Near-earth orbit neutron and gamma ray detector group, detection equipment and detection method

Abstract

The invention provides a near-earth orbit neutron and gamma ray detector group, detection equipment and a detection method, and the detection equipment is a neutron / gamma spectrometer which is small in size, small in mass, low in power consumption and high in speed and is designed based on a multilayer single / double sensitive area Si detector and a cadmium zinc telluride (CZT) detector array. The neutron / gamma spectrometer can serve as an independent load to be carried on a small satellite, and measurement of thermal neutrons, fast neutrons below 20 MeV and gamma rays is achieved. Different layers of the detector group in the detection equipment are matched to form a plurality of anticoincidence groups, so that the accuracy of energy spectrum inversion is improved. According to the detection method, a stacking and discarding algorithm is provided, so that interference caused by signal overlapping is avoided, and the system resolution of the whole neutron / gamma spectrometer is improved.

Description

Technical Field

[0001] The present invention relates to the field of radiation detection technology, and in particular to a low-Earth orbit neutron and gamma-ray detector group, detection equipment and detection method. Background Art

[0002] The radiation belt near the low-Earth orbit contains galactic cosmic rays, solar high-energy particles, and various derived secondary particles, and the radiation environment is extremely complex. Detecting neutrons and gamma rays in low-Earth orbit helps to gain a deeper understanding of space science issues, such as space station environment monitoring, the source of particles in the low-Earth orbit radiation belt, and physical phenomena related to solar high-energy particles.

[0003] Common detectors used to measure nuclear radiation mainly include gas discharge detectors, scintillator detectors and semiconductor detectors. Among them, gas discharge detectors have relatively low energy resolution and high operating voltage, making it difficult to distinguish radiation of different energies, and are often not suitable for energy spectrum detection. Scintillator detectors can detect various types of charged particles and neutral particles, with high detection efficiency and good time resolution, but their shortcomings are poor spatial resolution and high energy consumption. Semiconductor detectors have the advantages of low noise, low leakage current, high detection efficiency and energy resolution. They have different response characteristics for ionizing radiation and can reflect the radiation dose in human tissue or water through conversion coefficients. However, monolithic semiconductor detectors cannot effectively determine the LET value and dose equivalent, so silicon combined detectors with telescope structures have been proposed and widely used. However, silicon combined detectors are usually large in size and consume high electrical energy when working. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a low-Earth orbit neutron and gamma-ray detector group, detection equipment and detection method. The detection equipment is a set of small-volume, small-mass, low-power, high-rate neutron / gamma spectrometers designed based on multi-layer single / double sensitive area Si detectors and cadmium zinc telluride (CZT) detector arrays. The neutron / gamma spectrometer can be carried on a small satellite as an independent payload to achieve the measurement of thermal neutrons, fast neutrons below 20 MeV and gamma rays; wherein the cooperation between different layers of the detector group forms a variety of anti-coincidence groups to improve the accuracy of energy spectrum inversion. The detection method proposes a pile-up discarding algorithm, thereby avoiding the interference caused by signal overlap and improving the system resolution of the entire neutron / gamma spectrometer.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: In a first aspect, the present invention provides a low-Earth orbit neutron and gamma-ray detector assembly, comprising 15 detectors stacked in sequence, specifically comprising: The first detector and the fifteenth detector are single sensitive area CZT detectors for detecting gamma rays; The second detector is a single sensitive area Si detector, which is used to identify the direction of the incoming particles; The third, fourth and fifth detectors constitute a first anti-coincidence detection group, which are respectively composed of two single-sensitive-area Si detectors and a first double-sensitive-area Si detector containing a LiF coating therebetween; the twelfth, thirteenth and fourteenth detectors have the same structure as the first anti-coincidence detection group, and are further wrapped with a Gd layer on the outside, constituting a second anti-coincidence detection group; both the first anti-coincidence detection group and the second anti-coincidence detection group are used to detect thermal neutrons; The fifth, sixth, seventh and eighth detectors constitute the third anti-coincidence detection group, which are respectively a single sensitive area Si detector, a second dual sensitive area Si detector, a first dual sensitive area Si detector and a single sensitive area Si detector; the eighth, ninth, tenth and eleventh detectors constitute the fourth anti-coincidence detection group, which are respectively a single sensitive area Si detector, a first dual sensitive area Si detector including an HDPE coating, a second dual sensitive area Si detector and a single sensitive area Si detector; the fifth to eleventh detectors are used to detect fast neutrons.

[0006] Preferably, the sensitive layer of the single sensitive area CZT detector has a side length of 35 mm and a nominal thickness of 5 mm; The sensitive layer of the single sensitive area Si detector has a side length of 35 mm and a nominal thickness of 650 μm; The outer sensitive layer of the first dual-sensitive area Si detector has a side length of 35 mm, the inner sensitive area has a side length of 25 mm, and the thickness is nominally 300 μm; The outer sensitive layer of the second dual-sensitive area Si detector has a side length of 35 mm, the inner sensitive area has a side length of 25 mm, and the thickness is nominally 650 μm.

[0007] Preferably, the anti-coincidence detection group is used to remove interference from charged particles.

