DOSIMETER

Description

[0001] The present invention relates to a dosimeter for measuring a radiation dose of ionizing radiation, a use of such a dosimeter for measuring a radiation dose of ionizing radiation and a spectrometer for determining an energy-dependent radiation dose for ionizing radiation with an output energy spectrum using a plurality of such dosimeters.

[0002] Various types of dosimeters are known for measuring radiation doses from ionizing radiation, such as photons or electrons. For example, film dosimeters or thermoluminescence dosimeters (TLDs) are used to record radiation doses over longer periods. Ionization chambers, for example, are used to measure the instantaneous radiation dose. An ionization chamber is a measuring chamber filled with a counting gas. Electrodes are arranged inside it, between which a high voltage is applied. When ionizing radiation enters the chamber, the counting gas is ionized. The resulting charge carriers are collected at the electrodes, and an electric current can be measured that is proportional to the dose rate of the radiation.

[0003] However, existing dosimeters reach their limits when it comes to measuring radiation doses that occur over very short periods of time. For example, it is currently extremely complex to measure the instantaneous radiation dose of ionizing radiation that occurs when an ultrashort pulse laser beam strikes a workpiece, as saturation limits and the so-called "pile-up" complicate the measurement and lead to misinterpretations. Measuring the radiation dose that occurs during laser-induced particle acceleration, such as laser plasma acceleration, is similarly difficult.

[0004] An ultrashort pulse laser is defined here as a laser with a pulse duration in the picosecond, femtosecond, or shorter range. The radiation pulses generated when using such lasers are of a similar duration. Conventional dosimeters for measuring time-varying radiation doses or current radiation doses, such as ionization chambers, cannot measure the dose of such short radiation pulses, or can only do so inaccurately, because their temporal resolution is too low. For example, in a dosimeter, the collection of charge carriers at the electrodes takes approximately 1 µs, which is many times the duration of a radiation pulse generated by an ultrashort pulse laser. Furthermore, due to the short duration of the radiation pulse, the dose rate is very high even at relatively low radiation doses, so that saturation effects play a very significant role even at small doses.

[0005] EP 3 173 823 A1 discloses an alpha radiation monitoring device and an alpha radiation monitoring method which are specifically designed to measure alpha radiation and can evaluate a signal derived from alpha rays.

[0006] From EP 3 489 722 A1 a radiation monitor for measuring a dose rate is known which comprises a fluorescent solid.

[0007] EP 0 754 305 A1 discloses a device and a method for measuring the specific activity of tritium by gas scintillation.

[0008] Aspects of X-ray radiation protection during ultrashort laser processing are known from LEGALL HERBERT ET AL: "X-ray radiation protection aspects during ultrashort laser processing", JOURNAL OF LASER APPLICATIONS, LASER INSTITUTE OF AMERICA, US, Vol. 32, No. 2, 5.

[0009] Against this background, the skilled person is faced with the task of providing an active, i.e., non-integrating, dosimeter for measuring radiation doses of pulsed ionized radiation as well as a method for using such a dosimeter and a spectrometer for determining an energy-dependent radiation dose.

[0010] The object underlying the invention is achieved by a dosimeter according to claim 1, a method for using a dosimeter according to claim 11, and a spectrometer according to claim 12. Preferred embodiments of the various aspects of the invention are the subject of the respective dependent claims.

[0011] According to a first aspect, the problem underlying the invention is solved by a dosimeter for measuring a radiation dose of ionizing radiation, comprising a measuring chamber and a light sensor. The measuring chamber is filled with a fluorophore and is light-tight, so that no ambient light can enter the measuring chamber. The light sensor has a response time of less than 10 ns and is configured to detect fluorescent light generated by ionizing radiation in the fluorophore in the measuring chamber and to generate a signal proportional to the fluence of the detected fluorescent light.

[0012] In other words, a dosimeter according to the invention has a measuring chamber in which a light sensor with a preferably very short response time is arranged. The measuring chamber is filled with a medium in which fluorescence can be excited by ionizing radiation. Such media are referred to herein as a fluorophore. The fluorophore is preferably a gas. However, it is also conceivable to use a liquid or opaque glass, i.e. a translucent solid, as the fluorophore. The measuring chamber is light-tight, i.e. designed so that no ambient light falls into the measuring chamber and onto the light sensor. This prevents ambient light from falsifying the dose measurement. For this purpose, the measuring chamber is usually made of a light-absorbing material or is coated with such a material.

