strontium-90

strontium-90 is a radioactive isotope of the alkaline earth metal strontium, produced by nuclear fission in reactors and weapons tests. With a half-life of 28.79 years, it decays to yttrium-90 via beta emission, posing significant radiological hazards due to its chemical similarity to calcium. This biochemical behavior leads to its incorporation into bone and bone marrow, making it a particularly dangerous component of nuclear fallout.

Properties

Strontium-90 is a pure beta emitter, with a maximum decay energy of 0.546 MeV, and its decay product, yttrium-90, is also a high-energy beta emitter. The isotope's physical and chemical properties are identical to stable strontium isotopes, allowing it to readily participate in biological processes. Its decay chain contributes to the total ionizing radiation dose in contaminated environments, a principle central to the field of health physics. The measurement of its activity is often reported in units like the becquerel or the historical curie.

Production and occurrence

This radionuclide is primarily an artificial fission product, generated in significant quantities during the operation of nuclear reactors and the detonation of nuclear weapons. It is not found naturally except as a trace contaminant from anthropogenic sources. Major historical releases occurred during atmospheric testing, notably by the United States at the Nevada Test Site and by the Soviet Union at the Semipalatinsk Test Site. It was also a major component of fallout from incidents like the Chernobyl disaster and the Fukushima Daiichi nuclear disaster.

Health effects and biological role

Due to its chemical analogy to calcium, strontium-90 is absorbed by the body and deposited in mineralized tissues like bone and teeth. This internal emitter irradiates sensitive tissues, including the bone marrow, increasing the risk of cancers such as osteosarcoma and leukemia. Its presence was notably studied in populations exposed to fallout, such as residents near the Nevada Test Site and survivors of the atomic bombings of Hiroshima and Nagasaki. Regulatory limits for intake are set by bodies like the International Commission on Radiological Protection.

Applications

Despite its hazards, strontium-90 has specialized applications, primarily as a radioactive source. It is used in radioisotope thermoelectric generators (RTGs) for remote power, such as those deployed by the Soviet Union in unmanned lighthouses and by NASA in some space probes. The beta radiation from strontium-90, and its daughter yttrium-90, is also utilized in certain types of radiotherapy for treating conditions like synovitis, and in industrial thickness gauges.

Environmental presence and regulation

Strontium-90 persists in the environment, particularly in soils and sediments, and enters the food chain, concentrating in dairy products and bone-containing foods. Global dispersion was documented by networks like the United Nations Scientific Committee on the Effects of Atomic Radiation. Its environmental transport and regulation are governed by international treaties such as the Partial Nuclear Test Ban Treaty and agencies like the International Atomic Energy Agency and the U.S. Environmental Protection Agency. Cleanup of sites contaminated with strontium-90, such as the Hanford Site, remains a significant challenge.