[0008] Preferably, the fourth detector comprising the LiF coating is used to record the count of signals generated by the reaction of neutrons in all energy ranges with LiF; The Gd layer of the second anti-coincidence detection group is used to absorb thermal neutrons, wherein the thirteenth detector is used to record the count of the signal generated by the reaction of the remaining neutrons except the thermal neutrons with LiF; The thermal neutron flux on the track is obtained by dividing the difference in counts between the fourth detector and the thirteenth detector by the detection efficiency.

[0009] Preferably, the sixth and seventh detectors are used to detect signals generated by galactic cosmic rays or other secondary neutrons; The ninth and tenth detectors are used to detect recoil proton signals generated by neutrons in the low-Earth orbit passing through the high-density polyethylene conversion layer; Under the anti-coincidence condition, the total energy spectra of the ninth and tenth detectors and the sixth and seventh detectors are subtracted to obtain the energy spectrum of the recoil proton.

[0010] In a second aspect, the present invention provides a low-Earth orbit neutron and gamma-ray detection device, comprising a rectangular outer shell, and a front end plate, a data acquisition board, and a low-Earth orbit neutron and gamma-ray detector group as described in the first aspect inside the outer shell; The data acquisition board is connected to the detector group and the front-end board for providing analog and digital power; it includes an FPGA chip, a level conversion chip, a CAN chip, an EMMC, a Gigabit Ethernet PHY chip, a universal asynchronous receiver and transmitter chip, and an ADC chip; The front-end board is connected to the detector group in communication, and includes a preamplifier circuit composed of an ASIC chip and discrete devices; the ASIC chip is used to collect neutrons, and the preamplifier circuit is used to collect gamma rays; the front-end board is used to receive the particle signal transmitted by the detector group and convert it into a voltage pulse; The housing includes a plurality of mounting holes for securing to a load.

[0011] Preferably, a plurality of fixing brackets are arranged inside the outer shell to connect the side surfaces so as to ensure the stability of the detection device.

[0012] In a third aspect, the present invention provides a method for detecting neutrons and gamma rays in a low-Earth orbit, based on the low-Earth orbit neutron and gamma ray detection device in the second aspect, comprising: When the detection device is powered on, the data acquisition board is initialized; If the configuration is completed, it will enter the acquisition mode and start acquisition. The ADC will convert the collected random voltage pulses. The digital signal obtained after conversion will be cached in the DDR together with the corresponding trigger time. Then, it will be determined whether there is an accumulated signal based on the signal accumulation and discarding algorithm. If there is an accumulated signal, it will be marked with a different frame format and stored in the EMMC. If the upload instruction of the CAN interface is received, the data saved in the EMMC will be uploaded to the satellite via Ethernet, and the satellite host will upload the data when landing at the ground station.

[0013] Preferably, the initialization of the data acquisition board further includes: detecting whether the peripheral circuit is normal, and if the configuration signal of the satellite is not received or the configuration is abnormal, the relevant telemetry data will be sent to the satellite.

[0014] Preferably, the accumulation discard algorithm is: The rise time of a single event pulse is , is ns level, forming time Set to 10 us, the fast amplifier output pulse will generate a width of The rectangular wave, Less than the rise time of a single-event pulse When two consecutive particles enter the detector and cause signal accumulation, two pulses with a width of rectangular wave, when the distance between the two rectangular waves Less than the entire molding time When the signal is considered to be accumulated, the accumulated signal is stored in the EMMC in different frame formats to realize the accumulation discard function.

[0015] Compared with the prior art, the present invention has the following beneficial effects: In order to solve the problems of large size, high power consumption, low resolution and inability to use high throughput in the spectrometers corresponding to the current scintillator detectors, this application proposes a small-volume, low-mass, low-power, high-rate neutron / gamma spectrometer designed based on a single / double sensitive area Si detector and a cadmium zinc telluride (CdZnTe, CZT) detector array. The neutron / gamma spectrometer is intended to be carried on a small satellite as an independent payload.

[0016] At the same time, a pile-up discarding algorithm was proposed and an FPGA program was designed to meet the configuration and readout timing, data processing, storage and interface requirements of CPRE10-32. Finally, in order to verify the design goals of the neutron / gamma spectrometer, the basic performance of the neutron / gamma spectrometer was tested, and the neutron / gamma spectrometer was tested under the standard radiation source. , , The energy spectrum under irradiation was analyzed and the host computer interface was designed to observe the energy spectrum changes in real time and compare them with the simulation results of Geant4.

[0017] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings constituting a part of the present disclosure are used to provide a further understanding of the present disclosure. The exemplary embodiments of the present disclosure and the description thereof are used to explain the present disclosure but do not constitute a limitation of the present disclosure.

