Isotopes of tantalum

Natural tantalum (Ta) consists of two stable isotopes: ¹⁸¹Ta (99.988%) and ^180m
Ta
(0.012%).

The latter nuclide ^180m
Ta
(m denotes a metastable state) has sufficient energy to decay in three ways: isomeric transition to the ground state of ¹⁸⁰
Ta
, beta decay to ¹⁸⁰
W
, and electron capture to ¹⁸⁰
Hf
. However, no radioactivity from any decay mode of this nuclear isomer has ever been observed. Only a lower limit on its half-life of over 10¹⁵ years has been set, by observation. The very slow decay of ^180m
Ta
is attributed to its high spin (9 units) and the low spin of lower-lying states. Gamma or beta decay would require many units of angular momentum to be removed in a single step, so that the process would be very slow.^[1]

The very unusual nature of ^180mTa is that the ground state of this isotope is less stable than the isomer. The same property is exhibited in americium-242m (^242mAm). ¹⁸⁰
Ta
has a half-life of only 8 hours. ^180m
Ta
is the only naturally occurring nuclear isomer (excluding radiogenic and cosmogenic short-living nuclides). It is also the rarest primordial nuclide in the Universe observed for any element that has any stable isotopes.

There are also 35 known artificial radioisotopes, the longest-lived of which are ¹⁷⁹Ta with a half-life of 1.82 years, ¹⁸²Ta with a half-life of 114.43 days, ¹⁸³Ta with a half-life of 5.1 days, and ¹⁷⁷Ta with a half-life of 56.56 hours. All other isotopes have half-lives under a day, most under an hour. There are also numerous isomers, the most stable of which (other than ^180mTa) is ^178m1Ta with a half-life of 2.36 hours.

Tantalum has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of ¹⁸¹Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope ¹⁸²
Ta
with a half-life of 114.43 days and produce approximately 1.12 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several months. Such a weapon is not known to have ever been built, tested, or used.^[2]

Tantalum has a relative atomic mass of 180.94788(2).

