Isotopes of tantalum

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

The latter nuclide 180mTa (m denotes a metastable state) has sufficient energy to decay in three ways: isomeric transition to the ground state of 180Ta, beta decay to 180W, and electron capture to 180Hf. 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 180mTa 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). 180Ta has a half-life of only 8 hours. 180mTa 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 182Ta 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)
	excitation energy
155Ta	73	82	154.97459(54)#	13(4) µs [12(+4−3) µs]			(11/2−)
156Ta	73	83	155.97230(43)#	144(24) ms	β^+ (95.8%)	^156Hf	(2−)
					p (4.2%)	^155Hf
156mTa	102(7) keV			0.36(4) s	p	^155Hf	9+
157Ta	73	84	156.96819(22)	10.1(4) ms	α (91%)	^153Lu	1/2+
					β^+ (9%)	^157Hf
157m1Ta	22(5) keV			4.3(1) ms			11/2−
157m2Ta	1593(9) keV			1.7(1) ms	α	^153Lu	(25/2−)
158Ta	73	85	157.96670(22)#	49(8) ms	α (96%)	^154Lu	(2−)
					β^+ (4%)	^158Hf
158mTa	141(9) keV			36.0(8) ms	α (93%)	^154Lu	(9+)
					IT	^158Ta
					β^+	^158Hf
159Ta	73	86	158.963018(22)	1.04(9) s	β^+ (66%)	^159Hf	(1/2+)
					α (34%)	^155Lu
159mTa	64(5) keV			514(9) ms	α (56%)	^155Lu	(11/2−)
					β^+ (44%)	^159Hf
160Ta	73	87	159.96149(10)	1.70(20) s	α	^156Lu	(2#)−
					β^+	^160Hf
160mTa	310(90)# keV			1.55(4) s	β^+ (66%)	^160Hf	(9)+
					α (34%)	^156Lu
161Ta	73	88	160.95842(6)#	3# s	β^+ (95%)	^161Hf	1/2+#
					α (5%)	^157Lu
161mTa	50(50)# keV			2.89(12) s			11/2−#
162Ta	73	89	161.95729(6)	3.57(12) s	β^+ (99.92%)	^162Hf	3+#
					α (.073%)	^158Lu
163Ta	73	90	162.95433(4)	10.6(18) s	β^+ (99.8%)	^163Hf	1/2+#
					α (.2%)	^159Lu
164Ta	73	91	163.95353(3)	14.2(3) s	β^+	^164Hf	(3+)
165Ta	73	92	164.950773(19)	31.0(15) s	β^+	^165Hf	5/2−#
165mTa	60(30) keV						9/2−#
166Ta	73	93	165.95051(3)	34.4(5) s	β^+	^166Hf	(2)+
167Ta	73	94	166.94809(3)	1.33(7) min	β^+	^167Hf	(3/2+)
168Ta	73	95	167.94805(3)	2.0(1) min	β^+	^168Hf	(2−,3+)
169Ta	73	96	168.94601(3)	4.9(4) min	β^+	^169Hf	(5/2+)
170Ta	73	97	169.94618(3)	6.76(6) min	β^+	^170Hf	(3)(+#)
171Ta	73	98	170.94448(3)	23.3(3) min	β^+	^171Hf	(5/2−)
172Ta	73	99	171.94490(3)	36.8(3) min	β^+	^172Hf	(3+)
173Ta	73	100	172.94375(3)	3.14(13) h	β^+	^173Hf	5/2−
174Ta	73	101	173.94445(3)	1.14(8) h	β^+	^174Hf	3+
175Ta	73	102	174.94374(3)	10.5(2) h	β^+	^175Hf	7/2+
176Ta	73	103	175.94486(3)	8.09(5) h	β^+	^176Hf	(1)−
176m1Ta	103.0(10) keV			1.1(1) ms	IT	^176Ta	(+)
176m2Ta	1372.6(11)+X keV			3.8(4) µs			(14−)
176m3Ta	2820(50) keV			0.97(7) ms			(20−)
177Ta	73	104	176.944472(4)	56.56(6) h	β^+	^177Hf	7/2+
177m1Ta	73.36(15) keV			410(7) ns			9/2−
177m2Ta	186.15(6) keV			3.62(10) µs			5/2−
177m3Ta	1355.01(19) keV			5.31(25) µs			21/2−
177m4Ta	4656.3(5) keV			133(4) µs			49/2−
178Ta	73	105	177.945778(16)	9.31(3) min	β^+	^178Hf	1+
178m1Ta	100(50)# keV			2.36(8) h	β^+	^178Hf	(7)−
178m2Ta	1570(50)# keV			59(3) ms			(15−)
178m3Ta	3000(50)# keV			290(12) ms			(21−)
179Ta	73	106	178.9459295(23)	1.82(3) a	EC	^179Hf	7/2+
179m1Ta	30.7(1) keV			1.42(8) µs			(9/2)−
179m2Ta	520.23(18) keV			335(45) ns			(1/2)+
179m3Ta	1252.61(23) keV			322(16) ns			(21/2−)
179m4Ta	1317.3(4) keV			9.0(2) ms	IT	^179Ta	(25/2+)
179m5Ta	1327.9(4) keV			1.6(4) µs			(23/2−)
179m6Ta	2639.3(5) keV			54.1(17) ms			(37/2+)
180Ta	73	107	179.9474648(24)	8.152(6) h	EC (86%)	^180Hf	1+
					β^− (14%)	^180W
180m1Ta	77.1(8) keV			Observationally stable[n 3]			9−	1.2(2)×10^−4
180m2Ta	1452.40(18) keV			31.2(14) µs			15−
180m3Ta	3679.0(11) keV			2.0(5) µs			(22−)
180m4Ta	4171.0+X keV			17(5) µs			(23,24,25)
181Ta	73	108	180.9479958(20)	Observationally stable[n 4]			7/2+	0.99988(2)
181m1Ta	6.238(20) keV			6.05(12) µs			9/2−
181m2Ta	615.21(3) keV			18(1) µs			1/2+
181m3Ta	1485(3) keV			25(2) µs			21/2−
181m4Ta	2230(3) keV			210(20) µs			29/2−
182Ta	73	109	181.9501518(19)	114.43(3) d	β^−	^182W	3−
182m1Ta	16.263(3) keV			283(3) ms	IT	^182Ta	5+
182m2Ta	519.572(18) keV			15.84(10) min			10−
183Ta	73	110	182.9513726(19)	5.1(1) d	β^−	^183W	7/2+
183mTa	73.174(12) keV			107(11) ns			9/2−
184Ta	73	111	183.954008(28)	8.7(1) h	β^−	^184W	(5−)
185Ta	73	112	184.955559(15)	49.4(15) min	β^−	^185W	(7/2+)#
185mTa	1308(29) keV			>1 ms			(21/2−)
186Ta	73	113	185.95855(6)	10.5(3) min	β^−	^186W	(2−,3−)
186mTa				1.54(5) min
187Ta	73	114	186.96053(21)#	2# min [>300 ns]	β^−	^187W	7/2+#
188Ta	73	115	187.96370(21)#	20# s [>300 ns]	β^−	^188W
189Ta	73	116	188.96583(32)#	3# s [>300 ns]			7/2+#
190Ta	73	117	189.96923(43)#	0.3# s

1. Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
2. Bold for stable isotopes, bold italics for nearly-stable isotopes (half-life longer than the age of the universe)
3. 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
4. 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

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. (registration required (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. Lay summary.
• 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.
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.