Isotopes of terbium

Naturally occurring terbium (₆₅Tb) is composed of one stable isotope, ¹⁵⁹Tb. Thirty-seven radioisotopes have been characterized, with the most stable being ¹⁵⁸Tb with a half-life of 180 years, ¹⁵⁷Tb with a half-life of 71 years, and ¹⁶⁰Tb with a half-life of 72.3 days. All of the remaining radioactive isotopes have half-lives that are less than one week, and the majority of these have half-lives that are less than 24 seconds. This element also has 27 meta states, with the most stable being ^156m2Tb (t_1/2 = 24.4 hours), ^154m2Tb (t_1/2 = 22.7 hours) and ^154m1Tb (t_1/2 = 21.5 hours).

Isotopes of terbium (₆₅Tb)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 157Tb synth 71 y ε 157Gd 158Tb synth 180 y ε 158Gd β− 158Dy 159Tb 100% stable 160Tb synth 72.3 d β− 160Dy 161Tb synth 6.948 d β− 161Dy
Standard atomic weight Ar°(Tb)
	158.925354±0.000007[2] 158.93±0.01 (abridged)[3]
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The primary decay mode before the most abundant stable isotope, ¹⁵⁹Tb, is electron capture to gadolinium isotopes, and the primary mode after is beta decay to dysprosium isotopes.

