Plutonium (Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized before being found in nature, with the first isotope synthesized being Pu in 1940. Twenty-two plutonium radioisotopes have been characterized. The most stable are Pu with a half-life of 81.3 million years, Pu with a half-life of 375,000 years, Pu with a half-life of 24,110 years, and Pu with a half-life of 6,561 years. This element also has eight meta states; all have half-lives of less than one second.
The known isotopes of plutonium range from Pu to Pu. The primary decay modes before the most stable isotope, Pu, are spontaneous fission and alpha decay; the primary mode after is beta emission. The primary decay products before Pu are isotopes of uranium and neptunium (not considering fission products), and the primary decay products after are isotopes of americium.
List of isotopes
|-id=Plutonium-226 | Pu | style="text-align:right" | 94 | style="text-align:right" | 132 | 226.03825(22)# | style="text-align:center" | (2024) | ≥1 ms | α | U | 0+ | |-id=Plutonium-227 | Pu | style="text-align:right" | 94 | style="text-align:right" | 133 | 227.03947(11)# | style="text-align:center" | 2024 | | α | U | 5/2+# | |-id=Plutonium-228 | Pu | style="text-align:right" | 94 | style="text-align:right" | 134 | 228.038763(25) | style="text-align:center" | 1994 | 2.1(13) s | α | U | 0+ | |-id=Plutonium-229 | rowspan=3|Pu | rowspan=3 style="text-align:right" | 94 | rowspan=3 style="text-align:right" | 135 | rowspan=3|229.040145(65) | rowspan=3 style="text-align:center" | 1994 | rowspan=3|91(26) s | α (~50%) | U | rowspan=3|3/2+# | rowspan=3| |- | β (~50%) | Np |- | SF (<7%) | (various) |-id=Plutonium-230 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 136 | rowspan=2|230.039648(16) | rowspan=2 style="text-align:center" | 1990 | rowspan=2|105(10) s | α (>73%) | U | rowspan=2|0+ | rowspan=2| |- | β (<27%) | Np |-id=Plutonium-231 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 137 | rowspan=2|231.041126(24) | rowspan=2 style="text-align:center" | 1999 | rowspan=2|8.6(5) min | β (87%) | Np | rowspan=2|(3/2+) | rowspan=2| |- | α (13%) | U |-id=Plutonium-232 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 138 | rowspan=2|232.041182(18) | rowspan=2 style="text-align:center" | 1973 | rowspan=2|33.7(5) min | EC (77%)Branching ratio from ENSDF at | Np | rowspan=2|0+ | rowspan=2| |- | α (23%) | U |-id=Plutonium-233 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 139 | rowspan=2|233.042997(58) | rowspan=2 style="text-align:center" | 1957 | rowspan=2|20.9(4) min | β (99.88%) | Np | rowspan=2|5/2+# | rowspan=2| |- | α (0.12%) | U |-id=Plutonium-234 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 140 | rowspan=2|234.0433175(73) | rowspan=2 style="text-align:center" | 1949 | rowspan=2|8.8(1) h | EC (94%) | Np | rowspan=2|0+ | rowspan=2| |- | α (6%) | U |-id=Plutonium-235 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 141 | rowspan=2|235.045285(22) | rowspan=2 style="text-align:center" | 1957 | rowspan=2|25.3(5) min | β | Np | rowspan=2|(5/2+) | rowspan=2| |- | α (0.0028%) | U |-id=Plutonium-236 | rowspan=3|Pu | rowspan=3 style="text-align:right" | 94 | rowspan=3 style="text-align:right" | 142 | rowspan=3|236.0460567(19) | rowspan=3 style="text-align:center" | 1949 | rowspan=3|2.858(8) y | αTheorized to also undergo β+β+ decay to 236U | U | rowspan=3|0+ | rowspan=3| |- | SF (1.9 × 10%) | (various) |- | CD (2 × 10%) | Pb + Mg |-id=Plutonium-236m | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 1185.45(15) keV | style="text-align:center" | 2005 | 1.2(3) μs | IT | Pu | 5− | |-id=Plutonium-237 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 143 | rowspan=2|237.0484079(18) | rowspan=2 style="text-align:center" | 1949 | rowspan=2|45.64(4) d | EC | Np | rowspan=2|7/2− | rowspan=2| |- | α (0.0042%) | U |-id=Plutonium-237m1 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 145.543(8) keV | style="text-align:center" | 1957 | 180(20) ms | IT | Pu | 1/2+ | |-id=Plutonium-237m2 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 2600(20) keV | style="text-align:center" | 1969 | 103(7) ns | SF | (various)
|-id=Plutonium-237m3 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 2900(250) keV | style="text-align:center" | 1970 | 1.1(1) μs | SF | (various)
|-id=Plutonium-238 | rowspan=4|Pu | rowspan=4 style="text-align:right" | 94 | rowspan=4 style="text-align:right" | 144 | rowspan=4|238.0495582(12) | rowspan=4 style="text-align:center" | 1949 | rowspan=4|87.7(1) y | α | U | rowspan=4|0+ | rowspan=4|TraceDouble beta decay product of U |- | SF (1.9 × 10%) | (various) |- | CD (1.4 × 10%) | Hg + Si |- | CD (6 × 10%) | Pb + MgPb + Mg |-id=Plutonium-239 | rowspan=2|Pufissile nuclideMost useful isotope for nuclear weapons | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 145 | rowspan=2|239.0521616(12) | rowspan=2 style="text-align:center" | 1946 | rowspan=2|2.411(3)×104 y | α | U | rowspan=2|1/2+ | rowspan=2|TraceNeutron capture product of U |- | SF (3.1 × 10%) | (various) |-id=Plutonium-239m1 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 391.584(3) keV | style="text-align:center" | 1955 | 193(4) ns | IT | 239Pu | 7/2− | |-id=Plutonium-239m2 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 3100(200) keV | style="text-align:center" | 1970 | 7.5(10) μs | SF | (various) | (5/2+) | |-id=Plutonium-240 | rowspan=3|Pu | rowspan=3 style="text-align:right" | 94 | rowspan=3 style="text-align:right" | 146 | rowspan=3|240.0538117(12) | rowspan=3 style="text-align:center" | 1949 | rowspan=3|6.561(7)×10 y | α | U | rowspan=3|0+ | rowspan=3|TraceIntermediate decay product of Pu |- | SF (5.796 × 10%) | (various) |- | CD (<1.3 × 10%) | Hg + Si |-id=Plutonium-240m | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 1308.74(5) keV | style="text-align:center" | 1967 | 165(10) ns | IT | 240Pu | 5− | |-id=Plutonium-241 | rowspan=3|Pu | rowspan=3 style="text-align:right" | 94 | rowspan=3 style="text-align:right" | 147 | rowspan=3|241.0568497(12) | rowspan=3 style="text-align:center" | 1949 | rowspan=3|14.329(29) y | β | Am | rowspan=3|5/2+ | rowspan=3| |- | α (0.00245%) | U |- | SF (<2.4 × 10%) | (various) |-id=Plutonium-241m1 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 161.6853(9) keV | style="text-align:center" | 1975 | 0.88(5) μs | IT | 241Pu | 1/2+ | |-id=Plutonium-241m2 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 2200(200) keV | style="text-align:center" | 1970 | 20.5(22) μs | SF | (various)
|-id=Plutonium-242 | rowspan=2|Pu | rowspan=2 style="text-align:right" | 94 | rowspan=2 style="text-align:right" | 148 | rowspan=2|242.0587410(13) | rowspan=2 style="text-align:center" | 1950 | rowspan=2|3.75(2)×10 y | α | U | rowspan=2|0+ | rowspan=2| |- | SF (5.510 × 10%) | (various) |-id=Plutonium-243 | Pu | style="text-align:right" | 94 | style="text-align:right" | 149 | 243.0620021(27) | style="text-align:center" | 1951 | 4.9553(25) h | β | Am | 7/2+ | |-id=Plutonium-243m | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 383.64(25) keV | style="text-align:center" | 1975 | 