test bench70also comprises a set of several detachable lead plates, each with different thicknesses. InFIG.4, only one plate82of this set is shown. During the measurements, only one of the plates of this set is deposited onto the sensitive part78. This is shown inFIG.4in the particular case of the plate82. The plate82mainly extends in a horizontal plane perpendicular to the direction of propagation of the radiation 3minand 3max. The plate82is deposited directly onto the sensitive part78.

In order to construct the curve60, the source74is adjusted to emit the radiation 3min. During each measurement, the radiation 3minis generated by the source74and the detector72measures the flow of this radiation.

If a lead plate is deposited onto the sensitive part78, the detector72measures the number of photons per second generated by the material30after the radiation 3minhas passed through this lead plate.

In this case, a first measurement is carried out in the absence of a lead plate deposited onto the sensitive part78. This allows the point of the curve60to be acquired that corresponds to a zero thickness eTof amplifying material.

Then, measurements are taken for various thicknesses of the lead plate. To this end, the detachable lead plate is replaced by a lead plate with a different thickness each time. This allows different points of the curve60to be acquired for different thicknesses of the lead plate.

The curve60is then constructed by interpolation between the various measured points. For example, the interpolation is a polynomial interpolation per part.

During a step90, the curve62(FIG.3) is acquired. The curve62represents the evolution of the number of photons per second generated by the material30as a function of the thickness eTtraversed by the radiation 3max. The curve62is acquired as described in the case of the curve60except that the source74is adjusted to emit the radiation 3maxinstead of the radiation 3min.

During a step92, the abscissa emof the point of intersection between the curves60and62is determined. In this case, the abscissa emis less than or equal to 600 μm and greater than or equal to 450 μm. In this example, the abscissa emis equal to 0.5 mm. This point of intersection is particularly advantageous since this means that when the thickness eTis equal to or close to the value of the abscissa em, then the calibration of the detector2is independent of the energy of the radiation 3minand 3max.

In the case of the sensitive part6, the thickness eTis equal to 2e34since the primary ionizing radiation to be measured successively traverses the layer34, then the material30a first time, then the layer34a second time. When traversing the layer34the first and the second time, the layer34interacts with the primary ionizing radiation each time. The result of each of these interactions is that the layer34produces secondary ionizing particles with lower energy than the energy of the primary ionizing particles of the primary ionizing radiation. These secondary ionizing particles can be photons, electrons or positrons. These secondary ionizing particles are emitted in all directions by the layer34. Thus, even the second time traversing the layer34produces secondary ionizing particles that will then interact with the material30.

The thickness e34in this case is selected so as to be equal to em/2, i.e., equal to 300 μm. Under these conditions, the number of photons per second generated by the material30is identical both for the radiation 3minand for the radiation 3max. In addition, it has also been seen that the sensitivity of the detector2is substantially constant as long as the energy of the primary ionizing radiation to be measured using this detector2ranges between the values Vminand Vmax. Thus, the calibration of the detector2hardly varies as long as the energy of the primary ionizing radiation remains between the energy levels Vminand Vmax.

Once the thickness e34has been determined, the design phase ends and the method continues with a phase100of manufacturing the detector2.

During a step102, the stack of the thickness eTof amplifying material and of the thickness of transducing material is produced. For example, a liquid mixture of the polymer38and the scintillator40is prepared. Next, the distal end of the fiber4is soaked in this liquid mixture and then removed. The droplet of the liquid mixture that remains adhered to the distal end of the fiber4is then dried, for example, by placing it in a heated furnace for a few seconds. The droplet then becomes solid and forms the transducing material30.

Next, the layer32is deposited onto the transducing material30by a conventional deposition method such as by spraying or by evaporation. Depending on the deposition method that is implemented, a very thin adhesion layer is firstly deposited onto the transducing material30. The thickness of this adhesion layer is generally less than 20 nm. For example, the adhesion layer is made of titanium or chromium.

Finally, the layer34is deposited directly onto the layer32, for example, using the same deposition methods as those described in the particular case of the layer32. It also can be deposited using other faster and less expensive deposition methods, such as electrolysis or “electroless” deposition. Optionally, a very thin adhesion layer, that is less than 20 nm thick, is interposed between the layer32and the layer34.