[0013] The radiation preferably has a pulsed time structure with a pulse duration of less than one nanosecond. This short duration allows all of the radiation interacting with the gas in the measurement chamber in a single radiation pulse to pass through the measurement chamber in a very short time.

[0014] To measure a radiation dose, the chamber is placed in an area where the dose of ionizing radiation is to be measured. For example, the measuring chamber can be placed near an object being treated with an ultrashort pulse laser with a pulse length in the range of a few picoseconds, preferably shorter. The ionizing radiation, for example X-rays with an energy of 8 keV or higher, gamma radiation, high-energy neutrons, electrons, positrons, or protons, penetrates the wall of the measuring chamber and excites the fluorophore in the measuring chamber, which then emits fluorescent light. The lifetime of the excited states in the fluorophore is approximately 0.5 ns, i.e., fluorescent light is emitted approximately 0.5 ns after the ionizing radiation has excited the fluorophore. At low gas pressures, the lifetime of the excited states can increase to as low as 20 ns.

[0015] The emitted fluorescent light is captured by the light detector in the measuring chamber and converted into an electrical signal proportional to the fluence of the detected fluorescent light and thus also proportional to the dose of ionizing radiation that has entered the chamber. Due to the short lifetime of the excited states in the fluorophore and the speed of light in the measuring chamber, there is no significant delay in measuring the dose, unlike with conventional dosimeters such as ionization chambers. Furthermore, despite the high dose rates caused by the short pulse duration, no significant saturation occurs, which could complicate the measurement of the radiation dose. This is therefore an actively measuring and therefore not an integrating dosimeter, with which the instantaneous radiation dose can be measured even with very short radiation pulses.

[0016] In a preferred embodiment, the measuring chamber is filled with air, argon, nitrogen, carbon dioxide, or methane as a fluorophore. Thus, in the preferred embodiment, the measuring chamber is filled with a gas such as air or argon. A measuring chamber filled with air, in particular, offers significant advantages, as this significantly simplifies handling.

[0017] According to the invention, the light sensor has a response time of less than 10 ns and preferably less than 5 ns, wherein the light sensor is preferably a photomultiplier or a semiconductor detector. Response time can be understood, for example, as the time from the incidence of a photon into the light detector until a corresponding signal is present at a signal output of the light sensor. In an exemplary embodiment, a signal is present at a signal output when, for example, 50% or 90% of the signal level is reached. A short response time enables accurate measurement of the radiation dose despite short radiation pulses.

[0018] The measuring chamber is preferably made of a metal, a plastic, or a composite material. For example, the measuring chamber and, more precisely, the wall of the measuring chamber can be made of a carbon fiber reinforced plastic. However, other materials are also conceivable. The wall of the measuring chamber can also be made of different materials in different regions. For example, the measuring chamber can have reinforced regions that absorb ionizing radiation more strongly and thinner regions where ionizing radiation is absorbed less strongly. Such regions can, for example, form a measuring window through which ionizing radiation (but not light) enters the measuring chamber and only the smallest possible proportion of the radiation is absorbed.

[0019] In a preferred embodiment, the measuring chamber has a cylindrical shape. However, other configurations are also conceivable. For example, the measuring chamber can be spherical or cubic.

[0020] It is further preferred if a light source for calibrating the light sensor is arranged in the measuring chamber. For this purpose, a light source is used, for example, that emits light with a known fluence and preferably in the same wavelength range in which the fluorescent light generated by the ionizing radiation is observed. The light sensor can be calibrated using the light source because, when the light source is switched on, the fluence of the incident photons on the light sensor is known, and thus the relationship between the fluence of the photons incident on the light sensor and the output signal of the light sensor can be determined or adjusted.

[0021] In a preferred embodiment, the light sensor comprises at least one optical attenuator, which can be arranged in the measuring chamber in such a way that the optical attenuator reduces the fluence of the fluorescent light incident on the light sensor. This prevents saturation of the light sensor and adapts the dosimeter's measuring range to high radiation doses.

