Device and method for measuring proportion of photons to electrons in pulse hard X-ray radiation field

Abstract

The invention discloses a device and a method for measuring the proportion of photons to electrons in a pulse hard X-ray radiation field, which solve the problem that the measurement result of the proportion of photons to electrons in the existing pulse hard X-ray radiation field is not accurate enough, and the device comprises a calorimeter, a current coil arranged at the top of the calorimeter and a data processing unit, the calorimeter comprises a metal absorber, a shielding shell, a shielding film and a thermocouple; the shielding shell is barrel-shaped, and the axis of the shielding shell and the axis of the current coil are on the same straight line; the shielding film is arranged at the top end of the shielding shell, and a gap is formed between the shielding film and the current coil; the metal absorber is arranged in the shielding shell; one end of the thermocouple is connected with the metal absorber, and the other end extends out of the bottom end of the shielding shell; the data processing unit is connected with the other end of the thermocouple and the output end of the current coil and used for calculating the corresponding photon-electron proportion through the thermoelectromotive force output by the thermocouple and the current output by the current coil.

Description

Technical Field

[0001] The present invention relates to a device and method for measuring the photon-to-electron ratio, and particularly to a device and method for measuring the photon-to-electron ratio in a pulsed hard X-ray radiation field. Background Art

[0002] Most pulsed hard X-ray simulation devices use high-energy electrons to hit a target to generate bremsstrahlung, and the radiation field is inevitably accompanied by electrons and electromagnetic radiation. Among them, with the movement of the accompanying electrons, additional electromagnetic pulses will be generated. These interferences will have a great impact on the acquisition and analysis of experimental data, and even cause the measured response signal to be overwhelmed by the interference. Commonly used scattered electron and weak beam current measurement devices include: Rogowski coils (including differential and integral types), Faraday cylinders, wall resistance shunts, disk shunts, etc.

[0003] For the measurement of X-ray energy fluence (dose), the commonly used detectors are as follows: thermoluminescence dosimeter (TLD), scintillation detection system, semiconductor detectors (such as silicon photodiodes, diamond detectors, etc.), air ionization chambers or calorimeters, etc. The basic principle is that the X-ray energy incident on the detector surface is deposited in the detector, and the pulse X-ray energy fluence is obtained by measuring parameters proportional to the X-ray energy fluence (such as thermoluminescence, charge quantity, ionization energy, temperature change, etc.). There are also some similar devices that use dosimeter chips to measure the absorbed dose of hard X-rays. This method does not directly measure the energy fluence, but measures the absorbed dose of hard X-rays by the dosimeter chip. To obtain the energy fluence, it is also necessary to know the hard X-ray energy spectrum and perform back-calculation, and the process is relatively complex and inaccurate.

[0004] Some researchers have also proposed a pulsed hard X-ray energy fluence measurement technique using a phototube and a lutetium silicate (LSO) scintillator as a detection system. This method measures the energy fluence by using the approximate full absorption of hard X-rays by a high-density scintillator. However, the LSO scintillator has a non-flat response to the hard X-ray energy spectrum, resulting in a relatively large uncertainty in its measurement results, and further leading to inaccurate results of the measured photon-to-electron ratio. In addition, the upper limit of the high-dose-rate pulse linear response of the LSO crystal is relatively low, and this method is no longer applicable when the energy fluence of the device is relatively high. Summary of the Invention

[0005] In order to solve the technical problem that the measurement result of the photon-to-electron ratio in the existing pulsed hard X-ray radiation field is not accurate enough, the present invention provides a device and method for measuring the photon-to-electron ratio in a pulsed hard X-ray radiation field.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A measuring device for the photon-to-electron ratio in a pulsed hard X-ray radiation field, characterized in that it includes a calorimeter, a current coil arranged on the top of the calorimeter, and a data processing unit;

[0008] The calorimeter includes a metal absorber, a shielding housing, a shielding film, and a thermocouple; the shielding housing is cylindrical, its axis is on the same straight line as the axis of the current coil, its inner wall is a two-stage stepped cylinder, and the stepped surface between the two stages faces upward; the shielding film is arranged at the top of the shielding housing and there is a spacing between it and the current coil; the metal absorber is arranged inside the shielding housing and is parallel to be arranged between the shielding film and the stepped surface, and there is a spacing between it and the shielding film; one end of the thermocouple is connected to the metal absorber, and the other end extends out from the bottom end of the shielding housing for converting the temperature of the metal absorber into a thermal electromotive force;

[0009] The data processing unit is respectively connected to the other end of the thermocouple and the output end of the current coil, and is used for calculating the corresponding photon-to-electron ratio through the thermal electromotive force output by the thermocouple and the current output by the current coil.

