Isotopes of plutonium

Isotopes of plutonium  (₉₄Pu)

Main isotopes [1] Decay abun­dance half-life (t1/2) mode pro­duct 238Pu trace 87.7 y [2] α 234U SF – 239Pu trace 2.411×104 y α 235U SF – 240Pu trace 6.561×103 y α 236U SF – 241Pu synth 14.329 y β− 241Am α 237U SF – 242Pu synth 3.75×105 y α 238U SF – 244Pu trace 8.00×107 y α 240U SF –

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Plutonium (₉₄Pu) 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 long before being found in nature, the first isotope synthesized being ²³⁸Pu in 1940. Twenty-two plutonium radioisotopes have been characterized. The most stable are ²⁴⁴Pu with a half-life of 80.8 million years; ²⁴²Pu with a half-life of 373,300 years; and ²³⁹Pu with a half-life of 24,110 years; and ²⁴⁰Pu with a half-life of 6,560 years. This element also has eight meta states; all have half-lives of less than one second.

The known isotopes of plutonium range from ²²⁶Pu to ²⁴⁷Pu. The primary decay modes before the most stable isotope, ²⁴⁴Pu, are spontaneous fission and alpha decay; the primary mode after is beta emission. The primary decay products before ²⁴⁴Pu are isotopes of uranium and neptunium (not considering fission products), and the primary decay products after are isotopes of americium.

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da) [3] [n 2] [n 3]	Half-life [1]	Decay mode [1] [n 4]	Daughter isotope [n 5] [n 6]	Spin and parity [1] [n 7] [n 8]	Isotopic abundance
	Excitation energy
226Pu [4]	94	132	226.03825(22)#	≥1 ms	α	222U	0+
227Pu [5]	94	133	227.03947(11)#	0.78+0.39 −0.19 s	α	223U	5/2+#
228Pu	94	134	228.038763(25)	2.1(13) s	α	224U	0+
229Pu	94	135	229.040145(65)	91(26) s	α (~50%)	225U	3/2+#
					β+ (~50%)	229Np
					SF (<7%)	(various)
230Pu	94	136	230.039648(16)	105(10) s	α (>73%) [6]	226U	0+
					β+ (<27%)	230Np
231Pu	94	137	231.041126(24)	8.6(5) min	β+ (87%)	231Np	(3/2+)
					α (13%)	227U
232Pu	94	138	232.041182(18)	33.7(5) min	EC (>80%)	232Np	0+
					α (<20%)	228U
233Pu	94	139	233.042997(58)	20.9(4) min	β+ (99.88%)	233Np	5/2+#
					α (0.12%)	229U
234Pu	94	140	234.0433175(73)	8.8(1) h	EC (94%)	234Np	0+
					α (6%)	230U
235Pu	94	141	235.045285(22)	25.3(5) min	β+	235Np	(5/2+)
					α (0.0028%)	231U
236Pu	94	142	236.0460567(19)	2.858(8) y	α [n 9]	232U	0+
					SF (1.9×10−7%)	(various)
					CD (2×10−12%)	208Pb 28Mg
236mPu	1185.45(15) keV			1.2(3) μs	IT	236Pu	5−
237Pu	94	143	237.0484079(18)	45.64(4) d	EC	237Np	7/2−
					α (0.0042%)	233U
237m1Pu	145.543(8) keV			180(20) ms	IT	237Pu	1/2+
237m2Pu	2900(250) keV			1.1(1) μs	SF	(various)
238Pu	94	144	238.0495582(12)	87.7(1) y	α	234U	0+	Trace [n 10]
					SF (1.9×10−7%)	(various)
					CD (1.4×10−14%)	206Hg 32Si
					CD (<6×10−15%)	210Pb 28Mg
					CD (<6×10−15%)	208Pb 30Mg
239Pu [n 11] [n 12]	94	145	239.0521616(12)	2.411(3)×104 y	α	235U	1/2+	Trace [n 13]
					SF (3.1×10−10%)	(various)
239m1Pu	391.584(3) keV			193(4) ns	IT	239Pu	7/2−
239m2Pu	3100(200) keV			7.5(10) μs	SF	(various)	(5/2+)
240Pu	94	146	240.0538117(12)	6.561(7)×103 y	α	236U	0+	Trace [n 14]
					SF (5.796×10−6%)	(various)
					CD (<1.3×10−11%)	206Hg 34Si
240mPu	1308.74(5) keV			165(10) ns	IT	240Pu	5−
241Pu [n 11]	94	147	241.0568497(12)	14.329(29) y	β−	241Am	5/2+
					α (0.00245%)	237U
					SF (<2.4×10−14%)	(various)
241m1Pu	161.6853(9) keV			0.88(5) μs	IT	241Pu	1/2+
241m2Pu	2200(200) keV			20.5(22) μs	SF	(various)
242Pu	94	148	242.0587410(13)	3.75(2)×105 y	α	238U	0+
					SF (5.510×10−4%)	(various)
243Pu [n 11]	94	149	243.0620021(27)	4.9553(25) h	β−	243Am	7/2+
243mPu	383.64(25) keV			330(30) ns	IT	243Pu	(1/2+)
244Pu	94	150	244.0642044(25)	8.13(3)×107 y	α (99.88%)	240U	0+	Trace [n 15]
					SF (0.123%)	(various)
					β−β− (<7.3×10−9%)	244Cm
244mPu	1216.0(5) keV			1.75(12) s	IT	244Pu	8−
245Pu	94	151	245.067825(15)	10.5(1) h	β−	245Am	(9/2−)
245m1Pu	264.5(3) keV			330(20) ns	IT	245Pu	(5/2+)
245m2Pu	2000(400) keV			90(30) ns	SF	(various)
246Pu	94	152	246.070204(16)	10.84(2) d	β−	246Am	0+
247Pu	94	153	247.07430(22)#	2.27(23) d	β−	247Am	1/2+#
This table header & footer: view

