Isotopes of tantalum

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

Main isotopes of tantalum (₇₃Ta)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^177Ta syn 56.56 h ε ^177Hf ^178Ta syn 2.36 h ε ^178Hf ^179Ta syn 1.82 y ε ^179Hf ^180Ta syn 8.125 h ε ^180Hf β^− ^180W ^180mTa 0.012% stable ^181Ta 99.988% stable ^182Ta syn 114.43 d β^− ^182W ^183Ta syn 5.1 d β^− ^183W
Standard atomic weight Ar, standard(Ta)	180.94788(2)[1]

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]

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)
	Excitation energy[n 4]							Normal proportion	Range of variation
^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−)
					p (4.2%)	^155Hf
^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+
					β^+ (9%)	^157Hf
^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−)
					β^+ (4%)	^158Hf
^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+)
					α (34%)	^155Lu
^159m Ta	64(5) keV			514(9) ms	α (56%)	^155Lu	(11/2−)
					β^+ (44%)	^159Hf
^160 Ta	73	87	159.96149(10)	1.70(20) s	α	^156Lu	(2#)−
					β^+	^160Hf
^160m Ta	310(90)# keV			1.55(4) s	β^+ (66%)	^160Hf	(9)+
					α (34%)	^156Lu
^161 Ta	73	88	160.95842(6)#	3# s	β^+ (95%)	^161Hf	1/2+#
					α (5%)	^157Lu
^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+#
					α (.073%)	^158Lu
^163 Ta	73	90	162.95433(4)	10.6(18) s	β^+ (99.8%)	^163Hf	1/2+#
					α (.2%)	^159Lu
^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+
					β^− (14%)	^180W
^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

1. ^mTa – 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. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
5. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   p:	Proton emission

6. Bold italics symbol as daughter – Daughter product is nearly stable.
7. Bold symbol as daughter – Daughter product is stable.
8. ( ) spin value – Indicates spin with weak assignment arguments.
9. 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 4.5×10¹⁶ years
10. One of the few stable odd-odd nuclei
11. Believed to undergo α decay to ¹⁷⁷Lu

Tantalum-180m

The 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.[3]

The very unusual nature of ^180mTa is that the ground state of this isotope is less stable than the isomer. This phenomenon is exhibited in bismuth-210m (^210mBi) and americium-242m (^242mAm), among other nuclides. 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. In an s-process stellar environment with a thermal energy kT = 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.[4]

As of October 3, 2016 the half life of ^180mTa is calculated from experimental observation to be least 4.5×10¹⁶ (45 quadrillion) years.[5][6]

References

1. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
2. D. T. Win; M. Al Masum (2003). "Weapons of Mass Destruction" (PDF). Assumption University Journal of Technology. 6 (4): 199–219.
3. Quantum mechanics for engineers Leon van Dommelen, Florida State University
4. P. Mohr, F. Kaeppeler, and R. Gallino (2007). "Survival of Nature's Rarest Isotope 180Ta under Stellar Conditions". Phys. Rev. C. 75: 012802. arXiv:astro-ph/0612427. doi:10.1103/PhysRevC.75.012802.CS1 maint: multiple names: authors list (link)
5. Conover, Emily (2016-10-03). "Rarest nucleus reluctant to decay". Retrieved 2016-10-05.
6. Lehnert, Björn; Hult, Mikael; Lutter, Guillaume; Zuber, Kai (2017). "Search for the decay of nature's rarest isotope ^180mTa". Physical Review C. 95 (4): 044306. arXiv:1609.03725. Bibcode:2017PhRvC..95d4306L. doi:10.1103/PhysRevC.95.044306.

• 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. Lay summary.
• 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.