Four-quadrant gamma ray detector and gamma ray orientation method

Abstract

The invention provides a four-quadrant gamma ray detector and a gamma ray orientation method, and the detector comprises four gamma ray detection units with the same structure, the four gamma ray detection units are arranged in a 2 * 2 array, and each detection unit works independently and is used for converting an incident gamma ray into an electric signal; and the data acquisition and processing system is used for controlling a data acquisition time sequence and executing conformity judgment and selection logic and gamma ray direction resolving. The invention has the advantages that direction sensitive detection is realized through the four-quadrant array structure, and compared with the traditional collimator scheme, the weight is reduced by more than 70%; conventional background measurement and transient event capture are taken into account in a four-channel composite acquisition mode; the orientation algorithm based on the relative intensity ratio does not need absolute calibration, and the on-orbit calibration complexity is reduced. Tests show that the 1 MeV gamma ray orientation precision is superior to 5 degrees (half angle), and the requirements of space science exploration tasks are met.

Description

A four-quadrant gamma-ray detector and gamma-ray orientation method Technical Field

[0001] This application belongs to the field of space exploration technology, specifically relating to a four-quadrant gamma-ray detector and a gamma-ray orientation method. Background Technology

[0002] Gamma rays, as electrically neutral high-energy electromagnetic waves, are not deflected by interstellar magnetic fields during their propagation in space, exhibiting directional stability and long-distance propagation characteristics. Directional observation of gamma-ray sources is a key technological means in fields such as high-energy astrophysics research and space radiation environment monitoring.

[0003] However, gamma rays have high energy and strong penetrating power, and traditional directional techniques require heavy metal collimators (such as lead and tungsten) to mechanically restrict the incident direction. For example, a lead shield with an energy of 1 MeV requires a thickness greater than 70 mm to achieve a 99% attenuation rate. Due to strict limitations on payload weight in spacecraft, the large mass and volume of traditional collimators severely restrict their engineering application in spaceborne gamma ray detection.

[0004] In existing technologies, coded aperture imaging technology is also used to achieve gamma ray orientation, but its system complexity is high, data processing volume is large, and cost is high, making it difficult to meet the requirements of small satellite platforms for lightweight and low power consumption.

[0005] Therefore, there is an urgent need for a gamma-ray directional detection scheme that does not require a mechanical collimation structure, is lightweight, and has low power consumption. Summary of the Invention

[0006] The purpose of this application is to overcome the shortcomings of existing technologies in meeting the requirements of lightweight and low power consumption for small satellite platforms.

[0007] To achieve the above objectives, this application proposes a four-quadrant gamma-ray detector, which includes: four identical gamma-ray detection units arranged in a 2×2 array, each of which operates independently to convert incident gamma rays into electrical signals; and a data acquisition and processing system for controlling the data acquisition timing, executing compliance selection logic, and calculating the gamma-ray direction.

[0008] As an improvement to the aforementioned detector, the four identical gamma-ray detection units are four-quadrant sodium iodide scintillators, each independently packaged, with the quadrants isolated by a reflective layer and an aluminum film; a silicon photomultiplier is coupled to the light-emitting surface of each quadrant scintillator to convert the scintillating light signal into a charge signal.

[0009] As an improvement to the aforementioned detector, the incident surface of the sodium iodide scintillator is encapsulated with 2 mm thick aluminum material, and the light-emitting surface is made of 6 mm thick quartz optical glass, all encapsulated within an aluminum housing. The parameters of the sodium iodide scintillator include: density: 3.67 g / cm³. 3 Light yield: 38 photons / keV; peak wavelength: 415nm; decay time: 230ns.

[0010] As an improvement to the aforementioned detector, the parameters of the silicon photomultiplier include: photosensitive surface size: 3*3mm; fill factor: 64%; number of APD microcells: 4774; spectral response range: 250~950; peak response wavelength: 420nm; gain: 3E6; peak wavelength quantum efficiency: 31%; maximum dark count rate: 860kHz; maximum dark current: 443nA; rise time: 1.2ns; recovery time: 82ns.

