WO2009135350A1 - Gas radiation detector and radiation imaging system - Google Patents

Abstract

A gas radiation detector (1) includes an electrode pair, which includes several sub-electrode pairs. Said several sub-electrode pairs are arranged along an incident direction of radiation (2).

Description

 Gas radiation detector and radiation imaging system

 The invention relates to a gas radiation detector and a radiation imaging system. Background technique

 In the field of nuclear radiation detection and nuclear technology applications, it is often necessary to simultaneously detect gamma rays or X-rays of several different energies. Especially in the field of radiation imaging, the radiation of different energies is different from the reaction mechanism of different components in the sample. The detection of dual-energy or multi-energy gamma ray or X-ray can not only obtain the projected image of the sample due to the difference in density, but also The z-value distribution of the test object can be calculated to distinguish between dangerous substances such as metals and organic substances, drugs, explosives, and embargoed articles.

 Considering the source of radiation, dual-energy and multi-energy images can be obtained by: using gamma-ray sources of different energies; X-ray machines alternately using different high-voltages to generate multiple energies; X-ray machines are preceded by filters of different compositions, To achieve a variety of energy options. The advantages of these methods are simple and easy to implement. The disadvantage is that when the dual-energy or multi-energy data of the same part of the test object is obtained, the same part of the test object must be irradiated with different energy for multiple times, and the test dose is increased. , prolonged the time of detection and reduced the pass rate. No matter how the two-energy and multi-energy rays are generated, the corresponding dual-energy or multi-energy detectors are needed for detection.

 Considering the detector system, dual-energy and multi-energy images can be obtained by: Single detector can measure single-photon energy spectrum, and then imaged by energy partition; detector is divided into low-energy detector group and high-energy detector group, in ray The tracks are stacked one on the other to measure the high and low energy rays. The low energy ray filter layer can be sandwiched between different detectors to make the low energy rays completely blocked, while the high energy detectors only receive high energy rays; or low energy detection The components of the high-energy detectors are arranged in an array to detect high and low energy rays. In the energy spectrum counting method, the current of the X-ray machine is not too large, and the electronic system is fast enough to separate a single photon in a beam, and the detector is required to have high energy resolution performance. In the latter mode, the thickness of the solid detector required for low-energy rays is too thin to be easily cut and prepared, and the corresponding readout circuit thereafter has a certain absorption effect on the radiation.

It can be used as a multi-energy detector with a scintillation detector plus a photodiode, or a solid-state detector such as a semiconductor detector. They are small in size and easy to operate, but the low-energy detector required in the low-energy region is too thin to be easily prepared, and the semiconductor is The radiation resistance of the detector affects its useful life. Gas detectors are another type of multi-energy detector with the advantages of low cost, simple preparation and long service life. In order to improve the detection efficiency of the detector, high air pressure can be used, so that the detection efficiency of the radiation can be compared with the solid state detector. Dual energy solid detectors can be made up of two The gas detector is composed of a low-energy ray filter in the middle clamp; it can also be composed of a gas detector and a solid-state detector. The disadvantage of the former is the two detector chambers, which increases the complexity of the operation; the latter because of the two types of detectors, the signals generated by the two responses need to be corrected.

 The conventional ionization gas detector is a planar electrode in which a gas is trapped in a sealed gas chamber and two parallel plates are fixed inside. The electrode is a continuous metal layer for collecting the detection gas between the parallel plates and the radiation incident into the room. The charge generated by the reaction. The sealed outdoor shape can be rectangular or cylindrical, and the chamber wall can be aluminum, stainless steel or other materials with good sealing properties. The size of the detection chamber is determined by the needs of the application. The rays of all energy are simultaneously measured without distinction. Summary of the invention

 In view of the problems with the dual energy system described above, it is an object of the present invention to provide a gas detector that is capable of at least partially alleviating the above problems.

 Another object of the present invention is to provide a gas detector that can flexibly implement dual-energy and multi-energy X-ray detection.

 Another object of the present invention is to provide a gas detector capable of overcoming the disadvantages of a low-energy solid-state detector that is too thin and difficult to prepare, and at the same time, achieves multi-energy detection in a gas chamber, is easy to operate, and greatly improves each The consistency of the road signal also satisfies the long-life and low-cost requirements of the detector.

