Isotopes of uranium: Difference between revisions

Isotopes of uranium, ²³⁹U
General
Symbol	239U
Names	isotopes of uranium, 239U, U-239,; U-239
Protons (Z)	92
Neutrons (N)	147
Nuclide data
Natural abundance	0 (Artificial)
Half-life (t1/2)	23.45 mins
Decay products	239Np
Decay modes
Decay mode	Decay energy (MeV)
Beta decay 20%	1.28
Beta decay 80%	1.21
	Isotopes of uranium ; Complete table of nuclides

Isotopes of uranium, ²³²U
General
Symbol	232U
Names	isotopes of uranium, 232U, U-232
Nuclide data
Half-life (t1/2)	68.9 years
Parent isotopes	236Pu (α); 232Np (β+); 232Pa (β−)
Decay products	228Th
	Isotopes of uranium ; Complete table of nuclides

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Actinides and fission products by half-life v t e
Actinides^[1] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield^[2]
4n	4n + 1	4n + 2	4n + 3	Half-life range (a)	4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6 a		¹⁵⁵Eu^þ
²⁴⁸Bk^[3]				> 9 a
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29 a	⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97 a	¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ^[4]	430–900 a
		²²⁶Ra^№	²⁴⁷Bk	1.3–1.6 ka
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7–7.4 ka
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3–8.5 ka
			²³⁹Pu^ƒ	24.1 ka
		²³⁰Th^№	²³¹Pa^№	32–76 ka
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150–250 ka	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327–375 ka		⁷⁹Se^₡
				1.33 Ma	¹³⁵Cs^₡
	²³⁷Np^ƒ			1.61–6.5 Ma	⁹³Zr	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma		¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma^[5]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma^[5]
₡, 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)

Uranium (U) is a naturally occurring radioactive element that has no stable isotopes but two primordial isotopes (uranium-238 and uranium-235) that have long half-life and are found in appreciable quantity in Earth's crust, along with the decay product uranium-234. The average atomic mass of natural uranium is 238.02891(3) u. Other isotopes such as uranium-232 have been produced in breeder reactors.

Naturally occurring uranium is composed of three major isotopes, uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). All three isotopes are radioactive, creating radioisotopes, with the most abundant and stable being uranium-238 with a half-life of 4.51×10⁹ years (close to the age of the Earth), uranium-235 with a half-life of 7.13×10⁸ years, and uranium-234 with a half-life of 2.48×10⁵ years.^[6]

Uranium-238 is an α emitter, decaying through the 18-member uranium series into lead-206. The decay series of uranium-235 (historically called actino-uranium) has 15 members that ends in lead-207. The constant rates of decay in these series makes comparison of the ratios of parent to daughter elements useful in radiometric dating. Uranium-233 is made from thorium-232 by neutron bombardment.

The isotope uranium-235 is important for both nuclear reactors and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile, that is, can be broken apart by thermal neutrons. The isotope uranium-238 is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope plutonium-239, which also is fissile.

Uranium-232

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	Half-life range (a)	4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6 a		¹⁵⁵Eu^þ
²⁴⁸Bk^[9]				> 9 a
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29 a	⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97 a	¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ^[10]	430–900 a
		²²⁶Ra^№	²⁴⁷Bk	1.3–1.6 ka
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7–7.4 ka
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3–8.5 ka
			²³⁹Pu^ƒ	24.1 ka
		²³⁰Th^№	²³¹Pa^№	32–76 ka
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150–250 ka	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327–375 ka		⁷⁹Se^₡
				1.33 Ma	¹³⁵Cs^₡
	²³⁷Np^ƒ			1.61–6.5 Ma	⁹³Zr	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma		¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma^[11]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma^[11]
₡, 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)

Uranium 232 (²³²
₉₂U
, ²³²
U
, U-232) is an isotope of uranium. It has a half life of 68.9 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using ²³³U as the fissile material, because the intense gamma radiation of ²³²U's decay products makes the ²³³U contaminated with it more difficult to handle.

Production of ²³³U (through the irradiation of thorium-233) invariably produces small amounts of uranium-232 as an impurity, because of parasitic (n,2n) reactions on uranium-233 itself, or on protactinium-233:

²³²Th (n,γ) ²³³Th (β−) ²³³Pa (β−) ²³³U (n,2n) ²³²U

²³²Th (n,γ) ²³³Th (β−) ²³³Pa (n,2n) ²³²Pa (β−) ²³²U

The decay chain of U-232 quickly yields strong gamma radiation emitters:

²³²U (α, 72 years)

²²⁸Th (α, 1.9 year)

²²⁴Ra (α, 3.6 day, 0.24 MeV) (at this point, the decay chain is identical to that of ²³²Th)

²²⁰Rn (α, 55 s, 0.54 MeV)

²¹⁶Po (α, 0.15 s)

²¹²Pb (β−, 10.64 h)

²¹²Bi (α, 61 s, 0.78 MeV)

²⁰⁸Tl (β−, 3 m, 2.6 MeV)

²⁰⁸Pb (stable)

This makes manual handling in a glove box with only light shielding (as commonly done with plutonium) too hazardous, (except possibly in a short period immediately following chemical separation of the uranium from thorium-228, radium-224, radon-220, and polonium) and instead requiring remote manipulation for fuel fabrication.

