CHAPTER I
PRELIMINARY
1.1. Background
The alkali
metals are lithium (Li),sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).This group lies in the s-block of the periodic table as
all alkali metals have their outermost electron in an s-orbital. The alkali metals provide
the best example of group trends in properties in the periodic
table, with elements exhibiting well-characterized homologous behavior.
The alkali
metals, found in group 1 of the periodic table (formerly known as group IA),
are very reactive metals that do not occur freely in nature. These metals have
only one electron in their outer shell. Therefore, they are ready to lose that
one electron in ionic bonding with other elements. As with all metals, the
alkali metals are malleable, ductile, and are good conductors of heat and
electricity. The alkali metals are softer than most other metals. Cesium and
francium are the most reactive elements in this group. Alkali metals can
explode if they are exposed to water
Small amounts of caesium-134 and
caesium-137 were released into the environment during nearly all nuclear weapon
tests and some nuclear accidents, most notably the Chernobyl disaster. As of
2005, caesium-137 is the principal source of radiation in the zone of
alienation around the Chernobyl nuclear power plant. Together with caesium-134,
iodine-131, and strontium-90, caesium-137 was among the isotopes with greatest
health impact distributed by the reactor explosion.
The mean contamination of
caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m2.
This corresponds to a contamination of 1 mg/km2 of caesium-137, totaling about
500 grams deposited over all of Germany.Caesium-137 is unique in that it is
totally anthropogenic. Unlike most other radioisotopes, caesium-137 is not
produced from its non-radioactive isotope, but from uranium. It did not occur
in nature before nuclear weapons testing began. By observing the characteristic
gamma rays emitted by this isotope, it is possible to determine whether the
contents of a given sealed container were made before or after the advent of atomic
bomb explosions. This procedure has been used by researchers to check the
authenticity of certain rare wines, most notably the purported “Jefferson
bottles”.
