Radium is a chemical element with symbol Ra
and atomic number 88. It is the sixth element
in group 2 of the periodic table, also known
as the alkaline earth metals. The color of
pure radium is almost pure white, but it readily
oxidizes on exposure to air, becoming black
in color. All isotopes of radium are highly
radioactive, with the most stable isotope
being radium-226, which has a half-life of
1600 years and decays into radon gas. When
radium decays, ionizing radiation is a product,
which can excite fluorescent chemicals and
cause radioluminescence.
Radium, in the form of radium chloride, was
discovered by Marie Curie and Pierre Curie
in 1898. They extracted the radium compound
from uraninite and published the discovery
at the French Academy of Sciences five days
later. Radium was isolated in its metallic
state by Marie Curie and André-Louis Debierne
through the electrolysis of radium chloride
in 1910.
In nature, radium is found in uranium and
thorium ores in trace amounts as small as
a seventh of a gram per ton of uraninite.
Radium is not necessary for living organisms,
and adverse health effects are likely when
it is incorporated into biochemical processes
because of its radioactivity and chemical
reactivity. Currently, other than its use
in nuclear medicine, radium has no commercial
applications; formerly, it was used as a radioactive
source for radioluminescent devices and also
in radioactive quackery for its supposed curative
powers. Today, the latter usage is no longer
in vogue because radium's toxicity has since
become known, and less dangerous isotopes
such as tritium and promethium-147 are used
instead in radioluminescent devices.
Characteristics
Physical
Radium is the heaviest known alkaline earth
metal; its physical and chemical properties
mostly resemble those of its lighter congener
barium, although it is not as well-studied.
Pure radium is a white, silvery, solid metal,
melting at 700 °C or 960 °C and boiling
at 1737 °C, similar to but lower than those
of barium, confirming periodic trends down
the group 2 elements. At standard temperature
and pressure, radium crystallizes in the body-centered
cubic structure, like barium: the radium–radium
bond distance is 514.8 picometers. Radium
has a density of 5.5 g/cm3, again lower than
that of barium, confirming periodic trends;
the radium-barium density ratio is comparable
to the radium-barium atomic mass ratio, as
these elements have very similar body-centered
cubic structures. The white luster of radium
is rapidly lost upon oxidation in air, forming
the black radium nitride.
Chemical
The first two ionization energies of radium
and barium are very similar: 509.3 and 979.0
kJ·mol−1 for radium and 502.9 and 965.2
kJ·mol−1 for barium. These low figures
yield both elements' high reactivity and the
formation of the very stable Ra2+ ion and
similar Ba2+. When exposed to air, radium
reacts violently with it, forming radium nitride,
which causes blackening of this white metal.
It exhibits only the +2 oxidation state in
solution. Radium ions do not form complexes
easily, because of their high basicity. Most
radium compounds coprecipitate with all barium,
most strontium, and most lead compounds, and
are ionic salts. The radium ion is colorless,
making radium salts white when freshly prepared,
turning yellow and ultimately dark with age
owing to self-decomposition from the alpha
radiation. Compounds of radium flame red-purple
and give a characteristic spectrum. Like other
alkaline earth metals, radium reacts violently
with water to form radium hydroxide and is
slightly more volatile than barium. Because
of its geologically short half-life and intense
radioactivity, radium compounds are quite
rare, occurring almost exclusively in uranium
ores.
Radium chloride, radium bromide, radium hydroxide,
and radium nitrate are soluble in water, with
solubilities slightly lower than those of
barium analogs for bromide and chloride, and
higher for nitrate. Radium hydroxide is more
soluble than hydroxides of other alkaline
earth metals, actinium, and thorium, and more
basic than barium hydroxide. It can be separated
from these elements by their precipitation
with ammonia. Insoluble radium compounds include
radium sulfate, radium chromate, radium iodate,
radium carbonate, and radium tetrafluoroberyllate;
the radium sulfate is the most insoluble known
sulfate. Radium oxide remains uncharacterized,
despite the fact that oxides are common compounds
for other alkaline-earth metals. The 6s and
6p electrons participate in the bonding in
radium fluoride and radium astatide, making
the bonding there more covalent in character.