[0011] As an improvement to the aforementioned detector, the data acquisition and processing system includes: an eight-channel signal acquisition circuit corresponding to the four gamma-ray detection units, with each detection unit configured with one single-photon signal acquisition channel and one beam integration signal acquisition channel; an FPGA logic processing unit for controlling the data acquisition timing, executing compliance selection logic, and calculating gamma-ray direction; and a power management unit for providing secondary power distribution and power protection.

[0012] As an improvement to the aforementioned detector, the data acquisition and processing system further includes a communication interface unit for exchanging commands and data with the satellite platform.

[0013] As an improvement to the aforementioned detector, the single-photon signal processing circuit includes a charge-sensitive preamplifier, a main amplifier, a pulse shaping circuit, a peak holding circuit connected in sequence, and a trigger and reset circuit and an analog-to-digital converter connected in parallel; the single-photon signal acquisition channel operates in the energy range of 100 keV to 2 MeV and is used for energy and flux measurement of space gamma-ray photons.

[0014] As an improvement to the aforementioned detector, the beam integration signal processing circuit includes a main amplifier, as well as a parallel trigger and reset circuit and a high-speed ADC circuit; the beam integration signal acquisition channel operates in the energy range of 100 keV to 4 MeV, with a sampling rate of 15 MSPS, and is used for recording the time waveform of transient gamma-ray events.

[0015] This application also provides a gamma-ray orientation method based on the aforementioned four-quadrant gamma-ray detector. The method includes: establishing a coordinate system, defining the detection surface as the XOZ plane, the direction from the incident surface of the sodium iodide scintillator to the emitting surface as the +Y direction, α representing the angle between the gamma-ray incident direction and the YOZ plane, β representing the angle between the gamma-ray incident direction and the XOY plane, and the calculation method for the gamma-ray direction of incidence is as follows: ; ;in, This represents the charge signal counting rate of channels x, x=1,2,3,4.

[0016] Compared with existing technologies, the advantages of this application are as follows: This invention achieves direction-sensitive detection through a four-quadrant array structure, reducing weight by more than 70% compared to traditional collimator schemes; the four-channel composite acquisition mode takes into account both conventional background measurement and transient event capture; the orientation algorithm based on relative intensity ratio does not require absolute calibration, reducing the complexity of on-orbit calibration. Experiments show that the orientation accuracy of 1 MeV gamma rays is better than 5° (half an angle), meeting the requirements of space science exploration missions. Attached Figure Description

[0017] Figure 1 shows the system principle block diagram of the four-quadrant gamma ray detector; Figure 2 shows the structural schematic diagram of the four-quadrant NaI scintillator, where: 1 is quartz optical glass (thickness 6 mm), 2 is aluminum encapsulation shell (thickness 2 mm), and 3 is aluminum gamma ray entrance window (thickness 2 mm); Figure 3 shows the detector coordinate system definition and quadrant numbering schematic diagram. Detailed Implementation

[0018] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0019] This application provides a four-quadrant gamma-ray detector and a gamma-ray orientation method. The method determines the direction of the gamma-ray source by utilizing the relative positions and signal intensity differences between the four quadrant detection units, thus eliminating the need for a traditional collimator structure and significantly reducing system weight and power consumption. Simultaneously, a four-channel coincidence measurement technique improves the accuracy of the detection data and enables the capture and waveform recording of gamma-ray events. This invention is applicable to applications such as gamma-ray signal detection in the space environment, gamma-ray bursts, and observation of celestial gamma-ray sources.

[0020] Example 1: This application provides a spaceborne four-quadrant directional gamma-ray detector, including a gamma-ray detection unit and a data acquisition and processing system.

[0021] The four identical gamma-ray detection units are arranged in a 2×2 array. Each detection unit works independently to convert incident gamma rays into electrical signals.

[0022] The gamma-ray detection unit includes a four-quadrant sodium iodide (NaI) scintillator, with each quadrant independently encapsulated and separated from the quadrants by a reflective layer and an aluminum film to prevent optical crosstalk. Preferably, the NaI scintillator's incident surface is encapsulated with 2 mm thick aluminum material, and the emitting surface is made of 6 mm thick quartz optical glass. The entire unit is encapsulated within an aluminum housing. The scintillator parameters are as follows:

[0023] A silicon photomultiplier (SiPM) is coupled to the light-emitting surface of a scintillator in each quadrant and is used to convert scintillating light signals into charge signals.

