Listing description
Protactinium (pronounced /ˌproʊtækˈtɪniəm/, PROH-tak-TIN-ee-əm) is a chemical element with the symbol Pa and atomic number 91. Its longest-lived and most
abundant naturally occurring isotope by far, Pa-231, is a decay product of
uranium-235 (U-235), and it has a half-life of 32,760 years. Much smaller trace
amounts of the short-lived metastable isotope Pa-234m occur as decay products
of uranium-238 (U-238). Pa-233 results from the
decay of thorium-233 as part of the chain of events used
to produce uranium-233 by
neutron irradiation of thorium-232.
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Detailed description
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Protactinium (pronounced /ˌproʊtækˈtɪniəm/, PROH-tak-TIN-ee-əm) is a chemical element with the symbol Pa and atomic number 91. Its longest-lived and most
abundant naturally occurring isotope by far, Pa-231, is a decay product of
uranium-235 (U-235), and it has a half-life of 32,760 years. Much smaller trace
amounts of the short-lived metastable isotope Pa-234m occur as decay products
of uranium-238 (U-238). Pa-233 results from the
decay of thorium-233 as part of the chain of events used
to produce uranium-233 by
neutron irradiation of thorium-232.
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Characteristics
Protactinium is a
metallic element that belongs to the actinide group, with a bright metallic luster
that it retains for some time in contact with air.[2][3] Protactinium is superconductive at temperatures below 1.4 K.[4]
Applications
Because of its
scarcity, high radioactivity and high toxicity, there are currently no uses for
protactinium outside of scientific research.
Protactinium-231
is formed by the alpha
decay of U-235 followed by beta decay of thorium-231. The physicist Walter Seifritz once estimated that
protactinium might possibly be used to build a nuclear weapon with a critical mass of 750±180 kg. This possibility
(of a chain reaction) has been ruled out by other nuclear physicists since
then.
The ratio of
protactinium-231 to thorium-230 in ocean sediments has also been used in paleoceanography to reconstruct the movements of North Atlantic water bodies during the last melting
of Ice Age glaciers.[5]
History
In 1890, Mendeleev predicted the existence of an element between thorium and uranium. Due to the fact that the actinide
element group was unknown uranium was positioned below tungsten and thorium below zirconium leaving
the space below tantalum empty. Until the 1950s periodic tables were published
with this structure.[6] For a long time chemists searched for
eka-tantalum as an element with similar chemical properties as tantalum, making
a discovery of protactinium nearly impossible.
In 1900, William Crookes isolated protactinium as a
radioactive material from uranium; however, he did not identify it as a new
element.[7]
Protactinium was
first identified in 1913, when Kasimir Fajans and Oswald Helmuth Göhring
encountered the short-lived isotope Pa-234m (half-life of about 1.17 minutes),
during their studies of the decay chains of uranium-238 (U-238). They gave the new element
the name brevium (from the Latin word, brevis, meaning brief or
short);[8][9] the name was changed to protoactinium
(from Greek
πρῶτος + ἀκτίς meaning "first beam element") in 1918 when two groups
of scientists (lead by Otto
Hahn and Lise Meitner of Germany; and Frederick Soddy and John Cranston of Great Britain) independently discovered Pa-231. The
name was shortened to Protactinium in 1949.
