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H' at. wt. (natural) 1.007967
   at. wt. (H') 1.007822
   at. no. 1
   m.p. - 259.140C
   b.p. - 252.870C 
   density 0.08988 gm./l
   density (liquid) 70.8 gm/i. (-2530C)
   density (solid) 7016 gm/i. (-2620C)
   valence 1.

**Electronic configuration**
K	L	M	N	O	P	Q
1	2	3	4	5	6	7
s	s p	s p d	s p d f	s p d f	s p d f	s p d f
1

POLONIUM (Poland, native country of Mme. Curie), Po; at. mass. (~2l0); at. no.84; m.p. 2540C; b.p. 9620C; sp. gr. (alpha modification) 9.32; valence -.2,0, + 2, + 3(?), + 4, and +6. Polonium was the first element discovered by Mme. Curie, in 1898, while seeking the cause of radio- activity of pitchblende from Joachimsthal, Bohemia. The electroscope showed it separating with bismuth. Polonium is also called Radium F. Polonium is a' very rare natural element. Uranium ores contain only about 100 micrograms of the element per ton. Its abundance is qnty about 0.2% of that of radium. In 1934 it was found that when natural bismuth (Bi209) was bombarded by neutrons, Bi210, 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-2 10 is a low- melting, fairly volatile metal, 50% of which is, vaporized in air in 45 hours at 550C. It is an alpha-emitter with a half-life of 138.39 days. A milligram emits as many alpha particles as 5 grams of radium. The energy released by its decay is so THE ELEMENT~Contiiiued) large (27.5 calories per curie per day or 140 watts/gm.) that a capsule containing about half a gram reaches a temperature above 5000C. The capsule also presents a contact gamma- ray dose rate of 1.2 roentgens per hour. a A few curies of polonium exhibit a blue glow, caused by excitation of the surrounding gas. 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 light-weight heat source for thermoelectric power in space satellites. Polonium has more isotopes than any other el- ement. Thirty-four isotopes of polonium are known, with atomic masses ranging from 192 to 218. Polonium-210 is the most readily available. Isotopes of mass 209 (half-life of 103 yrs.) and mass 208 (half-life 2.9 yrs.) 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 hy- droxide and some other polonium compounds in the pres- ence ofconcentrated aqueous or anhydrous liquid ammonia. Two allotropic modifications are known to exist. Polonium is readily dissolved in dilute acids, but is only slightly soluble in alkalis. Polonium salts of organic acids char rapidly; halide ammines are reduced to the metal. Polonium can be mixed or alloyed with beryllium to provide a source of neutrons. It has been used in devices for eliminating static charges in textile mills, etc.; however, beta sources are more commonly used and are less dangerous. It is also used on brushes for removing dust from photographic films. The polonium for these is carefully sealed and controlled, mini- mizing hazards to the user. Polonium-210 is very dangerous to handle in even milligram or microgram amounts and special equipment arid strict control is' necessary. Damage arises from the complete adsorption of the energy of the alpha particle into tissue. The maximum permissible body-burden for ingested polonium is only 0.03 micro~uries, which repre- sents a particle weighing only 6.8 x 10-12 grams. Weight- for-weight it is about 2.5 x loll times as toxic as hydro- cyanic acid. The maximum allowable concentration for soluble polonium compounds in air is about 2 x 1011 microcuries/oc. Poloniuni is available commercially on special order with an A.E.C. permit from the Oak Ridge National Laboratory.

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