[0019] Figure 1 The package dimensions of the detector provided in the first embodiment of the present disclosure; (a) is the package dimensions of the detector with a single sensitive area; (b) is the package dimensions of the detector with a dual sensitive area; Figure 2 A schematic diagram of a basic anti-coincidence detector arrangement provided in Embodiment 1 of the present disclosure; Figure 3A schematic diagram of a low-Earth orbit neutron and gamma-ray detector group provided in Embodiment 1 of the present disclosure; Figure 4 A perspective view of the housing of a low-Earth orbit neutron and gamma-ray detection device provided in Embodiment 2 of the present disclosure; Figure 5 A single-channel logic block diagram of the CPRE10-32 chip provided in Embodiment 2 of the present disclosure; Figure 6 A hardware structure diagram of a low-Earth orbit neutron and gamma-ray detection device provided in Embodiment 2 of the present disclosure; Figure 7 A method for detecting neutrons and gamma rays in low-Earth orbit provided in Embodiment 3 of the present disclosure; Figure 8 A schematic diagram of a stacking and discarding algorithm provided in Embodiment 3 of the present disclosure; Fig. 9 A flowchart of a stacking and discarding algorithm provided in Embodiment 3 of the present disclosure; Fig.10 The energy spectrum obtained by using an α source to irradiate a 35 mm diameter Si detector provided in the embodiment of the present disclosure; Fig.11 The upper function spectrum of the test irradiated Si detector provided by the embodiment of the present disclosure; Fig.12 The system energy resolution of the radioactive source irradiating the Si detector provided in the embodiment of the present disclosure; Fig.13 The embodiments of the present disclosure provide Energy spectrum irradiating the CZT detector; Fig.14 The embodiments of the present disclosure provide System energy resolution for irradiating CZT detectors; Fig.15 The embodiments of the present disclosure provide Energy spectrum irradiating the CZT detector; Fig.16 Tests provided for embodiments of the present disclosure Irradiate the CZT detector upper function spectrum; Fig.17 The embodiments of the present disclosure provide , Neutron / gamma spectrometer calibration curves irradiating CZT detectors; Fig.18 The embodiments of the present disclosure provide Comparison and verification diagram with Geant4 spectrum; Fig.19 The embodiments of the present disclosure provide Comparison and verification chart with Geant4 spectrum. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] Embodiment 1 Si semiconductor detectors have low density, low leakage current, and high energy resolution. They are widely used in the field of particle detection. CZT detectors make up for the shortcomings of Si detectors in terms of technology, and their detection efficiency for gamma rays is usually several times that of Si detectors. Therefore, this embodiment uses Si detectors as neutron detectors in the detector group, and uses CZT detectors as gamma ray detectors in the detector group.

[0022] like Figure 1 As shown, this embodiment designs a single sensitive area detector and a dual sensitive area detector to meet the detection requirements. Specifically, it includes: Single sensitive area CZT detector, the sensitive layer side length is 35 mm, the thickness is nominally 5 mm; Single sensitive area Si detector, with a sensitive layer side length of 35 mm and a nominal thickness of 650 μm; The first dual-sensitive-area Si detector has an outer sensitive layer with a side length of 35 mm, an inner sensitive area with a side length of 25 mm, and a nominal thickness of 300 μm; The second dual-sensitive area Si detector has an outer sensitive layer with a side length of 35 mm, an inner sensitive area with a side length of 25 mm, and a nominal thickness of 650 μm.

[0023] For neutron detection in space, since the radiation environment in which the detector is located is relatively complex and there are charged particles and neutrons in space at the same time, it is necessary to use the anti-coincidence method to remove the interference of charged particles. Figure 2 As shown in the figure, the upper and lower detectors have larger areas, the middle detector has smaller area, and the red one is the neutron conversion layer. Anti-coincidence means that if there is a signal in detector A or C at the same time, it proves that the signal at this time is a charged particle, then the signal in detector B at this moment will be removed.

[0024] In order to improve the detection efficiency and remove the influence of charged particles, the single sensitive area detector and the dual sensitive area detector are used, and the detectors are arranged in an anti-coincidence manner to form a low-Earth orbit neutron and gamma ray detector group.

[0025] Considering that the number of charged particles in different environments to be detected in space is different, if there are many charged particles in the radiation environment to be detected, so that the anti-coincidence solid angle range exceeding 90% cannot maintain a high signal-to-noise ratio, the anti-coincidence design of the single sensitive area detector cannot meet the requirements. Therefore, this embodiment uses a dual-sensitive area detector to further increase the range of the anti-coincidence solid angle.

[0026] like Figure 3 As shown, the detector group includes 13 Si semiconductor detectors in the middle part and 2 CZT detectors on both sides, a total of 15 detectors stacked in sequence. The gamma-ray detection part uses 2 detectors, the thermal neutron detection part uses a total of 6 detectors and a Gd shielding layer composed of an anti-coincidence detector group, and the fast neutron detection part uses 7 detectors to achieve the detection of thermal neutrons, fast neutrons below 20 MeV, and gamma rays. The specific arrangement is: (1) Gamma ray detection part The first detector and the fifteenth detector are single sensitive area CZT detectors for detecting gamma rays.

[0027] In this embodiment, the second detector is a single sensitive area Si detector, which is used to identify the direction of the injection of the detection particles.

[0028] In this embodiment, since neutrons are uncharged and cannot interact with particles in the semiconductor detector, it is necessary to indirectly detect neutrons by detecting secondary particles produced after the neutrons interact with atomic nuclei. This embodiment proposes to use the nuclear reaction method to detect neutrons, that is, adding LiF and HDPE conversion layers in the detector to cause nuclear reactions between neutrons and atomic nuclei in the conversion layer.

[0029] (2) Thermal neutron detection part The third to fifth detectors constitute a first anti-coincidence detection group, the third and fifth detectors are single-sensitive-area Si detectors, and the fourth detector is a neutron conversion layer, specifically a first double-sensitive-area Si detector including a LiF coating; The twelfth to fourteenth detectors constitute a second anti-coincidence detection group, the twelfth and fourteenth detectors are single-sensitive-area Si detectors, and the thirteenth detector is a neutron conversion layer, specifically a first double-sensitive-area Si detector including a LiF coating; different from the first anti-coincidence detection group, the twelfth to fourteenth detectors are further wrapped with a Gd shielding layer; The first anti-coincidence detection group and the second anti-coincidence detection group are both used to detect thermal neutrons.