 According to an aspect of the invention, a gas radiation detector includes: an electrode pair including a plurality of sub-electrode pairs, the plurality of sub-electrode pairs being arranged in an incident direction of the ray.

 According to another aspect of the invention, each of the plurality of pairs of sub-electrode pairs has opposite sides extending generally perpendicular to an incident direction of the ray.

 According to another aspect of the invention, each of the plurality of pairs of sub-electrode pairs has a substantially rectangular shape.

 According to another aspect of the invention, the opposing electrode plates of each of the plurality of sub-electrode pairs are substantially parallel to each other.

 According to another aspect of the invention, the electrode plates of the anodes of each of the plurality of sub-electrode pairs have a plurality of electrode strips arranged in a direction perpendicular to the incident direction of the rays.

 According to another aspect of the invention, the plurality of electrode strips are elongated, and the plurality of electrode strips have a length direction substantially the same as an incident direction of the rays.

According to another aspect of the present invention, an electrode plate of an anode of each of the plurality of sub-electrode pairs The plurality of electrode strips have a generally rectangular shape.

 According to another aspect of the present invention, one electrode plate of each of the plurality of sub-electrode pairs is substantially in one plane, and the other electrode plates of each pair of electrodes of the plurality of sub-electrode pairs are Generally in another plane.

 According to an aspect of the invention, the present invention provides a radiation imaging system comprising: a radiation source for emitting radiation; and a detector for receiving radiation emitted by the radiation source, wherein the detection The device is the above gas radiation detector.

 The invention provides a gas detector capable of simultaneously realizing multi-energy segment X or gamma ray simultaneous measurement, capable of operating in an integrated current mode or a counting mode, which greatly increases the demand limit of the detection system on the source intensity. Since the composition of the gas can be helium, argon, formazan, etc., it can also be a mixture of various gases, so it can be flexibly used for testing needs of different applications and different energy regions. The pressure of the gas can also be adjusted with the energy and type of radiation being measured to meet high detection efficiency requirements.

 The principle of simultaneous detection of pluripotent X or gamma ray according to the present invention is designed according to different thicknesses of radiation of different energy rays in the detection medium, and the radiation source may be composed of a plurality of single-energy ray sources, or may be a single The energy emitted by the X-ray machine is continuous of X-rays. The distinction between high-energy and low-energy rays does not require the conversion of high-pressure X-ray machines or the use of filters and collimators before the optics, but by the geometry and physics of the detector itself. The measurement principle is implemented. The high-low energy region is detected in the same gas detection chamber. The cathode and anode electrode plates are separated by a certain distance. The electrode plate substrate can be a PCB board or ceramic, etc., which is covered with a solid metal layer and two electrodes. The space between the plates is filled with gas and is used to detect rays entering the detector. The metal layers on the two electrode plates of the cathode and the anode are divided into several sections corresponding to the energy section to be tested, and the length of the metal layer in the ray direction is determined by calculation of the detected ray energy and gas type and pressure. All pairs of electrode pairs and sub-electrodes may be on two opposite parallel plates, the plate may be a PCB board, or a ceramic or the like, and the sub-electrode pairs may be distinguished by a metal electrode layer formed by segmentation on opposite planes between the parallel plates. of)

 The multi-energy simultaneous detection principle of the present invention can also be applied to all microstrip gas detectors, including the working principle of the ionization chamber, and the electrode strip is a proportional amplification of the anode and cathode. The planar cathode metal layer is divided into several segments according to the detected energy, and the microstrip electrodes for signal collection or amplification are also divided into several segments. The metal layer electrodes at different locations can provide voltage from the back side of the substrate through the metal vias on the substrate and extract signals.

The current invention realizes the simultaneous measurement of multi-energy ray in the same gas chamber, the material cost is low, the geometric structure is simple, the operation is convenient, the service life is long, and the gas type and pressure can be flexibly adjusted according to the applied ray energy interval to achieve The high detection efficiency solves the low energy detector of the dual-energy solid-state detector. It is difficult to prepare, and the same gas chamber ensures high consistency of signals and subsequent data processing is simple. The invention can be widely applied to the field of radiation imaging. DRAWINGS

 1 is a multi-energy gas detector in accordance with an embodiment of the present invention

 2a-2d are energy deposition profiles of X-rays of different energies in a helium gas at 15 atm, in accordance with an embodiment of the present invention.

