In x-ray technology, this is understood to mean a material of a defined thickness and composition (e.g. copper, tin or lead sheet metal) which is placed on the emanation window of the x-ray tube to influence the x-rays. As the radiation passes through the material, low-energy parts are absorbed with higher proportion, whereby the medium radiation energy is shifted to higher values. This is known as beam hardening (Figs. 1 and 2, YXLON International GmbH).