Advanced Physics for Brachytherapy 2018

The method





Er

E f r

= dEEf



(

) ,

=

( , ) ( )(

1 )



E

The importance of f(E): The spectral weighting factor connects photon fluence to energy fluence at any point of a geometry and hence depends on the actual geometry and its physical properties.

However, as G increases, and ΔΕ G

become narrow, the energy group cross sections

μ

, μ s,g , become constant approximations of the continuous μ t (E), μ

(E)

t,g

s

and do not depend heavily on f(E).

This means that generic multi group cross sections (of ΔΕ G

<<) are used with analytic

or semi-analytic f(E) appropriate for the problem at hand .