Aristid von Grosse produced 2 mg of Pa2O5
in 1927,[10] and in 1934 performed the first
isolation of elemental protactinium from 0.1 mg of Pa2O5
using the iodide process:
converting the oxide to an iodide and then reducing it in a vacuum with an
electrically heated metal filament:
2 PaI5 → 2 Pa + 5 I2
In 1961, the
British Atomic Energy Authority (UKAEA) was able to produce 125 grams of
99.9% pure protactinium by processing 60 tons of waste material in a 12-stage
process. For many years, this was the world's only significant supply of
protactinium.[7]
Occurrence
Protactinium
occurs in pitchblende to the extent of about 3.0 part
231Pa per million parts of ore.[7] name Some ores from the Democratic Republic of the Congo have about 3.0 ppm. Protactinium is
one of the rarest and most expensive naturally occurring elements.[2]
Compounds
Examples of
protactinium compounds:
- Fluorides:
protactinium(IV) fluoride PaF4,
protactinium(V) fluoride PaF5 - Chlorides:
protactinium(IV) chloride PaCl4,
protactinium(V) chloride PaCl5 - Bromides:
protactinium(IV) bromide PaBr4,
protactinium(V) bromide PaBr5 - Iodides:
protactinium(III) iodide PaI3,
protactinium(IV) iodide PaI4,
protactinium(V) iodide PaI5 - Oxides:
protactinium(II) oxide PaO,
protactinium(IV) oxide PaO2,
protactinium(V) oxide Pa2O5
Isotopes
Twenty-nine radioisotopes of protactinium have been discovered,
with the most stable being Pa-231 with a half life of 32760 years, Pa-233 with a
half-life of 27.0 days, and Pa-230 with a half-life of 17.4 days. All of the
remaining radioactive isotopes have half-lives that are
less than 1.60 days, and the majority of these have half-lives that are less
than 1.8 seconds. Protactinium also has two meta states, Pa-217m (half-life 1.2 milliseconds)
and Pa-234m (half-life 1.17 minutes).
The primary decay mode for isotopes of protactinium lighter
than (and including) the most stable isotope Pa-231 (i.e., Pa-212 to Pa-231) is
alpha decay and the primary mode for the heavier
isotopes (i.e., Pa-232 to Pa-240) is beta decay. The primary decay products of isotopes of protactinium lighter
than (and including) Pa-231 are actinium isotopes and the primary decay
products for the heavier isotopes of protactinium are uranium isotopes.
Precautions
Protactinium is
both toxic and highly radioactive. It requires precautions similar to those
used when handling plutonium.
Uranium (pronounced /jʊˈreɪniəm/ yoo-RAY-nee-əm)
is a silvery-white metallic chemical element in the actinide series of the periodic table with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. The uranium nucleus binds between
141 and 146 neutrons, establishing six isotopes, the most
common of which are U-238 (146 neutrons) and U-235 (143 neutrons). All isotopes are unstable and uranium is weakly radioactive. Uranium has the second highest atomic weight of the naturally occurring elements,
lighter only than plutonium-244.[3] Its density is about 70% higher than that of lead, but not as dense as gold or tungsten. It occurs naturally in low
concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.
In nature,
uranium is found as uranium-238 (99.284%), uranium-235 (0.711%),[4] and a very small amount of uranium-234 (0.0058%). Uranium decays slowly by
emitting an alpha particle.
The half-life of uranium-238 is about 4.47 billion
years and that of uranium-235 is 704 million years,[5] making them useful in dating the age of the Earth.
Many contemporary
uses of uranium exploit its unique nuclear properties. Uranium-235 has the
distinction of being the only naturally occurring fissile isotope. Uranium-238 is fissionable by fast
neutrons, and is fertile,
meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear
technology. While uranium-238 has a small probability for spontaneous fission or even induced fission with fast neutrons,
uranium-235 and to a lesser degree uranium-233 have a much higher fission
cross-section for slow neutrons. In sufficient concentration, these isotopes
maintain a sustained nuclear chain reaction. This generates the heat in nuclear power
reactors, and produces the fissile material for nuclear weapons. Depleted uranium (U-238) is used in kinetic energy penetrators and armor plating.[6]
Uranium is used
as a colorant in uranium glass,
producing orange-red to lemon yellow hues. It was also used for tinting and
shading in early photography. The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the planet Uranus. Eugène-Melchior Péligot was the first person to isolate the metal and
its radioactive properties were uncovered in 1896 by Antoine Becquerel. Research by Enrico Fermi and others starting in 1934 led to
its use as a fuel in the nuclear power industry and in Little Boy, the first nuclear weapon used in war. An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear
weapons that used enriched uranium and uranium-derived plutonium. The security
of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is an ongoing concern for
public health and safety.
PRICE
$12,900/KG OR $5,863.63/IB
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