Isotopes of tantalum

Isotopes of tantalum (₇₃Ta)
β−	180W
Standard atomic weight Ar°(Ta)
	180.94788±0.00002; 180.95±0.01 (abridged);
	view; talk; edit;

Natural tantalum (₇₃Ta) consists of two stable isotopes: ¹⁸¹Ta (99.988%) and ^180m
Ta
(0.012%).

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. All isotopes and nuclear isomers of tantalum are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.

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.^[4] While the conversion factor from absorbed dose (measured in Grays) to effective dose (measured in Sievert) for gamma rays is 1 while it is 50 for alpha radiation (i.e., a gamma dose of 1 Gray is equivalent to 1 Sievert whereas an alpha dose of 1 Gray is equivalent to 50 Sievert), gamma rays are only attenuated by shielding, not stopped. As such, alpha particles require incorporation to have an effect while gamma rays can have an effect via mere proximity. In military terms, this allows a gamma ray weapon to deny an area to either side as long as the dose is high enough, whereas radioactive contamination by alpha emitters which do not release significant amounts of gamma rays can be counteracted by ensuring the material is not incorporated.

List of isotopes

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da) ^{[n 2]}^{[n 3]}	Half-life ^{[n 4]}	Decay mode ^{[n 5]}	Daughter isotope ^{[n 6]}^{[n 7]}	Spin and parity ^{[n 8]}^{[n 4]}	Natural abundance (mole fraction)
Nuclide ^{[n 1]}	Excitation energy^{[n 4]}			Half-life ^{[n 4]}	Decay mode ^{[n 5]}	Daughter isotope ^{[n 6]}^{[n 7]}	Spin and parity ^{[n 8]}^{[n 4]}	Normal proportion	Range of variation
¹⁵⁵ Ta	73	82	154.97459(54)#	2.9+1.5 −1.1 ms^[5]	p	¹⁵⁴Hf	(11/2−)
^155m Ta	~323 keV			12+4 −3 μs^[6]	p	¹⁵⁴Hf	11/2−?
¹⁵⁶ Ta ^[7]	73	83	155.97230(43)#	106(4) ms	p (71%)	¹⁵⁵Hf	(2−)
¹⁵⁶ Ta ^[7]	73	83	155.97230(43)#	106(4) ms	β⁺ (29%)	¹⁵⁶Hf	(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) y	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 9]}^{[n 10]}			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 11]}			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
This table header & footer: view

Tantalum-180m

The nuclide ^180m
Ta
(m denotes a metastable state) is one of a very few nuclear isomers which are more stable than their ground states. Although it is not unique in this regard (this property is shared by bismuth-210m (^210mBi) and americium-242m (^242mAm), among other nuclides), it is exceptional in that it is observationally stable: no decay has ever been observed. In contrast, ¹⁸⁰
Ta
has a half-life of only 8 hours.

^180m
Ta
has sufficient energy to decay in three ways: isomeric transition to the ground state of ¹⁸⁰
Ta
, beta decay to ¹⁸⁰
W
, or electron capture to ¹⁸⁰
Hf
. However, no radioactivity from any of these theoretically possible decay modes has ever been observed. As of 2023, the half-life of ^180mTa is calculated from experimental observation to be at least 2.9×10¹⁷ (290 quadrillion) years.^[8]^[9]^[10] 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.^[11]

Because of this stability, ^180m
Ta
is a primordial nuclide, the only naturally occurring nuclear isomer (excluding short-lived radiogenic and cosmogenic nuclides). It is also the rarest primordial nuclide in the Universe observed for any element which has any stable isotopes. In an s-process stellar environment with a thermal energy k_BT = 26 keV (i.e. a temperature of 300 million kelvin), the nuclear isomers are expected to be fully thermalized, meaning that ¹⁸⁰Ta rapidly transitions between spin states and its overall half-life is predicted to be 11 hours.^[12]

It is one of only five stable nuclides to have both an odd number of protons and an odd number of neutrons, the other four stable odd-odd nuclides being ²H, ⁶Li, ¹⁰B and ¹⁴N.^[13]

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
Isotopic compositions and standard atomic masses from:
- de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
- Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051.
"News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.
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.

[1]

[2]

[3]

[4]

[n 1]

[n 2]

[n 3]

[n 4]

[n 5]

[n 6]

[n 7]

[n 8]

[5]

[6]

[7]

[n 9]

[n 10]

[n 11]

[8]

[9]

[10]

[11]

[12]

[13]