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)^[3]^{[n 1]}	daughter isotope(s)^{[n 2]}	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	excitation energy			half-life	decay mode(s)^[3]^{[n 1]}	daughter isotope(s)^{[n 2]}	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
¹⁵⁵ Ta	73	82	154.97459(54)#	13(4) µs [12(+4−3) µs]			(11/2−)
¹⁵⁶ Ta	73	83	155.97230(43)#	144(24) ms	β⁺ (95.8%)	¹⁵⁶Hf	(2−)
¹⁵⁶ Ta	73	83	155.97230(43)#	144(24) ms	p (4.2%)	¹⁵⁵Hf	(2−)
^156m Ta	102(7) keV			0.36(4) s	p	¹⁵⁵Hf	9+
¹⁵⁷ Ta	73	84	156.96819(22)	10.1(4) ms	α (91%)	¹⁵³Lu	1/2+
¹⁵⁷ Ta	73	84	156.96819(22)	10.1(4) ms	β⁺ (9%)	¹⁵⁷Hf	1/2+
^157m1 Ta	22(5) keV			4.3(1) ms			11/2−
^157m2 Ta	1593(9) keV			1.7(1) ms	α	¹⁵³Lu	(25/2−)
¹⁵⁸ Ta	73	85	157.96670(22)#	49(8) ms	α (96%)	¹⁵⁴Lu	(2−)
¹⁵⁸ Ta	73	85	157.96670(22)#	49(8) ms	β⁺ (4%)	¹⁵⁸Hf	(2−)
^158m Ta	141(9) keV			36.0(8) ms	α (93%)	¹⁵⁴Lu	(9+)
					IT	¹⁵⁸Ta
					β⁺	¹⁵⁸Hf
¹⁵⁹ Ta	73	86	158.963018(22)	1.04(9) s	β⁺ (66%)	¹⁵⁹Hf	(1/2+)
¹⁵⁹ Ta	73	86	158.963018(22)	1.04(9) s	α (34%)	¹⁵⁵Lu	(1/2+)
^159m Ta	64(5) keV			514(9) ms	α (56%)	¹⁵⁵Lu	(11/2−)
^159m Ta	64(5) keV			514(9) ms	β⁺ (44%)	¹⁵⁹Hf	(11/2−)
¹⁶⁰ Ta	73	87	159.96149(10)	1.70(20) s	α	¹⁵⁶Lu	(2#)−
¹⁶⁰ Ta	73	87	159.96149(10)	1.70(20) s	β⁺	¹⁶⁰Hf	(2#)−
^160m Ta	310(90)# keV			1.55(4) s	β⁺ (66%)	¹⁶⁰Hf	(9)+
^160m Ta	310(90)# keV			1.55(4) s	α (34%)	¹⁵⁶Lu	(9)+
¹⁶¹ Ta	73	88	160.95842(6)#	3# s	β⁺ (95%)	¹⁶¹Hf	1/2+#
¹⁶¹ Ta	73	88	160.95842(6)#	3# s	α (5%)	¹⁵⁷Lu	1/2+#
^161m Ta	50(50)# keV			2.89(12) s			11/2−#
¹⁶² Ta	73	89	161.95729(6)	3.57(12) s	β⁺ (99.92%)	¹⁶²Hf	3+#
¹⁶² Ta	73	89	161.95729(6)	3.57(12) s	α (.073%)	¹⁵⁸Lu	3+#
¹⁶³ Ta	73	90	162.95433(4)	10.6(18) s	β⁺ (99.8%)	¹⁶³Hf	1/2+#
¹⁶³ Ta	73	90	162.95433(4)	10.6(18) s	α (.2%)	¹⁵⁹Lu	1/2+#
¹⁶⁴ Ta	73	91	163.95353(3)	14.2(3) s	β⁺	¹⁶⁴Hf	(3+)
¹⁶⁵ Ta	73	92	164.950773(19)	31.0(15) s	β⁺	¹⁶⁵Hf	5/2−#
^165m Ta	60(30) keV						9/2−#
¹⁶⁶ Ta	73	93	165.95051(3)	34.4(5) s	β⁺	¹⁶⁶Hf	(2)+
¹⁶⁷ Ta	73	94	166.94809(3)	1.33(7) min	β⁺	¹⁶⁷Hf	(3/2+)
¹⁶⁸ Ta	73	95	167.94805(3)	2.0(1) min	β⁺	¹⁶⁸Hf	(2−,3+)
¹⁶⁹ Ta	73	96	168.94601(3)	4.9(4) min	β⁺	¹⁶⁹Hf	(5/2+)
¹⁷⁰ Ta	73	97	169.94618(3)	6.76(6) min	β⁺	¹⁷⁰Hf	(3)(+#)
¹⁷¹ Ta	73	98	170.94448(3)	23.3(3) min	β⁺	¹⁷¹Hf	(5/2−)
¹⁷² Ta	73	99	171.94490(3)	36.8(3) min	β⁺	¹⁷²Hf	(3+)
¹⁷³ Ta	73	100	172.94375(3)	3.14(13) h	β⁺	¹⁷³Hf	5/2−
¹⁷⁴ Ta	73	101	173.94445(3)	1.14(8) h	β⁺	¹⁷⁴Hf	3+
¹⁷⁵ Ta	73	102	174.94374(3)	10.5(2) h	β⁺	¹⁷⁵Hf	7/2+
¹⁷⁶ Ta	73	103	175.94486(3)	8.09(5) h	β⁺	¹⁷⁶Hf	(1)−
^176m1 Ta	103.0(10) keV			1.1(1) ms	IT	¹⁷⁶Ta	(+)
^176m2 Ta	1372.6(11)+X keV			3.8(4) µs			(14−)
^176m3 Ta	2820(50) keV			0.97(7) ms			(20−)
¹⁷⁷ Ta	73	104	176.944472(4)	56.56(6) h	β⁺	¹⁷⁷Hf	7/2+
^177m1 Ta	73.36(15) keV			410(7) ns			9/2−
^177m2 Ta	186.15(6) keV			3.62(10) µs			5/2−
^177m3 Ta	1355.01(19) keV			5.31(25) µs			21/2−
^177m4 Ta	4656.3(5) keV			133(4) µs			49/2−
¹⁷⁸ Ta	73	105	177.945778(16)	9.31(3) min	β⁺	¹⁷⁸Hf	1+
^178m1 Ta	100(50)# keV			2.36(8) h	β⁺	¹⁷⁸Hf	(7)−
^178m2 Ta	1570(50)# keV			59(3) ms			(15−)
^178m3 Ta	3000(50)# keV			290(12) ms			(21−)
¹⁷⁹ Ta	73	106	178.9459295(23)	1.82(3) a	EC	¹⁷⁹Hf	7/2+
^179m1 Ta	30.7(1) keV			1.42(8) µs			(9/2)−
^179m2 Ta	520.23(18) keV			335(45) ns			(1/2)+
^179m3 Ta	1252.61(23) keV			322(16) ns			(21/2−)
^179m4 Ta	1317.3(4) keV			9.0(2) ms	IT	¹⁷⁹Ta	(25/2+)
^179m5 Ta	1327.9(4) keV			1.6(4) µs			(23/2−)
^179m6 Ta	2639.3(5) keV			54.1(17) ms			(37/2+)
¹⁸⁰ Ta	73	107	179.9474648(24)	8.152(6) h	EC (86%)	¹⁸⁰Hf	1+
¹⁸⁰ Ta	73	107	179.9474648(24)	8.152(6) h	β⁻ (14%)	¹⁸⁰W	1+
^180m1 Ta	77.1(8) keV			Observationally stable^{[n 3]}			9−	1.2(2)×10⁻⁴
^180m2 Ta	1452.40(18) keV			31.2(14) µs			15−
^180m3 Ta	3679.0(11) keV			2.0(5) µs			(22−)
^180m4 Ta	4171.0+X keV			17(5) µs			(23,24,25)
¹⁸¹ Ta	73	108	180.9479958(20)	Observationally stable^{[n 4]}			7/2+	0.99988(2)
^181m1 Ta	6.238(20) keV			6.05(12) µs			9/2−
^181m2 Ta	615.21(3) keV			18(1) µs			1/2+
^181m3 Ta	1485(3) keV			25(2) µs			21/2−
^181m4 Ta	2230(3) keV			210(20) µs			29/2−
¹⁸² Ta	73	109	181.9501518(19)	114.43(3) d	β⁻	¹⁸²W	3−
^182m1 Ta	16.263(3) keV			283(3) ms	IT	¹⁸²Ta	5+
^182m2 Ta	519.572(18) keV			15.84(10) min			10−
¹⁸³ Ta	73	110	182.9513726(19)	5.1(1) d	β⁻	¹⁸³W	7/2+
^183m Ta	73.174(12) keV			107(11) ns			9/2−
¹⁸⁴ Ta	73	111	183.954008(28)	8.7(1) h	β⁻	¹⁸⁴W	(5−)
¹⁸⁵ Ta	73	112	184.955559(15)	49.4(15) min	β⁻	¹⁸⁵W	(7/2+)#
^185m Ta	1308(29) keV			>1 ms			(21/2−)
¹⁸⁶ Ta	73	113	185.95855(6)	10.5(3) min	β⁻	¹⁸⁶W	(2−,3−)
^186m Ta				1.54(5) min
¹⁸⁷ Ta	73	114	186.96053(21)#	2# min [>300 ns]	β⁻	¹⁸⁷W	7/2+#
¹⁸⁸ Ta	73	115	187.96370(21)#	20# s [>300 ns]	β⁻	¹⁸⁸W
¹⁸⁹ Ta	73	116	188.96583(32)#	3# s [>300 ns]			7/2+#
¹⁹⁰ Ta	73	117	189.96923(43)#	0.3# s

