Isotopes of thorium#Thorium-237

{{Anchor|Thorium-209m|Thorium-233m|Thorium-239}}

{{Isotopes table

|symbol=Th

|refs=NUBASE2020, AME2020 II

|notes=m, histname, unc(), mass#, hl-nst, spin(), spin#, EC, CD, IT, daughter-st

}}

|-id=Thorium-207

| ²⁰⁷Th{{cite journal |title=New isotope ²⁰⁷Th and odd-even staggering in α-decay energies for nuclei with Z > 82 and N < 126 |last=Yang |first=H. B. |display-authors=et al. |journal=Physical Review C |year=2022 |volume=105 |number=L051302 |doi=10.1103/PhysRevC.105.L051302|bibcode=2022PhRvC.105e1302Y |s2cid=248935764 }}

|

| style="text-align:right" | 90

| style="text-align:right" | 117

|

| {{val|9.7|46.6|4.4|u=ms}}

| α

| ²⁰³Ra

|

|

|

|-id=Thorium-208

| ²⁰⁸Th

|

| style="text-align:right" | 90

| style="text-align:right" | 118

| 208.017915(34)

| 2.4(12) ms

| α

| ²⁰⁴Ra

| 0+

|

|

|-id=Thorium-209

| ²⁰⁹Th

|

| style="text-align:right" | 90

| style="text-align:right" | 119

| 209.017998(27)

| 3.1(12) ms

| α

| ²⁰⁵Ra

| 13/2+

|

|

|-id=Thorium-210

| ²¹⁰Th

|

| style="text-align:right" | 90

| style="text-align:right" | 120

| 210.015094(20)

| 16.0(36) ms

| α

| ²⁰⁶Ra

| 0+

|

|

|-id=Thorium-211

| ²¹¹Th

|

| style="text-align:right" | 90

| style="text-align:right" | 121

| 211.014897(92)

| 48(20) ms

| α

| ²⁰⁷Ra

| 5/2−#

|

|

|-id=Thorium-212

| ²¹²Th

|

| style="text-align:right" | 90

| style="text-align:right" | 122

| 212.013002(11)

| 31.7(13) ms

| α

| ²⁰⁸Ra

| 0+

|

|

|-id=Thorium-213

| ²¹³Th

|

| style="text-align:right" | 90

| style="text-align:right" | 123

| 213.0130115(99)

| 144(21) ms

| α

| ²⁰⁹Ra

| 5/2−

|

|

|-id=Thorium-213m

| style="text-indent:1em" | ^213mTh

|

| colspan="3" style="text-indent:2em" | 1180.0(14) keV

| 1.4(4) μs

| IT

| ²¹³Th

| (13/2)+

|

|

|-id=Thorium-214

| ²¹⁴Th

|

| style="text-align:right" | 90

| style="text-align:right" | 124

| 214.011481(11)

| 87(10) ms

| α

| ²¹⁰Ra

| 0+

|

|

|-id=Thorium-214m

| style="text-indent:1em" | ^214mTh

|

| colspan="3" style="text-indent:2em" | 2181.0(27) keV

| 1.24(12) μs

| IT

| ²¹⁴Th

| 8+#

|

|

|-id=Thorium-215

| ²¹⁵Th

|

| style="text-align:right" | 90

| style="text-align:right" | 125

| 215.0117246(68)

| 1.35(14) s

| α

| ²¹¹Ra

| (1/2−)

|

|

|-id=Thorium-215m

| style="text-indent:1em" | ^215mTh

|

| colspan="3" style="text-indent:2em" | 1471(50)# keV

| 770(60) ns

| IT

| ²¹⁵Th

| 9/2+#

|

|

|-id=Thorium-216

| ²¹⁶Th

|

| style="text-align:right" | 90

| style="text-align:right" | 126

| 216.011056(12)

| 26.28(16) ms

| α

| ²¹²Ra

| 0+

|

|

|-id=Thorium-216m1

| rowspan=2 style="text-indent:1em" | ^216m1Th

| rowspan=2|

| rowspan=2 colspan="3" style="text-indent:2em" | 2041(8) keV

| rowspan=2|135.4(29) μs

| IT (97.2%)

| ²¹⁶Th

| rowspan=2|8+

| rowspan=2|

| rowspan=2|

|-

| α (2.8%)

