bremsstrahlung
noun
brems·strah·lung ˈbrem(p)-ˌshträ-ləŋ 
: the electromagnetic radiation produced by the sudden deceleration of a charged particle in an intense electric field (as of an atomic nucleus)
also : the process that produces such radiation
Word History
Etymology
German, literally, decelerated radiation
First Known Use
1935, in the meaning defined above