CN108196294A - A kind of X ray air attenuation coefficient detecting system - Google Patents

Abstract

The embodiment of the present invention relates to an X-ray air attenuation coefficient detection system. The detection system includes: an X-ray machine placed on an optical platform for emitting X-rays; a vacuum device, which includes a vacuum chamber, a vacuum pump, and a vacuum gauge. , vacuum measuring instrument, temperature sensor and temperature controller; the central axis of the vacuum chamber coincides with the center of the X-ray exit port of the X-ray machine; there is a vacuum port on the vacuum chamber; the vacuum pump is connected to the vacuum chamber through the connecting pipe The vacuum gauge is set between the connecting pipe and the vacuum chamber to measure the vacuum value in the vacuum chamber; the vacuum measuring instrument is electrically connected to the vacuum gauge; the temperature sensor is set at the connection between the vacuum chamber and the connecting pipe to measure The temperature value in the vacuum chamber; the thermostat, the thermostat is electrically connected to the temperature sensor; the ionization chamber, the center of the X-ray entrance of the ionization chamber coincides with the central axis of the vacuum chamber. In the present invention, the experimental operation is simple and easy to control.

Description

A detection system for X-ray air attenuation coefficient

technical field

The invention relates to the technical field of measuring equipment, in particular to an X-ray air attenuation coefficient detection system.

Background technique

When reproducing the X-ray air kerma unit in ionizing radiation metrology, a free-air ionization chamber is usually used. However, there is a distance difference between the defined point and the actual measurement point when the free-air ionization chamber performs absolute measurement of X-ray air kerma. Therefore, the air kerma energy at the defined point is determined by using the ionization quantity obtained at the measuring point, and the air attenuation caused by this distance difference must be corrected. X-ray air attenuation correction is a large correction item in the reproduction of air kerma in a free air ionization chamber, and has a great influence on the uncertainty of the total correction factor.

It can be seen from the above that the measurement of X-ray air attenuation is very important, and the air attenuation correction factor is usually determined by measuring the X-ray air mass attenuation coefficient. At present, the method of measuring the X-ray air attenuation coefficient is mainly the moving distance method. The X-ray air attenuation coefficient measured by the moving distance method needs to keep the same X-ray fluence entering the ionization chamber before and after the moving distance. However, this is very difficult in the experimental process. difficult to control.

Contents of the invention

The object of the present invention is to provide an X-ray air attenuation coefficient detection system that is simple in experimental operation and easy to control in view of the problems existing in the prior art.

To achieve the above object, the present invention provides an X-ray air attenuation coefficient detection system, said detection system comprising:

X-ray machine, placed on the optical table, for emitting X-rays;

Vacuum pumping device, described vacuum pumping device comprises vacuum chamber, vacuum pump, vacuum gauge, vacuum gauge, temperature sensor and thermostat;

In the vacuum chamber, the central axis of the vacuum chamber coincides with the center of the X-ray exit port of the X-ray machine; the vacuum chamber is provided with a vacuum port;

The vacuum pump is connected to the vacuum port of the vacuum chamber through a connecting pipe; the vacuum pump is started according to the received pressure control signal, and the air in the vacuum chamber is pumped out to make the pressure in the vacuum chamber reach the specified level. The pressure value specified by the pressure control signal;

The vacuum gauge is arranged between the connecting pipe and the vacuum chamber to measure the vacuum value in the vacuum chamber;

The vacuum measuring instrument is electrically connected to the vacuum gauge and used to display the vacuum value;

The temperature sensor is arranged at the connection between the vacuum chamber and the connecting pipe, and measures the temperature value in the vacuum chamber;

The thermostat, the thermostat is electrically connected to the temperature sensor, and is used to display the temperature value;

An ionization chamber, the center of the X-ray entrance of the ionization chamber coincides with the central axis of the vacuum chamber.

Preferably, the detection system further includes a grating, and the grating is arranged between the X-ray exit port of the X-ray machine and the vacuum chamber.