[0030] In this embodiment, among the six detectors of the first anti-coincidence detection group and the second anti-coincidence detection group, the third, fifth, twelfth and fourteenth detectors have larger areas. As anti-coincidence detectors, they can remove a large number of charged particle signals through anti-coincidence. A 1 mm thick Gd is also wrapped around the outside of the twelfth, thirteenth and fourteenth detectors to absorb thermal neutrons. The fourth detector of the coating can detect neutrons in all energy ranges and The thirteenth detector wrapped in Gd in the second anti-coincidence detection group mainly records the signals generated by the reaction except thermal neutrons. The counts of the signals generated by the reaction and the thermal neutron flux on the track can be obtained by dividing the count difference of the two detectors by the detection efficiency.

[0031] (3) Fast neutron detection The fifth to eighth detectors constitute a third anti-coincidence detection group, the fifth detector is a single sensitive area Si detector, the sixth detector is a second dual sensitive area Si detector, the seventh detector is a first dual sensitive area Si detector, and the eighth detector is a single sensitive area Si detector; The eighth to eleventh detectors constitute a fourth anti-coincidence detection group, the eighth detector is a single sensitive area Si detector, the ninth detector is a first dual sensitive area Si detector including a HDPE coating, the tenth detector is a second dual sensitive area Si detector, and the eleventh detector is a single sensitive area Si detector; The third anti-coincidence detection group and the fourth anti-coincidence detection group share a Si detector, and the fifth to eleventh detectors are used to detect fast neutrons.

[0032] In this embodiment, the sixth and seventh detectors can detect signals generated by galactic cosmic rays or other secondary neutrons, while the ninth and tenth detectors can also detect recoil proton signals generated by neutrons in low-Earth orbit passing through the high-density polyethylene (HDPE) conversion layer. Therefore, under the anti-coincidence condition, the energy spectrum of the recoil protons can be obtained by subtracting the total energy spectrum of the ninth and tenth detectors from that of the sixth and seventh detectors. This symmetrical structure can effectively reduce the impact of background signals on the measurement and improve the accuracy of neutron energy spectrum inversion.

[0033] The low-Earth orbit neutron and gamma-ray detector group provided in this embodiment uses a total of 13 Si detectors and 2 CZT detectors. Si detectors are used in combination with a nuclear reaction method to detect neutrons, LiF and high-density polyethylene are used as neutron conversion layers, and the detectors are arranged in a stacked manner. The influence of charged particles can be removed by an anti-coincidence method, and gamma rays with a maximum deposited energy of 1.3 MeV can be detected by CZT detectors.

[0034] Embodiment 2 This embodiment provides a low-Earth orbit neutron and gamma-ray detection device, and its three-dimensional perspective view is as follows: Figure 4 As shown, it includes a rectangular outer shell, and a front end plate, a data acquisition board and a low-Earth orbit neutron and gamma-ray detector group as described in Example 1 inside the outer shell.

[0035] In this embodiment, the size of the outer shell is 93mm×87mm×93mm, and the flatness of the mounting surface is 0.1 / 100 mm×100 mm. The outer shell has four φ3 mounting holes for fixing to the payload and forming a Faraday cage with the satellite shell. The fixing bracket is used to connect the sides of the outer shell to provide support force to ensure the stability of the detection equipment. All outer shells and fixing brackets are made of aluminum alloy.

[0036] The outer shell includes two PCBs. The lower one is a front-end board with a preamplifier circuit composed of ASIC and discrete devices as the core, and the upper one is a data acquisition board equipped with FPGA, EMMC, ADC, Gigabit Ethernet and various required power supplies.

[0037] The data acquisition board is in communication connection with the detector group and the front end board, and is used for providing analog and digital power.

[0038] In this embodiment, the data acquisition board provides the analog and digital power required by the entire system. The data acquisition board uses FPGA as the core control chip, and mounts a level conversion chip, a CAN chip, an EMMC, a Gigabit Ethernet PHY chip, a Universal Asynchronous Receiver / Transmitter (UART) chip, and an ADC chip.

[0039] In this embodiment, the ASIC chip of the front-end board is powered by a single 5V power supply, while the HR Bank of the FPGA does not support 5V signal input. In order to achieve a higher dynamic range, the single-ended signal in the ASIC interacts with the FPGA through a level conversion chip. The CAN protocol in the communication interface is responsible for transmitting instructions, the Ethernet interface is used for data transmission, and the UART interface is used to communicate with the host computer during testing.

[0040] The front-end board is communicatively connected with the detector group, and includes a preamplifier circuit composed of an ASIC chip and discrete devices; the ASIC is used to collect neutrons, and the preamplifier circuit is used to collect gamma rays; the front-end board is used to receive particle signals transmitted by the detector group and convert them into voltage pulses.

[0041] Preferably, the ASIC chip used in this embodiment is a CPRE10-32 chip.

