Research On Radiation Environment And Space Dosimetry Application In Spacecraft

The space radiation environment poses health risks to astronauts during missions,which may lead to cancer.There are three main sources of space radiation:the first is the earth capture zone?including the inner radiation belt and the outer radiation belt?,the inner radiation belt is mainly composed of electrons,the outer radiation belt is mainly composed of protons,and the energy is as high as hundreds of MeV,.Secondly,solar particle events and galactic cosmic ray?GCR?,are mainly composed of protons and heavy ion?HZE?.NASA has developed radiation protection strategies to limit risks,including the use of countermeasures such as shielding protection.The correct risk assessment depends on the accurate assessment of the shielding effect o f the spacecraft structure against the radiation environment of the incident space.As the complex shielding geometry plays an important role,it is necessary to improve the existing transport procedures and calculate the dose deposition in human tissues.The computer simulation of the spacecraft is usually used to show the reduction of the equivalent dose provided by the spacecraft structure.However,according to published studies,increasing shielding does not always lead to a decrease in the equivalent dose.The launch cost of the spacecraft should be considered,and the increase of the shielding thickness is equivalent to the increase of the weight of the spacecraft.When these high-energy particles interact with the structure and shielding materials of the spacecraft,high-energy protons and HZE ions will produce secondary particles.Compared with the primary incident particles,secondary particles may cause greater biological damage,so the study of the interaction between different secondary particles and matter is very important to human tissues and organs or the equivalent absorbed dose and dose equivalent of human tissues.This paper mainly discusses the following three aspects,and obtains some valuable conclusions:In chaper 1,a method and tool for analyzing the transport of high-energy particles in space radiation environment is established based on the Geant4 program.The tool can analyze the secondary radiation environment and dose distribution of electrons,protons and heavy ions in the cabin after the shielding model of electrons,protons and heavy ions in the space radiation environment.The shielding properties of the four materials are compared by the integral method.It is calculated that the absorbed dose of monoenergetic proton,alpha,oxygen ion and iron ion is the lowest after passing through polyethylene,followed by water,carbon brazing dimension and aluminum,which shows that the shielding properties of the four materials are polyethylene,water,carbon brazing dimension and aluminum.Through the GRAS software package developed by ESA for the study of space radiation effects,the energy spectra of secondary particles produced by protons in the Milky way universe passing through the space modules with cylindrical shell and spherical shell structures and the dose equivalent of ICRU spheres in the module are calculated.The secondary electrons,photons,neutrons and protons passing through four kinds of materials with the same mass thickness are compared in detail.The calculation results show that the number of neutrons generated through polyethylene is the least.Secondly,when water and carbon brazing are used,the neutron flux generated by aluminum is the most,and when the shielding material is polyethylene,the absorbed dose and dose equivalent of ICRU sphere is also the lowest.In chaper 2,the depth dose distribution in the equivalent human tissue after proton incident shielding material was verified by accelerator test.The existing measurement of dose depth distribution is mainly through two methods:one is based on the superposition of materials with multi-thin layer thickness,and a large number of dose tablets are placed in different interlayers,and the material is divided into multiple layers,which will lead to irregular materials when processing multi-layers,and the influence of factors such as mixing air into the gap during measurement will lead to greater errors in the measurement results.Another method is to change the thickness of the test phantom to measure many times,the measurement procedure is tedious,repeated irradiation,increase the test cost and other shortcomings.In this paper,the dose depth distribution of the whole phantom can be obtained by special wedge-shaped material irradiation phantom with different inclination angle,and the measurement result is accurate,and it can be used for proton,electron,photon and other beam irradiation materials with different energy.the radiation phantom based on this structure is flexible,simple and suitable for the study of radiation effect of space materials.In the calculation,the calculated score of the area is used as the comparative verification parameter,and the deviation between the calculated value and the measured value is less than 20%.For the experimental verification of high energy heavy ions,the experimental measured depth dose distribution values of C,O and Ne ions are compared with the measured values published in the literature.There are C ions with three energies,O ions with three energies and Ne ions with one energy.the calculated results are in good agreement with the measured values,and the deviation is less than 20%.Therefore,the high-energy particle transport analysis method established in this experiment is effective and available.In chaper 3,The radiation simulation source for the study of total dose effect of ionization mainly uses ⁶⁰Co radiation source,so it is necessary to accurately measure the dose of cobalt source at different locations in the irradiation room.In this paper,a set of self-made cobalt source dose testing device is used to calibrate the three-dimensional dose field of cobalt source and the dose enhancement factor of cobalt source is measured by thin film dose sheet.The portable measuring device is used to calibrate the three-dimensional dose field of cobalt source,which is easy to carry and accurate,and can be measured from different angles at different heights and distances in the irradiation chamber of cobalt source.it is of great significance to improve the accuracy of the study of total ionizing dose effect and anti-radiation performance of electronic components,to promote the improvement of total dose effect test methods and standards,and to ensure the operation safety and life of spacecraft.