Simulation And Experimental Study Of A Spherical Tissue Equivalent Proportional Counter

Tissue equivalent proportional counter (TEPC) measures the lineal energy spectra of (mixed) radiation fields with which various dosimetric quantities like absorbed dose, mean quality factor and dose equivalent could be obtained. Therefore, development of TEPC is of importance for radiation protection. A good knowledge of physical process is helpful for detector design and applications. In this work, the structure parameters of a spherical TEPC were designed, the electric field distribution of the TEPC was analyzed. General-purpose Monte Carlo codes Geant4 was used to simulate the energy response, dose equivalent response and sensitivity of the TEPC to mono-energy neutrons; the absolute gas amplification factor for different detector bias was simulated with Garfield and ANSYS. In the last, the TEPC was developed and experiment was carried out for validation. As a consequence, a modeling method for TEPC properties was developed and relative parameters were obtained which are believed to be helpful for detector development.The thesis reviewed principles of the TEPC based on which Benjamin type TEPC was designed. With proper hypothesis, the electric field strength of a Benjamin and non-Benjamin type TEPC was analyzed with the FEM software ANSYS and the distribution of gas amplification factor along the anode wire was obtained. According to the analysis, it is found that Benjamin type TEPC has a more uniform electric strength and gas gain distribution along the anode wire than the non-Benjamin TEPC.The absolute gas amplification factor of Benjamin type TEPC was calculated by combining Garfield and ANSYS. The gas gain was measured by employing an internal241 Am alpha source for different detector bias and comparison with simulated result was conducted. The results showed that for each bias, the gas gain remain constant when the distance between initial position of electron and anode wire was larger than 0.04 cm. As the applied voltage increased, the variance of gas gain increased. Comparison showed that the simulation method is accurate enough for prediction of the gas gain in TEPC on the conditions that the TEPC was used to model 2 micron tissue volume.Geant4 Monte Carlo code was employed to simulate the energy response of the TEPC to neutrons of 1.3MeV, 1.0MeV,0.8MeV,0.65MeV and 0.36MeV. Dose equivalent response RH and sensitivity S of the TEPC were calculated according to the simulation results. Experiment was conducted on an electrostatic accelerator. The results showed that the simulated value of RH was below 1.0, the experiment determined RH was a bit smaller than simulated values, it is also found that the RH dose not vary with neutron energy significantly. The simulated S of TEPC showed that the S increases as the increase of the neutron energy. When neutron energy was above 0.8MeV, simulated S approximated well with the experimental values.In all, the thesis has developed a general technical routine oriented for modelling the physics of a TEPC. Various parameters of the TEPC as a neutron dosimeter were obtained. The combination of ANSYS and Garfield for TEPC gas gain simulation is an initiative, which avoids the complicated gradient field model based gas gain characterization process. Comparison between the experiment and simulation revealed the feasibility of the modeling method, it is believed that the method could acted as a guide for TEPC development in the future.