Isotopes
Radium has 25 different known isotopes, four
of which are found in nature, with 226Ra being
the most common. 223Ra, 224Ra, 226Ra and 228Ra
are all generated naturally in the decay of
either uranium or thorium. 226Ra is a product
of 238U decay, and is the longest-lived isotope
of radium with a half-life of 1600 years;
next longest is 228Ra, a product of 232Th
breakdown, with a half-life of 5.75 years.
Radium has no stable isotopes; however, four
isotopes of radium are present in decay chains,all
of which are present in trace amounts. The
most abundant and the longest-living one is
radium-226, with a half-life of 1600 years.
To date, 34 isotopes of radium have been synthesized,
ranging in mass number from 202 to 234.
At least 12 nuclear isomers have been reported;
the most stable of them is radium-205m, with
a half-life of between 130 and 230 milliseconds.
All ground states of isotopes from radium-205
to radium-214, and from radium-221 to radium-234,
have longer ones.
Three other natural radioisotopes had received
historical names in the early 20th century:
radium-223 was known as actinium X, radium-224
as thorium X and radium-228 as mesothorium
I. Radium-226 has given historical names to
its decay products after the whole element,
such as radium A for polonium-218.
Radioactivity
Radium-226 is 2.7 million times more radioactive
than the same molar amount of natural uranium,
due to its proportionally shorter half-life.
Both are components of the uranium/radium
decay series, so all the radium-226 in the
world today is the product of uranium-238
decay, hence its occurrence only in ores of
uranium. Radium's decay occurs in the last
nine steps of the fourteen step uranium series;
the successive decay products were studied
and were called radium emanation or "exradio",
radium A, radium B, radium C, and so on. Radon
is a heavy gas, and the later products are
solids. These products are themselves radioactive
elements until stable lead-206 is reached,
each with an atomic weight four atomic mass
units lower and atomic number two lower than
its predecessor in the case of alpha decay;
in the case of beta decay, the weight remains
unchanged, but the element transmutes to the
element one heavier or one lighter. Radium-226
loses about 1% of its activity in 25 years,
being transformed into elements of lower atomic
weight, with lead-206 being the final product
of disintegration, just as uranium-238 decays
down to radium-226.
A sample of radium metal maintains itself
at a higher temperature than its surroundings
because of the radiation it emits – alpha
particles, beta particles, and gamma rays.
More specifically, radium itself emits only
alpha particles, but other steps in the decay
chain emit alpha or beta particles, and almost
all particle emissions are accompanied by
gamma rays.
Occurrence
All radium occurring today is produced by
the decay of heavier elements, being present
in decay chains. Owing to such short half-lives
of its isotopes, radium is not primordial
but trace. It cannot occur in large quantities
due both to the fact that isotopes of radium
have short half-lives and that parent nuclides
have very long ones. Radium is found in tiny
quantities in the uranium ore uraninite and
various other uranium minerals, and in even
tinier quantities in thorium minerals.
Radium-226 is a decay product of uranium and
is therefore found in all uranium-bearing
ores.. All other isotopes of radium, produced
by the other two active decay chains and by
the occasional neutron capture, have much
shorter half lives than radium-226, so it
is the most common, predominant isotope of
the element.
Production
Uranium had no large scale application in
the late 18th century and therefore no large
uranium mines existed. In the beginning the
only larger source for uranium ore was the
silver mines at Joachimsthal in the Austrian
Empire. The uranium ore was only a by-product
of the mining activities. After the isolation
of radium by Marie and Pierre Curie from uranium
ore from Joachimsthal several scientists started
to isolate radium in small quantities. Later
small companies purchased mine tailings from
Joachimsthal mines and started isolating radium.
In 1904 the Austrian government took over
the ownership of the mines and stopped exporting
raw ore. For some time the radium availability
was low.
The formation of an Austrian monopoly and
the strong urge of other countries to have
access to radium led to a world wide search
for uranium ores. The United States took over
as leading producer in the early 1910s. The
Carnotite sands in Colorado provide some of
the element, but richer ores are found in
the Congo and the area of the Great Bear Lake
and the Great Slave Lake of northwestern Canada.
Radium can also be extracted from the waste
from nuclear reactors. Large radium-containing
uranium deposits are located in Russia, Canada,
the United States and Australia. Neither of
the deposits is mined for radium but the uranium
content makes mining profitable.
The amounts produced were always relatively
small; for example, in 1918 13.6 g of radium
were produced in the United States. As of
1954, the total worldwide supply of purified
radium amounted to about 5 pounds.