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][n 7]	Spin and parity[1] [n 8][n 4]	Isotopic abundance
	Excitation energy[n 4]
135Tb	65	70	134.96452(43)#	1.01(28) ms	p	134Gd	(7/2−)
139Tb	65	74	138.94833(32)#	1.6(2) s	β+	139Gd	5/2−#
140Tb	65	75	139.94581(86)	2.29(15) s	β+ (99.74%)	140Gd	(7+)
					EC (<3%)	140Gd
					β+, p (0.26%)	139Eu
141Tb	65	76	140.94145(11)	3.5(2) s	β+	141Gd	(5/2−)
141mTb[n 9][n 10]	0(200)# keV			7.9(6) s	β+	141Gd	11/2−#
142Tb	65	77	141.93928(75)	597(17) ms	β+ (96.8%)	142Gd	1+
					EC (3.2%)	142Gd
					β+, p (0.0022%)	141Eu
142m1Tb	279.7(4) keV			303(17) ms	IT	142Tb	5−
142m2Tb	652.1(6) keV			26(1) μs	IT	142Tb	8+
143Tb	65	78	142.935137(55)	12(1) s	β+	143Gd	(11/2−)
143mTb[n 9]	0(100)# keV			17(4) s			5/2+#
144Tb	65	79	143.933045(30)	~1 s	β+	144Gd	1+
144m1Tb	396.9(5) keV			4.25(15) s	IT (66%)	144Tb	6−
					β+ (34%)	144Gd
144m2Tb	476.2(5) keV			2.8(3) μs	IT	144Tb	(8−)
144m3Tb	517.1(5) keV			670(60) ns	IT	144Tb	(9+)
144m4Tb	544.5(6) keV			<300 ns	IT	144Tb	(10+)
145Tb	65	80	144.92872(12)	30.9(6) s	β+	145Gd	(11/2−)
145mTb[n 9]	860(230) keV						(3/2+)
146Tb	65	81	145.927253(48)	8(4) s	β+	146Gd	1+
146m1Tb[n 9]	150(100)# keV			24.1(5) s	β+	146Gd	5−
146m2Tb	930(100)# keV			1.18(2) ms	IT	146Tb	10+
147Tb	65	82	146.9240546(87)	1.64(3) h	β+	147Gd	(1/2+)
147mTb	50.6(9) keV			1.87(5) min	β+	147Gd	(11/2−)
148Tb	65	83	147.924275(13)	60(1) min	β+	148Gd	2−
148m1Tb	90.1(3) keV			2.20(5) min	β+	148Gd	(9)+
148m2Tb	8618.6(10) keV			1.310(7) μs	IT	148Tb	(27+)
149Tb	65	84	148.9232538(39)	4.118(25) h	β+ (83.3%)	149Gd	1/2+
					α (16.7%)	145Eu
149mTb	35.78(13) keV			4.16(4) min	β+ (99.98%)	149Gd	11/2−
					α (0.022%)	145Eu
150Tb	65	85	149.9236648(79)	3.48(16) h	β+	150Gd	(2)−
150mTb	461(27) keV			5.8(2) min	β+	150Gd	9+
151Tb	65	86	150.9231090(44)	17.609(1) h	β+ (99.99%)	151Gd	1/2+
					α (0.0095%)	147Eu
151mTb	99.53(5) keV			25(3) s	IT (93.4%)	151Tb	11/2−
					β+ (6.6%)	151Gd
152Tb	65	87	151.924082(43)	17.8784(95) h[5]	EC (83%)[5]	152Gd	2−
					β+ (17%)[5]
					α (<7×10−7%)[6]	148Eu
152m1Tb	342.15(16) keV			960(10) ns	IT	152Tb	5−
152m2Tb	501.74(19) keV			4.2(1) min	IT (78.9%)	152Tb	8+
					β+ (21.1%)	152Gd
153Tb	65	88	152.9234417(42)	2.34(1) d	β+	153Gd	5/2+
153mTb	163.175(5) keV			186(4) μs	IT	153Tb	11/2−
154Tb	65	89	153.924684(49)	9.994(39) h	β+	154Gd	3−
154m1Tb[n 9]	130(50)# keV			21.5(4) h	β+	154Gd	0−
154m2Tb[n 9]	200(150)# keV			22.7(5) h	β+	154Gd	7−
154m3Tb	405(150)# keV			513(42) ns	IT	154Tb
155Tb	65	90	154.923510(11)	5.32(6) d	EC	155Gd	3/2+
156Tb	65	91	155.9247542(40)	5.35(10) d	β+	156Gd	3−
156m1Tb	88.4(2) keV			5.3(2) h	IT	156Tb	(0+)
156m2Tb	100(50)# keV			24.4(10) h	IT	156Tb	(7−)
157Tb	65	92	156.9240319(11)	71(7) y	EC	157Gd	3/2+
158Tb	65	93	157.9254199(14)	180(11) y	β+ (83.4%)	158Gd	3−
					β− (16.6%)	158Dy
158m1Tb	110.3(12) keV			10.70(17) s	IT	158Tb	0−
158m2Tb	388.39(11) keV			0.40(4) ms	IT	158Tb	7−
159Tb[n 11]	65	94	158.9253537(12)	Stable			3/2+	1.0000
160Tb	65	95	159.9271746(12)	72.3(2) d	β−	160Dy	3−
161Tb[n 11]	65	96	160.9275768(13)	6.948(5) d	β−	161Dy	3/2+
162Tb	65	97	161.9292754(22)	7.60(15) min	β−	162Dy	(1−)
162mTb	286(3) keV			10# min			4−#
163Tb	65	98	162.9306536(44)	19.5(3) min	β−	163Dy	3/2+
164Tb	65	99	163.9333276(20)	3.0(1) min	β−	164Dy	(5+)
164mTb	145(12) keV			2# min			2+#
165Tb	65	100	164.9349552(17)	2.11(10) min	β−	165Dy	(3/2+)
165mTb	207(5) keV			0.81(8) μs	IT	165Tb	(7/2−)
166Tb	65	101	165.9379397(16)	27.1(15) s	β−	166Dy	(1−)
166mTb	159.0(15) keV			3.5(4) μs	IT	166Tb	4−#
167Tb	65	102	166.9400070(21)	18.9(16) s	β−	167Dy	(3/2+)
167mTb	200(6) keV			1.2(1) μs	IT	167Tb	(7/2−)
168Tb	65	103	167.9433371(45)	9.4(4) s	β−	168Dy	(4−)
168mTb	211(1) keV			0.71(3) μs	IT	168Tb	(6+)
169Tb	65	104	168.94581(32)#	5.13(32) s	β−	169Dy	3/2+#
170Tb	65	105	169.94986(32)#	960(78) ms	β−	170Dy	2−#
171Tb	65	106	170.95301(43)#	1.23(10) s	β−	171Dy	3/2+#
172Tb	65	107	171.95739(54)#	760(190) ms	β−	172Dy	6+#
173Tb	65	108	172.96081(54)#	400# ms [>550 ns]			3/2+#
174Tb	65	109	173.96568(54)#	240# ms [>550 ns]			2−#
This table header & footer: view

1. ^mTb – 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. Order of ground state and isomer is uncertain.
10. Discovery of this isotope is disputed.
11. Fission product

See also

Daughter products other than terbium

• Isotopes of dysprosium
• Isotopes of gadolinium
• Isotopes of europium