[0042] CPRE10-32 (Charge Pulse Readout Electronics, CPRE10-32) is a 32-channel universal readout chip designed for particle (nuclear) detector pulse signal readout. It has the advantages of energy and time readout function, low noise, low power consumption, and is equipped with convenient readout control logic, which can easily realize various readout schemes such as sparse, adjacent, and full channels. The original amplification factor of the chip is suitable for semiconductor particle detectors without multiplication effect such as Si-PIN and CZT; it can also be applied to detectors with a certain gain by using a smaller gain in the chip or an external charge distribution structure.

[0043] The single-channel logic block diagram of the CPRE10-32 chip is as follows: Figure 5 As shown, each channel of the chip includes a charge sensitive preamplifier, a filter shaping circuit, a peak detection and holding circuit and a timing circuit. The energy information held is sent to the analog output bus by the readout control logic for ADC reading; the timing information in the channel is held by the orthogonal timing peak holding circuit and sent to the analog bus. This chip is actually used for the first time after tape-out in this embodiment.

[0044] Through functional verification and performance testing of this chip, such as Figure 5 As shown in the figure, when the charge signal enters the chip from the input end, it first passes through the charge sensitive preamplifier, which converts the charge signal into a voltage signal, and then passes through the pole-zero cancellation circuit, using the differential amplifier circuit to gain the signal. The signal after gain is input into the slow forming and fast forming circuits, and the signal is compared with the configured threshold voltage. For the positive signal, it is greater than the threshold voltage, and for the negative signal, it is less than the threshold voltage. In this case, the comparator will output a valid signal to indicate that there is a channel trigger, and the signal can be read. At the same time, the signal will pass through the peak holding circuit, and the peak holding circuit will save the voltage peak of the signal for reading. Through the control of digital signals, the voltage in the peak holding circuit will be output to the analog output bus of the chip. After the voltage signal is converted to digital by the ADC, the data of the nuclear radiation event signal can be obtained.

[0045] Figure 5 The signal flow of a single channel is shown. In the case of multiple channels, it is an expansion of most circuit functions. The trigger signals of multiple channels are output in an OR relationship. When the comparator output of one channel is valid, the overall external trigger signal is in a valid state. When multiple channels are triggered, the signal peaks of each trigger channel are stored in their respective peak hold circuits, and are output to the analog output bus in sequence at the rising edge of each clock signal through the control of digital signals.

[0046] Since both Si detectors and CZT detectors are semiconductor detectors, the current pulses output by the detectors have a very short duration and very low energy, which can be regarded as charge signals. This signal cannot be detected directly, so an extremely high gain operational amplifier is required to convert the input charge signal into a voltage pulse.

[0047] In this embodiment, since the detection efficiency of the CZT detector for gamma rays is several orders of magnitude higher than the conversion efficiency of the Si detector with a neutron conversion layer, under the irradiation of the same energy level and the same number of neutrons and gamma rays, the number of particles detected by the CZT detector will be several times or even dozens of times the number of neutrons detected by the Si detector. However, all channels of the ASIC are only output to a group of analog buses. If the CZT detector is also connected to the ASIC, it will occupy the bandwidth of the ASIC and reduce the detection efficiency of neutrons. Therefore, the preamplifier provided by the Chinese invention patent CN118311640A-Single-channel signal analysis system and method applicable to multiple radiation detectors is used to complete the collection of gamma rays.

[0048] The overall architecture of the front-end board and data acquisition board is as follows: Figure 6 As shown in the figure, the front-end board and the data acquisition board are connected through a flexible flat cable (FFC). The signals in the flexible cable include low voltage differential signal (LVDS) signal, power supply and single-ended signal. Compared with the traditional TTL and CMOS interface, the LVDS signal adopts the transmission mode of differential signal. It is driven by a 3.5 mA constant current source and the terminal returns through a 100 Ω resistor. Therefore, the signal swing is only 350 mV, and the rate can reach hundreds of Mbit / s, which greatly reduces the power consumption of the communication process. And by using differential signals, common mode interference can be greatly reduced. The single-ended signal includes the analog output of the amplifier circuit and the analog output of CPRE10-32, the clock signal of CPRE10-32, and the digital signal of the trigger signal output.

[0049] In this embodiment, the front end board and the data acquisition board both have four φ3 mounting holes and are tightly coupled to the housing through metal screws.

[0050] The maximum total weight of the design standard of the low-Earth orbit neutron and gamma-ray detection equipment provided in this embodiment is 800 g, and the total weight after final assembly is 688 g. Among them, this embodiment selects CPRE10-32 to read out the particle signals of 13 Si detectors. The chip has 32 channels and a peak time of 200 ns. All channels are connected to the single-ended output pin DIRECTOUT of the analog readout bus. The amplifier circuit is used to read out the gamma rays of 2 CZT detectors. FPGA is used as the core of the data acquisition system to configure ASIC, read out, and set the threshold of the amplifier circuit. The analog signal read by CPRE10-32 and the amplifier circuit is converted into a digital signal through a high-speed ADC. The detection equipment communicates with the satellite host through two CANs and Gigabit Ethernet, one of which is the main control line and the other is a backup. The data in the detection equipment is uploaded to the satellite host through the Gigabit Ethernet on the PS side.