The thickness e34of the deposited layer34in this case is equal to that selected during the design phase50, i.e., equal to 300 μm.

Thus, in the direction Z of propagation of the incident radiation to be measured, a stack of amplifying material and of transducing material is acquired, in which stack the thickness eTof amplifying material traversed by the ionizing radiation to be measured is equal to em.

Then, during a step104, the proximal end of the fiber4is optically connected to the amplifier8and the amplifier8is optically connected to the sensor10.

During a step106, the sensor10is connected to the processing unit12.

The manufacture of the detector2is then completed and a use phase110can begin.

During the phase110, the detector2is used to measure the flow of multiple primary ionizing radiation levels, the energies of which are systematically included in the range [Vmin; Vmax].

Thus, during a step112, the sensitive part6of the detector2is positioned relative to the source of the primary ionizing radiation to be measured, as described with reference toFIG.1. Thus, the axis12extends horizontally and the ionizing radiation to be measured propagates parallel to the direction Z.

The sensitive part6is also placed, for example, inside an object to be treated or to be imaged with the primary ionizing radiation. The sensitive part6also can be placed in front of or behind this object to be treated.

Then, during a step114, the primary ionizing radiation is emitted and, at the same time, the detector2measures the number of photons per second generated by the material30. This measured number of photons per second is then multiplied, for example, by the exposure time of the object to this incident ionizing radiation and by the energy of this incident ionizing radiation in order to obtain a dose of the incident ionizing radiation applied to this object during step114. For example, during the first execution of step114, the primary ionizing radiation used is the radiation 3min

Then, during a step116, the adjustment of the primary ionizing radiation source is modified in order to emit another primary ionizing radiation with different energy. This different energy ranges between the values Vminand Vmax. Next, step114is executed again but this time with this other primary ionizing radiation. For example, during a second execution of step114, the primary ionizing radiation used is the radiation 3max.

Given that the detector2has been designed so that its calibration is the same for the radiation 3minas for the radiation 3max, the measurements of the detector2carried out during step114do not need to be corrected or are simpler to correct in order to compensate for a variation in the calibration of the detector2as a function of the energy of the primary ionizing radiation that is used.

The description provided above applies to amplifying materials other than lead. Although heavy materials such as gold, lead and tungsten are preferred for the applications targeted for the detector2, the description provided above also applies to other heavy materials with an atomic number that is less than 74. In particular, experiments were carried out in order to verify that there is always a point of intersection between curves similar to curves60and62, but constructed for other materials. In order to illustrate this, the graph ofFIG.5shows curves130and132acquired experimentally as described above but using a set of copper plates with different thicknesses instead of the set of lead plates. The curves130and132correspond to the 2 MeV and 4.5 MeV energies, respectively.

FIG.6shows experimentally measured curves134and136in the case where a set of aluminum plates with different thicknesses is used instead of the set of lead plates. The curves134and136correspond to the 2 MeV and 4.5 MeV energies, respectively. In this case, the thickness emis equal to 2,100 μm.

It should be noted that the value of the abscissa emincreases when the atomic number of the amplifying material that is used decreases. It has been determined that the abscissa emis less than 1 mm only if the amplifying material is mainly made of materials with atomic numbers that are greater than 74 or 79.

The teaching provided in the particular case of a fiber dosimeter also can be applied to the detectors in which the sensitive part comprises a transducing material that generates electrical charges when it is excited by the secondary ionizing radiation instead of photons. Such detectors are called “semi-conductor dosimeter”. They are also known using the term “electronic sensor” or “electronic detector” of the PIN or transistor or Schottky junction or avalanche diode type.

By way of an illustration,FIG.7shows a possible example of an arrangement of such a detector160. In this embodiment, the architecture of the detector160differs from that described with reference to FIG. 2 of application WO 2017/198630 mainly by the fact that it also comprises an amplifying layer. Thus, for further details concerning the known features of the architecture of the detector160or the various alternative embodiments of such an architecture, the reader can consult this application WO 2017/198630.