| ²¹²Ra

|-id=Thorium-216m2

| style="text-indent:1em" | ^216m2Th

|

| colspan="3" style="text-indent:2em" | 2648(8) keV

| 580(26) ns

| IT

| ²¹⁶Th

| (11−)

|

|

|-id=Thorium-216m3

| style="text-indent:1em" | ^216m3Th

|

| colspan="3" style="text-indent:2em" | 3682(8) keV

| 740(70) ns

| IT

| ²¹⁶Th

| (14+)

|

|

|-id=Thorium-217

| ²¹⁷Th

|

| style="text-align:right" | 90

| style="text-align:right" | 127

| 217.013103(11)

| 248(4) μs

| α

| ²¹³Ra

| 9/2+#

|

|

|-id=Thorium-217m1

| style="text-indent:1em" | ^217m1Th

|

| colspan="3" style="text-indent:2em" | 673.3(1) keV

| 141(50) ns

| IT

| ²¹⁷Th

| (15/2−)

|

|

|-id=Thorium-217m2

| style="text-indent:1em" | ^217m2Th

|

| colspan="3" style="text-indent:2em" | 2307(32) keV

| 71(14) μs

| IT

| ²¹⁷Th

| (25/2+)

|

|

|-id=Thorium-218

| ²¹⁸Th

|

| style="text-align:right" | 90

| style="text-align:right" | 128

| 218.013276(11)

| 122(5) ns

| α

| ²¹⁴Ra

| 0+

|

|

|-id=Thorium-219

| ²¹⁹Th

|

| style="text-align:right" | 90

| style="text-align:right" | 129

| 219.015526(61)

| 1.023(18) μs

| α

| ²¹⁵Ra

| 9/2+#

|

|

|-id=Thorium-220

| ²²⁰Th

|

| style="text-align:right" | 90

| style="text-align:right" | 130

| 220.015770(15)

| 10.2(3) μs

| α

| ²¹⁶Ra

| 0+

|

|

|-id=Thorium-221

| ²²¹Th

|

| style="text-align:right" | 90

| style="text-align:right" | 131

| 221.0181858(86)

| 1.75(2) ms

| α

| ²¹⁷Ra

| 7/2+#

|

|

|-id=Thorium-222

| ²²²Th

|

| style="text-align:right" | 90

| style="text-align:right" | 132

| 222.018468(11)

| 2.24(3) ms

| α

| ²¹⁸Ra

| 0+

|

|

|-id=Thorium-223

| ²²³Th

|

| style="text-align:right" | 90

| style="text-align:right" | 133

| 223.0208111(85)

| 0.60(2) s

| α

| ²¹⁹Ra

| (5/2)+

|

|

|-id=Thorium-224

| ²²⁴Th

|

| style="text-align:right" | 90

| style="text-align:right" | 134

| 224.021466(10)

| 1.04(2) s

| αTheorized to also undergo β⁺β⁺ decay to ²²⁴Ra

| ²²⁰Ra

| 0+

|

|

|-id=Thorium-225

| rowspan=2|²²⁵Th

| rowspan=2|

| rowspan=2 style="text-align:right" | 90

| rowspan=2 style="text-align:right" | 135

| rowspan=2|225.0239510(55)

| rowspan=2|8.75(4) min

| α (~90%)

| ²²¹Ra

| rowspan=2|3/2+

| rowspan=2|

| rowspan=2|

|-

| EC (~10%)

| ²²⁵Ac

|-id=Thorium-226

| rowspan=2|²²⁶Th

| rowspan=2|

| rowspan=2 style="text-align:right" | 90

| rowspan=2 style="text-align:right" | 136

| rowspan=2|226.0249037(48)

| rowspan=2|30.70(3) min

| α

| ²²²Ra

| rowspan=2|0+

| rowspan=2|

| rowspan=2|

|-

| CD (<{{val|3.2e-12}}%)

| ²⁰⁸Pb
¹⁸O

|-id=Thorium-227

| ²²⁷Th

| Radioactinium

| style="text-align:right" | 90

| style="text-align:right" | 137

| 227.0277025(22)

| 18.693(4) d

| α

| ²²³Ra

| (1/2+)

| TraceIntermediate decay product of ²³⁵U

|

|-

| rowspan=2|²²⁸Th

| rowspan=2|Radiothorium

| rowspan=2 style="text-align:right" | 90

| rowspan=2 style="text-align:right" | 138

| rowspan=2|228.0287397(19)