Preferably, the vacuum pumping device further includes a support frame, and the support frame includes a base, a support rod, a threaded rod and a mounting plate;

The base, the upper surface of the base is provided with a fixing ring;

The support rod, the support rod is a hollow rod; one end of the support rod is fixed in the fixed ring; the other end of the support rod is provided with a connector, and a threaded hole is opened on the connector;

The threaded rod passes through the connecting head through the threaded hole, and one end of the threaded rod extends into the support rod;

The mounting plate is fixed on the other end of the threaded rod and is used to fix the vacuum chamber.

Further preferably, the support rod is slidably connected to the connecting head, and the height of the mounting plate can be adjusted by turning the connecting head.

Further preferably, the fixing ring is fixedly connected to the base through a reinforcing rib.

Further preferably, the vacuum chamber includes a vacuum tube, two beryllium windows and a mounting frame;

For the vacuum tube, one end of the vacuum tube is provided with a fixed flange; the other end of the vacuum tube is provided with an open flange, and the open flange is provided with the vacuum port;

The two beryllium windows are respectively arranged on the fixed flange and the opening flange;

As for the mounting frame, one end of the mounting frame is fixedly mounted on the vacuum tube; the other end of the mounting frame is mounted on the mounting plate for fixing the vacuum chamber.

Still further preferably, the mounting frame and the mounting plate are connected by bolts.

Preferably, the connecting pipe is a corrugated pipe.

Preferably, a cut-off valve is provided at the connection between the vacuum pump and the connecting pipe.

Preferably, the vacuum gauge is a film gauge.

The X-ray air attenuation coefficient detection system provided by the embodiment of the present invention uses a vacuum pumping method to measure the X-ray air attenuation coefficient. A vacuum tube is placed between the X-ray source and the ionization chamber, and the vacuum pump is controlled to extract the air in the vacuum tube by adjusting the vacuum valve. Then monitor the air pressure and temperature in the vacuum tube before and after air pumping, and calculate the amount of air pumped out, thereby changing the thickness of the air mass that interacts with the air before the X-ray enters the ionization chamber, and calculating the air attenuation coefficient. This detection system can ensure that the amount of X-ray injection into the ionization chamber is always consistent during the experiment, and the experimental operation is simple and easy to control, which solves the problem that the X-ray injection amount of the ionization chamber is difficult to control in the moving distance method.

Description of drawings

Fig. 1 is a schematic structural diagram of an X-ray air attenuation coefficient detection system provided by an embodiment of the present invention;

Fig. 2 is a schematic diagram of the installation structure of the vacuum chamber and the support frame of the X-ray air attenuation coefficient detection system provided by the embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

The embodiment of the present invention relates to the X-ray air attenuation coefficient detection system provided. The vacuum method is used to measure the X-ray air attenuation coefficient, which ensures that the injection amount of X-rays entering the ionization chamber is always consistent during the experiment, and is simple to operate and easy to control. The problem that it is difficult to control the amount of X-ray injection in the ionization chamber in the moving distance method is solved.

Fig. 1 and Fig. 2 are respectively a structural schematic diagram of an X-ray air attenuation coefficient detection system provided by an embodiment of the present invention and a schematic diagram of the installation structure of a vacuum chamber and a support frame. Combined with Figure 1 and Figure 2:

The X-ray air attenuation coefficient detection system provided by the embodiment of the present invention specifically includes: an X-ray machine 1 , an optical table 2 , a vacuum device 3 , an ionization chamber 4 , a grating 5 , a support frame 6 and bolts 7 .

Specifically, the X-ray machine 1 is placed on the optical platform 2 for emitting X-rays.

