Radium is a chemical element with the symbol Ra and an atomic number of 88. It was discovered in 1898 by Marie and Pierre Curie. They extracted it from uranium ore. Twelve years later, Marie Curie and Andre Debierne isolated the pure metallic form of radium by electrolysis from radium chloride. It was given the French name radium from Latin radius or ray. The curie unit of radioactivity was named for Marie Curie and is based on the radioactivity of Ra-226.
Radium is one of the alkaline earth metals along with beryllium, magnesium, calcium, strontium and barium. Earth metals are soft with a silver color and they have low densities, melting points and boiling points. They form compounds with the halogens such as chlorine and react vigorously with water to form hydroxides.
All the isotopes of radium are highly radioactive. They have atomic weights from Ra-202 to Ra-234 and half lives from .85 microseconds for a excited state of Ra212m2 to 1600 years for Ra-226. There are a total of 35 radium isotopes with 11 of them being metastable states with excited nucleons.
Ra-226 is the most common radium isotope and is part of the chain of daughter products resulting from the breakdown of U-238. The next most common isotope is Ra-226 with a half life of 5.75 years. It is part of the radioactive decay chain of thorium. Radium is over a million times as radioactive as the same amount of uranium. It decays into radon which is a radioactive gas that is a health hazard. Other products of radium decay include polonium, bismuth and inert non-radioactive lead. All radium is created by the radioactive decay of other elements which have long half lives. With its short half life, radium is only found in minute quantities in association with naturally occurring uranium and thorium. Radium glows in the dark as a result of
. Radium was first produced commercially by Biraco in its Belgium plant at Olen in the early 20th Century. Radium ionizes air which give up its excitation in the form of blue light making radium glow in the dark. It can also energize substances that are referred to as radioluminescent and cause them to glow in the dark in a variety of colors. Luminescent paint made with Ra-226 was invented in 1908. Such paint was widely used in the 1920s and 1930s for such applications as watch dials and aircraft instruments.. Stored radium must be well ventilated to prevent buildup of radon gas.
The radioactivity of radium and its daughter products such as radon gas pose a serious health risk to anyone who is exposed. Radium emits alpha particles which can mutate cells and cause cancer. Because radium is very similar to calcium, it can be taken up by the processes that create and maintain bones. As women working with radium containing paints became ill, the deleterious health effects of radium became apparent. Ironically, health tonics containing radium had been sold before its dangers were clearly understood. Such used of radium were eventually outlawed.
Radium is currently used for medical purposes such as treatment of tumors with the gamma radiation that it emits. There are also industrial uses such as production of radon gas, manufacture of medical equipment and lightning rods and neutron generators,.
Picture of a radium tonic bottle from Oak Ridge Associated Universities:
