For nuclear batteries.
| Atomic Number: | 84 | Atomic Symbol: | Po |
| Atomic Weight: | 209 | Electron Configuration: | 2-8-18-32-18-6 |
| Shells: | 2,8,18,32,18,6 | Filling Orbital: | 6p4 |
| Melting Point: | 254oC | Boiling Point: | 962oC |
| Description: | Radioactive metal. |
History
(Poland, native country of Mme. Curie) Polonium, also called
Radium F, was the first element discovered by Mme. Curie in 1898 while seeking
the cause of radioactivity of pitchblend from Joachimsthal, Bohemia. The
electroscope showed it separating with bismuth.
Sources
Polonium is a very rare natural element. Uranium ores contain
only about 100 micrograms of the element per ton. Its abundance is only about
0.2% of that of radium.
In 1934, scientists discovered that when they bombarded natural bismuth
(209Bi) with neutrons, 210Bi, the parent of polonium, was obtained. Milligram
amounts of polonium may now be prepared this way, by using the high neutron
fluxes of nuclear reactors.
Polonium is available commercially on special order from the Oak Ridge
National Laboratory.
Properties
Polonium-210 is a low-melting, fairly volatile metal, 50% of
which is vaporized in air in 45 hours at 55C. It is an alpha emitter with a
half-life of 138.39 days. A milligram emits as many alpha particles as 5 g of
radium.
The energy released by its decay is so large (140W/g) that a capsule
containing about half a gram reaches a temperature above 500C. The capsule also
presents a contact gamma-ray does rate of 0.012 Gy/h. A few curies (1 curie =
3.7 x 10^10Bq) of polonium exhibit a blue glow, caused by excitation of the
surrounding gas.
Polonium is readily dissolved in dilute acids, but is only slightly soluble
in alkali. Polonium slats of organic acids char rapidly; halide amines are
reduced to the metal.
Uses
Because almost all alpha radiation is stopped within the solid
source and its container, giving up its energy, polonium has attracted attention
for uses as a lighweight heat source for thermoelectric power in space
satellites.
Polonium can be mixed or alloyed with beryllium to provide a source of
neutrons. The element has been used in devices for eliminating static charges in
textile mills, etc.; however, beta sources are both more commonly used and less
dangerous. It is also used on brushes for removing dust from photographic films.
The plonium for these is carefully sealed and controlled, minimizing hazards to
the user.
Isotopes
Twenty five isotopes of polonium are known, with atomic masses
ranging from 194 to 218. Polonium-210 is the most readily available. Isotopes of
mass 209 (half-life 103 years) and mass 208 (half-life 2.9 years) can be
prepared by alpha, proton, or deuteron bombardment of lead or bismuth in a
cyclotron, but these are expensive to produce.
Metallic polonium has been prepared from polonium hydroxide and some other
polonium compounds in the presence of concentrated aqueous or anhydrous liquid
ammonia. Two allotropic modifications are known to exist.
Hazards
Polonium-210 is very dangerous to handle in even milligram or
microgram amounts, and special equipment and strict control is necessary. Damage
arises from the complete absorption of the energy of the alpha particle into
tissue.
The maximum permissible body burden for ingested polonium is only 0.03
microcuries, which represents a particle weighing only 6.8 x 10^-12 g. Weight
for weight it is abot 2.5 x 10^11 times as toxic as hydrocyanic acid. The
maximum allowable concentration for soluble polonium compounds in air is about 2
x 10^-11 microcuries/cm^3.