structural:expansion
Radioactive strontium

Sr is the active ingredient in Metastron, a radiopharmaceutical used for bone pain secondary to metastatic bone cancer. The strontium is processed like calcium by the body, preferentially incorporating it into bone at sites of increased osteogenesis. This localization focuses the radiation exposure on the cancerous lesion.

Sr has been used as a power source for radioisotope thermoelectric generators (RTGs). Sr produces approximately 0.93 watts of heat per gram (it is lower for the form of Sr used in RTGs, which is strontium fluoride). However, Sr has one third the lifetime and a lower density than Pu, another RTG fuel. The main advantage of Sr is that it is significantly cheaper than Pu and is found in nuclear waste. The latter must be prepared by irradiating Np with neutrons then separating the modest amounts of Pu. The principal disadvantage of Sr is the high energy beta particles produce Bremsstrahlung as they encounter nuclei of other nearby heavy atoms such as adjacent strontium. This is mostly in the range of X-rays. Thus strong beta emitters also emit significant secondary X-rays in most cases. This requires significant shielding measures which complicates the design of RTGs using Sr. The Soviet Union deployed nearly 1000 of these RTGs on its northern coast as a power source for lighthouses and meteorology stations.