 3 is a one-dimensional position sensitive multi-energy gas detector in accordance with an embodiment of the present invention.

4 is a one-dimensional position sensitive multi-energy proportional counter type gas detector in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As shown in FIG. 1, a gas radiation detector according to the present invention includes: an electrode pair including a plurality of sub-electrode pairs arranged in an incident direction 2 of the ray. Specifically, in a detection chamber sealed and filled with a high-pressure detecting gas, a plurality of detecting gases such as helium gas, argon gas, or the like may be mixed. In the figure, 1 is a detector filled with a detecting gas, 2 is an incident direction of X-rays, 3 is a charge collecting anode plate segmented by energy, 4 is a cathode plate segmented by an energy region corresponding to the anode, and 5 is a driving ray. An electric field that drifts in charge generated in a gas. The two electrode plates are metal layers which are evaporated or electroplated on an insulating material such as a PCB board or ceramic. The cathode and anode electrode plates are divided into several sections along the direction of incidence of the radiation, that is, several energy zones, respectively for detecting Rays of different energies. The principle of energy-distribution detection is based on the difference in the depth of penetration of rays of different energy in the high-pressure detection gas. The detector is operated in an ionization chamber state. In addition, the electrode plates can be formed in other ways, for example, by fixing a plurality of metal plates in the detection chamber. The electrode of the present invention is not limited to the anode plate 3 and the cathode plate 4 described above. The electrode of the present invention may also be any suitable other electrode. The plurality of sub-electrode pairs in Figure 1 are formed by respective segments of the charge collection anode plate 3 and corresponding (i.e., opposite) segments of the cathode plate 4. Each of the plurality of pairs of sub-electrode pairs may have opposite sides extending generally perpendicular to an incident direction of the ray. As shown in FIG. 1, each of the pair of electrode pairs has a substantially rectangular shape. Obviously, when the detector is of other structure, each of the plurality of pairs of sub-electrode pairs may have opposite sides extending at an acute angle to the incident direction of the ray. In addition, each of the electrode plates of each pair of electrodes may have other shapes. For example, when the detector is cylindrical, the segments of the charge collecting anode plate 3 and the segments of the cathode plate 4 are integrally formed in a circular shape.

 According to an embodiment of the invention, the opposing electrode plates of each of the plurality of sub-electrode pairs are substantially parallel to each other. That is, the segments of the charge collecting anode plate 3 and the segments of the cathode plate 4 are substantially parallel. Alternatively, the segments of the charge collecting anode plate 3 and the segments of the corresponding cathode plate 4 may form an acute angle.

