Disclosed is a filter including a second layer disposed between a first layer and a third layer. The first layer is composed of iron. The second layer is composed of 1 part by volume of lithium fluoride, 20 to 50 parts by volume of aluminum, and 50 to 80 parts by volume of aluminum fluoride. The third layer is composed of a 1 part by weight of lithium fluoride and 99 to 100 parts by weight of magnesium fluoride.本發明提供之濾屏,包括:第一層,係由鐵組成;第二層,係由1體積份之氟化鋰、20至50體積份之鋁、與50至80體積份之氟化鋁組成;以及第三層,係由1重量份之氟化鋰與99至100重量份之氟化鎂組成,其中第二層位於第一層與第三層之間。14‧‧‧鉛壁15‧‧‧濾屏15A‧‧‧第一層15B‧‧‧第二層15C‧‧‧第三層20‧‧‧屏蔽
