ISOTOPES OF THORIUM

Although 'thorium' ('Th') has multiple 'isotopes', none of these isotopes are stable; however, one isotope is ''relatively'' stable (²³²Th). As such, it is considered a monoisotopic element. It has a characteristic terrestrial isotopic composition and thus an atomic mass can be given.

Standard atomic mass: 232.03806(2) u
Isotopes of thorium occurring within the radioactive disintegration chains of actinium, thorium and uranium were known as:

★ ''radio-actinium'' : Th

★ ''radio-thorium'' : Th

★ ''ionium'' : Th

★ ''uranium Y'' : Th

★ ''uranium X'' : Th
Twenty-seven radioisotopes have been characterized, with the most abundant and/or stable being ²³²Th with a half-life of 14.05 billion years, ²³⁰Th with a half-life of 75,380 years, ²²⁹Th with a half-life of 7340 years, and ²²⁸Th with a half-life of 1.92 years. All of the remaining radioactive isotopes have half-lives that are less than thirty days and the majority of these have half-lives that are less than ten minutes. One isotope, ²²⁹Th, has a nuclear isomer (or metastable state) with a remarkably low excitation energy of 3.5 eV. ^[1]
The known isotopes of thorium range in atomic weight from 210 u (²¹⁰Th)^[2] to 236 u (²³⁶Th).

Contents

Table

Notes

References

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
209Th	90	119	209.01772(11)	7(5) ms [3.8(+69-15)]	5/2-#
210Th	90	120	210.015075(27)	17(11) ms [9(+17-4) ms]	0+
211Th	90	121	211.01493(8)	48(20) ms [0.04(+3-1) s]	5/2-#
212Th	90	122	212.01298(2)	36(15) ms [30(+20-10) ms]	0+
213Th	90	123	213.01301(8)	140(25) ms	5/2-#
214Th	90	124	214.011500(18)	100(25) ms	0+
215Th	90	125	215.011730(29)	1.2(2) s	(1/2-)
216Th	90	126	216.011062(14)	26.8(3) ms	0+
216m1Th	2042(13) keV			137(4) µs	(8+)
216m2Th	2637(20) keV			615(55) ns	(11-)
217Th	90	127	217.013114(22)	240(5) µs	(9/2+)
218Th	90	128	218.013284(14)	109(13) ns	0+
219Th	90	129	219.01554(5)	1.05(3) µs	9/2+#
220Th	90	130	220.015748(24)	9.7(6) µs	0+
221Th	90	131	221.018184(10)	1.73(3) ms	(7/2+)
222Th	90	132	222.018468(13)	2.237(13) ms	0+
223Th	90	133	223.020811(10)	0.60(2) s	(5/2)+
224Th	90	134	224.021467(12)	1.05(2) s	0+
225Th	90	135	225.023951(5)	8.72(4) min	(3/2)+
226Th	90	136	226.024903(5)	30.57(10) min	0+
227Th	90	137	227.0277041(27)	18.68(9) d	1/2+
228Th	90	138	228.0287411(24)	1.9116(16) a	0+
229Th	90	139	229.031762(3)	7.34(16)E+3 a	5/2+
229mTh	0.0035(10) keV			70(50) h	3/2+
230Th	90	140	230.0331338(19)	7.538(30)E+4 a	0+
231Th	90	141	231.0363043(19)	25.52(1) h	5/2+
232Th	90	142	232.0380553(21)	1.405(6)E+10 a	0+	1.0000
233Th	90	143	233.0415818(21)	21.83(4) min	1/2+
234Th	90	144	234.043601(4)	24.10(3) d	0+
235Th	90	145	235.04751(5)	7.2(1) min	(1/2+)#
236Th	90	146	236.04987(21)#	37.5(2) min	0+
237Th	90	147	237.05389(39)#	4.8(5) min	5/2+#
238Th	90	148	238.0565(3)#	9.4(20) min	0+

Notes

★ Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.

★ 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

★ Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in ''Nuclear Physics'' A729 (2003).

★ Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). ''Pure Appl. Chem.'' Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).

★ Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.

★
★ Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).

★
★ National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).

★
★ David R. Lide (ed.), Norman E. Holden in ''CRC Handbook of Chemistry and Physics, 85th Edition'', online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.