[0024] Preferably, the SiPM sensor parameters are:

[0025] The data acquisition and processing system includes: an eight-channel signal acquisition circuit corresponding to the four detection units, with each detection unit configured with one single-photon signal acquisition channel and one beam integration signal acquisition channel; an FPGA logic processing unit for controlling the data acquisition timing, executing conformance selection logic and direction calculation algorithm; a power management unit for providing secondary power distribution and power protection; and a communication interface unit for exchanging commands and data with the satellite platform.

[0026] The single-photon signal acquisition channel operates in the energy range of 100 keV to 2 MeV and is used for measuring the energy and flux of space gamma-ray photons. The beam integration signal acquisition channel operates in the energy range of 100 keV to 4 MeV with a sampling rate of 15 MSPS and is used for recording the time waveform of transient gamma-ray events. When all four single-photon channels detect valid signals within a preset time window, the FPGA triggers the coincidence measurement mode and starts the beam integration channel for waveform acquisition.

[0027] The power management unit includes: a current overload protection circuit, which uses a 3A fuse to achieve continuous overcurrent protection; a magnetic latching power-on control relay, which responds to command pulses with a response width of 80 ms and an amplitude of 5 V; a soft-start circuit, which consists of an RC network and a MOSFET, used to limit power-on surge current; and a filter and a DC-DC conversion module, which convert the satellite's primary power supply into a secondary power supply of +3.3 V, ±15 V, and +5.2 V.

[0028] The single-photon signal processing circuit includes a charge-sensitive preamplifier, a main amplifier, a pulse shaping circuit, a peak hold circuit connected in sequence, and a trigger and reset circuit and an analog-to-digital converter connected in parallel, which are used to extract energy information of single-photon events.

[0029] The beam integration signal processing circuit includes a main amplifier, as well as a parallel trigger and reset circuit and a high-speed ADC circuit, for recording the time-varying waveform of the beam signal.

[0030] Example 2: This invention also provides a gamma-ray orientation method based on the above-mentioned detector, comprising: establishing a coordinate system, defining the detection surface as the XOZ plane, the direction from the incident surface of the sodium iodide scintillator to the emitting surface as the +Y direction, α representing the angle between the incident direction of the gamma rays and the YOZ plane, β representing the angle between the incident direction of the gamma rays and the XOY plane, and the specific calculation method for the direction of gamma rays is as follows:

[0031]

[0032] in, This represents the charge signal counting rate of channels x, x=1,2,3,4.

[0033] Example 3 This example provides a spaceborne four-quadrant directional gamma-ray detector with a total weight of 8 kg and a power consumption of 15 W. The design specifications are as follows:

[0034] As shown in Figure 1, the detector includes four gamma-ray detection units, a data acquisition circuit, an FPGA logic processing unit, a power management unit, and a communication unit. Each gamma-ray detection unit contains a four-quadrant NaI scintillator, a SiPM sensor, and its driving circuit.

[0035] In a typical space gamma-ray background environment, the flux is low (<10). 3 photons / cm 2 When the beam integration channel has no effective output, the system operates in single-photon counting mode: the single-photon signal acquisition channel measures the energy and arrival time of the incident gamma-ray photon, and the FPGA records the energy spectrum data of each quadrant.

[0036] When a transient gamma-ray event occurs (such as a solar flare or gamma-ray burst), the flux increases sharply to >10. 6 photons / cm 2 On the order of s, all four single-photon channels detected signals above the threshold within a 100 μs time window. The FPGA triggered the conformal logic, started the beam integration acquisition channel, and recorded the time waveforms of the four signals at a rate of 15 MSPS, thus achieving complete capture of transient events.

[0037] Directional calculation: Suppose that in a certain observation, the count rates measured in the four quadrants are respectively: Q CH1 = 1250 counts / sQ CH2 = 1850 counts / sQ CH3 = 980 counts / sQCH4 = 1420 counts / s, then the total count rate ΣQ = 5500 counts / s.

