Chemical symbol: Ra

Atomic number: 88

Oxidation number: 2+

Forms: Has 25 isotopes, of which Ra 226, with a half-life of 1,600 years, is the most stable. Six of the isotopes are found in nature.

Characteristics:

• Radium is an atomic element, a member of the same “alkaline earth metal” family on the Periodic Table that includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba). Radium is the heaviest atom of that group.


• Emits alpha, beta and gamma radiation. Radium is 1 million times more radioactive than the same mass of uranium.


• Pure radium is a silvery white metal at room temperature, but blackens on exposure to air. Melting point: 700°C, 1,292°F.

History: Discovered in 1898 by Polish chemist Marie Sklodowska Curie and her husband, French chemist Pierre Curie. Early in the 20th century, it was used to make self-luminous dials for watches and other instruments, and even was a food additive, until it was found to be too hazardous.

Where found:

• Natural: Radium is present in very low levels in rocks and soil. It is also in earth ores (typically pitchblende) that also contain uranium, which decays into radium. Found in higher concentrations in water near uranium mines.


• Man-made: Can be refined from uranium ore, and is often sold as radium chloride (RaCl2) or radium bromide (RaBr2). May be higher concentrations near radioactive waste disposal sites.

Common uses: Production of radon gas, to treat some cancers. Less hazardous substances have replaced radium in some other applications.

Potential health effects:
A known human carcinogen.

Regulation:

• US EPA Maximum Contaminant Level (MCL) in drinking water: 5 picocuries per liter (pCi/L) of combined Ra 226 and Ra 228.


• A picocurie (pCi) is a measure of radioactivity. One pCi is equal to 0.037 nuclear disintegrations per second.


• Another unit of measurement is the becquerel (Bq), which is equal to one nuclear disintegration per second. One pCi equals 0.037 Bq.


• US EPA MCL Goal: zero.

Common water treatment methods:

• Cation exchange softening.


• Reverse osmosis (RO) will remove 95 to 98 percent of radioactivity in water.

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Sources: US Environmental Protection Agency (EPA), US Agency for Toxic Substances and Disease Registry, Los Alamos National Labs, Water Quality Association, industry sources.