Unusually for an isotope with even mass number, U-232 has a significant neutron absorption cross section for fission (thermal neutrons 75 barns (b), resonance integral 380 b) as well as for neutron capture (thermal 73 b, resonance integral 280 b).

Lighter: uranium-231	Isotopes of uranium is an isotope of uranium	Heavier: uranium-233
Decay product of: plutonium-236 (α) neptunium-232 (β⁺) protactinium-232 (β⁻)	Decay chain of isotopes of uranium	Decays to: thorium-228 (α)

Uranium-239

Uranium-239 is an isotope of uranium. It is usually produced by exposing uranium-238 to neutron radiation in a nuclear reactor. Uranium-239 has a half-life of about 23.45 minutes and decays into neptunium-239 through beta decay, with a total decay energy of about 1.29 Mev.^[12]. The most common gamma decay at 74.660 kev accounts for the difference in the two major channels of beta emission energy, at 1.28 and 1.21 Mev.^[13]

Neptunium-239 further decays to plutonium-239, in a second important step which ultimately produces fissile plutonium-239 (used in weapons and for nuclear power), from uranium-238 in reactors.

Lighter: Uranium-238	Isotopes of uranium is an isotope of Uranium	Heavier: Uranium-240
Decay product of: Protactinium-239 (β-)	Decay chain of isotopes of uranium	Decays to: Neptunium-239 (β-)

