@R05048@ may be scattered by its @T06477@ through a medium containing particles. If the scatter results in no significant change in the @W06659@ relative to the primary radiation it is called elastic @S05487@. In cases where the @S05487@ centres are small compared to the @W06659@ of the radiation the elastic @S05487@ is called @R05160@ and @M03919@ if this condition is not fulfilled.