[0022] In a preferred embodiment, the measuring chamber is configured so that a volume of the measuring chamber can be changed in order to change a sensitivity of the dosimeter. In this preferred embodiment, the measuring chamber is filled with a gas or a fluid. For example, the volume of the measuring chamber can be changed by using a measuring chamber with flexible or expandable walls or, for example, a movable wall element can be moved within a chamber to adjust the volume of the actual measuring chamber. By changing the volume of the measuring chamber, the amount of fluorophore with which the ionizing radiation can interact is also changed, and thus the fluence of the fluorescent light generated by the radiation.For example, a larger volume can be used to more accurately measure low radiation doses, and a smaller volume can be used to measure high radiation doses where the light sensor would otherwise saturate due to the amount of fluorescent light generated.

[0023] Alternatively or additionally, the dosimeter can be designed so that the pressure of the fluorophore in the measuring chamber can be varied to alter the sensitivity of the dosimeter. For this purpose, a fluorophore in the form of a gas or other compressible fluid is preferably used.

[0024] In a preferred embodiment, a scintillator is arranged in the measuring chamber next to the fluorophore, and the light sensor is configured to detect scintillation light generated by ionizing radiation in the scintillator and generate a signal proportional to the fluence of the detected scintillation light. The use of scintillators for measuring radiation doses is well known to those skilled in the art. By arranging a scintillator in the measuring chamber, the dosimeter can also be advantageously used to measure the radiation dose of ionizing radiation where insufficient fluorescent light is generated for a dose measurement.

[0025] The dosimeter preferably comprises a diaphragm that can be arranged between the scintillator and the light sensor so that no scintillation light generated by ionizing radiation in the scintillator is detected by the light sensor. In other words, the diaphragm can be placed between the scintillator and the light sensor so that no light from the scintillator enters the light sensor. This ensures that only light generated by fluorescence processes can be measured by the light sensor. If light generated in the scintillator is also to be detected by the light sensor, the diaphragm is removed.

[0026] In an alternative, preferred embodiment, the measuring chamber is completely filled with the fluorophore and no scintillator is arranged in the measuring chamber.

[0027] In a second aspect, a dosimeter according to one of the preceding claims is used to measure a radiation dose of ionizing radiation. The advantages of using a dosimeter according to the invention correspond to the advantages of the corresponding dosimeter.

[0028] It is preferred if the dosimeter is used to measure the radiation dose of pulsed ionizing radiation with radiation pulses having a length of less than 10 ns, preferably less than 5 ns and even more preferably less than 1 ns.

[0029] In a preferred embodiment, the dosimeter is used to measure the radiation dose of gamma radiation with an energy of more than 8 keV, preferably more than 10 keV.

[0030] In a third aspect, the problem underlying the invention is solved by a spectrometer for determining an energy-dependent radiation dose for ionizing radiation with an output energy spectrum having a plurality of dosimeters according to one of the preceding embodiments, wherein a wall of the measuring chamber of each dosimeter of the plurality of dosimeters has different absorption properties than a wall of at least one other dosimeter of the plurality of dosimeters, so that the ionizing radiation that generates fluorescent light in the measuring chamber of the respective dosimeter has an energy spectrum that differs both from the output energy spectrum and from the energy spectrum of the ionizing radiation that generates fluorescent light in the measuring chamber of the at least one dosimeter with a wall with different absorption properties.

[0031] In other words, in the preferred embodiment, several dosimeters according to at least one of the previously described embodiments are combined to determine the energy dependence of the radiation dose. For this purpose, dosimeters are used in which radiation doses for radiation with different energy spectra are measured through walls with different absorption properties in at least two of the dosimeters used, so that the difference between the radiation doses can be used to draw conclusions about the energy dependence of the radiation. Different absorption properties can be achieved, for example, by using walls of different thicknesses or walls made of different materials.

[0032] In a preferred embodiment, the wall of the measuring chamber of each dosimeter of the plurality of dosimeters has absorption properties that differ from the absorption properties of the wall of the measuring chamber of any other dosimeter of the plurality of dosimeters. In other words, with an identical output spectrum, each of the dosimeters measures a radiation dose for a different energy spectrum.