[0051] Embodiment 3 like Figure 7 As shown, this embodiment provides a method for detecting neutrons and gamma rays in low-Earth orbit, based on the detection device provided in the second embodiment, including: when the detection device is powered on, the data acquisition system will be initialized and the peripheral circuit will be detected to be normal. If the configuration signal of the satellite is not received or the configuration is abnormal, the relevant telemetry data will be sent to the satellite. If the configuration is completed, the acquisition mode will be entered and the acquisition will be performed. The ADC will convert the collected random voltage pulses. The digital signal obtained after the conversion will be cached in the DDR together with the corresponding trigger time. After that, it will be determined whether there is an accumulated signal according to the signal accumulation and discarding algorithm. If there is an accumulated signal, it will be marked with a different frame format and stored in the EMMC. If the upload instruction of the CAN interface is received, the data stored in the EMMC will be uploaded to the satellite through Ethernet, and the satellite host will upload the data when landing on the ground station.

[0052] In this specific embodiment, after the detection device is powered on, each module is initialized first, including serial port initialization, ADC initialization, etc. When the initialization is normal, the device works normally and CPRE configuration begins; when the device does not work normally, the indicator light flashes to remind.

[0053] The CPRE single-channel configuration is carried out in sequence: channel selection, preamplifier feedback capacitor and resistor selection, main amplifier gain selection, pole-zero cancellation function selection, slow shaping time selection, reference voltage selection, fast and slow DAC threshold selection, and fast and slow trigger enable selection.

[0054] The above process is repeated until all 32 channels are configured. Then the peak hold function is turned on and the signal is ready for reading.

[0055] Since the readout signal is an analog signal, it needs to be connected to the ADC sampling and converted into a digital readout. Since the 32 channels are parallel input and serial output, FIFO buffering and data channel processing are required. After channel division, two operations are performed simultaneously: determining the particle type and distinguishing whether there is accumulation. When there is signal accumulation, the format is changed to store the data. When there is no accumulation, the data is directly stored and finally uploaded to the host computer.

[0056] Since particle signals are random, when the counting rate is high, the voltage pulses output by slow shaping will accumulate signals. If the accumulated signals are not processed, the system resolution of the entire neutron / gamma spectrometer will be reduced, so an accumulation discarding algorithm is needed to discard the accumulated signals. The schematic diagram of the accumulation discarding algorithm is shown in the figure. Figure 8 shown.

[0057] The rise time of a single event pulse is , generally in the nanosecond range, forming time In this embodiment, it is set to 10us. After the fast amplifier output pulse passes through the fast discriminator, it will generate a pulse with a width of The rectangular wave, Less than the rise time of a single-event pulse When two consecutive particles enter the detector and cause signal accumulation, two pulses with a width of rectangular wave, when the distance between the two rectangular waves Less than the entire molding time When the signal is considered to be accumulated, the accumulated signal is stored in EMMC in different frame formats to realize the accumulation discard function. The signal accumulation discard algorithm flow chart is as follows Fig. 9 shown.

[0058] The shape time (Shape Time) or shape constant (τ) is an important parameter in the filter shaping circuit, which defines the time characteristics of the circuit's response to the input signal.

[0059] The shaping time is usually the time required for a circuit to reach 63.2% of its final steady-state value. In physics and engineering, shaping time more specifically describes the exponential response time of a first-order linear dynamic system. For a first-order RC filter, the shaping time τ is determined by the product of the resistance R and the capacitance C, that is, τ = R × C.

[0060] In nuclear instruments and radiation detectors, filter shaping circuits are used to convert the original signal (usually a fast pulse) output by the detector into a slow signal that is easy to measure and analyze. This slow signal is usually easier to digitize and can reduce the impact of noise and improve the signal-to-noise ratio.

[0061] The choice of shaping time depends on the specific application requirements, including the characteristics of the signal, the required time resolution, and the accuracy of the measurement. Shorter shaping times provide faster response but may sacrifice some signal quality, while longer shaping times provide better signal quality but slower response.

[0062] The shaping time is obtained by measuring the waveform and time span of the main amplifier output by an oscilloscope. As can be seen from the above, the size can be adjusted according to the resistance and capacitance.

[0063] In order to verify the performance of the detector group and detection equipment provided by the present invention, the detector of the neutron / gamma spectrometer and the entire system are tested by α and γ radiation sources, wherein the α radiation source is used to test the Si detector and ASIC readout performance, and the γ radiation source is used to test the CZT detector and amplifier circuit readout performance.

[0064] (1) α radiation source test and charged particle energy resolution test In order to verify the performance of Si detectors and charged particle energy resolution, the neutron / gamma spectrometer was irradiated with americium-241. The nuclide symbol of americium-241 is , with a half-life of 432.2 a. It is an alpha radiator. During the decay process, it can release three groups of alpha particles, as well as gamma rays and X-rays of a certain energy. The α source generated by the radioactive source irradiates the detector. Since the α particle rays cannot penetrate multiple detectors, testing one of them can obtain The energy spectrum is as follows Fig.10 As shown, the blue data is the data without the pile-up discarding algorithm, and the red data is the energy spectrum after the pile-up discarding control algorithm. The energy spectrum of the Si detector is shown in Fig.11 .

[0065] The measurement system is not evacuated during the test, and the α particles will react with the air and their energy will change. An alpha radiation source cannot be used to calibrate the neutron / gamma spectrometer. The energy spectrum only verifies whether the entire neutron / gamma spectrometer system is working properly. Fig.10 Gaussian fitting is performed on the source data to obtain the relative energy resolution of the entire system. The system energy resolution of the radiation source irradiating the Si detector is as follows Fig.12 As shown, in The energy resolution of the system under radiation source irradiation is 4.6%.