1. ^mPu – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Modes of decay:

   CD:	Cluster decay
   EC:	Electron capture
   IT:	Isomeric transition
   SF:	Spontaneous fission

5. Bold italics symbol as daughter – Daughter product is nearly stable.
6. Bold symbol as daughter – Daughter product is stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
9. Theorized to also undergo β⁻β⁻ decay to ²³⁶U
10. Double beta decay product of ²³⁸U
11. fissile nuclide
12. Most useful isotope for nuclear weapons
13. Neutron capture product of ²³⁸U
14. Intermediate decay product of ²⁴⁴Pu
15. Interstellar, some may also be primordial but such claims are disputed

Actinides vs fission products

Actinides and fission products by half-life v t e
Actinides [7] by decay chain				Half-life range (a)	Fission products of 235U by yield [8]
4n	4n + 1	4n + 2	4n + 3		4.5–7%	0.04–1.25%	<0.001%
228 Ra№				4–6 a		155 Euþ
248 Bk [9]				> 9 a
244 Cmƒ	241 Puƒ	250 Cf	227 Ac№	10–29 a	90 Sr	85 Kr	113m Cdþ
232 Uƒ		238 Puƒ	243 Cmƒ	29–97 a	137 Cs	151 Smþ	121m Sn
	249 Cfƒ	242m Amƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	241 Amƒ		251 Cfƒ [10]	430–900 a
		226 Ra№	247 Bk	1.3–1.6 ka
240 Pu	229 Th	246 Cmƒ	243 Amƒ	4.7–7.4 ka
	245 Cmƒ	250 Cm		8.3–8.5 ka
			239 Puƒ	24.1 ka
		230 Th№	231 Pa№	32–76 ka
236 Npƒ	233 Uƒ	234 U№		150–250 ka	99 Tc₡	126 Sn
248 Cm		242 Pu		327–375 ka		79 Se₡
				1.33 Ma	135 Cs₡
	237 Npƒ			1.61–6.5 Ma	93 Zr	107 Pd
236 U			247 Cmƒ	15–24 Ma		129 I₡
244 Pu				80 Ma	... nor beyond 15.7 Ma [11]
232 Th№		238 U№	235 Uƒ№	0.7–14.1 Ga
₡,  has thermal neutron capture cross section in the range of 8–50 barns ƒ,  fissile №,  primarily a naturally occurring radioactive material (NORM) þ,  neutron poison (thermal neutron capture cross section greater than 3k barns)

