| Since last century discovered the element radon, along with the progress and development of science technique, people broaden the application field of radon gas continuously. The study of radon release and transfer is the basic theoretical issue of radon measurement, which has close relationship with its extensive application in geosciences, environmental science and so on. Among them, the role of radon gas in earthquake prediction has called attention to earthquake workers. In recent years, many scholars at home and abroad had engaged in the research of underground radon in the earthquake, they not only discussed the feasibility of using radon gas to forecast earthquake, but they monitored for a long time on the spots, got a large amount of data and did a lot of research on the efficiency of radon gas forecasting earthquake.The data shows, the radon concentration of the monitor spots will be anomaly before and after the earthquake, which provides a possibility for earthquake prediction and shows significant results in practical. However, in the research on radon migration of underground medium, the existing migration theory and migration patterns doesn’t take the radon migration ability and the radon release ability affected by the change of rock physical conditions in the process of earthquake preparation into account, but these factors are very important to radon anomaly formation and the judgment of amplitude of anomaly. In our study of radon, the research on mechanism of radon anomaly in earthquake is very little and the data of research on rock’s radon release quantity under press is very limited.According to the key questions above to be solved, on the basis of the study about underground radon monitoring methods and the change of radon gas before and after the rock fission, relying on the project of "The research on the mechanism of radon concentration anomaly in earthquake", financed by National Natural Science Foundation of China (No:41074093), the author discussed the sources of radon and its distribution, clarified the significance of doing research on radon exhalation rules of rock specimen under different axial press, analyzed the mechanism of radon release from rock specimens and its related factors in detail. The principles、instruments and methods of measuring radon release quantity were also described in details. Through the research of attenuation and diffusion transfer law of radon under ideal condition, the author established radon concentration distribution mathematical expressions of different position form rock specimens, and gained the simulate fit curve of radon concentrations at measuring points, at the same time, the mechanism of radon release and transfer form rock samples had been studied by experimentation and theory.Basing on experiment, this thesis used the solid state nuclear track accumulation and semiconductor instantaneous radon measurement method to study the radon transfer regularity and release quantity under different axial pressure. In order to overcome the convection, humidity and pressure difference effect on the experiment and ensure radon transfer is in an environment which is closed, no convection, no humidity difference and no pressure difference, this thesis used multiple sets of devices to do the radon experiments indoor and gained a series of experimental data. The experiment found that:1) Using the IED-3000F to measure radon release quantity of granite specimens, the radon release from the granite specimen shows paroxysmal and spontaneity.2) In the experiment in relationship of axial press and axial displacement of specimens, when the granite specimen is under different axial press, it will have a physical deformation in the stress direction and the original micro fissures and cracks inside will gradually decrease which cause the axial displacement of the specimen is slowly to stabilize after the increase. And in a certain pressure range, the displacement fitting curve present logarithm change:the logarithmic function of axial displacement fitting is y=0.01031n(x)+0.0121and the fitting degree is0.9446when the axial pressure is60kN; the fitting function changes into y=0.00651n(x)+0.00067along with a fitting degree0.9292when the axial pressure is120kN; when the axial pressure is180kN, we fit the measurement data of120h before then get the logarithmic function is y=0.00631n(x)+0.0042and the fitting degree is0.9367.3) In the experiment of radon release quantity of specimen under press, due to the low level of radon concentration, the author used the solid state nuclear track detector to measure radon release quantity of granite specimen, which has characteristics such as high sensitivity and good stability. The result shows that within a certain range of axial press, the radon release quantity has a negative correlation with axial press of granite rock, the quadratic function of them is y=0.0004x2-0.2025x+65.918with a fitting degree0.98; and the fitting liner function y=-0.1293x+64.455with the fitting degree0.95. From the experimental results, when geologic body is in the stage of compaction, its radon release quantity will decrease continuously with the increase of the pressure, which is completely consistent with predecessors’corollary that radon concentration is negative anomaly before the earthquake.4) By studying the radon concentration data of different spots from specimen, the author used anti-diffusion to modify the radon migration model and set up the anti-diffusion migration model, the anti-diffusion coefficient of10cm off the specimen is0.0107according to the model. After that, the author combined the steady state diffusion equation and transient diffusion equation with the anti-diffusion coefficient, simulated the effect curve of rock specimens to radon concentration of measure spot. The two fitting curves shows that radon concentration will down slowly after a sudden increase to a certain height, then it will be stable. After the comparison analysis of radon concentrations between transient simulation and cumulative simulation at measuring points, we found out the correlation coefficient is up to0.9991, and the trend of experimental measurement is the same as the theoretical simulation curve.5) This thesis confirmed that the radon release quantity is related to the specimens’ lithology、humidity and the size of the fracture area. In the experiment, the author used the solid state nuclear track detector to measure radon release quantity of different lithologies, the result shows that the radon release quantity of yellow sandstone is2.18times as much as the granite specimen when the226Ra content of yellow sandstone is2.31times as much as the granite specimen. It follows that in geological body of different lithologies, the higher the uranium content is, the higher radon concentration can be measured in the same condition. The research on the relationship between moisture content of specimens and radon release shows that the radon release quantity from geological body is less if the moisture content is higher which reduced the radon migration channels. But in a certain range, the radon release quantity is affected more by the size of the fracture area than by the moisture content.The conclusion above has a significance of radon measurement application in geology and environment, as well as, it can play a practical role on enriching and developing the existed theories, improving the reliability and veracity of radon measurement in earthquake prediction and widening the application fields. |
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