The detector160comprises a sensitive part170located on an axis171, along which the primary ionizing radiation propagates. The sensitive part170is centered on the axis171. More specifically, in this embodiment, the sensitive part170is a rotational cylinder, the axis of revolution of which coincides with the axis171.

The sensitive part170has an inlet face172located in a vertical plane parallel to directions X and Y of an orthogonal XYZ coordinate system, where the direction Z is parallel to the axis171. The face172is directly exposed to the incident primary ionizing radiation166. The sensitive part170also comprises an outlet face174located in another vertical plane perpendicular to the axis171. The portion of the beam166that has not interacted with the sensitive part170, emerges from the detector160via the face174and forms a beam168.

The sensitive part170comprises a transducing material able to generate electrical charges when it is traversed by the primary ionizing radiation. In this embodiment, the transducing material is a depletion region176also called “space charge zone”. This region176produces a first type of charge carriers and a second type of charge carriers when it is traversed by the radiation166. This region176is located between the face172and a limit173represented by a dotted line parallel to the directions X and Y.

In this example, the detector160comprises a semi-conductive layer178and a conductive layer180directly deposited onto the face of the layer178oriented toward the incident ionizing radiation166. The face172in this case is formed by the outer face of the layer180oriented toward the incident ionizing radiation166. The face174of the sensitive part170is formed by the face of the layer178oriented away from the face172.

The region176is located in the region of the layer178in contact with the conductive layer180. The association of the layers178and180forms a junction with a rectifying effect, and more specifically a Schottky diode in this embodiment.

The semi-conductor material used to produce the layer178comprises two energy bands known under the terms “valence band” and “conduction band”, respectively. In the case of semi-conductor materials, these two energy bands are separated from each other by a band gap more commonly known as “gap”. Preferably, the semiconductor material used to produce the layer178is a wide-gap semi-conductor material, i.e., a semi-conductor material having a gap with a value that is at least two times greater than the value of the gap of the silicon. Typically, the gap of the semi-conductor material used for the layer178is therefore greater than 2.3 eV.

In this case, the layer178is made of SiC-4H silicon carbide. Furthermore, the semi-conductor layer178is also doped. For example, when the semi-conductor layer178is made of silicon carbide, P-doping can be obtained by implanting boron atoms and, alternatively, N-doping can be obtained by implanting nitrogen atoms.

In this embodiment, the layers178and180transversely extend beyond the sensitive part170in order to form a peripheral part184that completely surrounds the sensitive part170. Unlike the sensitive part170, the peripheral part184is not traversed by the radiation166. The portion186of the conductive layer180that extends beyond the sensitive part170forms a first electrode that collects the first type of charge carriers produced by the region176.

In this case, the thickness of the semi-conductor layer178in the peripheral part forms the side walls of a blind hole188, the bottom of which coincides with the face174.

Finally, only in the peripheral part184, the face of the semi-conductor layer178located on the side opposite the face172is covered with a conductive layer190. The conductive layer190forms a second electrode that collects the second type of charge carriers produced by the region176.

In this embodiment, the conductive layer180also acts as an amplifying layer. To this end, it is mainly made of heavy metals and its thickness e180is greater than 15 μm and, preferably, greater than 30 μm or 50 μm. The conductive layer180is, for example, made of metal such as copper, zinc, tungsten, gold or lead.

In this embodiment, the layer180is formed by stacking several sub-layers on top of each other that are each made of a different heavy material. The thickness of each of these sub-layers is, for example, greater than 15 μm or 30 μm or 50 μm. In this case, preferably, the sub-layers are stacked on one another in the ascending order of the atomic numbers of their constituent heavy materials. The sub-layer made up of the heavy material with the smallest atomic number is closest to the transducing material. For example, the amplifying layer180in this case comprises, in this order, a sub-layer200of gold and then a sub-layer202of copper. In this case, when the primary ionizing radiation reaches the outer sub-layer200, this sub-layer200absorbs the primary ionizing radiation and reemits a lower energy secondary ionizing radiation than the primary ionizing radiation. This secondary radiation is better adapted to exciting the next sub-layer202. When the next sub-layer202is excited, it in turn generates secondary ionizing radiation with even lower energy. The energy of the secondary ionizing radiation is thus gradually reduced before reaching the transducing material. This allows the sensitivity of the dosimeter to the radiation166to be enhanced.