The vacuuming device 3 includes a vacuum chamber 31 , a vacuum pump 32 , a vacuum gauge 33 , a vacuum measuring instrument 34 , a temperature sensor 35 and a temperature controller 36 . Wherein, the central axis of the vacuum chamber 31 coincides with the center of the X-ray exit port 11 of the X-ray machine 1 , and a vacuum port 311 is opened on the vacuum chamber 31 . The vacuum pump 32 is connected to the vacuum port 311 of the vacuum chamber 31 through the connecting pipe 37. The vacuum pump 32 is started according to the received pressure control signal, and the air in the vacuum chamber 31 is drawn out so that the pressure in the vacuum chamber 31 reaches the specified pressure control signal. pressure value. The vacuum gauge 33 is arranged between the connecting pipe 37 and the vacuum chamber 31 to measure the vacuum degree value in the vacuum chamber 31 . The vacuum gauge 34 is electrically connected to the vacuum gauge 33 for displaying the vacuum value. The temperature sensor 35 is arranged at the connection between the vacuum chamber 31 and the connecting pipe 37 to measure the temperature value in the vacuum chamber 31 for displaying the temperature value. The temperature controller 36 is electrically connected to the temperature sensor 35 .

The center of the X-ray entrance 41 of the ionization chamber 4 coincides with the central axis of the vacuum chamber 31 .

In addition, the detection system further includes a grating 5 , which is arranged between the X-ray exit port 11 of the X-ray machine 1 and the vacuum chamber 31 .

In a specific implementation process, the connecting pipe 37 is a corrugated pipe, the connection between the vacuum pump 32 and the connecting pipe 37 is provided with a stop valve, and the vacuum gauge 33 is a thin film gauge.

For fixed installation of the vacuum chamber 31 , the vacuum device 3 also includes a support frame 6 , and the support frame 6 includes a base 61 , a support rod 62 , a threaded rod 63 and a mounting plate 64 . A fixing ring 65 is provided on the upper surface of the base 61 , and the fixing ring 65 and the base 61 are fixedly connected by reinforcing ribs 67 . The support rod 62 is a hollow rod, one end of the support rod 62 is fixed in the fixed ring 65, and the other end of the support rod 62 is provided with a connecting head 66, which is slidably connected between the supporting rod 62 and the connecting head 66, and can be adjusted and installed by rotating the connecting head 66. The height of the plate 64, threaded holes (not shown) are provided on the connector 66. The threaded rod 63 passes through the connecting head 66 through the threaded hole, and one end of the threaded rod 63 extends into the supporting rod 62 . The mounting plate 64 is fixed on the other end of the threaded rod 63 for fixing the vacuum chamber 31 .

Meanwhile, the vacuum chamber 31 includes a vacuum tube 312 , two beryllium windows 313 and a mounting frame 314 . One end of the vacuum tube 312 is provided with a fixed flange 315, and the other end of the vacuum tube 312 is provided with an open flange 316, and the open flange 316 is provided with a vacuum port 311. Two beryllium windows 313 are respectively arranged on the fixed flange 315 and the opening flange 316 . One end of the mounting frame 314 is fixedly mounted on the vacuum tube 312 , and the other end of the mounting frame 314 is mounted on the mounting plate 64 , and the mounting frame 314 and the mounting plate 64 are connected by bolts 7 for fixing the vacuum chamber 31 .

The above is an introduction to the various components of the X-ray air attenuation coefficient detection system provided in this embodiment and the connection relationship between them. The complete structure and working principle of the X-ray air attenuation coefficient detection system will be described below in conjunction with Fig. 1 and Fig. 2 to elaborate.

In the X-ray air attenuation coefficient detection system provided in this embodiment, the X-ray machine 1 provides the X-ray source, placed on the optical platform 2, and the ionization chamber 4 realizes the absolute measurement of the X-ray photon flux. The X-rays emitted by 1 can be received by the ionization chamber 4, and the center of the X-ray entrance 41 of the ionization chamber 4 is aligned with the center of the X-ray exit 11 of the X-ray machine 1.

In order to solve the problem that it is difficult to control the injection amount of X-rays in the ionization chamber in the moving distance method, this embodiment adopts a vacuum pumping method, without changing the relative distance between the X-ray machine 1 and the ionization chamber 4, directly changing the X-rays entering the ionization chamber. 4 The thickness of the air mass interacting with the air before, by measuring the relevant experimental data, that is, the air pressure value and temperature value in the vacuum tube 312 before and after vacuuming, and calculating the change in the thickness of the air mass in the vacuum tube 312 before and after vacuuming, Finally, the X-ray air attenuation coefficient is calculated according to the current value before and after vacuuming and the change in the thickness of the air mass in the vacuum tube 312 .

