Radium «RAY dee uhm», is a highly radioactive, metallic
element. It occurs chiefly in uranium and thorium ores. The
French physicists Marie and Pierre Curie and a co-worker, Gustave Bemont,
discovered radium in 1898 while processing pitchblende, a uranium ore.
Before the mid-1950's, radium was widely used for treating cancer.
It also was a key ingredient in fluorescent paint used for watch and instrument
dials. Today, safer and cheaper sources of radiation have replaced
radium for most medical and industrial uses. These sources include
the isotope cobalt 60, particle accelerators, and X-ray machines.
Radium releases large amounts of high-energy radiation, which can be
harmful to human health. The element resembles calcium chemically,
and so it tends to accumulate in the bones after being absorbed by the
body. The radiation given off by radium bombards the bone marrow
and destroys tissue that produces red blood cells. It also can cause
bone cancer. In the past, some workers who handled radium in factories
that produced fluorescent watch dials died because they had absorbed the
radioactive material. However, under normal conditions, there is
almost no danger of absorbing hazardous amounts of radium because it occurs
in such tiny quantities in the environment.
Properties: Radium is silver-white. Its chemical symbol
is Ra, and its atomic number is 88. Radium is the heaviest member
of the group of elements called alkaline earth metals. Radium has
at least 26 isotopes, all of which are radioactive. The
atomic mass number of the most stable isotope is 226. Radium
melts at 700 °C and boils at 1140 °C. It has a density of 5 grams
per cubic centimeter at 20 °C.
How radium forms and breaks down: Radium is constantly being formed
in nature by the radioactive decay of uranium. During radioactive decay,
uranium 238, the heaviest isotope of uranium, emits radiation in the form
of alpha particles, beta particles, and gamma rays. In doing so, uranium
238 becomes uranium 234, which later changes into thorium 230. This
unstable (radioactive) isotope, in turn, breaks down into radium 226.
Concentrations of radium in nature are low because its isotopes disintegrate
continually. Radium 226 decays into an unstable isotope of a gas
called radon and eventually into a stable isotope of lead. |