Notable isotopes

• Plutonium-238 has a half-life of 87.74 years ^[12] and emits alpha particles. Pure ²³⁸Pu 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 ²³⁸Pu, originating from ²³⁷Np, alpha decay of ²⁴²Cm, or (n,2n) reactions.
• Plutonium-239 has half-life 24,100 years. ²³⁹Pu and ²⁴¹Pu 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. ²³⁹Pu 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 ²⁴⁰Pu: 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 ²⁴³Pu has a short half-life, but some is produced in nuclear explosions. ²⁴⁴Pu has been found in interstellar space ^[13] and has the second longest half-life of any non-primordial radioisotope.

Production and uses

A pellet of Pu, glowing from its own heat, used for radioisotope thermoelectric generators.

Transmutation flow between Pu and Cm in LWR.
Transmutation speed not shown and varies greatly by nuclide. Cm– Cm are long-lived with negligible decay.

²³⁹Pu, 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.

²⁴⁰Pu, ²⁴¹Pu, and ²⁴²Pu are produced by further neutron capture. The odd-mass isotopes ²³⁹Pu and ²⁴¹Pu have about a 3/4 chance of undergoing fission on capture of a thermal neutron and about a 1/4 chance of retaining the neutron and becoming the next heavier isotope. The even-mass isotopes are fertile but not fissile and also have a lower probability (cross section) of neutron capture; therefore, they tend to accumulate in nuclear fuel used in a thermal reactor, the design of nearly all nuclear power plants today. In plutonium that has been used a second time in thermal reactors in MOX fuel, ²⁴⁰Pu may even be the most common isotope. All plutonium isotopes and other actinides, however, are fissionable with fast neutrons. ²⁴⁰Pu does have a moderate thermal neutron absorption cross section, so that ²⁴¹Pu production in a thermal reactor becomes a significant fraction as large as ²³⁹Pu production.

²⁴¹Pu has a half-life of 14 years, and has slightly higher thermal neutron cross sections than ²³⁹Pu for both fission and absorption. While nuclear fuel is being used in a reactor, a ²⁴¹Pu nucleus is much more likely to fission or to capture a neutron than to decay. ²⁴¹Pu accounts for a significant portion of fissions in thermal reactor fuel that has been used for some time. However, in spent nuclear fuel that does not quickly undergo nuclear reprocessing but instead is cooled for years after use, much or most of the ²⁴¹Pu will beta decay to americium-241, one of the minor actinides, a strong alpha emitter, and difficult to use in thermal reactors.

²⁴²Pu has a particularly low cross section for thermal neutron capture; and it takes three neutron absorptions to become another fissile isotope (either curium-245 or ²⁴¹Pu) and fission. Even then, there is a chance either of those two fissile isotopes will fail to fission but instead absorb a fourth neutron, becoming curium-246 (on the way to even heavier actinides like californium, which is a neutron emitter by spontaneous fission and difficult to handle) or becoming ²⁴²Pu again; so the mean number of neutrons absorbed before fission is even higher than 3. Therefore, ²⁴²Pu is particularly unsuited to recycling in a thermal reactor and would be better used in a fast reactor where it can be fissioned directly. However, ²⁴²Pu's low cross section means that relatively little of it will be transmuted during one cycle in a thermal reactor. ²⁴²Pu's half-life is about 15 times as long as ²³⁹Pu's half-life; therefore, it is 1/15 as radioactive and not one of the larger contributors to nuclear waste radioactivity. ²⁴²Pu's gamma ray emissions are also weaker than those of the other isotopes. ^[15]

²⁴³Pu has a half-life of only 5 hours, beta decaying to americium-243. Because ²⁴³Pu has little opportunity to capture an additional neutron before decay, the nuclear fuel cycle does not produce the long-lived ²⁴⁴Pu in significant quantity.