[0066] (2) Gamma radiation source and gamma ray energy resolution test In order to verify the performance and system energy resolution of CZT (CdZnTe) detectors, irradiation tests were performed on CZT detectors using two nuclides, cesium-137 and cobalt-60. The nuclide symbol of cesium-137 is , its half-life is 30.17 years, After emitting 512 keV beta rays, it transforms into . It decays by isotropic transition with a gamma energy of 662 keV. Often used to test the gamma ray energy resolution of the system. The gamma rays generated by the radiation source irradiate the CZT detector, and after being processed by the pile-up discarding algorithm, we can get The energy spectrum is as follows Fig.13 As shown, the blue color represents the data without the pile-up discarding algorithm, and the red color represents the energy spectrum after the pile-up discarding control algorithm.

[0067] Will Fig.13 The processed data is then fitted with a Gaussian to obtain the relative energy resolution of the entire system. The system energy resolution of the radiation source irradiating the CZT detector is as follows: Fig.14 As shown: the system energy resolution is 2.8% under radiation source irradiation.

[0068] At the same time, in order to calibrate the system, the CZT detector is irradiated with cobalt-60. The nuclide symbol of cobalt-60 is , its half-life is 5.27 years, The same β decay produces γ rays with energies of 1173 keV and 1333 keV. The gamma rays generated by the radiation source irradiate the CZT detector, and after being processed by the stacking and discarding algorithm, we can get The energy spectrum is as follows Fig.15 As shown in the figure, the blue is the data without the pile-up discarding algorithm, and the red is the energy spectrum after the pile-up discarding control algorithm. Fig.16 .

[0069] (3) Spectrometer calibration and Geant4 spectrum verification The above (1) and (2) have been tested by two gamma nuclides, neutron / gamma spectrometer, the two nuclides are , The gamma ray calibration was performed based on the three full energy peak energies of the radioactive source: 662 keV, 1173 keV, and 1333 keV. , The calibration curve of the neutron / gamma spectrometer irradiating the CZT detector is as follows: Fig.17 shown.

[0070] After normalizing the data simulated by Geant4, we compared and verified it with the energy spectrum tested by the neutron / gamma spectrometer. Geant4 simulated , Energy spectra of two nuclides. Comparison and verification with Geant4 spectrum Fig.18 shown.

[0071] Depend on Fig.18 It can be seen that the neutron / gamma spectrometer tested 137 C S The full energy peak position and Compton platform position of the neutron / γ spectrometer are consistent. 60 The Co energy spectrum is compared and verified with the energy spectrum simulated by Geant4. 60 Co and Geant4 spectrum comparison verification diagram Fig.19 shown.

[0072] Depend on Fig.19 It can be seen that the neutron / gamma spectrometer tested The full energy peak position and Compton platform position are consistent. It can be judged that the neutron / gamma spectrometer is working properly and the pileup discard algorithm has a good effect, which is in line with the design expectations.

[0073] The present invention tests the basic performance, power consumption, interface function, and energy resolution of α and γ radiation sources of the first neutron / γ spectrometer. , The energy spectrum of the ASIC chip CPRE10-32 is compared with the energy spectrum simulated by Geant4 software for observation and verification. The main purpose is to verify whether the frequency performance, baseline, linearity, count rate and energy resolution of the amplifier circuit meet the design expectations. When the detection efficiency of the ASIC is greater than 95%, the count rate is greater than 60kHz, and the linearity of the system linear region is greater than 0.998. When the detection efficiency of the amplifier circuit is greater than 98%, the count rate is greater than 100 kHz, and the linearity of the amplifier circuit is greater than 0.999. After the pile-up discard algorithm The system energy resolution of the Si detector irradiated by the radiation source was improved from 7.8% to 4.6%. The energy resolution of the system under the radiation source irradiation CZT detector was improved from 4.8% to 2.8%. The interface function and storage function of the neutron / gamma spectrometer were tested. , The simulation results are normalized and compared with the tested energy spectrum. After comparison, the energy and position of the full energy peak position and the Compton platform are consistent with the simulation results. The present invention tests the communication speed of the CAN interface and Gigabit Ethernet, and tests the read and write speed of the memory EMMC in the neutron / gamma spectrometer. In all tests, they meet the design expectations.

[0074] Each step or module involved in the above embodiments 2 to 3 corresponds to the embodiment 1. For the specific implementation, please refer to the relevant description part of the embodiment 1. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-Earth orbit neutron and gamma-ray detector set, characterized in that: It includes 15 detectors stacked in sequence, including: The first detector and the fifteenth detector are single sensitive area CZT detectors for detecting gamma rays; The second detector is a single sensitive area Si detector, which is used to identify the direction of the incoming particles; The third, fourth and fifth detectors constitute a first anti-coincidence detection group, which are respectively composed of two single-sensitive-area Si detectors and a first double-sensitive-area Si detector containing a LiF coating therebetween; the twelfth, thirteenth and fourteenth detectors have the same structure as the first anti-coincidence detection group, and are further wrapped with a Gd layer on the outside, constituting a second anti-coincidence detection group; both the first anti-coincidence detection group and the second anti-coincidence detection group are used to detect thermal neutrons; The fifth, sixth, seventh and eighth detectors constitute the third anti-coincidence detection group, which are respectively a single sensitive area Si detector, a second dual sensitive area Si detector, a first dual sensitive area Si detector and a single sensitive area Si detector; the eighth, ninth, tenth and eleventh detectors constitute the fourth anti-coincidence detection group, which are respectively a single sensitive area Si detector, a first dual sensitive area Si detector including an HDPE coating, a second dual sensitive area Si detector and a single sensitive area Si detector; the fifth to eleventh detectors are used to detect fast neutrons.