[0010] Further, it also includes a collimator;

[0011] The collimator is arranged at the top of the current coil, the axis of its collimation hole is on the same straight line as the axis of the current coil, and the aperture of the collimation hole is smaller than the inner diameter of the current coil.

[0012] Further, the metal absorber is made of tantalum, tungsten or gold, and its thickness range is 0.5 mm to 1 mm.

[0013] Further, the type of the thermocouple is type E, type T, type J or type K, and its diameter range is 0.05 mm to 0.25 mm.

[0014] Further, the shielding film is made of aluminum, copper or iron, and its thickness range is 10 μm to 50 μm.

[0015] Further, the collimator is made of tungsten or lead, and its thickness range is 0.8 cm to 1.2 cm.

[0016] Further, the calorimeter also includes a plurality of support rods arranged inside the shielding housing;

[0017] The plurality of support rods are vertically installed between the shielding film and the stepped surface and are evenly arranged around the inner wall of the shielding housing; the corresponding edges of the metal absorber are embedded in the middle of the corresponding support rods.

[0018] Further, the support rods are made of insulating materials, and their diameter range is 1 mm to 2 mm; one end of the thermocouple is welded to the metal absorber.

[0019] A method for measuring the photon-to-electron ratio in a pulsed hard X-ray radiation field, using the above-mentioned measuring device for the photon-to-electron ratio in a pulsed hard X-ray radiation field, is characterized in that it includes the following steps:

[0020] Step 1: The current coil receives the current generated by the induction of electrons in the radiation field where the pulsed hard X-ray to be measured is located, and outputs it to the data processing unit;

[0021] Step 2: After the visible light and electrons are shielded by the shielding film, the pulsed hard X-ray to be measured is absorbed by the metal absorber, and the temperature of the metal absorber rises;

[0022] Step 3: The thermocouple converts the temperature of the metal absorber into a thermal electromotive force and transmits it to the data processing unit;

[0023] Step 4: The data processing unit calculates the number of electrons according to the acquired current, calculates the average number of photons according to the thermal electromotive force, and then calculates the photon-to-electron ratio according to the average number of photons and the number of electrons to complete the measurement.

[0024] Further, step 1 is specifically:

[0025] The radiation field where the pulsed hard X-ray to be measured is located is collimated by a collimator, and the current coil receives the current generated by the induction of electrons in the collimated radiation field and outputs it to the data processing unit.

[0026] Advantages of the present invention:

[0027] 1. The measuring device and method for the photon-to-electron ratio in a pulsed hard X-ray radiation field provided by the present invention use a current coil to measure the number of electrons passing through the collimator, and use a calorimeter to measure the energy fluence of the pulsed hard X-ray. The number of photons can be calculated from the average photon energy; the present invention has a flat sensitivity response to hard X-rays in the energy range of 10 keV to 200 keV, can directly measure the energy fluence of X-rays in this energy range, and can obtain the photon-to-electron ratio in the pulsed hard X-ray radiation field more accurately compared with other methods.

[0028] 2. In the present invention, the calorimeter selects appropriate absorber materials and thicknesses according to the energy spectrum of the pulsed hard X-ray radiation source, can achieve accurate measurement of the energy fluence of the pulsed hard X-ray, and has advantages such as small detector size and strong anti-electromagnetic interference ability. Description of the Drawings

[0029] Figure 1 is a schematic structural diagram of an embodiment of the measuring device for the photon-to-electron ratio in a pulsed hard X-ray radiation field of the present invention;

[0030] Figure 2 is a graph of the X-ray absorption rate of tantalum sheets with different thicknesses in the embodiment of the present invention.

[0031] Reference numerals in the drawings:

[0032] 1 - Metal absorber, 2 - Support rod, 3 - Shielding housing, 4 - Shielding film, 5 - Thermocouple, 6 - Collimator, 7 - Current coil. Specific implementation manner

[0033] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] A measuring device for the photon - to - electron ratio in a pulsed hard X - ray radiation field provided by an embodiment of the present invention, as Figure 1 shown. The measuring device includes a collimator 6, a current coil 7, and a calorimeter arranged in sequence from top to bottom; the calorimeter includes a metal absorber 1, a shielding housing 3, a shielding film 4, a thermocouple 5, and four support rods 2.

