Monte Carlo Simulation For Energy Deposition Of Ionization Chamber Based On The Equivalent Electron Source Theory And Experimental Verification For The Theory

Human are exposed to natural ionizing radiation sources (such as environmental exposure) all the time, and to artificial ionizing radiation sources (such as occupational exposure and medical exposure) to varying degrees with the increase of nuclear activities. Radiation application significantly influences on human's life, only by the reasonable utilization can man get benefit. Therefore it is very important to measure dose correctly. Dose is mostly measured by all kinds of dose meter, most of which are based on the cavity ionization theory used widely. The cavity ionization theory is improving step by step on the basis of Bragg-Gray theory, Spencer-Attix theory, the equivalent electron source theory, Burlin model and Kearsley model. It makes the design of dose meter and the measurement of radiation dose more precise.The equivalent electron source theory advanced 40 years ago regards the cavity ionization theory as a transport problem and reaches an almost perfect conclusion theoretically. Many researchers in the same field from different countries are very interested in it after published in an international science publication. However, the theory lacks in practical application, for one thing, it is difficult to write out the general computer code due to the very complicated calculation of dose based on the equivalent electron source theory, especially under the complicated geometrical condition, the ionization produced by the equivalent electron source in the cavity is regarded as an electron transport problem in inhomogeneous media, for another, the feasible calculation tools for particular objects can be available for the particle transport problem with the development of computer technologies and the wide use of general calculation methods (such as Monte Carlo). This work manages to explore the practical application of the equivalent electron source theory, accordingly, compares the results of calculations usingtwo methods with those of experiments.The main research described in this paper includes three sections. Firstly, research the response of the stainless steel ball-shaped ionization chamber by experimental methods. The chamber has wide application on the measurement of radiation field for its good intensity allows different gases filled, but at present, there are not many systemic experiment works for it. Therefore a series of experiments for the stainless steel ionization chamber are performed and include the saturation characteristic of gases, the energy response of the chamber and the sensitivity under the unit pressure of the chamber. In the experiments, the gas pressures in the chamber are from 4kPa up to lOOOkPa, the gases include He, N2, Ar, Kr and Xe with the atomic numbers from 2 to 54 and the energies from 33keV to 1.25MeV. Secondly calculate the response of the chamber with the general Monte Carlo code-EGS4 code in order to compare with the equivalent electron source theory by calculation methods. The calculations cover the effects of the different electrode sizes on the response of the NE2571 ionization chamber, the energy response of the chamber and the sensitivity under unit pressure. Finally, calculate the response of the ionization chamber with the equivalent electron source theory. After the equivalent electron source is obtained by analytical method, Monte Carlo method is used to calculate its energy deposition in the ionization chamber. The calculation method combines the equivalent electron source theory with Monte Carlo method.The results show that the calculated responses of the ionization chamber based on the equivalent electron source theory are closest to the experimental values and still keep consistency with the experimental ones with its maximum range up to several ten times. Except for the values when the energy of primary ray is 33keV and the pressure meter indicates 0.05atm, the relative biases between the values of the equivalent electron source theory and those of the experiments are within ?5%(except for 1 point) for Ar, within ?5% for Kr, within ?9% for N2, within ?...