Studies On The General Cavity Theory Based On Virtual Electron Source Concept

The precise determination of the absorbed dose is essential in radiation science and technology. The cavity theory is used to determine how to translate the detector response to the radiation dose deposited in the surrounding medium. So cavity ion chamber theories play a central role in the measurement of ionizing radiation and consequently a large amount of theoretical and experimental work has been devoted. The dose in the cavity does not only depend on the size, atomic composition and density of the cavity and the surrounding medium, but also depend on the character, energy and intensity of incident rays.The cavity theory based on application of the electron transport equation in the cavity and in the surrounding medium, which is called L-L cavity theory in this paper, is a very detailed theory that considers electron production in the cavity as well as the wall medium, and is applicable to all cavity size. The main idea of this cavity theory is that the effect of the cavity on the energy deposition of electrons inside this cavity can be attributed to a virtual electron source uniformly distributed in the cavity. In order to calculate the effect of the virtual electron source on the relative ionization density in the cavity, in this paper the Monte Carlo method hasbeen applied into the calculation for the parameter k(E, a), which is the fraction of energy deposited in cavity relative with the initial energy of electrons if there isan electron source distributing uniformly in the cavity. It is Monte Carlo method with which the energy deposition of the virtual electron source in the cavity can be calculated conveniently. So the total energy deposition of electrons in the cavity can be obtained much accurately. Since other cavity theories are fairly restrictive in their applicability at low energies, L-L cavity theory has given more accurate prediction for cavity response at a large range of energy, including low energy.The experimental results reported by Attix et al(1958) show that the ion-chamber response varies with the wall separation of the ion-chamber. In this paper we compare the calculation results by L-L cavity theory with the ion-chamber experimental results of Attix et al. The EGS4 Monte Carlo system is used to calculate the mean deposited energy ratios of equivalent electron sources in the chamber which were calculated by the analytical method before. All of the calculations are done with the PRESTA algorithm. The calculated results with this theory match the experimental results by Attix et.al acceptably well. The main goals of the paper are to l)give validation of L-L theory; 2) illustrate applicability of L-L theory to white region of cavity sizes; 3) attempt to explain some experimental results that were not explained in the limits of conventional cavity theories.