Dual-detector calibrated ultra-high dose rate proton beam monitoring system and method

Abstract

The application belongs to the technical field of radiation monitoring, and particularly relates to a double-probe calibrated ultra-high dose rate proton beam monitoring method, which comprises the following steps: 1, obtaining an efficiency ratio curve of a first probe and a second probe; 2, calculating a real-time dose rate according to the efficiency ratio curve; 3, adjusting a beam flow according to the real-time dose rate; and 4, irradiating a sample, and monitoring the beam flow in real time by the probe. The application can effectively correct the problem of the decrease of the detection efficiency of the probe such as an ionization chamber under the ultra-high dose rate, greatly improve the accuracy of the ultra-high dose rate proton dose measurement, and has an online real-time monitoring function to meet the actual application.

Description

Technical Field

[0001] This invention belongs to the field of radiation monitoring technology, specifically relating to an ultra-high dose rate proton beam monitoring system and method with dual detector calibration. Background Technology

[0002] Under irradiation by ultra-high dose rate (>40 Gy / s) particle beams, traditional ionization chamber detectors will suffer from reduced charge collection efficiency, signal weakening or distortion due to effects such as charge reconciliation and ion recombination. This results in reduced detection efficiency and accuracy, making it impossible to accurately monitor the beam dose rate in real time.

[0003] The highest-energy proton accelerator currently in use in China is the 100MeV high-current proton cyclotron accelerator at the China Institute of Atomic Energy, which can extract proton beams with current intensity in the microampere range. The S3 beamline established on it has already carried out relevant work on the biological effects of proton radiation.

[0004] Current methods using SEEM detectors and Faraday lamp calibration can only obtain the fluence and flux of protons at conventional dose rates (<200 Gy / min). Under ultra-high dose rate proton radiation, the capacitance saturates within just a few seconds. Therefore, the proton dose calculated using SEEM and Faraday lamp methods only reflects the beam state over a very short period. Since the beam intensity of an accelerator inevitably fluctuates over long periods of operation, traditional methods are insufficient for long-term monitoring of whether the proton beam is stable and whether the dose rate remains constant under ultra-high dose rates. Therefore, research on dose monitoring technology at ultra-high dose rates is essential. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a method for monitoring and correcting ultra-high dose rate proton beams using dual-detector calibration. This method involves adding a beam switch with an adjustable duty cycle to the beamline to modulate the proton beam into a pulse-like beam. A Faraday cage is still used as the calibration detector. Finally, a shield is constructed at the rear end of the sample using lead bricks, and another PTW ionization chamber detector is placed within the shield of a certain thickness as the calibration detector. By combining theoretical simulations with experimental data fitting, and by fitting three parameters—accelerator beam intensity, Faraday cage charge collection efficiency, and PTW ionization chamber parameters—the proton dose rate data at the irradiated sample can be obtained. This solves the problem of short-term charge saturation in traditional Faraday cages, resulting in real-time and accurate proton dose rate monitoring data during ultra-high dose rate proton beam delivery.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0007] A method for monitoring ultra-high dose rate proton beams with dual detector calibration includes the following steps:

[0008] Step 1: Obtain the efficiency ratio curve of the first detector and the second detector; the first detector is placed in front of the irradiated sample, and the second detector is placed in the shielded space behind the irradiated sample.

[0009] Step 2: Calculate the real-time dose rate based on the efficiency ratio curve;

[0010] Step 3: Adjust the beam current based on the real-time dose rate;

[0011] Step 4: Irradiate the sample, and the detector monitors the beam current in real time.

[0012] Furthermore, step 1 includes the following steps:

[0013] Step 11: Align the laser with the beam center height so that the beam center, the center of the first detector, and the center of the second detector are at the same center height;

[0014] Step 12: Activate the beam shutter located in front of the first detector, so that it modulates the beam to form a pulse-like beam with a duty cycle of a set value according to the set working mode;

[0015] Step 13: Adjust the accelerator beam current to increase gradually from 0. At each beam current value, collect the charge data of the first detector multiple times. Then remove the first detector and collect the dose rate data of the second detector set in the shielded space multiple times.