| rowspan=2|1.9125(7) y

| α

| ²²⁴Ra

| rowspan=2|0+

| rowspan=2|TraceIntermediate decay product of ²³²Th

| rowspan=2|

|-

| CD (1.13×10⁻¹¹%)

| ²⁰⁸Pb
²⁰O

|-

| ²²⁹Th

|

| style="text-align:right" | 90

| style="text-align:right" | 139

| 229.0317614(26)

| 7916(17) y

| α

| ²²⁵Ra

| 5/2+

| TraceIntermediate decay product of ²³⁷Np

|

|-

| style="text-indent:1em" | ^229mTh

|

| colspan="3" style="text-indent:2em" | 8.355733554021(8) eV

| 7(1) μs

| ITNeutral ^229mTh decays rapidly by internal conversion, ejecting an electron. There is not enough energy to eject a second electron, so ^229mTh⁺ ions live much longer, decaying by gamma emission. See {{alink|Thorium-229m}}.

| ²²⁹Th⁺

| 3/2+

|

|

|-

| style="text-indent:1em" | ^229mTh⁺

|

| colspan="3" style="text-indent:2em" | 8.355733554021(8) eV

| 29(1) min

| γ

| ²²⁹Th⁺

| 3/2+

|

|

|-

| rowspan=3|²³⁰ThUsed in Uranium–thorium dating

| rowspan=3|Ionium

| rowspan=3 style="text-align:right" | 90

| rowspan=3 style="text-align:right" | 140

| rowspan=3|230.0331323(13)

| rowspan=3|7.54(3)×10⁴ y

| α

| ²²⁶Ra

| rowspan=3|0+

| rowspan=3|0.0002(2)Intermediate decay product of ²³⁸U

| rowspan=3|

|-

| CD (5.8×10⁻¹¹%)

| ²⁰⁶Hg
²⁴Ne

|-

| SF (<4×10⁻¹²%)

| (Various)

|-

| ²³¹Th

| Uranium Y

| style="text-align:right" | 90

| style="text-align:right" | 141

| 231.0363028(13)

| 25.52(1) h

| β⁻

| ²³¹Pa

| 5/2+

| Trace

|

|-

| rowspan=4|²³²ThPrimordial radionuclide

| rowspan=4|Thorium

| rowspan=4 style="text-align:right" | 90

| rowspan=4 style="text-align:right" | 142

| rowspan=4|232.0380536(15)

| rowspan=4|1.40(1)×10¹⁰ y

| αTheorized to also undergo β⁻β⁻ decay to ²³²U

| ²²⁸Ra

| rowspan=4|0+

| rowspan=4|0.9998(2)

| rowspan=4|

|-

| SF (1.1×10⁻⁹%)

| (various)

|-

| CD (<2.78×10⁻¹⁰%)

| ²⁰⁸Hg
²⁴Ne

|-

| CD (<2.78×10⁻¹⁰%)

| ²⁰⁶Hg
²⁶Ne

|-

| ²³³Th

|

| style="text-align:right" | 90

| style="text-align:right" | 143

| 233.0415801(15)

| 21.83(4) min

| β⁻

| ²³³Pa

| 1/2+

| TraceProduced in neutron capture by ²³²Th

|

|-

| ²³⁴Th

| Uranium X₁

| style="text-align:right" | 90

| style="text-align:right" | 144

| 234.0435998(28)

| 24.107(24) d

| β⁻

| ^234mPa

| 0+

| Trace

|

|-id=Thorium-235

| ²³⁵Th

|

| style="text-align:right" | 90

| style="text-align:right" | 145

| 235.047255(14)

| 7.2(1) min

| β⁻

| ²³⁵Pa

| 1/2+#

|

|

|-id=Thorium-236

| ²³⁶Th

|

| style="text-align:right" | 90

| style="text-align:right" | 146

| 236.049657(15)

| 37.3(15) min

| β⁻

| ²³⁶Pa

| 0+

|

|

|-id=Thorium-237

| ²³⁷Th

|

| style="text-align:right" | 90

| style="text-align:right" | 147

| 237.053629(17)

| 4.8(5) min

| β⁻

| ²³⁷Pa

| 5/2+#

|

|

|-id=Thorium-238

| ²³⁸Th

|

| style="text-align:right" | 90

| style="text-align:right" | 148

| 238.05639(30)#

| 9.4(20) min

| β⁻

| ²³⁸Pa

| 0+

|

|

{{Isotopes table/footer}}

Thorium has been suggested for use in thorium-based nuclear power.

