Isotopes of erbium

Naturally occurring erbium (₆₈Er) is composed of six stable isotopes, with ¹⁶⁶Er being the most abundant (33.503% natural abundance). Thirty-nine radioisotopes have been characterized with between 74 and 112 neutrons, or 142 to 180 nucleons, with the most stable being ¹⁶⁹Er with a half-life of 9.4 days, ¹⁷²Er with a half-life of 49.3 hours, ¹⁶⁰Er with a half-life of 28.58 hours, ¹⁶⁵Er with a half-life of 10.36 hours, and ¹⁷¹Er with a half-life of 7.516 hours. All of the remaining radioactive isotopes have half-lives that are less than 3.5 hours, and the majority of these have half-lives that are less than 4 minutes. This element also has numerous meta states, with the most stable being ^167mEr (t_1/2 = 2.269 seconds).

Isotopes of erbium (₆₈Er)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 160Er synth 28.58 h ε 160Ho 162Er 0.139% stable 164Er 1.60% stable 165Er synth 10.36 h ε 165Ho 166Er 33.5% stable 167Er 22.9% stable 168Er 27.0% stable 169Er synth 9.4 d β− 169Tm 170Er 14.9% stable 171Er synth 7.516 h β− 171Tm 172Er synth 49.3 h β− 172Tm
Standard atomic weight Ar°(Er)
	167.259±0.003[2] 167.26±0.01 (abridged)[3]
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The isotopes of erbium range in atomic weight from 141.9723 u (¹⁴²Er) to 179.9644 u (¹⁸⁰Er). The primary decay mode before the most abundant stable isotope, ¹⁶⁶Er, is electron capture, and the primary mode after is beta decay. The primary decay products before ¹⁶⁶Er are holmium isotopes, and the primary products after are thulium isotopes. All isotopes of erbium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[4] [n 2][n 3]	Half-life[1] [n 4]	Decay mode[1] [n 5]	Daughter isotope [n 6]	Spin and parity[1] [n 7][n 4]	Natural abundance (mole fraction)
	Excitation energy[n 4]							Normal proportion[1]	Range of variation
143Er	68	75	142.96655(43)#	200# ms			9/2−#
144Er	68	76	143.96070(21)#	400# ms [>200 ns]			0+
145Er	68	77	144.95787(22)#	900(200) ms	β+	145Ho	1/2+#
					β+, p (?%)	144Dy
145mEr	205(4)# keV			1.0(3) s	β+	145Ho	(11/2-)
					β+, p (?%)	144Dy
146Er	68	78	145.952418(7)	1.7(6) s	β+	146Ho	0+
					β+, p (?%)	145Dy
147Er	68	79	146.94996(4)#	3.2(12) s	β+	147Ho	(1/2+)
					β+, p (?%)	146Dy
147mEr[n 8]	100(50)# keV			1.6(2) s	β+	147Ho	(11/2−)
					β+, p (?%)	146Dy
148Er	68	80	147.944735(11)#	4.6(2) s	β+ (99.85%)	148Ho	0+
					β+, p (0.15%)	147Dy
148mEr	2.9132(4) MeV			13(3) μs	IT	148Er	(10+)
149Er	68	81	148.94231(3)	4(2) s	β+ (93%)	149Ho	(1/2+)
					β+, p (7%)	148Dy
149m1Er	741.8(2) keV			8.9(2) s	β+ (96.3%)	149Ho	(11/2−)
					IT (3.5%)	149Er
					β+, p (0.18%)	148Dy
149m2Er	2.6111(3) MeV			0.61(8) μs	IT	149Er	(19/2+)
149m3Er	3.302(7) MeV			4.8(1) μs	IT	149Er	(27/2−)
150Er	68	82	149.937916(18)	18.5(7) s	β+	150Ho	0+
150mEr	2.7965(5) MeV			2.55(10) μs	IT	150Er	10+
151Er	68	83	150.937449(18)	23.5(20) s	β+	151Ho	(7/2−)
151m1Er	2.5860(5) MeV			580(20) ms	IT (95.3%)	151Er	(27/2−)
					β+ (4.7%)	151Ho
151m2Er	10.2866(10) MeV			0.42(5) μs	IT	151Er	(65/2-, 61/2+)
152Er	68	84	151.935050(9)	10.3(1) s	α (90%)	148Dy	0+
					β+ (10%)	152Ho
153Er	68	85	152.935086(10)	37.1(2) s	α (53%)	149Dy	7/2−
					β+ (47%)	153Ho
153m1Er	2.7982(10) MeV			373(9) ns	IT	153Er	(27/2-)
153m2Er	5.2481(10) MeV			248(32) ns	IT	153Er	(41/2-)
154Er	68	86	153.932791(5)	3.73(9) min	β+ (99.53%)	154Ho	0+
					α (0.47%)	150Dy
155Er	68	87	154.933216(7)	5.3(3) min	β+ (99.978%)	155Ho	7/2−
					α (0.022%)	151Dy