[0033] In a preferred embodiment, the walls of the measuring chambers of the plurality of dosimeters are made of identical materials, and differing absorption properties are created by differing wall dimensions. Alternatively or additionally, the walls of the measuring chambers of the plurality of dosimeters are made of different materials and therefore have differing absorption properties.

[0034] The advantages of the various embodiments of a spectrometer correspond to the advantages of the dosimeters used for the spectrometer.

[0035] Several embodiments of a dosimeter and a spectrometer are described below with reference to the drawing. Figure 1 shows a first embodiment of a dosimeter, Figure 2 shows a second embodiment of a dosimeter, Figure 3 shows a third embodiment of a dosimeter, Figure 4 shows a fourth embodiment of a dosimeter and Figure 5 shows an embodiment of a spectrometer.

[0036] In the Figures 1 to 5 Unless otherwise stated, elements with the same designation are provided with the same reference symbols.

[0037] Figure 1shows a first embodiment of a dosimeter 1 with a measuring chamber 3, which is filled with a fluorophore 5 and in which a light sensor 7 is arranged. In the embodiment in Figure 1 The fluorophore is a gas, preferably air, that completely fills the measuring chamber 3. The measuring chamber 3 is made of a light-tight plastic so that no light from the environment enters the measuring chamber 3.

[0038] A photomultiplier with a response time of less than 5 ns is used as the light sensor 7. The light sensor 7 is connected via a signal output 9 to an evaluation unit 11, which may be, for example, a data processing device.

[0039] Dosimeter 1 is used to measure the radiation dose of pulsed ionizing radiation with very short radiation pulses. The duration of the radiation pulses is, for example, less than 1 ns. Figure 1A workpiece 13 is shown schematically, which is processed with an ultrashort pulse laser 15. The ultrashort pulse laser 15 is in Figure 1 represented by dashed lines with arrowheads and has a pulse length in the range of a few femtoseconds. When the laser beam hits the workpiece 13, ionizing radiation 17 is generated in the form of X-rays 17, which Figure 1 represented by dashed lines. The X-ray radiation 17 is also pulsed with a similar pulse length to the laser 15. A portion of the X-ray radiation 17 penetrates the wall 19 of the measuring chamber 3 and generates fluorescent light by exciting the fluorophore 5. The fluorescent light is captured by the light sensor 7 configured for this purpose, which outputs a signal to the evaluation unit 11 via the signal output 9. The signal is proportional to the detected fluorescent light and thus also proportional to the radiation dose of the incident ionizing radiation 17.

[0040] Due to the short lifetime of the excitation states in the fluorophore 5 of approximately 0.5 ns and the short response time of the light sensor 7, which is in the same temporal order of magnitude, the sensor can measure the radiation dose over very short periods of time even at - relatively - high radiation doses without immediate saturation effects.

[0041] In Figure 2 An alternative embodiment of a dosimeter 1 is shown, which is based on the dosimeter 1 of Figure 1 The representation of a signal output, an evaluation unit and a radiation source has been omitted. Dosimeter 1 from Figure 2 but can be determined according to the dosimeter 1 from Figure 1 be connected to an evaluation unit via a signal output. The following is Figure 2 Dosimeter 1 shown in Figure 1 is only explained in more detail insofar as it differs from the one shown in Figure 1 shown dosimeter.

[0042] The dosimeter 1 in Figure 2 In addition to the dosimeter 1 Figure 1 a light source 21 which is arranged in the measuring chamber and can be used to calibrate the light sensor 7. Furthermore, Figure 2 An optical attenuator 23 is shown, which can be arranged between the light sensor 7 and the fluorophore to reduce the fluence of the generated fluorescent light, so that even higher radiation doses can be measured without saturating the light sensor 7. In the exemplary embodiment, the optical attenuator 23 is designed such that it can be optionally arranged in front of the light sensor 7 or removed again. The optical attenuator 23 and the light source 21 are independent of each other and can also be used without the other component.

[0043] In Figure 3An alternative embodiment of a dosimeter 1 is shown, which is based on the dosimeter 1 of Figure 1 The representation of a signal output, an evaluation unit and a radiation source has been omitted. Dosimeter 1 from Figure 3 but can be determined according to the dosimeter 1 from Figure 1 be connected to an evaluation unit via a signal output. The following is Figure 3 Dosimeter 1 shown in Figure 1 is only explained in more detail insofar as it differs from the one shown in Figure 1 shown dosimeter.

