[填空题]
A mixture of iron and p kd- i(3s0uf(i7jo eaans0b z6( zg4q((uhq gmn unknown material is bombarded with electrons. The wavele0z( 6nm(4z sghqb g(qungth of the $K_\alpha$ lines are $194 \, \text{pm}$ for iron and $229 \, \text{pm}$ for the unknown. What is the unknown material?