History
Radium was discovered by Marie Skłodowska-Curie
and her husband Pierre on 21 December 1898,
in a uraninite sample. While studying the
mineral, the Curies removed uranium from it
and found that the remaining material was
still radioactive. They then separated out
a radioactive mixture consisting mostly of
compounds of barium which gave a brilliant
green flame color and crimson carmine spectral
lines that had never been documented before.
The Curies announced their discovery to the
French Academy of Sciences on 26 December
1898. The naming of radium dates to about
1899, from the French word radium, formed
in Modern Latin from radius, called for its
power of emitting energy in the form of rays.
In 1910, radium was isolated as a pure metal
by Curie and André-Louis Debierne through
the electrolysis of a pure radium chloride
solution using a mercury cathode and distilling
in an atmosphere of hydrogen gas. The same
year, E. Eoler produced radium by heating
its azide, Ra(N3)2. The Curies' new element
was first industrially produced in the beginning
of the 20th century by Biraco, a subsidiary
company of Union Minière du Haut Katanga
in its Olen plant in Belgium. UMHK offered
to Marie Curie her first gram of radium. It
gave historical names to the decay products
of radium, such as radium A, B, C, etc., now
known to be isotopes of other elements.
On 4 February 1936, radium E became the first
radioactive element to be made synthetically
in the United States. Dr. John Jacob Livingood,
at the radiation lab at University of California,
Berkeley, was bombarding several elements
with 5-MeV deuterons. He noted that irradiated
bismuth emits fast electrons with a 5-day
half-life, which matched the behavior of radium
E.
The common historical unit for radioactivity,
the curie, is based on the radioactivity of
226Ra.
Historical applications
Some of the few practical uses of radium are
derived from its radioactive properties. More
recently discovered radioisotopes, such as
60Co and 137Cs, are replacing radium in even
these limited uses because several of these
isotopes are more powerful emitters, safer
to handle, and available in more concentrated
form.
Luminescent paint
Radium was formerly used in self-luminous
paints for watches, nuclear panels, aircraft
switches, clocks, and instrument dials. A
typical self-luminous watch that uses radium
paint contains around 1 microgram of radium.
In the mid-1920s, a lawsuit was filed against
the United States Radium Corporation by five
dying "Radium Girl" dial painters who had
painted radium-based luminous paint on the
dials of watches and clocks. The dial painters
routinely licked their brushes to give them
a fine point, thereby ingesting radium. Their
exposure to radium caused serious health effects
which included sores, anemia, and bone cancer.
This is because radium is treated as calcium
by the body, and deposited in the bones, where
radioactivity degrades marrow and can mutate
bone cells.
During the litigation, it was determined that
the company's scientists and management had
taken considerable precautions to protect
themselves from the effects of radiation,
yet had not seen fit to protect their employees.
Worse, for several years the companies had
attempted to cover up the effects and avoid
liability by insisting that the Radium Girls
were instead suffering from syphilis. This
complete disregard for employee welfare had
a significant impact on the formulation of
occupational disease labor law.
As a result of the lawsuit, the adverse effects
of radioactivity became widely known, and
radium-dial painters were instructed in proper
safety precautions and provided with protective
gear. In particular, dial painters no longer
licked paint brushes to shape them. Radium
was still used in dials as late as the 1960s,
but there were no further injuries to dial
painters. This highlighted that the harm to
the Radium Girls could easily have been avoided.
From the 1960s the use of radium paint was
discontinued. In many cases luminous dials
were implemented with non-radioactive fluorescent
materials excited by light; such devices glow
in the dark after exposure to light, but the
glow fades. Where indefinite self-luminosity
in darkness was required, safer radioactive
promethium paint was initially used, later
replaced by tritium which continues to be
used today. Tritium emits beta radiation which
cannot penetrate the skin, rather than the
penetrating gamma radiation of radium and
is regarded as safer. It has a half-life of
12 years.
Clocks, watches, and instruments dating from
the first half of the 20th century, often
in military applications, may have been painted
with radioactive luminous paint. They are
usually no longer luminous; however, this
is not due to radioactive decay of the radium
but to the fluorescence of the zinc sulfide
fluorescent medium being worn out by the radiation
from the radium. The appearance of an often
thick layer of green or yellowish brown paint
in devices from this period suggests a radioactive
hazard. The radiation dose from an intact
device is relatively low and usually not an
acute risk; but the paint is dangerous if
released and inhaled or ingested.