According to an aspect of the invention, one electrode plate of each of the plurality of sub-electrode pairs is substantially in one plane, and the other electrode plate of each of the plurality of sub-electrode pairs is substantially In another plane. That is, the segments of the charge collecting anode plate 3 are substantially in one plane, and the segments of the cathode plate 4 are substantially in one plane. Alternatively, the segments of the charge collection anode plate 3 may not be in one plane and/or the segments of the cathode plate 4 may not be in one plane. The atomic number of the radiation detecting gas in the detector determines the thickness of the radiation of different energy rays in the gas, and also determines the reaction mechanism of the radiation and the gas is mainly the photoelectric reaction. We used the Monte Carlo method to simulate the energy deposition caused by the absorption of 15 atmospheres of helium to lOkeV to 160 keV X-rays. The vertical axis represents the photoelectric conversion rate of the ray, and the horizontal axis represents the thickness (unit: mm) of the helium gas passing through the ray in the incident direction. As shown in Fig. 2a, the calculated thickness of 15 atm of helium completely prevents lOkeV X-rays, 98% of 20 keV X-rays are blocked at 20 mm thick, and 30 atm of 15 atm xenon for X-rays below 40 keV. The blocking rate is nearly 90%, so the low-energy detection zone can be selected from 0 to 30 paintings of 15 atm helium; as shown in Figure 2b, for 50-70 keV X-rays, the 60-mm thick 15 atm helium has a blocking rate of nearly 90%, so The middle energy zone can be selected from the 30-60mm helium zone. At the same time, the X-ray spectrum of the X-ray machine is also the high-count X-ray characteristic peak in this energy zone. As shown in Fig. 2c, as the ray energy increases, The distribution of energy deposition in the gas is changed. The proportion of energy deposition in the initial path of the ray is reduced to 10%, and the thickness of the gas that penetrates is increased. Therefore, this energy region is selected as a helium region of 60 mm - 120 mm thick, for 80 keV - l lOkeV's X-ray absorption ratio is nearly 90%. As shown in Figure 2d, when the X-ray energy is increased again, it will deposit a small amount of energy evenly over the entire path through which the ray passes, such as less than 10%. Energy, the thickness of penetration is greatly increased, so this is high District election For the 120mm - 360mm thick helium region, the absorption ratio of X-rays from 120keV to 160keV is nearly 90%. If it is two or more single-energy sources, the data correction of energy deposition of high-energy rays in the low-energy detection zone is relatively simple. According to the distribution of the energy deposition in the gas, the energy deposition of the high energy ray is obtained from the signal value of the high energy detection zone, wherein the proportion of the energy energy deposited by the high energy ray in the low energy detection zone can be calculated by the ratio of the energy deposition distribution calculated by the simulation. Got it. The energy deposition in the lower energy zone is then calculated, and so on, the energy deposition of the ray of all energy segments in different test zones of the detector is calculated. For the continuous energy spectrum of the X-ray machine, the energy values of the different energy regions can be obtained by using the average energy or by integrating the X-ray continuous energy spectrum. In the high-energy detection zone, in order to obtain more accurate measurements of high-energy rays, a low-energy ray filter can be added between different energy measurement zones to absorb a certain proportion of low-energy rays, ensuring that there are no adjacent adjacent high-energy measurement zones. Energy deposition of low energy rays in the low energy region. However, the high-energy ray has energy deposition in the adjacent low-energy region, and at the same time, in the detection data of the high-energy ray, the absorption of the high-energy ray by the low-energy filter is taken into consideration at the same time. This simple structure of multi-energy gas detectors can be used for simple energy segmentation purposes only. It can also be applied to dosimeters, making it easier to distinguish the contribution of low-energy rays in the overall dose for accurate correction. Rather than relying solely on the shield between the radiation source term and the dosimeter to block low energy rays, since the actual state is low energy radiation also produces a dose. Another embodiment of the present invention is shown in FIG. 3, the cathode of the detector is still a segmented planar electrode plate, and the block planar electrode plate of the original signal collecting anode is changed to a uniform micro strip electrode strip 33 segmented by the energy region. Achieve one-dimensional position sensitivity while having the ability to measure multiple energy segments. The principle of segmentation of each energy zone is the same as above. As shown in FIG. 3, the electrode plates of the anodes of each of the plurality of sub-electrode pairs have a plurality of electrode strips 33 arranged in a direction perpendicular to the incident direction of the rays. Preferably, the electrode strip 33 has a generally rectangular shape. According to an aspect of the invention, the plurality of electrode strips 33 are elongated, and the longitudinal direction of the plurality of electrode strips 33 is substantially the same as the incident direction of the rays. Obviously, the width of the electrode strip 33 can be changed as needed, for example, the width of the electrode strip 33 can be several millimeters, several micrometers, or the like. Another embodiment of the invention is shown in Figure 4. The cathode of the detector is still a segmented planar electrode, the signal The collecting electrode becomes a negative-positive electrode segmented by an energy region, the cathode of the detector is used to illuminate the electric field of the generated charge, and the cathode 32 and the anode 31 at the signal collecting portion generate an electric field for proportional amplification of the electrons migrated thereto, It is eventually collected by the anode 31. The principle of segmentation of each energy zone is the same as above. The main way in which the gas reacts with the ray is the photoelectric effect due to the range of values of the selected gas and the energy segment of the X or gamma ray. Another method for more accurately separating the energy deposition of high-energy low-energy rays when the gas detector is operating in the counting mode is that the counter of each energy region is set to two thresholds, the energy generated by the high-energy rays deposited in the same energy region. Large, low-energy ray deposition energy produces a small signal, so increasing the low threshold of each energy region can further effectively remove a small portion of the energy deposition of low-energy rays in adjacent low-energy ray regions in the high-energy region, while appropriately reducing each energy. The high threshold of the zone can effectively remove the energy deposition of adjacent high energy rays in the low energy zone. The two extended-use one-dimensional position sensitive detectors of the invention can be applied to radiation imaging. The energy region within 160 keV is the X-ray energy region for small object security inspection, and the medical imaging energy is also within 160 keV. Therefore, according to the ray energy required for the specific application, the corresponding gas type and gas pressure are calculated, and the size and data correction of the high and low energy regions are determined according to the thickness of the gas to the different energy rays. When the one-dimensional position sensitive multi-energy gas detector plus electronic processing system, and the radiation source, mechanical scanning device, electrical control system, computer and system operation and image processing software form a line scan imaging device, The object to be inspected between the detectors is imaged, and multi-energy segmentation measurement is performed to identify the atomic number z of the object to be distributed. For the simple pluripotent detector shown in Figure 1, the anode plane of the signal readout is divided into sections by energy region, and there are several corresponding signal readout channels, each signal representing an energy. Because of the limited division of the energy region, the readout electronics of this structure is relatively simple. For the one-dimensional position sensitive multi-energy detector of Fig. 3, the anode strip of the signal readout is divided into several sections according to the energy region, and each electrode strip in each energy section is a readout channel, in each energy region. Each channel of the readout gives a one-dimensional spatial distribution of the rays that produce the signal in this energy region. The readout channels of all energy zones are processed by multi-channel front-end amplifiers, digitized by AD analog-to-digital conversion, into signal transmission and processing, system and data control, and finally into the computer for imaging processing. The electronic system provides both systems and detection. The power required to operate the unit.