[0035] The central axis of the collimation hole of the collimator 6 and the axis of the current coil 7 are on the same straight line, and the aperture of the collimation hole is smaller than the inner diameter of the current coil 7. The collimator 6 is made of high - Z elements such as tungsten or lead, and its thickness ranges from 0.8 cm to 1.2 cm. In this embodiment, lead with a thickness of 1 cm is preferably used, and the diameter of the collimation hole is 10 mm.

[0036] The shielding housing 3 is cylindrical, its axis is on the same straight line as the axis of the current coil 7, its inner wall is a two - stage stepped cylinder, and the step surface between the two - stage steps faces upward; in this embodiment, the shielding housing 3 is made of tungsten with a thickness of 8 mm.

[0037] The current coil 7 selects the 8600 model produced by Pearson Company and is used to measure current.

[0038] The shielding film 4 is arranged at the top of the shielding housing 3 and there is a spacing between it and the current coil 7; the shielding film 4 is made of low - atomic - number metals with a thickness ranging from 10 μm to 50 μm, such as aluminum, copper, iron, etc. In this embodiment, an aluminum film with a thickness of 30 μm is preferably used. It shields visible light, debris, and electromagnetic interference.

[0039] The metal absorber 1 is disposed within the shielding housing 3, and is arranged parallel between the shielding film 4 and the stepped surface, with a spacing provided between the metal absorber 1 and the shielding film 4; the metal absorber 1 is made of a high atomic number metal with a thickness range of 0.5 mm to 1 mm, such as tantalum, tungsten, gold, etc. The specific heat or heat capacity of the absorber is a thermodynamic property of the material itself. It is assumed that the absorber remains solid under constant pressure, and at the same time, there is no phase change or other processes that can complicate the simple relationship. The temperature rise of the metal absorber is related to the energy (enthalpy or dose) it absorbs through the specific heat; the thickness of the tantalum sheet affects the energy spectrum response, temperature rise, and thermal equilibrium time of the calorimeter, and needs to be reasonably selected according to the experimental conditions. In this embodiment, a tantalum sheet with a thickness of 1 mm and a diameter of 11 mm is preferably selected. The X-ray absorption rate curves of tantalum with different thicknesses are as Figure 2 shown. When the thickness of the tantalum sheet reaches more than 1 mm, its absorption rate of 200 keV photons can reach 70%.

[0040] One end of the thermocouple 5 is welded to the metal absorber 1, and the other end extends from the bottom end of the shielding housing 3; the type of the thermocouple 5 is type E, type T, type J or type K, etc., and its diameter range is 0.05 mm to 0.25 mm. In this embodiment, an E-type thermocouple wire with a diameter of 0.08 mm is preferably selected. The electromotive force of the E-type (nickel-chromium - copper-nickel) thermocouple is the highest, and the differential thermoelectromotive force in the range of 20 °C to 30 °C is 60.5 μV / °C.

[0041] Four support rods 2 are disposed within the shielding housing 3, and are vertically installed between the shielding film 4 and the stepped surface, and a plurality of support rods 2 are uniformly arranged around the inner wall of the shielding housing 3; the corresponding edges of the metal absorber 1 are embedded in the middle of the corresponding support rods 2; the support rods 2 are made of an insulating material with a diameter range of 1 mm to 2 mm, such as nylon, polytetrafluoroethylene, etc. In this embodiment, polytetrafluoroethylene with a diameter of 1 mm is preferably selected.

[0042] The data processing unit is respectively connected to the other end of the thermocouple 5 and the output end of the current coil 7, and its sampling frequency ≥ 1 kHz, which can directly calculate the thermocouple temperature, has a cold junction compensation function, and is used to calculate the corresponding photon-to-electron ratio through the thermal electromotive force output by the thermocouple 5 and the current output by the current coil 7.

[0043] The calorimeter has a flat energy response to hard X-ray photons in the energy range of 10 keV to 200 keV, and can directly obtain the energy fluence of pulsed hard X-rays. The number of photons can be calculated from the average photon energy. The current coil measures the number of electrons passing through the collimator. The photon-to-electron ratio is accurately obtained based on the measurement results of the number of photons and the number of electrons.

[0044] The calorimetry method used by the calorimeter is the method that is closest to directly measuring the dose or energy flux among all dose measurement methods. Without considering heat loss, only the specific heat and the temperature rise of the absorber are related to the X-ray absorption amount. Heat loss occurs in several ways, including heat leakage, heat loss due to chemical reactions or phase changes, and energy loss during energy flux measurement.

[0045] The measurement of the photon-to-electron ratio in a pulsed hard X-ray radiation field is carried out using the above-mentioned measurement device, including the following steps:

[0046] Step 1: The collimator 6 collimates the radiation field where the pulsed hard X-ray to be measured is located. The current coil 7 receives the current generated by induction of the electrons in the collimated radiation field and outputs it to the data processing unit.