Commercial use
Radium was once an additive in products such
as toothpaste, hair creams, and even food
items due to its supposed curative powers.
Such products soon fell out of vogue and were
prohibited by authorities in many countries
after it was discovered they could have serious
adverse health effects. Spas featuring radium-rich
water are still occasionally touted as beneficial,
such as those in Misasa, Tottori, Japan. In
the U.S., nasal radium irradiation was also
administered to children to prevent middle-ear
problems or enlarged tonsils from the late
1940s through the early 1970s.
Medical use
Radium was used in medicine to produce radon
gas which in turn was used as a cancer treatment;
for example, several of these radon sources
were used in Canada in the 1920s and 1930s.
The isotope 223Ra was approved by the FDA
in 2013 for use in medicine as a cancer treatment
of bone metastasis.
Howard Atwood Kelly, one of the founding physicians
of Johns Hopkins Hospital, was a major pioneer
in the medical use of radium to treat cancer.
His first patient was his own aunt in 1904,
who died shortly after surgery. Kelly was
known to use excessive amounts of radium to
treat various cancers and tumors. As a result,
some of his patients died from high amounts
of radium exposure. His method of radium application
was inserting a radium capsule near the affected
area then sewing the radium "points" directly
to the tumor. This was the same method used
to treat Henrietta Lacks, the host of the
original HeLa cells, for cervical cancer.
Research
In 1909, the famous Rutherford experiment
used radium as an alpha source to probe the
atomic structure of gold. This experiment
led to the Rutherford model of the atom and
revolutionized the field of nuclear physics.
When mixed with beryllium, it is a neutron
source. This type of neutron source were for
a long time the main source for neutrons in
research.
Precautions
Radium is highly radioactive and its decay
product, radon gas, is also radioactive. Since
radium is chemically similar to calcium, it
has the potential to cause great harm by replacing
calcium in bones. Exposure to radium can cause
cancer and other disorders, because radium
and its decay product radon emit alpha particles
upon their decay, which kill and mutate cells.
At the time of the Manhattan Project in 1944,
the "tolerance dose" for workers was set at
0.1 microgram of ingested radium.
Some of the biological effects of radium were
apparent from the start. The first case of
so-called "radium-dermatitis" was reported
in 1900, only 2 years after the element's
discovery. The French physicist Antoine Becquerel
carried a small ampoule of radium in his waistcoat
pocket for 6 hours and reported that his skin
became ulcerated. Marie Curie experimented
with a tiny sample that she kept in contact
with her skin for 10 hours, and noted that
an ulcer appeared several days later. Handling
of radium has been blamed for Curie's death
due to aplastic anemia. Stored radium should
be ventilated to prevent accumulation of radon.
Emitted energy from the decay of radium also
ionizes gases, fogs photographic emulsions,
and produces many other detrimental effects.
See also
Notes
References
Bibliography
Kirby, H. W; Salutsky, Murrell L. The Radiochemistry
of Radium. National Academies Press. 
Further reading
Albert Stwertka. Guide to the Elements –
Revised Edition. Oxford University Press.
ISBN 0-19-508083-1. 
Denise Grady. "A Glow in the Dark, and a Lesson
in Scientific Peril". The New York Times.
Retrieved 25 December 2007. 
Nanny Fröman. "Marie and Pierre Curie and
the Discovery of Polonium and Radium". Nobel
Foundation. Retrieved 25 December 2007. 
Macklis, R. M.. "The great radium scandal".
Scientific American 269: 94–99. doi:10.1038/scientificamerican0893-94.
PMID 8351514. 
Clark, Claudia. Radium Girls: Women and Industrial
Health Reform, 1910–1935. University of
North Carolina Press. ISBN 0-8078-4640-6. 
External links
Lateral Science – Radium Discovery
Photos of Radium Water Bath in Oklahoma
NLM Hazardous Substances Databank – Radium,
Radioactive
Reproduction of a 1942 comic book ad selling
a "Radiumscope" to children
Annotated bibliography for radium from the
Alsos Digital Library for Nuclear Issues
The Poisoner Next Door – Japan Today, 102001
Radium at The Periodic Table of Videos
Radioactivity.eu.com