[0016] Step 14: Using the Monte Carlo simulation program, calculate the theoretical values ​​of the detection data collected by the first detector and the second detector set in the shielded space. Based on the measured values ​​of the detection data collected by the first detector and the second detector in Step 13, divide the measured values ​​by the corresponding theoretical values ​​to obtain the detection efficiency of the first detector and the second detector for different beam current values.

[0017] Step 15: Using the detection efficiency data of the first and second detectors corresponding to different beam current values ​​obtained in Step 14, fit the curve equations of the relationship between beam current and detection efficiency of the first and second detectors respectively.

[0018] Step 16: Calculate the efficiency ratio curve describing the relationship between the detection efficiency ratio of the first detector and the second detector and the beam current using the curve equation of the relationship between the beam current and the beam current of the first detector and the second detector in Step 15.

[0019] Furthermore, step 2 includes the following steps;

[0020] Step 21: First, the dose rate is initially modulated to the target dose rate. A dose film is placed at the irradiation sample, and a shielding space and a second detector are placed behind it. The dose film is then irradiated with an ultra-high dose rate proton beam.

[0021] Step 22: Divide the dose rate reading of the second detector by the result of calculating the shielding loss after obtaining the irradiation dose at the irradiated sample through dose film scanning to obtain the detection efficiency E2 of the second detector;

[0022] Step 23: Calculate the detection efficiency E1 of the first detector using the efficiency ratio curve in Step 1 and the detection efficiency E2 of the second detector in Step 22.

[0023] Step 24: Move the first detector to the beamline position and calculate the real-time dose rate D based on the charge reading C of the first detector and the detection efficiency E1 of the first detector in step 23.

[0024] Furthermore, in step 3, the proton beam is adjusted according to the real-time dose rate in step 2 until the target dose rate is obtained at the irradiated sample, and then the first detector is removed.

[0025] Furthermore, in step 4, the irradiation dose of the irradiated sample is controlled by controlling the time parameter or the charge parameter.

[0026] Furthermore, in step 1, the first detector is a Faraday cylinder, and the second detector is a probe of the PTW ionization chamber.

[0027] Furthermore, in step 12, the beam shutter operates by opening for 1 second and closing for 9 seconds, with a duty cycle of 10% for the pulse-like beam.

[0028] Furthermore, in step 24, the formula for calculating the real-time dose rate D is as follows:

[0029] D = C@E p / (C p ·E1), where C is the charge reading of the first detector, E p The energy carried by a single proton, C p E1 represents the charge carried by a single proton, and E1 represents the detection efficiency of the first detector.

[0030] Furthermore, in step 13, the shielding space is a shielding space sealed by lead bricks.

[0031] A high dose rate proton beam monitoring system that uses the above method to achieve dual detector calibration includes a beam transport pipe, a beam shutter, a first detector, an irradiated sample, and a second detector located in a shielded space, arranged sequentially in the beam direction. The beam shutter is used to modulate the beam to form a pulse-like beam with a duty cycle of a set value. The first detector is used to detect charge data, and the second detector is used to detect dose rate data.

[0032] The beneficial effects of this invention are as follows:

[0033] The application of this method can effectively correct the problem of decreased detection efficiency of detectors such as ionization chambers under ultra-high dose rates, greatly improve the accuracy of ultra-high dose rate proton dose measurement, and has online real-time monitoring function to meet practical applications. Attached Figure Description

[0034] Figure 1 A schematic diagram of the layout of an ultra-high dose rate proton beam monitoring system calibrated with dual detectors;

[0035] Figure 2 This is a calibration diagram for the detection efficiency of the dual detectors.

[0036] In the above figures, 1 is the beam transport pipe; 2 is the beam shutter; 3 is the first detector; 4 is the irradiated sample; and 5 is the second detector located in the shielded space. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] A method for monitoring ultra-high dose rate proton beams with dual detector calibration includes the following steps:

[0039] Step 1: Obtain the efficiency ratio curve of the first detector and the second detector; the first detector is placed in front of the irradiated sample, and the second detector is placed in the shielded space behind the irradiated sample.

