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