A GENERAL CAVITY THEORY

A cavity theory is used to relate the dose deposited in the cavity (se nsitive volume of the detector) to that in the surrounding medium whic h may be of different atomic number or composition. Burlin proposed a general cavity theory to include all cavity sizes. The Burlin theory i gnores all secondary-electron scattering effects which results in larg e discrepancies in dose to the cavity compared with the experimental r esults in high atomic number media. Kearsley proposed a new general ca vity theory which includes secondary-electron scattering at the cavity boundary. The Kearsley theory showed excellent agreement with experim ental results for Co-60 gamma-rays but poor correlation for 10 MV x-ra ys. The Kearsley theory has numerous parameters and the magnitude of t he input parameters is arbitrary; therefore the dose to the cavity dep ends on the choice of parameters. We have developed a new cavity theor y which includes secondary-electron backscattering from the medium int o the cavity. The strengths of this proposed theory are that it contai ns few parameters and a methodical way of determining the magnitude of the parameters experimentally. The proposed theory gives better agree ment with experimental results in lithium fluoride thermoluminescence dosimeters for Co-60 gamma-rays and 10 MV x-rays in aluminium, copper and lead than do the Burlin and Kearsley cavity theories.