An important example is in nuclear engineering: In countries such as France, the construction of power stations involves lots of nuclear engineers. One of the more important isotopes is 235U. There are also nuclear reactors used for producing diverse isotopes for medical and other uses. Some bad and good news: in various countries, engineers are involved both in the building and the dismantling of nuclear weapons. Radioactive isotopes are used in some measurement devices. The domestic smoke detector is the most common: they sometimes use Americium. Radioactive sources are also used to measure the thickness and composition of thin films (suitably calibrated, a measure of transmitted radiation tells you how much material was present to absorbe the radiation.