radium 音标拼音: [r'ediəm]
n . 镭
镭
radium n 1 :
an intensely radioactive metallic element that occurs in minute amounts in uranium ores [
synonym : {
radium }, {
Ra },
{
atomic number 88 }]
Radium \
Ra `
di *
um \ (
r [=
a ]"
d [
i ^]*[
u ^]
m ),
n . [
NL .,
fr .
L .
radius ray .] (
Chem .)
An intensely radioactive metallic element found (
combined )
in minute quantities in pitchblende ,
and various other uranium minerals .
Symbol ,
Ra ;
atomic weight ,
226 .
4 .
Radium was discovered by M .
and Mme .
Curie ,
of Paris ,
who in 1902 separated compounds of it by a tedious process from pitchblende .
Its compounds color flames carmine and give a characteristic spectrum .
It is divalent ,
resembling barium chemically .
The main isotope of radium found in pitchblende ,
radium -
226 ,
has a half -
life of 1620 years ,
decaying first by alpha emission to {
radon }.
Note :
Radium preparations are remarkable for maintaining themselves at a higher temperature than their surroundings ,
and for their radiations ,
which are of three kinds :
alpha rays ,
beta rays ,
and gamma rays (
see these terms ).
The beta and gamma rays seen in radium preparations are in fact due to disintegration of decay products of radium rather than the radium itself .
By reason of these rays they ionize gases ,
affect photographic plates ,
cause sores on the skin ,
and produce many other striking effects .
Their degree of activity depends on the proportion of radium present ,
but not on its state of chemical combination or on external conditions .
The radioactivity of radium is therefore an atomic property ,
and is due to an inherent instability of the atomic nucleus which causes its decay in a process whose rate is first order .
The disintegration of the radium nucleus is only the first in a series of nuclear disintegrations leading to production of a series of elements and isotopes .
The chain has at least seven stages ;
the successive main products have been studied and are {
radon },
a gaseous radioactive element belonging chemically to the inert noble gas series (
originally called radium emanation or exradio ,
radium A ,
radium B ,
radium C ,
etc .
The successive products are unstable isotopes of several different elements ,
each with an atomic weight a little lower than its predecessor .
Lead is the stable end product .
At the same time ,
the light gas helium is formed ,
being generated when the expelled alpha particles (
positively charged helium nuclei )
acquire electrons .
Radium ,
in turn ,
is formed in the pitchblende ore by a slow disintegration of uranium .
Natural radium and also an isotope (
radium -
228 ,
also called mesothorium I )
formed by the decay of thorium ,
were at one time used to make a luminous paint for watch dials ,
until the danger of the radioactivity became fully appreciated ,
and use of such material in watches was discontinued .
See also {
mesothorium }.
[
Webster 1913 Suppl .
PJC ]
45 Moby Thesaurus words for "
radium ":
acid ,
actual cautery ,
americium ,
astatine ,
atomic cocktail ,
berkelium ,
brand ,
brand iron ,
branding iron ,
caustic ,
cauter ,
cauterant ,
cauterizer ,
cautery ,
cobalt ,
corrosive ,
curium ,
einsteinium ,
electrocautery ,
escharotic ,
fermium ,
francium ,
hahnium ,
hot iron ,
lunar caustic ,
mendelevium ,
mordant ,
moxa ,
neptunium ,
plutonium ,
polonium ,
potential cautery ,
promethium ,
protactinium ,
radiocalcium ,
radiocarbon ,
radioelement ,
radioiodine ,
radioisotope ,
radiosodium ,
radon ,
tagged element ,
technetium ,
tracer ,
uranium
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