Plutonium, Radioactive

Other Properties

Plutonium exists as a number of isotopes. The common isotope plutonium-239 is an alpha emitter (5 MeV); plutonium-238 is also an alpha emitter. Plutonium exhibits valences (3+) to (6+) in solutions, but in most common biological and physiological conditions it occurs as Pu(4+). /Plutonium isotopes/

All plutonium isotopes are radioactive. Isotopes with even mass numbers (except mass number 246) are primarily alpha emitters. Isotopes of mass numbers 232, 233, 234, 235, and 237 also decay by electron capture; isotopes of mass numbers 241, 243, 245, and 246 decay by beta emission. Many of the alpha-emitting isotopes, such as plutonium-238 and plutonium-240, also fission spontaneously and emit neutrons. All of the particle emissions are accompanied by X-ray and gamma-ray emissions over a wide range of energies. /Plutonium isotopes/

While several plutonium nuclides can fission, only plutonium-239 is of practical importance as a criticality concern. /Plutonium-239/

Absolute entropy of alpha-plutonium at 298 K= 55.4461 J/(mol.K); heat capacity of alpha-plutonium at 298 K= 31.192 J/(mol.K); entropy of vaporization: from 1200-1790 K= 345.2 kJ/mol; from 1724-2219 K= 342 kJ/mol /alpha-plutonium/

The self heating of a plutonium-239 metal sphere: (1.923+/-0.019)X10-3 watts/g (1.82+/ -0.18 Btu/(sec gram) /Plutonium-239/

Atomic wt (most stable known isotopes) 242, 244

In groundwater (ionic strength of about 3.7 mmol; total dissolved carbonate of 2.8 mmol) plutonium has a solubility of 4.70X10-8 M at pH 6.0 and 25 deg C. /Plutonium metal/

Vapor pressure of liquid, logP in kPa: -(17,066+/-208)/T + 6.664 +/- 0.050

Calculated density: alpha allotrope: 19.86 g/cu cm; beta allotrope: 17.70 g/cu cm; gamma allotrope: 17.14 g/cu cm; delta allotrope:15.92 g/cu cm; delta prime allotrope: 16.00 g/cu cm; epsilon allotrope: 16.51 g/cu cm /Plutonium allotropes/

alpha allotrope: stability range: <124.5 deg C; primitive monoclinic; beta allotrope: stability range: 124.5-214.8 deg C; body-centered monoclinic; gamma allotrope: stability range: 214.8-320 deg C; face-centered orthorhombic; delta allotrope: stability range: 320-462.9 deg C; face-centered cubic; delta prime allotrope: 462.9-482.6 deg C; body-centered tetragonal; epsilon allotrope: stability range: 482.6-640 deg C; body-centered cubic /Plutonium allotropes/

The metal has a bright, silver-like appearance at first, but it oxidizes very quickly to a dull gray. It is about as hard and brittle as gray cast iron unless it is alloyed with other metals to make it soft and ductile. Although it is a metal, it is not a good conductor of heat or electricity like most other metals. /Plutonium metal/

Metallic plutonium readily dissolves in concentrated HCl, H3PO4, HI, or HClO4; nitric acid forms a protective oxide coating on the metal that can be removed by ca. 0.05 M HF; plutonium metal does not readily dissolve in H2SO4; alpha-plutonium oxidizes very slowly in dry air, the bright metal surface tarnishes rapidly in normal environments and a powdery surface forms, eventually green PuO2 covers the surface; the reaction of plutonium metal with liquid water produces both oxides and oxide-hydroxides; the reaction with water vapor above 100 deg C produces oxides and hydride. /Plutonium metal forms/

The metallic state of plutonium is undoubtedly the most complicated of all the elements. Plutonium is a silvery-white metal, much like nickel in appearance. It has a low melting point (640 deg C) and an unusually high boiling point (3,327deg C). The metal exists in six allotropic forms. Two of the allotropic forms contract upon heating; the other forms expand upon heating. At room temperature, pure plutonium ... has a triclinic structure with a theoretical density of about 19.86 g/cu cm. ... The combination of a high specific activity and low thermal conductivity can result in significant dimensional distortion during metal-forming operations. For this reason, a .. gallium alloy, which has a density of about 15.75 g/cu cm, is used when a more dimensionally stable plutoniuum is desired. /Plutonium metal/