330(30) ns | IT | 243Pu | (1/2+) | |-id=Plutonium-244 | rowspan=3|Pu | rowspan=3 style="text-align:right" | 94 | rowspan=3 style="text-align:right" | 150 | rowspan=3|244.0642044(25) | rowspan=3 style="text-align:center" | 1954 | rowspan=3|8.13(3)×10 y | α (99.88%) | U | rowspan=3|0+ | rowspan=3|TraceInterstellar, some may also be primordial but such claims are disputed |- | SF (0.123%) | (various) |- | ββ (<7.3 × 10%) | Cm |-id=Plutonium-244m | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 1216.0(5) keV | style="text-align:center" | 2016 | 1.75(12) s | IT | 244Pu | 8− | |-id=Plutonium-245 | Pu | style="text-align:right" | 94 | style="text-align:right" | 151 | 245.067825(15) | style="text-align:center" | 1955 | 10.5(1) h | β | Am | (9/2−) | |-id=Plutonium-245m1 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 264.5(3) keV | style="text-align:center" | 2007 | 330(20) ns | IT | 245Pu | (5/2+) | |-id=Plutonium-245m2 | style="text-indent:1em" | Pu | colspan="3" style="text-indent:2em" | 2000(400) keV | style="text-align:center" | (1980) No evidence of this isomeric state in the refereed literature | 90(30) ns | SF | (various)
|-id=Plutonium-246 | Pu | style="text-align:right" | 94 | style="text-align:right" | 152 | 246.070204(16) | style="text-align:center" | 1955 | 10.84(2) d | β | Am | 0+ | |-id=Plutonium-247 | Pu | style="text-align:right" | 94 | style="text-align:right" | 153 | 247.07430(22)# | style="text-align:center" | 1983 | 2.27(23) d | β | Am | 1/2+# |
Actinides vs fission products
Notable isotopes Plutonium-238 has a half-life of 87.74 years and emits alpha particles. Pure Pu for radioisotope thermoelectric generators that power some spacecraft is produced by neutron capture on neptunium-237 but plutonium from spent nuclear fuel can contain as much as a few percent Pu, originating from Np, alpha decay of Cm, or (n,2n) reactions. Plutonium-239 has half-life 24,100 years. Pu and Pu are fissile; meaning their nuclei can split by being bombarded by slow thermal neutrons, releasing energy, gamma radiation and more neutrons. It can therefore sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. Pu is synthesized by irradiating uranium-238 with neutrons in a nuclear reactor, then recovered via nuclear reprocessing of the fuel. Further neutron capture produces successively heavier isotopes. Plutonium-240 has a high rate of spontaneous fission, raising the background neutron radiation of plutonium. Plutonium is graded by proportion of Pu: weapons grade (<7%), fuel grade (7–19%) and reactor grade (>19%). Lower grades are less suited for bombs and thermal reactors but can fuel fast reactors. Plutonium-241 is fissile, but beta decays with a half-life of 14 years to americium-241. Plutonium-242 is not fissile, nor very fertile (requiring 3 more neutron captures to become fissile); and has a low neutron capture cross section, and a longer half-life than any of the lighter isotopes. Plutonium-244 is the most stable isotope of plutonium, with a half-life of about 80 million years. It is not significantly produced in nuclear reactors because Pu has a short half-life, but some is produced in nuclear explosions. Pu has been found in interstellar space and has the second longest half-life of any non-primordial radioisotope.
Production and uses
Pu, a fissile isotope that is the second most used nuclear fuel in nuclear reactors after uranium-235, and the most used fuel in the fission portion of nuclear weapons, is produced from uranium-238 by neutron capture followed by two beta decays.