Dose Due to Photons

The dose rate due to a beam of photons is calculated based on an equation similar to Eq. 16.7  

Notice the two main differences between Eq. 16.7 and Eq. 16.12. For photons, 2( ) = 1 and dE/dx is replaced by the product EpJ E). As with charged particles, the analytic form of ( ) and pJ E) is seldom known. Instead, one has to work with a set of energy groups, and Eq. 16.12 takes the form 

As with charged particles, tables have been developed that provide a flux-to-dose-rate conversion factor as a function of photon energy (Table 16.3 and Fig. 16.1). Using the conversion factor C( ), Eqs. 16.12 and 16.13 take the 

Answer In both cases the dose rate is calculated by using Eq. 16.15 with a dose-to-flux conversion factor obtained from Table 16.3 for 0.662-MeV gammas. Using linear interpolation, that factor is 4.05 X 10 (Sv/s)/[y/(m s)]. 

The flux at r meters from the source is given by /Airr, where 

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