Plutonium

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Plutonium
By Sean Byrne
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History
The production of plutonium and neptunium by
bombarding uranium-238 with neutrons was
predicted in 1940 by two teams working
independently. Plutonium was first produced and
isolated on February 23, 1941 by deuteron
bombardment of uranium in the 60-inch cyclotron
at Berkeley. The discovery was kept secret due to
the war. It was named after Pluto, having been
discovered directly after neptunium.
                            Glenn Seaborg
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Chemical Physical Properties

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General Information
244Pu is the nucleon-richest atom that naturally
occurs in the Earth's crust. Plutonium has been
called "the most complex metal" and "a
physicist's dream but an engineer's nightmare"for
its peculiar physical and chemical properties.
It has six allotropes normally and a seventh
under pressure, each of which have very similar
energy levels but with significantly varying
densities, making it very sensitive to changes in
temperature, pressure, or chemistry, and allowing
for dramatic volume changes following phase
transitions The most significant isotope of
plutonium is 239Pu .
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General Information
All 15 plutonium isotopes are radioactive, and
most emit relatively weak alpha radiation which
can be blocked even by a sheet of paper. The
main isotopes of plutonium are Pu-238,
(half-life 88 years, alpha decay) Pu-239,
fissile (half-life 24 000 years, alpha decay)
Pu-240, fertile (half-life 6 560 years, alpha
decay) Pu-241, fissile (half-life 14.3 years,
beta decay) Pu-242, (half-life 376 000 years,
alpha decay) Pluto was considered to be a
planet at the time (though technically it should
have been "plutium", Seaborg said that he did not
think it sounded as good as "plutonium"). Seaborg
chose the letters "Pu" as a joke, which passed
without notice into the periodic table.
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Uses By Man
The isotope 239Pu is a key fissile component in
nuclear weapons, due to its ease of fissioning
and availability. The critical mass for an
unreflected sphere of plutonium is 16 kg, but
through the use of a neutron-reflecting tamper
the pit of plutonium in a fission bomb is reduced
to 10 kg. Complete detonation of plutonium will
produce an explosion equivalent to the explosion
of 20 kilotons of trinitrotoluene (TNT) per
kilogram.
                                            
Hanford Site plutonium production reactors along
the Columbia River during the Manhattan Project.
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Uses By Man
The isotope plutonium-238 (238Pu) has a
half-life of 88 years and emits a large amount of
thermal energy as it decays. These
characteristics make it well suited for safe
electrical power generation for devices which
must function without direct maintenance for
timescales approximating a human lifetime. It is
therefore used in radioisotope thermoelectric
generators such as those powering the Cassini and
New Horizons (Pluto) space probes. 238Pu has been
used successfully to power artificial heart
pacemakers, to reduce the risk of repeated
surgery. It has been largely replaced by lithium
based primary cells, but as of 2003 there were
somewhere between 50 and 100 plutonium-powered
pacemakers still implanted and functioning in
living patients.
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Chemistry

• It displays five ionic oxidation states in
  aqueous solution
• Pu(III), as Pu3 (blue lavender)
• Pu(IV), as Pu4 (yellow brown)
• Pu(V), as PuO2 (thought to be pink this ion is
  unstable in solution and will disproportionate
  into Pu4 and PuO22.)
• Pu(VI), as PuO22 (pink orange)
• Pu(VII), as PuO52- (dark red) the heptavalent
  ion is rare and prepared only under extreme
  oxidizing conditions.
• Plutonium reacts readily with oxygen, forming PuO
  and PuO2, as well as intermediate oxides. It
  reacts with the halogens, giving rise to
  compounds such as PuX3 where X can be F, Cl, Br
  or I PuF4 and PuF6 are also seen. The following
  oxyhalides are observed PuOCl, PuOBr and PuOI.
  It will react with carbon to form PuC, nitrogen
  to form PuN and silicon to form PuSi2.

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Compounds
Plutonium reacts readily with oxygen, forming PuO
and PuO2, as well as intermediate oxides. It
reacts with the halogens, giving rise to
compounds such as PuX3 where X can be F, Cl, Br
or I. The following oxyhalides are observed
PuOCl, PuOBr and PuOI. It will react with carbon
to form PuC, nitrogen to form PuN and silicon to
form PuSi2. Plutonium like other actinides
readily forms a dioxide plutonyl core (PuO2). In
the environment, this plutonyl core readily
complexes with carbonate as well as other oxygen
moieties (OH-, NO2-, NO3-, and SO4-2) to form
charged complexes which can be readily mobile
with low affinities to soil. PuO2(CO3)1-2
PuO2(CO3)2-4 PuO2(CO3)3-6 PuO2 Plutonium also
readily shifts valences between the 3, 4, 5
and 6 states. It is common for some fraction of
plutonium in solution to exist in all of these
states in equilibrium.