Plutonium is an active metal. In moist air or moist argon, the metal oxidizes rapidly, producing a mixture of oxides and hydrides. If the metal is exposed long enough, an olive-green powdery surface coating of PuO2 is formed. With this coating, the metal is pyrophoric, so plutonium metal is usually handled in an inert, dry atmosphere of nitrogen or argon. Oxygen retards the effects of moisture and acts as a passivating agent. /Plutonium metal/

Plutonium metal also reacts with most common gases at elevated temperatures. Plutonium metal is rapidly dissolved by HCl, HBr, 72% HClO4, 85% H3PO4, concentrated CCl3COOH (trichloroacetic acid), sulfamic acid, and boiling concentrated HNO3 in the presence of 0.005M HF. The metal reacts slowly with water, dilute sulfuric acid, and dilute acetic acid. There is no reaction with the metal in pure HNO3 at any concentration, with concentrated acetic acid, nor with dilute sodium hydroxide. /Plutonium metal/

Valence: 3,4,5, and 6; 19 known isotopes

In aqueous solutions, plutonium (III) is oxidized into plutonium (IV), which is the most stable state. The compounds PuF4, Pu(I03)4, Pu(OH)4, and Pu(C2O4)2 6H2O (plutonium oxalate) are insoluble in water. The chlorides, nitrates, perchlorates, and sulfates are soluble in water. Plutonium (IV) ions complex readily with organic and inorganic compounds. /Plutonium compounds/

Plutonium (IV) nitrate is the most used of all plutonium compounds. Essentially all chemical processing of plutonium has been conducted in nitrate solutions. These solutions of appropriate acidities range from concentrations of 10 grams to 250 grams of Pu/L for efficient precipitation processes. Intermediate compounds are also used in the processing of plutonium prepared from the nitrate: plutonium (III) fluoride, plutonium (II or IV) oxalate, and plutonium peroxide. Plutonium (IV) fluoride can be prepared from any of the preceding solids by hydrofluorination. Plutonium fluoride has been the compound of choice for reduction to the metal with calcium, principally because it is nonhygroscopic. /Plutonium compounds/

Plutonium hexafluoride is the only volatile plutonium compound (bp 62 deg C) and is marginally stable. It can be prepared by oxidizing PuF4 with F2 at an elevated temperature. It can also be prepared at low temperatures by a fluorinating agent, fluorine dioxide. /Plutonium hexafluoride/

Plutonium dioxide is formed when plutonium or its compounds (except the phosphates) are ignited in air, and often results when oxygen-containing compounds are heated in vacuo or in an inert atmosphere to 1,000 deg C. Loose PuO2 powder, as formed by calcination, usually has a density of about 2 g/cm3. If the oxide is pressed and sintered into pellets, it may have a density of about 10.3 to 11.0 g/cm3. ... Plutonium oxide fired at temperatures >600 C is difficult to rapidly or completely dissolve in common acids or molten salts. The best solvents are 12 to 16M HNO3 with 0.10 to 0.1M HF, 5 to 6M HI, and 9M HBr. /Plutonium oxides/

General solubility characteristics include the insolubility of the hydroxides, fluorides, iodates, phosphates, carbonates, and oxalates of Pu+3 and Pu+4. Some of these can be dissolved in acid solution, however. The corresponding compounds of PuO2 +1 and PuO2 +2 are soluble, with the exception of the hydroxides. The binary compounds represented by the carbides, silicides, sulfides, and selenides are of particular interest because of their refractory nature. One of the complicating factors of plutonium chemistry is the formation of a polymeric material by hydrolysis in dilute acid or neutral solutions. The polymeric material can be a complicating factor in radiochemical procedures and be quite unyielding in attempts to destroy it.

The equilibration problems of plutonium are among the most complex encountered in radiochemistry. Of the five oxidation states that plutonium may have, the first four are present in solution as Pu+3, Pu+4, PuO2 +1, PuO2 +2. They coexist in dilute acid solution, and sometimes all four are present in substantial quantities. Problems of disproportionation and auto-oxidation in freshly prepared solutions also complicate the chemistry of plutonium. ... The +4 ion can form long chain polymers that do not exhibit the usual chemical behavior of the +4 oxidation state. Finally, the different oxidation states exhibit radically different chemical behavior. As a result of these effects, it is possible to mix a plutonium sample with plutonium tracer, subject the mixture to a relatively severe chemical treatment using hot acids or similar reagents, and still selectively recover portions of either the tracer or the sample. This characteristic explains the challenge in achieving reproducible radiochemical results for plutonium.