[0040] Step 2: Calculate the real-time dose rate based on the efficiency ratio curve;

[0041] Step 3: Adjust the beam current based on the real-time dose rate;

[0042] Step 4: Irradiate the sample, and the detector monitors the beam current in real time.

[0043] A high dose rate proton beam monitoring system for dual detector calibration includes a beam transport pipe, a beam shutter, a first detector, an irradiated sample, and a second detector located in a shielded space, arranged sequentially in the beam direction. The beam shutter is used to modulate the beam to form a pulse-like beam with a duty cycle of a set value. The first detector is used to detect charge data, and the second detector is used to detect dose rate data.

[0044] To address the issue of online real-time dose monitoring in ultra-high dose rate proton irradiated samples, a dual-detector calibration monitoring method was designed. The specific technical solution is as follows:

[0045] 1. Record the beam intensity of the accelerator on the S3 beamline in real time, and record it as I.

[0046] 2. After the protons are extracted into the atmosphere, a beam shutter is set at the isocenter height. Its thickness is sufficient to completely block the proton beam. Its working mode is set to open for 1 second and close for 9 seconds, thereby modulating the proton beam to form a pulse-like beam with a duty cycle of 10%.

[0047] 3. Set up an atmospheric Faraday cup after the beam shutter, such as... Figure 1 As shown. The Faraday tube has an outer diameter of 26mm, a length of 40mm, an inner diameter of 10mm, and an inner depth of 25mm. It contains a vacuum chamber and is designed with a front panel, a rear panel, and a suction nozzle. The front panel collimates the beam, the rear panel converts the signal, and the suction nozzle connects to the vacuum pump. The tube is made of brass. The Faraday tube collects the charge count, recording the charge passing through the beam during each 1-second beam shutter opening as C. It automatically releases the charge after the beam stops, waiting for the next beam pulse to restart the counting.

[0048] 4. Remove the Faraday cylinder and build a sealed shielded space with lead bricks at the rear end of the irradiated sample. The lead brick shielding thickness is 2cm. Place the probe of a PTW proton ionization chamber detector in the shielded space and record the real-time proton dose rate D.

[0049] 5. Starting from 0, continuously increase the accelerator beam current, obtain the relationship between I and C and I and D respectively, and fit the response curve.

[0050] 6. Calculate the values ​​of C and D under ideal conditions in the Monte Carlo program, and compare them with the measured values. The response curve corresponding to the ratio of measured to theoretical values ​​is the E1 / E2-I curve (efficiency ratio curve).

[0051] 7. Remove the Faraday tube, make preliminary adjustments to the approximate beam current, obtain the measured dose at the irradiated sample location using a dosimeter, and simultaneously record the PTW value inside the shield. The detection efficiency E2 can be obtained by comparison.

[0052] 8. The detection efficiency E1 of the Faraday cage can be obtained from the efficiency ratio curve. After placing the irradiated sample at the irradiation position, the Faraday cage is first moved to the beam center. Since the Faraday cage has a beam-blocking function, the irradiated sample is not irradiated at this time, but the dose rate D at the irradiated sample after the Faraday cage is moved away can be calculated from the Faraday cage reading and E1. r .

[0053] 9. After fine-tuning the beam current to achieve the target dose rate at the irradiated sample, remove the Faraday cylinder and irradiate the sample.

[0054] 10. Record the PTW reading inside the shield during irradiation. Since the reading is recorded in real time during irradiation, the accuracy of the irradiated dose of the sample and the stability of the beam during irradiation can be deduced from E2, which serves as a dose verification method.

[0055] Example

[0056] The present invention discloses a layout for a dual-detector calibrated ultra-high dose rate proton beam monitoring system, as follows: Figure 1 As shown,

[0057] 1. First, align the laser with the beam center height to ensure that the beam center, Faraday tube center, and PTW probe center are at the same center height.

