| In space,the radiation environment is extremely complex.Radiation belts near low-earth orbit contain galactic cosmic rays,Solar energetic particles and various types of secondary particles.Detecting neutrons in low Earth orbit can help solve many scientific problems,such as the source of particles in the radiation belt and the principle of acceleration of particles by the sun.Since neutrons are not charged,they are usually detected indirectly,and neutron detection is often influenced by charged particles and secondary neutrons.The neutron spectrometer designed by the author’s team will be carried on MN30-4 as an independent payload for neutron detection mission in low Earth orbit,the detected neutrons are thermal neutrons and fast neutrons with energy less than 20 MeV.In this thesis,the types and arrangement of silicon detectors are designed,15 silicon detectors are used to detect neutrons by nuclear reaction method and anti-coincidence method,and 6LiF conversion layer is used to convert thermal neutrons,fast neutrons are converted using a high-density polyethylene transfer layer,and the non-detection surface of the neutron spectrometer is shielded using a gadolinium shielding layer the above design can eliminate the influence of charged particles and secondary neutrons to a certain extent,and improve the accuracy of neutron detection.In this thesis,the general structure of the neutron spectrometer is designed.The electronics part consists of three circuit boards,which are power board,front-end board and data board,responsible for the power supply of each device in neutron spectrometer and the generation of detector bias.The front-end board is connected to the detector,and the SKROC2A chip is used as the front-end read-out chip.The data board includes the FPGA chip,the single-chip computer chip and the memory chip,etc.the read-out data is transmitted to STM32 MCU by Serial Peripheral Interface(SPI),at the same time,the interface between CAN bus and Ethernet is designed to communicate with satellite.The shell of the neutron spectrometer is made of aluminum alloy and anodized surface.The dimensions of the three sides are 93 mm × 87 mm × 93 mm and the total weight is 791 g.In order to verify the validity and accuracy of the neutron spectrometer design,the basic performance of the front-end readout chip is tested in this thesis,the RMS of all channels is less than 2.0 ADC codes,and the linearity of amplification and conversion circuit is more than 0.99.After basic testing,the author and his team went to several accelerators and radiation sources in China,the neutron spectrometer is tested by using the-source,14 MeV neutron beam,2.5 MeV neutron beam,neutron source and 14 MeV proton beam,the data obtained from neutron spectrometer are in good agreement with the simulation results,and accord with the design expectation.At the same time,based on neutron spectrometer,a neutron dosimeter is designed and manufactured,which can provide neutron dosimetry service for astronaut’s extravehicular activity or future Moon landing mission.In order to reduce the size and power consumption,neutron dosimeters have reduced the size of detectors compared with neutron spectrometers,and used separate components to build up an amplifier circuit and a sample-and-hold circuit,the low-power MSP430 MCU with internal ADC is used as the main control chip to read and process the data.The neutron dosimeter was tested with a Function generator.The amplifier circuit worked well and the linearity was greater than that of the 0.998.The power consumption of the whole unit was rated at 11.7 MW,and the working time of the neutron dosimeter could be up to 10 days. |
