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 6.907 days, 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 ^156m1Tb (t_1/2 = 24.4 hours), ^154m2Tb (t_1/2 = 22.7 hours) and ^154m1Tb (t_1/2 = 9.4 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
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, and the primary mode behind is beta decay. The primary decay products before ¹⁵⁹Tb are element Gd (gadolinium) isotopes, and the primary products after ¹⁵⁹Tb are element Dy (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 (.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