[0058] 2. Start the beam shutter and repeat the motion at a frequency of 1 second open and 9 seconds closed.

[0059] 3. The accelerator beam is gradually increased from 0. Charge data of the Faraday tube is collected ten times at each beam value. Then the Faraday tube is removed and the dose rate values ​​collected by the probe of the PTW proton ionization chamber are recorded ten times.

[0060] 4. Using the Monte Carlo simulation program, the number of particles to be deposited in the Faraday tube and the shielded space can be calculated from the accelerator beam. After being converted into the corresponding charge and dose rate data, they are used as theoretical values. By dividing the measured values ​​by the theoretical values, the detection efficiency E1 of the Faraday tube and the detection efficiency E2 of the PTW proton ionization chamber probe under different beam conditions can be obtained.

[0061] The relationship curves between the accelerator beam I and the detection efficiency of the PTW proton ionization chamber probe in the Faraday cage and the shielded space were fitted using MATLAB software, as follows: Figure 2 As shown. The fitting curve obtained shows the relationship between the Faraday tube detection efficiency E1 and the accelerator beam I: E1 = -1E-07I 2 -0.0002I+0.9982; The detection efficiency E2 of the PTW proton ionization chamber probe in the shielded space varies with the accelerator beam current I according to the curve: E2=-3E-08I 2-0.0002I+1.006; At high dose rates, the detection efficiency E1 of the Faraday tube is a polynomial fit, while the detection efficiency E2 of the PTW proton ionization chamber probe in the shielded space is more approximately a straight line. Thus, the efficiency ratio curve of E2 / E1 (or E1 / E2) can be obtained.

[0062] 5. Since the accelerator transmission efficiency is affected by many factors such as vacuum parameters and beam transmission line parameters, the curve relationship between the accelerator beam I and the detection efficiency of the two detectors is not constant. However, under the same beam conditions, that is, when the accelerator vacuum series parameters, beam line series parameters and magnetic field parameters are the same, the efficiency ratio curves of the two detectors are still stable and effective, and there is no need to recalibrate.

[0063] 6. When irradiating a sample with ultra-high dose rate protons, first pre-modulate the dose rate to (near) the target dose rate. Place a dosing film at the irradiation site, and then place a shield and the PTW proton ionization chamber probe inside it. Divide the PTW proton ionization chamber reading by the irradiation dose at the irradiated sample obtained by scanning with the dosing film, after calculating the shielding loss, to obtain the detection efficiency E2 of the PTW proton ionization chamber probe. Compare this to the efficiency ratio curve to obtain the detection efficiency E1 of the Faraday cup. Move the Faraday cup to the beamline position, and calculate the accurate dose rate D based on the Faraday cup reading C: D = C·E p / (C p ·E1), E p The energy carried by a single proton, C p The electric charge carried by a single proton.

[0064] 7. After calculating the precise dose rate based on the Faraday tube reading, the beam is fine-tuned until the desired target dose rate is obtained. Then, the Faraday tube is removed, and the dose is controlled by time or charge parameters to irradiate the sample. The PTW proton ionization chamber probe in the shielding body after irradiation can monitor the stability of the irradiation beam in real time.

[0065] 8. This method can also be extended to different types of detectors and different types of shielding layers. For example, using a flat plate ionization chamber as a calibration detector or using water as a shielding layer to calibrate the detector can all be promoted and used.