Table

nuclide symbol	historic name	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)^[14]^{[n 1]}	daughter isotope(s)	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	historic name	excitation energy			half-life	decay mode(s)^[14]^{[n 1]}	daughter isotope(s)	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
²¹⁷U		92	125	217.02437(9)	26(14) ms [16(+21-6) ms]			1/2-#
²¹⁸U		92	126	218.02354(3)	6(5) ms	α	²¹⁴Th	0+
²¹⁹U		92	127	219.02492(6)	55(25) ms [42(+34-13) ms]	α	²¹⁵Th	9/2+#
²²⁰U		92	128	220.02472(22)#	60# ns	α	²¹⁶Th	0+
²²⁰U		92	128	220.02472(22)#	60# ns	β⁺ (rare)	²²⁰Pa	0+
²²¹U		92	129	221.02640(11)#	700# ns	α	²¹⁷Th	9/2+#
²²¹U		92	129	221.02640(11)#	700# ns	β⁺ (rare)	²²¹Pa	9/2+#
²²²U		92	130	222.02609(11)#	1.4(7) ms [1.0(+10-4) ms]	α	²¹⁸Th	0+
²²²U		92	130	222.02609(11)#	1.4(7) ms [1.0(+10-4) ms]	β⁺ (1E-6%)	²²²Pa	0+
²²³U		92	131	223.02774(8)	21(8) ms [18(+10-5) ms]	α	²¹⁹Th	7/2+#
²²⁴U		92	132	224.027605(27)	940(270) ms	α	²²⁰Th	0+
²²⁵U		92	133	225.02939#	61(4) ms	α	²²¹Th	(5/2+)#
²²⁶U		92	134	226.029339(14)	269(6) ms	α	²²²Th	0+
²²⁷U		92	135	227.031156(18)	1.1(1) min	α	²²³Th	(3/2+)
²²⁷U		92	135	227.031156(18)	1.1(1) min	β⁺ (.001%)	²²⁷Pa	(3/2+)
²²⁸U		92	136	228.031374(16)	9.1(2) min	α (95%)	²²⁴Th	0+
²²⁸U		92	136	228.031374(16)	9.1(2) min	EC (5%)	²²⁸Pa	0+
²²⁹U		92	137	229.033506(6)	58(3) min	β⁺ (80%)	²²⁹Pa	(3/2+)
²²⁹U		92	137	229.033506(6)	58(3) min	α (20%)	²²⁵Th	(3/2+)
²³⁰U		92	138	230.033940(5)	20.8 d	α	²²⁶Th	0+
						SF (1.4E-10%)	(various)
						β⁺β⁺	²³⁰Th
²³¹		92	139	231.036294(3)	4.2(1) d	EC	²³¹Pa	(5/2)(+#)
²³¹		92	139	231.036294(3)	4.2(1) d	α (.004%)	²²⁷Th	(5/2)(+#)
²³²U		92	140	232.0371562(24)	68.9(4) y	α	²²⁸Th	0+
						CD (8.9E-10%)	²⁰⁸Pb, ²⁴Ne
						CD (5E-12%)	²⁰⁴Hg, ²⁸Mg
						SF (1E-12%)	(various)
²³³U		92	141	233.0396352(29)	1.592(2)×10⁵ y	α	²²⁹Th	5/2+
						SF (6E-9%)	(various)
						CD (7.2E-11%)	²⁰⁹Pb, ²⁴Ne
						CD (1.3E-13%)	²⁰⁵Hg, ²⁸Mg
²³⁴U^{[n 2]}^{[n 3]}	Uranium II	92	142	234.0409521(20)	2.455(6)×10⁵ y	α	²³⁰Th	0+	[0.000054(5)]^{[n 4]}	0.000050-0.000059
						SF (1.73E-9%)	(various)
						CD (1.4E-11%)	²⁰⁶Hg, ²⁸Mg
						CD (9E-12%)	¹⁸⁴Hf, ²⁶Ne, ²⁴Ne
^234mU		1421.32(10) keV			33.5(20) ms			6-
²³⁵U^{[n 5]}^{[n 6]}^{[n 7]}	Actin Uranium Actino-Uranium	92	143	235.0439299(20)	7.04(1)×10⁸ y	α	²³¹Th	7/2-	[0.007204(6)]	0.007198-0.007207
						SF (7E-9%)	(various)
						CD (8E-10%)	¹⁸⁶Hf, ²⁵Ne, ²⁴Ne
^235mU		0.0765(4) keV			~26 min	IT	²³⁵U	1/2+
²³⁶U		92	144	236.045568(2)	2.342(3)×10⁷ y	α	²³²Th	0+
²³⁶U		92	144	236.045568(2)	2.342(3)×10⁷ y	SF (9.6E-8%)	(various)	0+
^236m1U		1052.89(19) keV			100(4) ns			(4)-
^236m2U		2750(10) keV			120(2) ns			(0+)
²³⁷U		92	145	237.0487302(20)	6.75(1) d	β^-	²³⁷Np	1/2+
²³⁸U^{[n 5]}^{[n 3]}^{[n 6]}	Uranium I	92	146	238.0507882(20)	4.468(3)×10⁹ y	α	²³⁴Th	0+	[0.992742(10)]	0.992739-0.992752
						SF (5.45E-5%)
						β^-β^- (2.19E-10%)	²³⁸Pt
^238mU		2557.9(5) keV			280(6) ns			0+
²³⁹U		92	147	239.0542933(21)	23.45(2) min	β^-	²³⁹Np	5/2+
^239m1U		20(20)# keV			>250 ns			(5/2+)
^239m2U		133.7990(10) keV			780(40) ns			1/2+
²⁴⁰U		92	148	240.056592(6)	14.1(1) h	β^-	²⁴⁰Np	0+
²⁴⁰U		92	148	240.056592(6)	14.1(1) h	α (1E-10%)	²³⁶Th	0+
²⁴¹U		92	149	241.06033(32)#	5# min	β^-	²⁴¹Np	7/2+#
²⁴²U		92	150	242.06293(22)#	16.8(5) min	β^-	²⁴²Np	0+

^ Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission
^ Used in uranium-thorium dating
^ ^a ^b Used in uranium-uranium dating
^ Occurs as an intermediate decay product of ²³⁸U
^ ^a ^b Primordial radionuclide
^ ^a ^b Used in Uranium-lead dating
^ Important in nuclear reactors

Notes

Evaluated isotopic composition is for most but not all commercial samples.
The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

^ 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.
^ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
^ 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]."
^ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
^ 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.
^ Seaborg, Encyclopedia of the Chemical Elements (1968), page 777
^ 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.
^ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
^ 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]."
^ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
^ 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.
^ CRC Handbook, 57th Ed. p. B-345
^ Ibid. p. B-423
^ http://www.nucleonica.net/unc.aspx

Isotope masses from:
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
Isotopic compositions and standard atomic masses from:
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.{{cite journal}}: CS1 maint: multiple names: authors list (link)
- M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. {{cite journal}}: Unknown parameter |laysummary= ignored (help)
Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. {{cite web}}: Check date values in: |accessdate= (help)
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide (ed.). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)

[15] Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission

[16] Used in uranium-thorium dating

[uu-17] Used in uranium-uranium dating

[18] Occurs as an intermediate decay product of ²³⁸U

[pn-19] Primordial radionuclide

[ul-20] Used in Uranium-lead dating

[21] Important in nuclear reactors

[1] 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.

[2] Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.

[3] 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]."

[4] This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".

[5] 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.

[EncyChem777-6] Seaborg, Encyclopedia of the Chemical Elements (1968), page 777

[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] CRC Handbook, 57th Ed. p. B-345

[13] Ibid. p. B-423

[14] ttp://www.nucleonica.net/unc.aspx

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