The invention also provides a radiation imaging system. The radiation imaging system comprises: a radiation for emitting radiation a line source; a detector for receiving radiation emitted by the radiation source, wherein the detector is the gas radiation detector described above. Since the other components of the radiation imaging system may be any existing components other than the gas radiation detector described above, they will not be described again here. In other words, the gas radiation detector of the present invention can be applied to a variety of suitable existing radiation imaging systems. The invention realizes the simultaneous measurement function of the multi-energy ray in the same gas chamber through a simple geometric structure, the material cost is low, the operation is simple, and the gas type and pressure can be flexibly adjusted according to the applied ray energy interval to achieve high detection. The efficiency solves the problem that the low-energy detector of the dual-energy solid-state detector is too thin and difficult to prepare, and the same gas chamber ensures high consistency of each signal, and subsequent data processing is simple. The multi-energy ray simultaneous detection technology of the invention has the characteristics of low noise, high detection efficiency, low cost, simple structure, convenient operation and long service life. Using sophisticated board fabrication techniques, high position resolution is achieved with micron-sized electrode strip widths. The multi-energy detection technology can be widely used in the field of radiation detection, especially in the field of radiation imaging, and the contrast of radiation imaging is improved. The detector system can be used for both simultaneous pluripotent ray detection and for radiation imaging detector systems in line arrays or area arrays.

 Furthermore, the various structures or features in the above embodiments may be combined with each other to form a new embodiment, unless such a combination is not feasible.

Claims

Rights request A gas radiation detector comprising:  An electrode pair comprising a plurality of sub-electrode pairs arranged in an incident direction of the ray.  2. The gas radiation detector according to claim 1, wherein each of the pair of the plurality of sub-electrode pairs has opposite sides extending substantially perpendicular to an incident direction of the ray.  3. The gas radiation detector according to claim 2, wherein each of the pair of electrode pairs has a substantially rectangular shape.  4. The gas radiation detector according to claim 3, wherein the opposing electrode plates of each of the plurality of sub-electrode pairs are substantially parallel to each other.  The gas radiation detector according to claim 4, wherein the electrode plates of the anodes of each of the plurality of sub-electrode pairs have a plurality of electrode strips arranged in a direction perpendicular to an incident direction of the rays.  6. The gas radiation detector according to claim 5, wherein the plurality of electrode strips of the electrode plates of the anode of each of the plurality of sub-electrode pairs have a substantially rectangular shape.  The gas radiation detector according to any one of claims 2 to 6, wherein one of each of the plurality of sub-electrode pairs is substantially in one plane, and the plurality of sub-portions The other electrode plate of each of the pair of electrodes is generally in the other plane.  8. The gas radiation detector according to claim 5, wherein the plurality of electrode strips are elongated, and the length direction of the plurality of electrode strips is substantially the same as the incident direction of the rays.  9. A radiation imaging system comprising:  a source of radiation for emitting radiation;  A detector for receiving radiation emitted by the radiation source, wherein the detector is a gas radiation detector according to any one of claims 1-7.