Therefore, a vacuum device 3 is provided between the X-ray machine 1 and the ionization chamber 4. The vacuum device 3 mainly includes a vacuum chamber 31, a vacuum pump 32, a vacuum gauge 33, a vacuum measuring instrument 34, a temperature sensor 35 and a temperature controller 36.

Wherein, the main body of the vacuum chamber 31 is a vacuum tube 312, in order to be connected with the vacuum pump 32 and to seal the two ends of the vacuum tube 312, the two ends of the vacuum tube 312 are respectively provided with a fixed flange 315 and an opening flange 316, and the fixed flange 315 and the opening All the flanges 316 are sealed with beryllium windows 313, and the open flange 316 is provided with a vacuum port 311 for connecting the vacuum chamber 31 with the vacuum pump 32, so that the vacuum pump 32 can vacuum the vacuum tube 312 of the vacuum chamber 31. At the same time, in order to ensure that the X-rays can pass through the vacuum tube 312 accurately, the center of the X-ray entrance 41 of the ionization chamber 4 and the center of the X-ray exit 11 of the X-ray machine 1 are all at the center of the vacuum tube 312. On the axis, in order to facilitate the adjustment of the position of the vacuum tube 312, the vacuum chamber 31 needs to be placed on a support that can be adjusted, so the vacuum chamber 31 also includes a mounting frame 314 that is connected to the frame. One end of the mounting frame 314 is a double support plate. For the fixing of the vacuum tube, the other end of the installation frame 314 is a connecting plate connected with the double supporting plates, and is used for being installed on the bracket.

The vacuum device 3 adopts a height-adjustable support frame 6, and the upper surface of the base 61 of the support frame 6 is provided with a fixed ring 65 for fixing the support rod 62, and one end of the support rod 62 is inserted in the fixed ring 65 to ensure For the firmness of the fixation, the fixed ring 65 and the base 61 are strengthened and fixedly connected by reinforcing ribs 67 . In order to install the vacuum tube 312 , the support frame 6 also includes a mounting plate 64 , and the other end connecting plate of the mounting frame 314 is mounted on the mounting plate 64 through bolts 7 . Wherein, the connection mode of mounting plate 64 and support rod 62 adopts the simplest and continuously adjustable screw connection, so the other end of support rod 62, that is, the end connected with mounting plate 64, is provided with connecting head 66 and threaded rod 63. The head 66 has a threaded hole matched with the threaded rod 63. The threaded rod 63 adjusts the height of the mounting plate 64 by rotating in the threaded hole in the connecting head 66. In order to ensure that the threaded rod 63 has enough adjustment space, the support rod 62 is set as a hollow rod-shaped structure. Since the central axis of the vacuum tube 312 and the center of the X-ray exit port 11 of the X-ray machine 1 are on the same plane perpendicular to the horizontal ground when the height is adjusted, the center of the X-ray exit port 11 of the X-ray machine 1 is the alignment point, and the vacuum tube 312 Up and down adjustment, when the central axis of the vacuum tube 312 is aligned with the center of the X-ray exit port 11 of the X-ray machine 1, the height adjustment is completed, but if the connection head 66 is fixedly connected with the support rod 62, then the adjustment of the mounting plate 64 When the height is high, the rotation of the threaded rod 63 will also drive the rotation of the mounting plate 64, and the rotation of the mounting plate 64 will cause the central axis of the vacuum tube 312 to rotate. It is necessary to readjust the horizontal position of the vacuum tube 312, which increases the difficulty of adjustment. Therefore, in this process, in order to simplify During the experiment, it is necessary to ensure that the mounting plate 64 does not rotate with the change of height, so the support rod 62 is slidingly connected with the connecting head 66. When the connecting head 66 is rotated, the threaded rod 63 does not rotate absolutely, and the mounting plate 64 is driven to adjust the height up and down. At the same time, the sliding between the connecting head 66 and the support rod 62 also ensures that the support rod 62 will not rotate absolutely, which simplifies the experiment process and makes the operation easier.