In many countries the use of thorium in consumer products is banned or discouraged because it is radioactive.

It is currently used in cathodes of vacuum tubes, for a combination of physical stability at high temperature and a low work energy required to remove an electron from its surface.

It has, for about a century, been used in mantles of gas and vapor lamps such as gas lights and camping lanterns.

Thorium was also used in certain glass elements of Aero-Ektar lenses made by Kodak during World War II. Thus they are mildly radioactive.[http://new55project.blogspot.co.uk/2012/02/f25-aero-ektar-lenses.html f2.5 Aero Ektar Lenses ]{{Dead link|date=February 2023 |bot=InternetArchiveBot |fix-attempted=yes }} Some images. Two of the glass elements in the f/2.5 Aero-Ektar lenses are 11% and 13% thorium by weight. The thorium-containing glasses were used because they have a high refractive index with a low dispersion (variation of index with wavelength), a highly desirable property. Many surviving Aero-Ektar lenses have a tea colored tint, possibly due to radiation damage to the glass.

These lenses were used for aerial reconnaissance because the radiation level is not high enough to fog film over a short period. This would indicate the radiation level is reasonably safe. However, when not in use, it would be prudent to store these lenses as far as possible from normally inhabited areas; allowing the inverse square relationship to attenuate the radiation.{{Cite web|title = Aero-Ektar Lenses|url = http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html|author = Michael S. Briggs|date = January 16, 2002|access-date = 2015-08-28|archive-url = https://web.archive.org/web/20150812205035/http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html|archive-date = August 12, 2015|url-status = dead}}

{{Actinidesvsfissionproducts}}

{{Clear}}

²²⁸Th is an isotope of thorium with 138 neutrons. It was once named Radiothorium, due to its occurrence in the disintegration chain of thorium-232. It has a half-life of 1.9116 years. It undergoes alpha decay to ²²⁴Ra. Occasionally it decays by the unusual route of cluster decay, emitting a nucleus of ²⁰O and producing stable ²⁰⁸Pb. It is a daughter isotope of ²³²U in the thorium decay series.

²²⁸Th has an atomic weight of 228.0287411 grams/mole.

Together with its decay product ²²⁴Ra it is used for alpha particle radiation therapy.{{cite web | url=https://www.scatecinnovation.no/artikler/thor-medical-production-of-alpha-emitters-for-cancer-treatment | title=Thor Medical – production of alpha emitters for cancer treatment | date=May 2023}}

²²⁹Th is a radioactive isotope of thorium that decays by alpha emission with a half-life of 7917 years.

²²⁹Th is produced by the decay of uranium-233, and its principal use is for the production of the medical isotopes actinium-225 and bismuth-213.[http://www.ne.doe.gov/pdfFiles/U233RptConMarch2001.pdf Report to Congress on the extraction of medical isotopes from U-233] {{webarchive|url=https://web.archive.org/web/20110927225711/http://www.ne.doe.gov/pdfFiles/U233RptConMarch2001.pdf |date=2011-09-27 }}. U.S. Department of Energy. March 2001

²²⁹Th has a nuclear isomer, {{SimpleNuclide|Th|229|m}}, with a remarkably low excitation energy of {{val|{{#expr:(2020407384335*6.62607015/1.602176634e12) round 12}}|(8)|u=eV}}.

Due to this low energy, the lifetime of ^229mTh very much depends on the electronic environment of the nucleus. In neutral ²²⁹Th, the isomer decays by internal conversion within a few microseconds.{{cite journal

| last1=Karpeshin |first1=F.F. |last2=Trzhaskovskaya |first2=M.B.

| title = Impact of the electron environment on the lifetime of the ²²⁹Th^m low-lying isomer

| journal = Physical Review C

| volume = 76 | issue=5 | date = November 2007 | article-number = 054313

| page=

| doi = 10.1103/PhysRevC.76.054313

|bibcode=2007PhRvC..76e4313K

}}{{cite journal

| last1=Seiferle |first1=B. |last2=von der Wense |first2=L. |last3=Thirolf |first3=P.G.

