The Monte Carlo simulation of ion chamber response to 60Co-resolution of anomalies associated with interfaces

The reliability of Monte Carlo calculations of ion chamber response depends critically upon the details of the electron transport, particularly at media interfaces. Improper handling of electron transport algorithms near boundaries can lead to anomalous results which the authors call 'interface artefacts'. This effect is demonstrated for two computer codes, EGS and CYLTRAN/ETRAN, and the underlying physics is described. Details are also given of a Monte Carlo code suitable for the calculation of ion chamber response to 60Co without calculational artefacts and of various variance reduction techniques that greatly reduce the computing time required.