Secondary radiation from a spherical tissue-equivalent phantom irradiated with 60Co gamma radiation and 6 MV X-rays

The angular dependence and the dependence on the phantom mass of the secondary exposure rate from spherical tissue-equivalent phantoms irradiated with 60Co gamma radiation and 6 MV X-rays have been investigated both by measurement and by calculation using the Monte Carlo method and approximate methods. A nonlinear dependence on the phantom mass was found. Calculation of the differential photon fluence was also made. These measurements and calculations can be used when calculating the required barrier thickness for walls which are not hit by primary radiation.