Furthermore, the thickness e180of the layer180is selected so that the sensitivity of the detector160is the same when it measures the flow of the radiation 3minand when it measures the flow of the radiation 3max. To this end, the thickness e180is selected by implementing the same methodology as that described with reference toFIG.2. In particular, curves similar to the curves60and62are acquired as described above except that the set of lead plates is replaced by a set of plates each comprising the sub-layer202of thickness e202and the sub-layer200of thickness e200. The plates of this set differ from one another only by the thickness e200, which is different for each plate. The thickness e202is constant, for example, and is selected before step54. The abscissa emand the total thickness eTare then determined as described above.

In this case, the total thickness eTof amplifying material traversed by the radiation 3minand 3maxis equal to the thickness e180. Under these conditions, the thickness10) e180is selected between 0.9 emand 1.1 em. For example, the thickness e180is selected so as to be equal to em. The thickness e200is then taken as equal to e180-e202.

The operation of the layer180is deduced from the explanations provided in the previous embodiment.

Alternative Embodiments of the Transducing Material:

It is possible to use other luminescent materials generating light at wavelengths λfother than those included between 1,360 nm and 1,625 nm. In this case, the optical fiber must be adapted to exhibit propagation losses that are as low as possible at the selected wavelength λf. For example, the description provided in this application can be applied to the case of luminescent materials generating light at a wavelength ranging between 350 nm and 2,000 nm or even outside this wavelength range.

Other scintillators are known and can be used instead of the scintillator40. For example, any scintillator with a small ternary or quaternary gap based on GaAs or InP or GaSb emitting in the infrared domain is suitable. The selected scintillator particularly depends on the desired wavelength λf. By way of an example of other scintillators that can be used with X-rays, it is possible to cite barium platinocyanate, ZnS alloy doped with silver (Ag), Ag2S alloy doped with europium (Eu), Gd2O2S alloy doped with europium (Eu), ZnWO3alloy, Csl alloy doped with europium (Eu), quantum dots, etc.

In a particular embodiment, the luminescent material is integrated inside the core14of the optical fiber. For example, the distal end of the core14of the optical fiber is doped with a dopant that converts the secondary ionizing radiation into light. For example, this dopant is Erbium incorporated by ion implantation. In this embodiment, the reflective layer is deposited directly onto this doped distal end and the amplifying layer is deposited onto the reflective layer. For example, to this end, the outer face of the doped distal end of the core14is exposed and the reflecting and amplifying layers are deposited onto this exposed face. In this case, the optical fiber does not have a light inlet face since the light is directly generated by the dopant inside the core of the optical fiber.

In the embodiment ofFIG.1, the transducing material can assume other shapes such as part of a sphere or a cylinder. The dimensions of the scintillator grains of the transducing material30can be smaller. For example, as an alternative embodiment, the greatest length of the scintillator grains is less than 10 nm.

Alternative Embodiments of the Amplifying Material:

The amplifying layer can be mainly produced by a set of one or more heavy metals selected from the group made up of silver (Ag), zinc (Zn), copper (Cu), titanium (Ti), cobalt (Co), chromium (Cr), tungsten (W), gold (Au) and lead (Pb). Since the bulk of the sensitive part decreases when the atomic number of the one or more heavy materials used increases, the selection of the amplifying material to be used also can be restricted by a limit on the maximum bulk of the sensitive part. The amplifying layer also can be made of 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 of an alloy of several heavy materials and, for example, of an alloy of gold and lead.

As illustrated in the particular case of the embodiment ofFIG.7, the amplifying layer is not necessarily formed of 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 sub-layer closest to the scintillator comprises an element of the scintillator. For example, if the scintillator is ZnS, then the sub-layer closest to this scintillator is made of zinc. This allows the ultimate metal layer closest to the scintillator to generate X-ray photons in line with the absorption of the scintillator.