²³⁸Pu is not normally produced in as large quantity by the nuclear fuel cycle, but some is produced from neptunium-237 by neutron capture (this reaction can also be used with purified neptunium to produce ²³⁸Pu relatively free of other plutonium isotopes for use in radioisotope thermoelectric generators), by the (n,2n) reaction of fast neutrons on ²³⁹Pu, or by alpha decay of curium-242, which is produced by neutron capture of ²⁴¹Am. It has significant thermal neutron cross section for fission, but is more likely to capture a neutron and become ²³⁹Pu.

Manufacture

Plutonium-240, -241 and -242

The fission cross section for ²³⁹Pu is 747.9 barns for thermal neutrons, while the activation cross section is 270.7 barns (the ratio approximates to 11 fissions for every 4 neutron captures). The higher plutonium isotopes are created when the uranium fuel is used for a long time. For high burnup used fuel, the concentrations of the higher plutonium isotopes will be higher than the low burnup fuel that is reprocessed to obtain weapons grade plutonium.

The formation of ²⁴⁰Pu, ²⁴¹Pu, and ²⁴²Pu from ²³⁸U

Isotope	Thermal neutron cross section [16] (barns)		Decay Mode	Half-life
	Capture	Fission
238U	2.683	0.000	α	4.468 x 109 years
239U	20.57	14.11	β−	23.45 minutes
239Np	77.03	–	β−	2.356 days
239Pu	270.7	747.9	α	24,110 years
240Pu	287.5	0.064	α	6,561 years
241Pu	363.0	1012	β−	14.325 years
242Pu	19.16	0.001	α	373,300 years

Plutonium-239

Main article: Plutonium-239

A 5.3 kg ring of weapons-grade electrorefined plutonium, 99.96% purity. This is enough plutonium for an efficient nuclear weapon. The ring shape is needed to depart from a spherical shape and avoid criticality.

²³⁹Pu is one of the three fissile materials used for the production of nuclear weapons and in some nuclear reactors as a source of energy. The other fissile materials are uranium-235 and uranium-233. ²³⁹Pu is virtually nonexistent in nature. It is made by bombarding uranium-238 with neutrons. Uranium-238 is present in quantity in most reactor fuel; hence ²³⁹Pu is continuously made in these reactors. Since ²³⁹Pu can itself be split by neutrons to release energy, ²³⁹Pu provides a portion of the energy generation in a nuclear reactor.

The formation of ²³⁹Pu from ²³⁸U ^[17]

Element	Isotope	Thermal neutron capture cross section (barn)	Thermal neutron fission Cross section (barn)	decay mode	Half-life
U	238	2.68	5·10−6	α	4.47 x 109 years
U	239	22	15	β−	23 minutes
Np	239	30	1	β−	2.36 days
Pu	239	271	750	α	24,110 years

Plutonium-238

Main article: Plutonium-238

There are small amounts of ²³⁸Pu in the plutonium from usual reactors. However, isotopic separation would be quite expensive compared to another method: when ²³⁵U captures a neutron, it is converted to an excited state of ²³⁶U. Some of the excited ²³⁶U nuclei undergo fission, but some decay to the ground state of ²³⁶U by emitting gamma radiation. Further neutron capture creates ²³⁷U; which, with a half-life of 7 days, decays to ²³⁷Np. Since nearly all neptunium is produced in this way or consists of isotopes that decay quickly, one gets nearly pure ²³⁷Np. After chemical separation of neptunium, ²³⁷Np is again irradiated by reactor neutrons to be converted to ²³⁸Np, which decays to ²³⁸Pu with a half-life of 2 days.

