Radium

Radium (chemical symbol: Ra) is a chemical element with atomic number 88. It belongs to the group of alkaline earth metals, meaning its chemistry is similar to barium and calcium. All isotopes of radium are radioactive and decay continuously, emitting radiation.

Radium does not occur in significant quantities in a pure state in nature. It arises from the decay chains of uranium and thorium, and so is found in tiny amounts in uranium ores such as pitchblende (uraninite). Because of its rapid decay, the quantity present in the Earth's crust is very small compared to uranium.

Discovery and history

Radium was identified in 1898 when Marie Curie and Pierre Curie analyzed residues from pitchblende ore in Paris. Using electrical conductivity measurement of air (ionization), they found that the residue emitted stronger radiation than uranium, leading them to isolate new elements—polonium and radium. Subsequently they extracted pure radium chloride, work that was foundational to the science of radioactivity.

Properties

Pure radium is a silvery-white metal that rapidly darkens when exposed to air, forming a nitride. It reacts vigorously with water. The most stable isotope is Ra-226, with a half-life of approximately 1,600 years; it decays to radon, a radioactive gas. Other isotopes such as Ra-223, Ra-224, and Ra-228 have much shorter half-lives.

Applications and hazards

In the early twentieth century, radium was added to luminous paint used on watch faces and aircraft instruments, and was employed in medical treatments and health products. Female workers who painted these watch dials—known as "Radium Girls"—developed bone and blood disorders, which led to lawsuits and new workplace safety regulations. Its use today is restricted; it has been replaced by safer isotopes. Ra-223 (as dichloride) is now used to treat some forms of bone cancer.