Estudo computacional de uma câmara de ionização de extrapolação em feixes padrões de radiodiagnóstico

Abstract

In this work, we studied the influence of the components of an extrapolation ionization chamber on its response. This study was performed using the MCNP-4C Monte Carlo code, and the standard diagnostic radiology qualities for direct beams RQR3, RQR5 and RQR8. The influence of the components of the ionization chamber on its response was determined as the ratio of the energy deposited on the sensitive volume, without the studied component, by the deposited energy on the sensitive volume, considering the complete ionization chamber. To study the ionization chamber without the component, the material constituting the studied component was replaced by air, the same air that surrounds the ionization chamber. Using tally F6 (MeV/g/particle) and 2.1 x109 histories of simulated particles, it was possible to observe that the collecting electrode and the support plate were the components with the greatest influence on the ionization chamber response. In the second part of this work, different materials were evaluated to compose the collecting electrode. The material that least influenced the ionization chamber response was the graphite, the original material of the extrapolation ionization chamber. Therefore, the results indicated that the configuration and materials used in the construction of the extrapolation ionization chamber did not significantly alter the energy deposited in the sensitive volume of the ionization chamber. In addition, this ionization chamber has several advantages: low cost, easy assembly and robustness.