Radium
Symbol: Ra
Atomic Number: 88
Atomic Mass: 226.0 amu (atomic mass units)
Melting Point: 700.0 C (973.15 K, 1292.0 F)
Boiling Point: 1737.0 C (2010.15 K, 3158.6 F)
Number of Protons: 88
Number of Electrons: 88
Number of Neutrons: 138
Classification: Alkaline Earth Metal
Crystal Structure: Cubic
Density @ 293 K: 5.0 grams per cubic centimeter
Color: silver
Radium gets its name from the Latin word “radius” meaning ray. Marie Sklodowska Curie, a Polish chemist, discovered the element working with her husband, the French chemist Pierre Curie, in 1898. They had noted that a sample of the uranium ore pitchblende emitted more radiation than could be accounted for by the recovered uranium. Reasoning that the ore must contain another radioactive element they eventually discovered two new radioactive elements radium and polonium. To make their discovery the had to refine a large amount of the uranium ore as one ton of pitchblende contains about 0.14 grams of radium.
The pure element was isolated by Marie Curie and Andre-Louis Debierne in 1911. They used a mercury cathode in electrolysis of a sample of radium chloride. This produced a radium amalgam. To obtain the pure metal from the amalgam it was distilled in a hydrogen atmosphere. In the same year Marie was awarded the noble prize for chemistry for her discovery of radium and polonium.
Radium is over a million times more radioactive than uranium. It emits alpha, beta and gamma rays. Exposure to radium is a severe health hazard frequently leading to the formation of cancer. The laboratory notebooks in which the Curies documented their findings are contaminated with the element and are now considered too dangerous to be handled. The curie is a unit based on radium-226 that used to measure the radioactivity of a substance. One curie is equal to the number of atoms in a one gram sample of radium-226 that will decay in one second, or 37,000,000,000 decays per second.
All of radium’s isotopes are unstable. Its most stable isotope, radium-226, has a half life of 1600 years. Radium-226 will decay to form the gas radon-222 through alpha decay or to form lead-212 by ejecting a carbon-14 nucleus. Thirty five other isotopes of this element have been identified; of these, radium-216 has the shortest half life at 182 nanoseconds.
When freshly prepared, radium metal is a brilliant white, but it becomes blackened on exposure to air. This blackening is probably due to the formation of radium nitride. The metal is luminescent as are all of its salts. The element will decompose in water. When held in a flame radium produces a carmine red color.
Radium is recovered as a by-product from the refining of uranium. It is not usually supplied as a pure metal but rather as salt normally either radium chloride or radium bromide. It has a number of uses.
* Radium has been used to produce the luminescent paint used on watch and aircraft dials. In this function it has been replaced by cobalt-60 which is a safer but still radioactive material.
* Mixed with beryllium, radium will emit neutrons. This mixture is used as a neutron source.
* Radium decays to form radon which can be used in radiotherapy of some cancers. One gram of radium-226 produces 0.0001 milliliters of radon per day.