^ Abbreviations:
EC: Electron capture
IT: Isomeric transition
^ Bold for stable isotopes, bold italics for nearly-stable isotopes (half-life longer than the age of the universe)
^ Only known observationally stable nuclear isomer, believed to decay by isomeric transition to ¹⁸⁰Ta, β⁻ decay to ¹⁸⁰W, or electron capture to ¹⁸⁰Hf with a half-life over 1.2×10¹⁵ years
^ Believed to undergo α decay to ¹⁷⁷Lu

Notes

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

^ Quantum mechanics for engineers Leon van Dommelen, Florida State University
^ D. T. Win; M. Al Masum (2003). "Weapons of Mass Destruction" (PDF). Assumption University Journal of Technology. 6 (4): 199–219.
^ "Universal Nuclide Chart". nucleonica. {{cite web}}: Unknown parameter |registration= ignored (|url-access= suggested) (help)

Isotope masses from:
- G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
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; 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.
- 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; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
- 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 978-0-8493-0485-9. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)

[4] Abbreviations:
EC: Electron capture
IT: Isomeric transition

[5] Bold for stable isotopes, bold italics for nearly-stable isotopes (half-life longer than the age of the universe)

[6] Only known observationally stable nuclear isomer, believed to decay by isomeric transition to ¹⁸⁰Ta, β⁻ decay to ¹⁸⁰W, or electron capture to ¹⁸⁰Hf with a half-life over 1.2×10¹⁵ years

[7] Believed to undergo α decay to ¹⁷⁷Lu

[1] Quantum mechanics for engineers Leon van Dommelen, Florida State University

[2] D. T. Win; M. Al Masum (2003). "Weapons of Mass Destruction" (PDF). Assumption University Journal of Technology. 6 (4): 199–219.

[3] "Universal Nuclide Chart". nucleonica. {{cite web}}: Unknown parameter |registration= ignored (|url-access= suggested) (help)

[1]

[2]

[3]

[n 1]

[n 2]

[n 3]

[n 4]