Simultaneously, in order to prevent the X-rays emitted by the X-ray machine 1 from irradiating the edge of the beryllium window 313 of the vacuum tube 312 and affecting the experimental data, an additional installation can be made between the X-ray exit port 11 of the X-ray machine 1 and the vacuum chamber 31. The grating 5, the grating 5 plays the role of blocking light and releasing scattering, so that the measured experimental data is more accurate.

In this embodiment, the vacuum pump 32 is used to evacuate the vacuum chamber 31. The vacuum pump 32 is connected to the vacuum port 311 of the vacuum chamber 31 through the connecting pipe 37. Preferably, the connecting pipe 37 is suitable for measuring low pressure and has high sensitivity. Bellows, in addition, in order to stabilize the chamber pressure in the vacuum pipe 312 at a stable value, a cut-off valve is provided at the connection between the vacuum pump 32 and the connecting pipe 37, which can adjust the effective pumping speed of the system to the vacuum chamber 31. At the same time, The bellows cut-off valve of the intake air is used to adjust the intake air volume so that the pressure in the vacuum tube 312 is stabilized at the pressure value required for work. The pressure in the vacuum tube 312 is measured by a vacuum gauge 33 , and the measured value is displayed by a vacuum gauge 34 . The temperature in the vacuum chamber 312 is measured by a temperature sensor 35 , and the measured value is displayed by a temperature controller 36 .

In this embodiment, the positions of the variable X-ray machine 1 , the vacuum tube 312 and the ionization chamber 4 are first installed and calibrated, and an infrared laser beam is used for auxiliary calibration. First align the infrared laser beam to the center of the X-ray exit port 11 of the X-ray machine 1, and use the aligned infrared laser beam to calibrate the mounting plate 64 of the support frame 6, because the vacuum tube 312 is installed in the center of the mounting plate 64 by the bolt 7 Position, so the centerline of the upper plane of the calibration mounting plate 64 coincides with the aligned infrared laser beam, and ensure that the upper plane of the mounting plate 64 is horizontal. Afterwards, the vacuum chamber 31 is installed on the mounting plate 64 and fine-tuned so that the aligned infrared laser beam and the central axis of the vacuum tube 312 are on the same vertical level, and then the height of the vacuum chamber 312 is adjusted by rotating the connecting head 66 , so that the infrared laser beam coincides with the central axis of the vacuum tube 312 . Finally, use the infrared laser beam to adjust the position of the ionization chamber 4 so that the center of the X-ray entrance 41 of the ionization chamber 4 and the center of the X-ray exit 11 of the X-ray machine 1 are all on the central axis of the vacuum tube 312, thereby completing the entire process. installation of the device.

In the measurement process, at first utilize the vacuum gauge 33 and the vacuum measuring instrument 34 to measure the pressure value in the vacuum tube 312 before vacuuming, and utilize the temperature sensor 35 and the temperature controller 36 to measure the temperature value in the vacuum tube 312 before the vacuuming, and record Then control the vacuum pump 32 to vacuumize the vacuum tube 312 in the vacuum chamber 31, then use the vacuum gauge 33 and the vacuum measuring instrument 34 to measure the pressure value in the vacuum tube 312 after vacuuming, and use the temperature sensor 35 and temperature The controller 36 measures the temperature value in the vacuum tube 312 after evacuation, and at the same time, records the ionization current measured by the ionization chamber 4 after evacuation. The change of air mass thickness in the vacuum tube is calculated by the pressure value and temperature value before and after vacuuming, and finally the X-ray air attenuation coefficient is calculated by using the change of air mass thickness in the vacuum tube and the ionization current before and after vacuuming.