Apart from the disproportionation reactions, the oxidation state of plutonium ions in solution is affected by its own decay radiation or external gamma and X-rays. At high levels, radiolysis products of the solution can oxidize or reduce the plutonium, depending on the nature of the solution and the oxidation state of plutonium. Therefore, the stated oxidation states of old plutonium solutions, particularly old HClO4 and H2SO4 solutions, should be viewed with suspicion. Plutonium also tends to hydrolyze and polymerize in solution, further complicating the situation.

Plutonium isotopes with mass number 232 through 246 have been identified and all are radioactive

Atomic mass: 238.049553 /Plutonium-238/

Atomic mass: 239.052156 /Plutonium-239/

Atomic mass: 240.053807; half-life /Plutonium-240/

Atomic mass: 241.056844 /Plutonium-241/

Atomic mass: 242.058736 /Plutonium-242/

DECAY PATHWAY: Plutonium-236, half-life 2.851 years, decays via alpha emission, 5867 keV (69.3% 5767.7 keV; 30.6% 5721.0 keV) to uranium-232, half-life 68.9 years; decays via alpha emission, 5414 keV (68.2% 5320.1 keV; 31.6% 5263.4 keV) to thorium-228, half-life 1.9116 years; decays via alpha emission, 5520 keV (72.2% 5423.2 keV; 27.2% 5340.4 keV) to radium-224, half-life 3.66 days; decays via alpha emission, 5789 keV (94.9% 5685.4 keV; 5.06% 5448.6 keV) to radon-220, half-life 55.6 seconds; decays via alpha emission, 99.9% 6405 keV, to polonium-216, half-life 0.145 seconds; decays via alpha emission, 99.998% 6778.3 keV, to lead-212, half-life 10.64 hours; decays via beta(-) emission (82.5% 335 keV maximum, 94.8 average energy; 12.3% 173.1 keV average energy)and gamma emission (abs intensity: 100% 238.6 keV) to bismuth-212, half-life 60.55 minutes; 64.06% of bismuth-212 decays via beta (-) emission (86.6%, 832.5 average energy; 6.81%, 531.5 keV average energy) to polonium-212, half-life 45.1 seconds; 35.94% of bismuth-212 decays via alpha emission, 6207 keV (69.9% 6050.8 keV; 27.1% 6089.9 keV) to thallium-208, half-life 3.053 minutes; polonium-212 decays via alpha emission, 8954 keV (96.9% 11650 keV) to lead-208, half life stable; thallium-208 decays via beta (-) emission (48.7%, 1796.3 keV maximum, 647.4 average energy; 24.5%, 1285.6 keV maximum, 439.6 keV; 21.8%, 1518.9 keV maximum, 533.3 keV average energy) and gamma emission (abs intensities: 85.2% 583.2 keV; 22.8% 510.8 keV; 12.5% 860.6 keV) to lead-208, half-life stable.

DECAY PATHWAY: Plutonium-238, half-life 87.7 years, decays via alpha emission, 5593 keV (70.9% 5499 keV; 28.9% 5456 keV) to uranium-234, half-life 245,500 years

DECAY PATHWAY: Plutonium-239, half-life 24,110 years, decays via alpha emission, 5245 keV (73.3% 5156 keV; 15.1% 5144 keV) to uranium-235, half-life 7.028X10+8 years

DECAY PATHWAY: Plutonium-240, half-life 6564 years, decays via alpha emission, 5256 keV (72.8% 5168 keV; 27.1% 5144 keV) to uranium-235, half-life 2.342X10+7 years

DECAY PATHWAY: Plutonium-241, half-life 14.35 years, decays via beta (-) emission (100%, 20.8 keV maximum, 5.23 keV average energy) to americium-241, half-life 432.2 years; decays via alpha emission, 5683 keV (84.5% 5486 keV; 13.0% 5443keV) to neptunium-237, half-life 2,144,000 years

DECAY PATHWAY: Plutonium-242, half-life 373,300 years, decays via alpha emission, 4984 keV (77.5% 4901 keV; 22.4% 4856 keV) to uranium-238, half-life 4.468X10+9 years

Find more information on this substance at: Hazardous Substances Data Bank , TOXNET , PubMed