[0044] The dosimeter 1 in Figure 3 In addition to the dosimeter 1, it includes Figure 1a scintillator 25, which is arranged in the measuring chamber and can be used to measure radiation doses from continuous radiation sources or pulsed radiation sources with significantly longer radiation pulses. The scintillation light generated by the ionizing radiation in the scintillator 25 is also received by the light sensor 7 configured for this purpose, which at its signal output (in Figure 3not shown) outputs a signal that is proportional to the generated scintillation light and thus also proportional to the radiation dose. The use of scintillators 25 for dose measurement is sufficiently known to those skilled in the art, so a more detailed description will be omitted here. To prevent scintillation light from distorting the measurement results in the case of pulsed radiation sources, an aperture 27 is provided, which can be selectively moved between the scintillator 25 and the fluorophore 5. The aperture 27 prevents scintillation light from falling onto the light sensor 7 or being detected by it.

[0045] In Figure 4 An alternative embodiment of a dosimeter 1 is shown, which is based on the dosimeter 1 of Figure 1 The representation of a signal output, an evaluation unit and a radiation source has been omitted. Dosimeter 1 from Figure 4 but can be determined according to the dosimeter 1 from Figure 1be connected to an evaluation unit via a signal output. The following is Figure 4 Dosimeter 1 shown in Figure 1 is only explained in more detail insofar as it differs from the one shown in Figure 1 shown dosimeter.

[0046] In the Figure 4 In the illustrated embodiment, a movable wall 29 is provided in the measuring chamber 3, via which the volume of the measuring chamber 3, in which the gaseous fluorophore is arranged, can be changed. By changing the volume, the amount of fluorescent light generated at the same radiation dose can be changed, and thus the sensitivity of the dosimeter can be adapted to different radiation sources.

[0047] The embodiments of the Figures 1 to 4may be combined with each other, unless expressly excluded. For the sake of completeness, it should be noted that the illustrated geometries and arrangements of the components of the dosimeters 1 are purely schematic and do not constitute an obstacle to the combination of the embodiments.

[0048] Finally, in Figure 5 an embodiment of a spectrometer 31 is shown, which comprises three dosimeters 33, 35, 37, each of which, like the dosimeter 1 from Figure 1 However, dosimeters 33, 35, 37 could also be used like one of the dosimeters 1 from the Figures 2, 3, 4The dosimeters 33, 35, and 37 differ from one another in that they have walls 19 of different thicknesses, as indicated by lines of different thicknesses representing the walls 19. The representation of the walls 19 is purely schematic, ie, the actual thickness of the walls 19 cannot be deduced from the thickness of the lines.

[0049] The different wall thicknesses 19 exhibit different absorption properties. In particular, thicker walls 19 absorb ionizing radiation with low energies to a greater extent than ionizing radiation with higher energies. This results in radiation with a different energy spectrum interacting with the fluorophore 5 in each dosimeter 33, 35, 37, despite an identical initial energy spectrum in the respective measuring chamber 3. Thus, an energy dependence of the radiation dose of the ionizing radiation can be determined by comparing the radiation doses measured for the different energy spectra. List of reference symbols

[0050] 1 Dosimeter 3 Measuring chamber 5 Fluorophore 7 Light sensor 9 Signal output 11 Evaluation unit 13 Workpiece 15 Ultrashort pulse laser 17 X-ray radiation 19 Wall 21 Light source 23 Optical attenuator 25 Scintillator 27 Aperture 29 Movable wall 31 Spectrometer 33 Dosimeter 35 Dosimeter 37 Dosimeter

Claims

1. A dosimeter (1) for measuring a radiation dose of ionizing radiation (17) with a measuring chamber (3) and a light sensor (7), wherein the measuring chamber (3) is filled with a fluorophore (5) and is light-tight such that no light from the environment can enter the measuring chamber, and wherein the light sensor (7) is configured to detect fluorescent light generated in the fluorophore (5) in the measuring chamber (3) by ionizing radiation (17) and to generate a signal that is proportional to the fluence of the detected fluorescent light, characterized in that the light sensor (7) has a response time of less than 10 ns.