The formation of ²³⁸Pu from ²³⁵U

Element	Isotope	Thermal neutron cross section	decay mode	Half-life
U	235	99	α	703,800,000 years
U	236	5.3	α	23,420,000 years
U	237	—	β−	6.75 days
Np	237	165 (capture)	α	2,144,000 years
Np	238	—	β−	2.11 days
Pu	238	—	α	87.7 years

Plutonium-240 as an obstacle to nuclear weapons

²⁴⁰Pu undergoes spontaneous fission at a small but significant rate (5.8×10⁻⁶%). ^[1] The presence of ²⁴⁰Pu limits the plutonium's use in a nuclear bomb, because a neutron from spontaneous fission starts the chain reaction prematurely, causing an early release of energy that disperses the core before full implosion is reached. This prevents most of the core from participation in the chain reaction and reduces the bomb's yield.

Plutonium consisting of more than about 90% ²³⁹Pu is called weapons-grade plutonium; plutonium from spent nuclear fuel from commercial power reactors generally contains at least 20% ²⁴⁰Pu and is called reactor-grade plutonium. However, modern nuclear weapons use fusion boosting, which mitigates the predetonation problem; if the pit can generate a nuclear weapon yield of even a fraction of a kiloton, which is enough to start deuterium–tritium fusion, the resulting burst of neutrons will fission enough plutonium to ensure a yield of tens of kilotons.

Contamination due to ²⁴⁰Pu is the reason plutonium weapons must use the implosion method. Theoretically, pure ²³⁹Pu could be used in a gun-type bomb, but achieving this level of purity is prohibitively difficult. ²⁴⁰Pu contamination has proven a mixed blessing. While it created delays and headaches during the Manhattan Project because of the need to develop implosion technology, those same difficulties are a barrier to nuclear proliferation. Implosion bombs are also inherently more efficient and less prone to accidental detonation than are gun-type bombs.

References

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN   978-0-8493-0485-9.

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2. Magurno & Pearlstein 1981, pp. 835 ff.
3. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
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5. Yang, H. B.; Gan, Z. G.; Zhang, Z. Y.; Huang, M. H.; Ma, L.; Yang, C. L.; Zhang, M. M.; Tian, Y. L.; Wang, Y. S.; Wang, J. G.; Zhou, H. B.; Hua, W.; Wang, J. Y.; Qiang, Y. H.; Zhao, Z.; Huang, X. Y.; Wen, X. J.; Li, Z. Y.; Zhang, H. T.; Xu, S. Y.; Li, Z. C.; Zhou, H.; Zhang, X.; Zhu, L.; Wang, Z.; Guan, F.; Yang, H. R.; Huang, W. X.; Ren, Z. Z.; Zhou, S. G.; Xu, H. S. (3 October 2024). "α decay of the new isotope Pu 227". Physical Review C. 110 (4). doi:10.1103/PhysRevC.110.044302.
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7. Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
8. Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
9. Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
   "The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
10. This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
11. Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is eight quadrillion years.
12. Makhijani, Arjun; Seth, Anita (July 1997). "The Use of Weapons Plutonium as Reactor Fuel" (PDF). Energy and Security. Takoma Park, MD: Institute for Energy and Environmental Research. Retrieved 4 July 2016.
13. Wallner, A.; Faestermann, T.; Feige, J.; Feldstein, C.; Knie, K.; Korschinek, G.; Kutschera, W.; Ofan, A.; Paul, M.; Quinto, F.; Rugel, G.; Steier, P. (2015). "Abundance of live 244Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis". Nature Communications. 6: 5956. arXiv: 1509.08054 . Bibcode:2015NatCo...6.5956W. doi:10.1038/ncomms6956. ISSN   2041-1723. PMC   4309418 . PMID   25601158.
14. Sasahara, Akihiro; Matsumura, Tetsuo; Nicolaou, Giorgos; Papaioannou, Dimitri (April 2004). "Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels". Journal of Nuclear Science and Technology. 41 (4): 448–456. doi: 10.3327/jnst.41.448 .
15. "Plutonium Isotopic Results of Known Samples Using the Snap Gamma Spectroscopy Analysis Code and the Robwin Spectrum Fitting Routine" (PDF). Archived from the original (PDF) on 2017-08-13. Retrieved 2013-03-15.
16. National Nuclear Data Center Interactive Chart of Nuclides Archived 2011-07-21 at the Wayback Machine
17. Miner 1968 , p. 541

Sources

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