[0047] Step 2: The pulsed hard X-ray to be measured is shielded from visible light and electrons by the shielding film 4 and then absorbed by the metal absorber 1, and the temperature of the metal absorber 1 increases.

[0048] Step 3: The thermocouple 5 converts the temperature of the metal absorber 1 into a thermal electromotive force and transmits it to the data processing unit.

[0049] Step 4: The data processing unit calculates the number of electrons based on the acquired current, calculates the average number of photons based on the thermal electromotive force output by the thermocouple 5, and then calculates the photon-to-electron ratio based on the average number of photons and the number of electrons to complete the measurement.

[0050] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any change or replacement within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claimed rights.

Claims

1. A device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field, characterized in that: It comprises a calorimeter, a current coil (7) arranged on the top of the calorimeter, and a data processing unit; The calorimeter comprises a metal absorber (1), a shielding shell (3), a shielding film (4) and a thermocouple (5); the shielding shell (3) is in the shape of a cylinder, the axis of which is in the same straight line as the axis of the current coil (7), the inner wall of which is in the shape of a two-step cylinder, and the step surface between the two steps faces upward; the shielding film (4) is arranged at the top of the shielding shell (3), and a gap is provided between the shielding film (4) and the current coil (7); the metal absorber (1) is arranged in the shielding shell (3), and is arranged parallel to the shielding film (4) and the step surface, and a gap is provided between the shielding film (4); one end of the thermocouple (5) is connected to the metal absorber (1), and the other end extends from the bottom end of the shielding shell (3), and is used to convert the temperature of the metal absorber (1) into a thermoelectric potential; The data processing unit is connected to the other end of the thermocouple (5) and the output end of the current coil (7) respectively, and is used to calculate the corresponding ratio of photons to electrons through the thermoelectromotive force output by the thermocouple (5) and the current output by the current coil (7).

2. The device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to claim 1, characterized in that: Also includes a collimator (6); The collimator (6) is arranged at the top of the current coil (7), the axis of its collimation hole and the axis of the current coil (7) are located on the same straight line, and the aperture of the collimation hole is smaller than the inner diameter of the current coil (7).

3. The device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to claim 2, characterized in that: The metal absorber (1) is made of tantalum, tungsten or gold, and has a thickness ranging from 0.5 mm to 1 mm.

4. The device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to claim 3, characterized in that: The type of the thermocouple (5) is E type, T type, J type or K type, and its diameter ranges from 0.05 mm to 0.25 mm.

5. The device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to claim 4, characterized in that: The shielding film (4) is made of aluminum, copper or iron, and has a thickness ranging from 10 μm to 50 μm.

6. The device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to claim 5, characterized in that: The collimator (6) is made of tungsten or lead and has a thickness ranging from 0.8 cm to 1.2 cm.

7. The device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to any one of claims 1 to 6, characterized in that: The calorimeter further comprises a plurality of support rods (2) arranged in the shielding shell (3); A plurality of support rods (2) are vertically installed between the shielding film (4) and the step surface, and are evenly arranged around the inner wall of the shielding shell (3); the corresponding edges of the metal absorber (1) are embedded in the middle of the corresponding support rods (2).

8. The device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to claim 7, characterized in that: The support rod (2) is made of insulating material and has a diameter ranging from 1 mm to 2 mm; one end of the thermocouple (5) is welded to the metal absorber (1).

9. A method for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field, using the device for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1, the current coil (7) receives the current generated by the electrons in the radiation field of the pulsed hard X-ray to be measured after being induced, and outputs it to the data processing unit; Step 2, the pulsed hard X-ray to be measured is absorbed by the metal absorber (1) after being shielded by the shielding film (4) from visible light and electrons, and the temperature of the metal absorber (1) increases; Step 3, the thermocouple (5) converts the temperature of the metal absorber (1) into thermoelectromotive force and transmits it to the data processing unit; Step 4: The data processing unit calculates the number of electrons according to the acquired current, calculates the average number of photons according to the thermoelectromotive force, and then calculates the ratio of photons to electrons according to the average number of photons and the number of electrons to complete the measurement.

10. The method for measuring the ratio of photons to electrons in a pulsed hard X-ray radiation field according to claim 9, characterized in that: Step 1 is as follows: The radiation field where the pulsed hard X-ray to be measured is collimated by a collimator (6), and the current coil (7) receives the current generated by the electrons in the collimated radiation field after being induced, and outputs it to the data processing unit.

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