2. The dosimeter (1) according to claim 1, wherein the fluorophore (5) is a gas, preferably air, argon, or nitrogen.

3. The dosimeter (1) according to claim 1 or 2, wherein the light sensor (7) has a response time of less than 5 ns, and / or wherein the light sensor (7) is preferably a photomultiplier or a semiconductor detector.

4. The dosimeter (1) according to claim 1, 2, or 3, wherein the measuring chamber (3) is formed from a metal or a plastic, wherein the plastic is preferably a carbon fiber-reinforced plastic.

5. The dosimeter (1) according to one of the preceding claims, wherein a light source (21) for calibrating the light sensor (7) is arranged in the measuring chamber (3).

6. The dosimeter (1) according to one of the preceding claims, wherein the light sensor (7) comprises at least one optical attenuator (23), which can be arranged in the measuring chamber (3) such that the fluence of the fluorescent light falling on the light sensor (7) is reduced by the optical attenuator (23).

7. The dosimeter (1) according to one of the preceding claims, wherein the measuring chamber (3) is configured such that a volume of the measuring chamber (3) can be changed in order to change the sensitivity of the dosimeter (1).

8. The dosimeter (1) according to one of the preceding claims, wherein the fluorophore (5) is a gas, and wherein the dosimeter (1) is designed such that a pressure of the gas in the measuring chamber (3) can be changed in order to change the sensitivity of the dosimeter (1).

9. The dosimeter (1) according to one of the preceding claims, wherein a scintillator (25) is arranged in the measuring chamber (3) in addition to the fluorophore (5), and wherein the light sensor (7) is configured to detect scintillation light generated in the scintillator (25) by ionizing radiation and to generate a signal that is proportional to the fluence of the detected scintillation light.

10. The dosimeter (1) according to claim 9, wherein the dosimeter (1) comprises a shutter (27), which can be arranged between the scintillator (25) and the light sensor (7) such that no scintillation light generated in the scintillator (25) by ionizing radiation is detected by the light sensor (7).

11. Use of a dosimeter (1) according to one of the preceding claims to measure a radiation dose of an ionizing radiation (13), wherein the dosimeter (1) is preferably used to measure the radiation dose of a pulsed ionizing radiation (13) with radiation pulses with a length of less than 10 ns, preferably less than 5 ns and even more preferably with a length of less than 1 ns, and / or wherein the ionizing radiation is preferably gamma radiation with an energy of more than 8 keV, even more preferably more than 10 keV.

12. A spectrometer (31) for determining an energy-dependent radiation dose for ionizing radiation (17) with an output energy spectrum with a plurality of dosimeters (33, 35, 37) according to one of claims 1 to 9, wherein a wall (19) of the measuring chamber (3) of each dosimeter (33, 35, 37) of the plurality of dosimeters (33, 35, 37) has different absorption characteristics than a wall (19) of at least one other dosimeter (33, 35, 37) of the plurality of dosimeters (33, 35, 37), such that the ionizing radiation that generates fluorescent light in the measuring chamber (3) of each dosimeter (33, 35, 37) has an energy spectrum that differs both from the output energy spectrum and from the energy spectrum of the ionizing radiation that generates fluorescent light in the measuring chamber (3) of the at least one dosimeter (33, 35, 37) having a wall (19) with differing absorption characteristics.

13. The spectrometer (31) according to claim 12, wherein the wall (19) of the measuring chamber (3) of each dosimeter (33, 35, 37) of the plurality of dosimeters (33, 35, 37) has absorption characteristics that differ from the absorption characteristics of the wall (19) of the measuring chamber (3) of each of the other dosimeters (33, 35, 37) of the plurality of dosimeters (33, 35, 37).

14. The spectrometer (31) according to claim 12 or 13, wherein the walls (19) of the measuring chambers (3) of the plurality of dosimeters (33, 35, 37) are formed from identical materials, and differing absorption characteristics are generated through differing dimensions of the walls (19).

15. The spectrometer (31) according to claim 12, 13, or 14, wherein the walls (19) of the measuring chambers (3) of the plurality of dosimeters (33, 35, 37) are formed from different materials and have differing absorption characteristics.