In a particular embodiment, the amplifying layer of the detector160comprises a single amplifying layer. In this case, the amplifying layer of the semi-conductor dosimeter does not comprise a stack of several amplifying sub-layers.

Other Alternative Embodiments of the Detector:

Other materials can be used to produce the reflective layer32. For example, the layer32also can be made of another metal or even using a stack of thin dielectric layers designed to reflect light.

When the amplifying layer is sufficient to on its own cause a sufficient amount of photons to be generated that penetrate inside the core14, then the reflective layer32is omitted. The reflective layer also can be omitted when the amplifying layer sufficiently reflects the light generated by the luminescent material. This is the case, for example, when the amplifying layer is made of metal. For example, in a simplified embodiment, a single layer made of gold, with a thickness greater than 15 μm, fulfils both the functions of the amplifying and reflecting layers.

In a particular embodiment, the sensitive parts of several identical dosimeters are grouped together in rows and columns in order 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.

The various alternative embodiments of the sensitive part6and of the fiber4described in the application filed under the number PCT/EP2020/074364 are applicable to the various embodiments described herein.

Numerous other embodiments of the detector160are possible. For example, the depletion region176also can 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 semi-conductor dosimeter applies to the various architectures of such a semi-conductor dosimeter described in application WO 2017/198630 A1.

As an alternative embodiment, the order in which the thicknesses of amplifying material and transducing material are stacked is reversed. In this case, the incident ionizing radiation firstly traverses the transducing material before reaching the amplifying material. The operation of such an embodiment is similar to that described above.

As an alternative embodiment, the detector can comprise layers of transducing material separated from one another by one or more layers of amplifying material.

30) As an alternative embodiment, the incident ionizing radiation to be measured propagates parallel to the axis12of the detector2. In this case, it only traverses the layer34once. Consequently, the thickness e34is then selected between 0.9 emand 1.1 emin order to acquire a calibration for this detector that hardly varies as a function of the energy of the incident ionizing radiation.

The description provided herein for the thickness of the layer34applies to any other embodiment of the sensitive part6. For example, the sensitive part6can be produced as described with reference to FIGS. 3 and 4 of the application filed under the number PCT/EP2020/074364.

Alternative Embodiments of the Manufacturing Method:

As an alternative embodiment, the detector used to construct the curves60and62does not have the same architecture as the detector2. For example, the volume of transducing material used during steps54and90can differ from the volume of transducing material of the detector2. Preferably, the transducing materials used in the detector2and during steps54and90are the same. The amplifying material used to construct the curves60and62must be the same as that used to manufacture the sensitive part6of the detector2.

As illustrated by step54, the lateral dimensions of the plates that are used, i.e., in this case the dimensions perpendicular to the direction of propagation of the measured ionizing radiation, can be very different from those implemented in the manufactured sensitive part6. For example, during the design phase, these lateral dimensions can be several centimeters, whereas in the sensitive part these lateral dimensions are less than 1 mm or 500 μm.

The construction of the curves60and62can be carried out upstream of the phase50of designing the detector2. For example, such curves are constructed beforehand for a large number of different values of the energy of the ionizing radiation to be measured and for several heavy materials, including lead, gold and tungsten. Step54then simply involves selecting, from among these various curves previously constructed for the same material as that used for manufacturing the layer34, the two curves constructed for values V1and V2that are close to the values Vminand Vmax, respectively.

As an alternative embodiment, the curves60and62are not measured experimentally but are computed by means of numerical simulation. For example, the following relations (1) and (2) are used to construct these curves:

where:N is the number of photons generated per second;NOEis the number of photons generated per second by a detector identical to the detector2except that it is devoid of the amplifying layer34;“exp ( . . . )” denotes the exponential function;Φ0is the density of the flow of primary ionizing particles of the primary ionizing radiation that reaches the transducing material, with this density being expressed as a number of primary ionizing particles per second and per square meter;S is the surface of transducing material exposed to the primary incident ionizing radiation;μE0,pis the absorption rate, by the transducing material, of primary ionizing particles of the primary ionizing radiation of energy E;d is the thickness of transducing material traversed by the primary ionizing radiation;YE0,pis the probability that the transducing material generates a visible photon when this transducing material absorbs and interacts with a primary ionizing particle of the primary ionizing radiation of energy E;μE1,pis the absorption rate of primary ionizing particles of the primary ionizing radiation of energy E by the amplifying material;t is equal to the thickness of amplifying material traversed by the primary incident ionizing radiation before reaching the transducing material when the detector is exposed to this ionizing radiation;the symbol “Σ” denotes the sum ranging from i=1 to i=Tmax, where Tmaxis the number of different types of secondary ionizing particles generated by the amplifying material when it is exposed to the primary ionizing radiation of energy E;TE1,iis the probability that following an interaction between a primary ionizing particle of the primary ionizing radiation of energy E with the amplifying material, a secondary ionizing particle of type i is generated;i is an identifier of a particular type of secondary ionizing particles capable of being generated by interaction between the primary ionizing radiation and the amplifying material;μE0,iis the absorption rate of secondary ionizing particles of type i and of energy E′ by the transducing material;YE0,iis the probability that the transducing material generates a visible photon when it absorbs and interacts with a secondary ionizing particle of type i and energy E′.

In this case, the interaction of a primary ionizing particle with the amplifying material can produce four different types of secondary ionizing particles, namely a photon, a positron, a neutron or an electron. In this case, values 1 to 4 of the index i respectively correspond to a photon, to a positron, to a neutron and to an electron. Tmaxis equal to four.

In the case of lead and of values V1and V2equal to 2 MeV and 4.5 MeV, respectively, the available literature indicates that U21,pis equal to 0.52 cm−1and that μ4.51,pis equal to 0.48 cm−1. Thus, for low thicknesses of amplifying material, the relation (1) can be approximated by the following relation (3):

The description provided in the particular case whereby the values V1and V2are equal to 2 MeV and 4.5 MeV, respectively, is applicable to other values of V1and V2. In particular, it is worthwhile selecting the values V1and V2that are equal to 500 keV and to 10 Mev, respectively. Indeed, this allows to obtain a detector that can be used for practically all the applications related to the field of characterizing materials and to the medical field. It is also worthwhile selecting the values V1and V2equal to 100 keV and to 600 keV, respectively, because the range [100 keV; 600 keV] of energies is significantly used in brachytherapy. Other energy ranges are of interest. In particular, the ranges [25 MeV; 50 MeV] and [230 MeV; 250 MeV] are of interest because they are used in the medical field, in particular when the ionizing radiation is a proton beam. By way of an illustration, the order of magnitude of the thickness em, acquired from a limited number of experiments in the case whereby the amplifying material is lead, is provided below for different energy ranges:em=400 μm when the values V1and V2are equal to 1 MeV and 2 MeV, respectively;em=400 μm when the values V1and V2are equal to 1 MeV and 3 MeV, respectively;em=460 μm when the values V1and V2are equal to 1 MeV and 4.5 MeV, respectively;em=450 μm when the values V1and V2are equal to 2.5 MeV and 3 MeV, respectively; andem=600 μm when the values V1and V2are equal to 3 MeV and 4 MeV, respectively.

As an alternative embodiment, the radiation 3minand the radiation 3maxare simultaneously applied to the detector2. In this case, the flow of ionizing particles measured by the detector2is the accumulation of the flow of ionizing particles generated by the radiation 3minand 3max. It should be noted that this measurement of the combined flows of the radiation 3minand 3maxis made possible since the calibration of the detector2is the same for the two energies of both the radiation 3minand the radiation 3max.

As alternative embodiments, measuring the intensity of the ionizing radiation simply involves detecting that the intensity of the ionizing radiation exceeds a predetermined threshold.

