| slovo | definícia |
radium F
(gcide) | Polonium \Po*lo"ni*um\ (p[-o]*l[=o]"n[i^]*[u^]m), n. [NL. So
named after Poland, in L. form Polonia, one of the
discoverers being a Pole.] (Chem.)
A radioactive chemical element, discovered by M. and MMe.
Curie in pitchblende, and originally called radium F. It
has atomic number 84 and an atomic weight of 210. It is a
very rare natural element, having an abundance in uranium
ores only 0.2% that of radium. It is closely related
chemically to bismuth. It emits only alpha rays, and has a
half-life of 138 days. It is thus more unstable than radium,
and a milligram of polonium emits as many alpha particles as
5 grams of radium. Twenty-seven isotopes are known, with
atomic masses from 192 to 218. At present a more practical
method of preparation than isolation from ores is the
preparation by neutron bombardment of bismuth in a nuclear
reactor, and it may be obtained commercially by users having
an appropriate permit. --[HBCF61]
[Webster 1913 Suppl. +PJC] |
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