The X-ray air attenuation coefficient detection system provided by the embodiment of the present invention uses a vacuum pumping method to measure the X-ray air attenuation coefficient. A vacuum tube is placed between the X-ray source and the ionization chamber, and the vacuum pump is controlled to extract the air in the vacuum tube by adjusting the vacuum valve. Then monitor the air pressure and temperature in the vacuum tube before and after air pumping, and calculate the amount of air pumped out, thereby changing the thickness of the air mass that interacts with the air before the X-ray enters the ionization chamber, and calculating the air attenuation coefficient. This detection system can ensure that the amount of X-ray injection into the ionization chamber is always consistent during the experiment, and the experimental operation is simple and easy to control, which solves the problem that the X-ray injection amount of the ionization chamber is difficult to control in the moving distance method.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (10)

1. An X-ray air attenuation coefficient detection system is characterized in that, the detection system comprises: X-ray machine, placed on the optical table, for emitting X-rays; Vacuum pumping device, described vacuum pumping device comprises vacuum chamber, vacuum pump, vacuum gauge, vacuum gauge, temperature sensor and thermostat; In the vacuum chamber, the central axis of the vacuum chamber coincides with the center of the X-ray exit port of the X-ray machine; the vacuum chamber is provided with a vacuum port; The vacuum pump is connected to the vacuum port of the vacuum chamber through a connecting pipe; the vacuum pump is started according to the received pressure control signal, and the air in the vacuum chamber is pumped out to make the pressure in the vacuum chamber reach the specified level. The pressure value specified by the pressure control signal; The vacuum gauge is arranged between the connecting pipe and the vacuum chamber to measure the vacuum value in the vacuum chamber; The vacuum measuring instrument is electrically connected to the vacuum gauge and used to display the vacuum value; The temperature sensor is arranged at the connection between the vacuum chamber and the connecting pipe, and measures the temperature value in the vacuum chamber; The thermostat, the thermostat is electrically connected to the temperature sensor, and is used to display the temperature value; An ionization chamber, the center of the X-ray entrance of the ionization chamber coincides with the central axis of the vacuum chamber. 2. The X-ray air attenuation coefficient detection system according to claim 1, characterized in that, the detection system also includes a grating, and the grating is arranged between the X-ray exit port of the X-ray machine and the vacuum between rooms. 3. The X-ray air attenuation coefficient detection system according to claim 1, wherein the vacuum pumping device also includes a support frame, and the support frame includes a base, a support rod, a threaded rod and a mounting plate; The base, the upper surface of the base is provided with a fixing ring; The support rod, the support rod is a hollow rod; one end of the support rod is fixed in the fixed ring; the other end of the support rod is provided with a connector, and a threaded hole is opened on the connector; The threaded rod passes through the connecting head through the threaded hole, and one end of the threaded rod extends into the support rod; The mounting plate is fixed on the other end of the threaded rod and is used to fix the vacuum chamber. 4 . The X-ray air attenuation coefficient detection system according to claim 3 , characterized in that, the support rod is slidingly connected to the connecting head, and the height of the mounting plate is adjusted by rotating the connecting head. 5 . The X-ray air attenuation coefficient detection system according to claim 3 , characterized in that, the fixed ring is fixedly connected to the base by reinforcing ribs. 6 . 6. X-ray air attenuation coefficient detection system according to claim 3, is characterized in that, described vacuum chamber comprises vacuum tube, two beryllium windows and mounting frame; For the vacuum tube, one end of the vacuum tube is provided with a fixed flange; the other end of the vacuum tube is provided with an open flange, and the open flange is provided with the vacuum port; The two beryllium windows are respectively arranged on the fixed flange and the opening flange; As for the mounting frame, one end of the mounting frame is fixedly mounted on the vacuum tube; the other end of the mounting frame is mounted on the mounting plate for fixing the vacuum chamber. 7. The X-ray air attenuation coefficient detection system according to claim 6, characterized in that, the mounting bracket and the mounting plate are connected by bolts. 8. The X-ray air attenuation coefficient detection system according to claim 1, characterized in that the connecting pipe is a corrugated pipe. 9 . The X-ray air attenuation coefficient detection system according to claim 1 , wherein a cut-off valve is provided at the connection between the vacuum pump and the connecting pipe. 10. The X-ray air attenuation coefficient detection system according to claim 1, wherein the vacuum gauge is a film gauge.