[0066] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A method for monitoring ultra-high dose rate proton beams with dual detector calibration, characterized in that, Includes the following steps: Step 1: Obtain the efficiency ratio curves of the first detector and the second detector; The first detector is positioned in front of the irradiated sample, and the second detector is positioned within a shielded space behind the irradiated sample; wherein, step 1 specifically includes: Step 11: Align the laser with the beam center height so that the beam center, the center of the first detector, and the center of the second detector are at the same center height; Step 12: Activate the beam shutter located in front of the first detector, so that it modulates the beam to form a pulse-like beam with a duty cycle of a set value according to the set working mode; Step 13: Adjust the accelerator beam current to increase gradually from 0. At each beam current value, collect the charge data of the first detector multiple times. Then remove the first detector and collect the dose rate data of the second detector set in the shielded space multiple times. Step 14: Using the Monte Carlo simulation program, calculate the theoretical values ​​of the detection data collected by the first detector and the second detector set in the shielded space. Based on the measured values ​​of the detection data collected by the first detector and the second detector in Step 13, divide the measured values ​​by the corresponding theoretical values ​​to obtain the detection efficiency of the first detector and the second detector for different beam current values. Step 15: Using the detection efficiency data of the first and second detectors corresponding to different beam current values ​​obtained in Step 14, fit the curve equations of the relationship between beam current and detection efficiency of the first and second detectors respectively. Step 16: Calculate the efficiency ratio curve describing the relationship between the detection efficiency ratio of the first detector and the second detector and the beam current using the curve equation of the relationship between the beam current and the beam current of the first detector and the second detector in Step 15. Step 2: Calculate the real-time dose rate based on the efficiency ratio curve; specifically, Step 2 includes: Step 21: First, the dose rate is initially modulated to the target dose rate. A dose film is placed at the irradiation sample, and a shielding space and a second detector are placed behind it. The dose film is then irradiated with an ultra-high dose rate proton beam. Step 22: Divide the dose rate reading of the second detector by the result of calculating the shielding loss after obtaining the irradiation dose at the irradiated sample through dose film scanning to obtain the detection efficiency E2 of the second detector; Step 23: Calculate the detection efficiency E1 of the first detector using the efficiency ratio curve in Step 1 and the detection efficiency E2 of the second detector in Step 22. Step 24: Move the first detector to the beamline position and calculate the real-time dose rate D based on the charge reading C of the first detector and the detection efficiency E1 of the first detector in step 23. Step 3: Adjust the beam current based on the real-time dose rate; Step 4: Irradiate the sample, and the detector monitors the beam current in real time.

2. The method for monitoring ultra-high dose rate proton beams with dual detector calibration as described in claim 1, characterized in that: In step 3, the proton beam is adjusted according to the real-time dose rate in step 2 until the target dose rate is obtained at the irradiated sample, and then the first detector is removed.

3. The method for monitoring ultra-high dose rate proton beams with dual detector calibration as described in claim 1, characterized in that: In step 4, the irradiation dose of the irradiated sample is controlled by controlling the time parameter or the charge parameter.

4. The method for monitoring ultra-high dose rate proton beams with dual detector calibration as described in claim 1, characterized in that: In step 1, the first detector is a Faraday tube, and the second detector is a probe of the PTW ionization chamber.

5. A dual-detector calibrated method for monitoring ultra-high dose rate proton beams as described in claim 1, characterized in that: In step 12, the beam shutter operates by opening for 1 second and closing for 9 seconds, with a duty cycle of 10% for the pulse-like beam.

6. The method for monitoring ultra-high dose rate proton beams with dual detector calibration as described in claim 1, characterized in that: In step 24, the formula for calculating the real-time dose rate D is as follows: D=C·E p / (C p ·E1), where C is the charge reading of the first detector, E p The energy carried by a single proton, C p E1 represents the charge carried by a single proton, and E1 represents the detection efficiency of the first detector.

7. The method for monitoring ultra-high dose rate proton beams with dual detector calibration as described in claim 1, characterized in that: In step 13, the shielding space is a shielding space sealed by lead bricks.

8. A high dose rate proton beam monitoring system employing the method described in any one of claims 1-7 to achieve dual detector calibration, characterized in that: The device includes a beam transport pipe (1), a beam shutter (2), a first detector (3), an irradiated sample (4), and a second detector (5) located in the shielded space, arranged sequentially in the beam direction. The beam shutter (2) is used to modulate the beam to form a pulse-like beam with a duty cycle of a set value. The first detector is used to detect charge data, and the second detector is used to detect dose rate data.

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