2. A low-Earth orbit neutron and gamma-ray detector assembly as claimed in claim 1, characterized in that: The sensitive layer of the single sensitive area CZT detector has a side length of 35 mm and a nominal thickness of 5 mm; The sensitive layer of the single sensitive area Si detector has a side length of 35 mm and a nominal thickness of 650 μm; The outer sensitive layer of the first dual-sensitive area Si detector has a side length of 35 mm, the inner sensitive area has a side length of 25 mm, and the thickness is nominally 300 μm; The outer sensitive layer of the second dual-sensitive area Si detector has a side length of 35 mm, the inner sensitive area has a side length of 25 mm, and the thickness is nominally 650 μm.

3. A low earth orbit neutron and gamma ray detector assembly as claimed in claim 1, characterized in that: The anti-coincidence detection group is used to remove interference from charged particles.

4. A low earth orbit neutron and gamma ray detector assembly as claimed in claim 1, characterized in that: The fourth detector including the LiF coating is used to record the count of signals generated by the reaction of neutrons in all energy ranges with LiF; The Gd layer of the second anti-coincidence detection group is used to absorb thermal neutrons, wherein the thirteenth detector is used to record the count of the signal generated by the reaction of the remaining neutrons except the thermal neutrons with LiF; The thermal neutron flux on the track is obtained by dividing the difference in counts between the fourth detector and the thirteenth detector by the detection efficiency.

5. A low-Earth orbit neutron and gamma-ray detector assembly as claimed in claim 1, characterized in that: The sixth and seventh detectors are used to detect signals generated by galactic cosmic rays or other secondary neutrons; The ninth and tenth detectors are used to detect recoil proton signals generated by neutrons in the low-Earth orbit passing through the high-density polyethylene conversion layer; Under the anti-coincidence condition, the total energy spectra of the ninth and tenth detectors and the sixth and seventh detectors are subtracted to obtain the energy spectrum of the recoil proton.

6. A low-Earth orbit neutron and gamma-ray detection device, characterized in that: It comprises a rectangular outer shell, and a front end plate, a data acquisition board and a low-Earth orbit neutron and gamma-ray detector group as claimed in any one of claims 1 to 5 inside the outer shell; The data acquisition board is connected to the detector group and the front-end board for providing analog and digital power; it includes an FPGA chip, a level conversion chip, a CAN chip, an EMMC, a Gigabit Ethernet PHY chip, a universal asynchronous receiver and transmitter chip, and an ADC chip; The front-end board is connected to the detector group in communication, and includes a preamplifier circuit composed of an ASIC chip and discrete devices; the ASIC chip is used to collect neutrons, and the preamplifier circuit is used to collect gamma rays; the front-end board is used to receive the particle signal transmitted by the detector group and convert it into a voltage pulse; The housing includes a plurality of mounting holes for securing to a load.

7. The low-Earth orbit neutron and gamma-ray detection device according to claim 6, characterized in that: A plurality of fixed brackets are arranged inside the outer shell to connect the side surfaces to ensure the stability of the detection equipment.

8. A method for detecting neutrons and gamma rays in low-Earth orbit, based on the low-Earth orbit neutron and gamma ray detection device according to claim 6, characterized in that: include: When the detection device is powered on, the data acquisition board is initialized; If the configuration is completed, it will enter the acquisition mode and start acquisition. The ADC will convert the collected random voltage pulses. The digital signal obtained after conversion will be cached in the DDR together with the corresponding trigger time. Then, it will be determined whether there is an accumulated signal based on the signal accumulation and discarding algorithm. If there is an accumulated signal, it will be marked with a different frame format and stored in the EMMC. If the upload instruction of the CAN interface is received, the data saved in the EMMC will be uploaded to the satellite via Ethernet, and the satellite host will upload the data when landing at the ground station.

9. A method for detecting neutrons and gamma rays in low-Earth orbit as claimed in claim 8, characterized in that: The initialization of the data acquisition board also includes: detecting whether the peripheral circuit is normal. If the configuration signal of the satellite is not received or the configuration is abnormal, the relevant telemetry data will be sent to the satellite.

10. A method for detecting neutrons and gamma rays in low-Earth orbit according to claim 8, characterized in that: include: The stacking discard algorithm is: The rise time of a single event pulse is , is ns level, forming time Set to 10 us, the fast amplifier output pulse will generate a width of The rectangular wave, Less than the rise time of a single-event pulse When two consecutive particles enter the detector and cause signal accumulation, two pulses with a width of rectangular wave, when the distance between the two rectangular waves Less than the entire molding time When the signal is considered to be accumulated, the accumulated signal is stored in the EMMC in different frame formats to realize the accumulation discard function.

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