156Er	68	88	155.931066(26)	19.5(10) min	β+	156Ho	0+
					α (1.2×10−5%)	152Dy
157Er	68	89	156.931923(28)	18.65(10) min	β+	157Ho	3/2−
157mEr	155.4(3) keV			76(6) ms	IT	157Er	9/2+
158Er	68	90	157.929893(27)	2.29(6) h	EC	158Ho	0+
159Er	68	91	158.930691(4)	36(1) min	β+	159Ho	3/2−
159m1Er	182.602(24) keV			337(14) ns	IT	159Er	9/2+
159m2Er	429.05(3) keV			590(60) ns	IT	159Er	11/2−
160Er	68	92	159.929077(26)	28.58(9) h	EC	160Ho	0+
161Er	68	93	160.930004(9)	3.21(3) h	β+	161Ho	3/2−
161mEr	396.44(4) keV			7.5(7) μs	IT	161Er	11/2−
162Er	68	94	161.9287873(8)	Observationally Stable[n 9]			0+	0.00139(5)
162mEr	2.02601(13) MeV			88(16) ns	IT	162Er	7(-)
163Er	68	95	162.930040(5)	75.0(4) min	β+	163Ho	5/2−
163mEr	445.5(6) keV			580(100) ns	IT	163Er	(11/2−)
164Er	68	96	163.9292077(8)	Observationally Stable[n 10]			0+	0.01601(3)
165Er	68	97	164.9307335(10)	10.36(4) h	EC	165Ho	5/2−
165m1Er	551.3(6) keV			250(30) ns	IT	165Er	11/2-
165m2Er	1.8230(6) MeV			370(40) ns	IT	165Er	(19/2)
166Er	68	98	165.9303011(4)	Observationally Stable[n 11]			0+	0.33503(36)
167Er	68	99	166.9320562(3)	Observationally Stable[n 12]			7/2+	0.22869(9)
167mEr	207.801(5) keV			2.269(6) s	IT	167Er	1/2−
168Er	68	100	167.93237828(28)	Observationally Stable[n 13]			0+	0.26978(18)
168mEr	1.0940383(16) MeV			109.0(7) ns	IT	168Er	4-
169Er	68	101	168.9345984(3)	9.392(18) d	β−	169Tm	1/2−
169m1Er	92.05(10) keV			285(20) ns	IT	169Er	(5/2)-
169m2Er	243.69(17) keV			200(10) ns	IT	169Er	7/2+
170Er	68	102	169.9354719(15)	Observationally Stable[n 14]			0+	0.14910(36)
171Er	68	103	170.93803746(15)	7.516(2) h	β−	171Tm	5/2−
171mEr	198.61(9) keV			210(10) ns	IT	171Er	1/2−
172Er	68	104	171.939363(4)	49.3(5) h	β−	172Tm	0+
172mEr	1.5009(3) MeV			579(62) ns	IT	172Er	(6+)
173Er	68	105	172.94240(21)#	1.434(17) min	β−	173Tm	(7/2−)
174Er	68	106	173.94423(32)#	3.2(2) min	β−	174Tm	0+
174mEr	1.1115(7) MeV			3.9(3) s	IT	174Er	8-
175Er	68	107	174.94777(43)#	1.2(3) min	β−	175Tm	9/2+#
176Er	68	108	175.94994(43)#	12# s [>300 ns]			0+
177Er	68	109	176.95399(54)#	8# s [>300 ns]			1/2−#
178Er	68	110	177.95678(64)#	4# s [>300 ns]			0+
179Er	68	111	178.96127(54)#	3# s [>550 ns)]			3/2−#
180Er	68	112	179.96438(54)#	2# s [>550 ns]			0+
This table header & footer: view

1. ^mEr – 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 symbol as daughter – Daughter product is stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. Order of ground state and isomer is uncertain.
9. Believed to undergo α decay to ¹⁵⁸Dy or β⁺β⁺ to ¹⁶²Dy with a half-life over 1.40×10¹⁴ years
10. Believed to undergo α decay to ¹⁶⁰Dy or β⁺β⁺ to ¹⁶⁴Dy
11. Believed to undergo α decay to ¹⁶²Dy
12. Believed to undergo α decay to ¹⁶³Dy
13. Believed to undergo α decay to ¹⁶⁴Dy
14. Believed to undergo α decay to ¹⁶⁶Dy or β⁻β⁻ to ¹⁷⁰Yb with a half-life over 4.10×10¹⁷ years

References

1. Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
2. "Standard Atomic Weights: Erbium". CIAAW. 1999.
3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
4. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.

• Isotope masses from:
  • Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
• Isotopic compositions and standard atomic masses from:
  • Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  • 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.
  • Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  • 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.