Other Alternative Embodiments:

The description provided in the particular case where the ionizing radiation is an X-ray, applies to any type of ionizing radiation. For example, the description provided herein can be adapted to gamma ray or to radiation of charged particles or neutrons. Since neutrons are not charged, they do not directly produce ionizations by traversing the material. However, the neutrons cause, by traversing the amplifying material, nuclear reactions, which generate ionizing radiation. Thus, the neutrons are indirectly ionizing since it is the fact that they are captured by the nuclei or that they interact therewith that generates gamma rays and/or various ionizing particles. For this reason, neutron radiation is considered herein to be ionizing radiation. The charged particle radiation is, for example, alpha, beta+, beta− particle radiation, any type of ions, for example, carbon or proton ions. In these cases, the amplifying material and/or the transducing material30must be adapted to the incident ionizing radiation. More specifically, the amplifying material must generate, in response to the incident ionizing radiation, secondary radiation able to excite the transducing material. Thus, the transducing material itself does not need to be directly excitable by the primary ionizing radiation. In fact, it simply needs to be sensitive to the secondary ionizing radiation generated by the thickness of amplifying material. By way of an illustration, in the case where the primary ionizing radiation is a high-energy gamma ray, it is possible to select a luminescent material that is only sensitive to X-rays. In this case, the amplifying material is a material that generates radiation with lower energies when it is exposed to the high-energy gamma ray. This latter embodiment is even advantageous in the case where several sensitive parts of several detectors are located next to one another because it limits any interference between these different sensitive parts.

In response to its exposure to the primary or secondary ionizing radiation, the transducing material can also emit a lower energy ionizing radiation which excites itself.

By way of an illustration and in order to limit the thickness em, when the primary ionizing radiation is a high-energy electron beam, the amplifying material is selected as described above in the case where the primary ionizing radiation is a high-energy X-ray. For example, the amplifying material is lead in this case. When the primary ionizing radiation is an ion beam, such as, for example, carbon ions, with very high energy, i.e., the energy of which ranges, for example, between 1 MeV and 50 MeV, preferably, the amplifying material that is selected is slightly lighter. For example, the amplifying material selected in this case is aluminum. Indeed, a lead thickness of 500 μm can significantly attenuate the primary ionizing radiation in such a case. The amplification principle is the same, but the selected amplifying material must be adapted to the radiated particles.

The description provided herein also applies to the case where the primary ionizing radiation is a low-energy ionizing radiation. In this latter case, the secondary ionizing radiation is generally lower energy X-rays or electrons.

Chapter Ill: Advantages of the Described Embodiments:

Incident ionizing radiation, especially when it is high energy, reacts with the atoms of the amplifying material in order to generate lower energy secondary ionizing radiation. The secondary ionizing radiation then in turn reacts with the transducing material in order to generate light or electrical charges. Thus, due to the presence of the amplifying layer, the transducing material is exposed to an amount of low-energy ionizing radiation that is greater than when the amplifying layer is absent. It therefore produces a greater amount of light or electrical charges for the same intensity of the primary ionizing radiation than in the absence of this amplifying layer. The sensitivity of the dosimeter is therefore enhanced.

The described manufacturing method allows a detector to be obtained that, like that described in JP 2011/191255 A, has a calibration that hardly varies as a function of the energy of the primary ionizing radiation to be measured from the moment this energy ranges between the values Vminand Vmaxtaken into account when designing this detector.

Furthermore, for the same range [Vmin; Vmax] of constant calibration and when the same heavy materials are used in the detector of JP 2011/191255 and in the detector2, the detector2uses a much lower total thickness eTof amplifying material. For example, when the detector described in JP 2011/191255 uses gold thicknesses that are several millimeters, the detector2only uses a total gold thickness that is less than 1 mm in order to acquire the same range [Vmin; Vmax] of constant calibration.

Producing the amplifying layer mainly from heavy material, the atomic number of which is greater than or equal to 74, allows a value of the abscissa emto be acquired that is less than 1 mm. This allows the bulk of the sensitive part to be significantly reduced and therefore allows the spatial resolution of the detector2to be enhanced.

The fact that the total thickness of amplifying material is less than 1 mm or 600 μm allows a very small footprint to be acquired for the sensitive part of the fiber dosimeter. Under these conditions, 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 thus allows the doses of radiation applied to the tumor to be better controlled.

The fact that the amplifying layer is itself formed by a stack of several sub-layers amplifying atomic numbers that decrease as the transducing material is approached allows the sensitivity of the dosimeter to be enhanced even further compared to the case of a single-layer amplifying layer.