[0038] Substituting into the direction calculation formula: α = [(1850 + 1420) - (1250 + 980)] / 5500 = 0.188 β = [(1250 + 1850) - (980 + 1420)] / 5500 = 0.127 This result shows that the incident direction of the gamma-ray source relative to the detector coordinate system is: biased towards the +Z axis (α>0) and biased towards the +X axis (β>0). Based on this, the azimuth and elevation angles of the gamma-ray source in space can be deduced.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application do not depart from the spirit and scope of the technical solutions of this application, and should all be covered within the scope of the claims of this application.

Claims

1. A four-quadrant gamma-ray detector, characterized in that, The detector includes: four identical gamma-ray detection units arranged in a 2×2 array, each of which operates independently to convert incident gamma rays into electrical signals; and a data acquisition and processing system for controlling the data acquisition timing, executing compliance selection logic, and calculating the gamma-ray direction.

2. The four-quadrant gamma-ray detector according to claim 1, characterized in that, The four identical gamma-ray detection units are four-quadrant sodium iodide scintillators, each independently packaged, with the quadrants isolated by a reflective layer and an aluminum film; a silicon photomultiplier is coupled to the light-emitting surface of each quadrant scintillator to convert the scintillating light signal into a charge signal.

3. The four-quadrant gamma-ray detector according to claim 2, characterized in that, The incident surface of the sodium iodide scintillator is encapsulated with 2 mm thick aluminum material, and the light-emitting surface is made of 6 mm thick quartz optical glass, all encapsulated within an aluminum housing. The parameters of the sodium iodide scintillator include: density: 3.67 g / cm³. 3 Light yield: 38 photons / keV; peak wavelength: 415nm; decay time: 230ns.

4. The four-quadrant gamma-ray detector according to claim 2, characterized in that, The parameters of the silicon photomultiplier include: photosensitive surface size: 3*3mm; fill factor: 64%; number of APD microcells: 4774; spectral response range: 250~950; peak response wavelength: 420nm; gain: 3E6; peak wavelength quantum efficiency: 31%; maximum dark count rate: 860kHz; maximum dark current: 443nA; rise time: 1.2ns; recovery time: 82ns.

5. The four-quadrant gamma-ray detector according to claim 1, characterized in that, The data acquisition and processing system includes: an eight-channel signal acquisition circuit corresponding to the four gamma-ray detection units, with each detection unit configured with one single-photon signal acquisition channel and one beam integration signal acquisition channel; an FPGA logic processing unit for controlling the data acquisition timing, executing compliance selection logic and gamma-ray direction calculation; and a power management unit for providing secondary power distribution and power protection.

6. The four-quadrant gamma-ray detector according to claim 5, characterized in that, The data acquisition and processing system also includes a communication interface unit for exchanging commands and data with the satellite platform.

7. The four-quadrant gamma-ray detector according to claim 5, characterized in that, The single-photon signal processing circuit includes a charge-sensitive preamplifier, a main amplifier, a pulse shaping circuit, a peak hold circuit connected in sequence, and a trigger and reset circuit and an analog-to-digital converter connected in parallel; the single-photon signal acquisition channel operates in the energy range of 100 keV to 2 MeV and is used for energy and flux measurement of space gamma-ray photons.

8. The four-quadrant gamma-ray detector according to claim 5, characterized in that, The beam integration signal processing circuit includes a main amplifier, as well as a parallel trigger and reset circuit and a high-speed ADC circuit; the beam integration signal acquisition channel operates in the energy range of 100 keV to 4 MeV, with a sampling rate of 15 MSPS, and is used for recording the time waveform of transient gamma-ray events.

9. A gamma-ray orientation method, implemented based on the four-quadrant gamma-ray detector according to any one of claims 1-8, the method comprising: Establish a coordinate system, define the detection surface as the XOZ plane, the direction from the incident surface of the sodium iodide scintillator to the emitting surface as the +Y direction, α represents the angle between the incident direction of the gamma rays and the YOZ plane, and β represents the angle between the incident direction of the gamma rays and the XOY plane. The method for calculating the direction of gamma ray incidence is as follows: ； ;in, This represents the charge signal counting rate of channels x, x=1,2,3,4.

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