| title = Lifetime measurement of the ²²⁹Th nuclear isomer

| journal = Physical Review Letters

| volume = 118 | issue=4 | date = January 2017 | article-number = 042501

| page=

| doi = 10.1103/PhysRevLett.118.042501

| pmid=28186791 | arxiv=1801.05205

| bibcode=2017PhRvL.118d2501S |s2cid=37518294

| quote=A half-life of {{val|7|1|u=us}} has been measured

}} However, the isomeric energy is not enough to remove a second electron (thorium's second ionization energy is {{val|11.5|u=eV}}), so internal conversion is impossible in Th⁺ ions. Radiative decay occurs with a half-life {{#expr:(ln(1740/7e-6)/ln10) round 1}} orders of magnitude longer, in excess of 1000 seconds.{{cite journal

| last1=Tkalya |first1=Eugene V. |last2=Schneider |first2=Christian

| last3=Jeet |first3=Justin |last4=Hudson |first4=Eric R.

| title = Radiative lifetime and energy of the low-energy isomeric level in ²²⁹Th

| journal = Physical Review C

| volume = 92 | issue=5 | date = 25 November 2015 | article-number = 054324

| page=

| doi = 10.1103/PhysRevC.92.054324

| arxiv=1509.09101

| bibcode=2015PhRvC..92e4324T |s2cid=118374372

}}{{cite journal

| last1=Minkov |first1=Nikolay |last2=Pálffy |first2=Adriana

| title = Reduced transition probabilities for the gamma decay of the 7.8 eV isomer in ^229mTh

| journal = Phys. Rev. Lett.

| volume = 118 | issue=21 | article-number = 212501

| date = 23 May 2017

| page=

| doi = 10.1103/PhysRevLett.118.212501

| arxiv = 1704.07919

| pmid = 28598657

| bibcode=2017PhRvL.118u2501M |s2cid=40694257

}} Embedded in ionic crystals, ionization is not quite 100%, so a small amount of internal conversion occurs, leading to a recently measured lifetime of ≈{{val|600|u=s}},{{r|Tiedau2024|Elwell2024}} which can be extrapolated to a lifetime for isolated ions of {{val|1740|50|u=s}}.{{r|Tiedau2024}}

This excitation energy corresponds to a photon frequency of {{val|2020407384335|2|u=kHz}} (wavelength {{val|{{#expr:(299792458e6/2020407384335) round 10}}|(15)|u=nm}}).{{cite journal

|title=Frequency ratio of the ^229mTh nuclear isomeric transition and the ⁸⁷Sr atomic clock

|first1=Chuankun |last1=Zhang |first2=Tian |last2=Ooi

|first3=Jacob S. |last3=Higgins |first4=Jack F. |last4=Doyle

|first5=Lars |last5=von der Wense |first6=Kjeld |last6=Beeks

|first7=Adrian |last7=Leitner |first8=Georgy |last8=Kazakov

|first9=Peng |last9=Li |first10=Peter G. |last10=Thirolf

|first11=Thorsten |last11=Schumm |first12=Jun |last12=Ye |author-link12=Jun Ye

|journal=Nature |volume=633 |issue=8028 |pages=63–70

|date=4 September 2024

|doi=10.1038/s41586-024-07839-6

|arxiv=2406.18719

|quote=The transition frequency between the {{math|1=I = 5/2}} ground state and the {{math|1=I = 3/2}} excited state is determined as: {{math|1=

𝜈_Th = {{sfrac|1|6}} (𝜈_a + 2𝜈_b + 2𝜈_c + 𝜈_d) = {{val|2020407384335|(2)|u=kHz}}}}.

}}{{r|Thirolf2024|Tiedau2024|Elwell2024}} Although in the very high frequency vacuum ultraviolet frequency range, it is possible to build a laser operating at this frequency, giving the only known opportunity for direct laser excitation of a nuclear state,{{cite journal

| first1=E.V. |last1=Tkalya

| first2=V.O. |last2=Varlamov

| first3=V.V. |last3=Lomonosov

| first4=S.A. |last4=Nikulin

| title=Processes of the nuclear isomer ^229mTh(3/2⁺, 3.5±1.0 eV) Resonant excitation by optical photons

| journal=Physica Scripta

| volume=53 | issue=3

| pages=296–299

| date=1996

| doi=10.1088/0031-8949/53/3/003

| bibcode=1996PhyS...53..296T

| s2cid=250744766

}} which could have applications like a nuclear clock of very high accuracy{{cite journal

| title=Towards a ²²⁹Th-based nuclear clock

| first1=Lars |last1=von der Wense

| first2=Benedict |last2=Seiferle

| first3=Peter G. |last3=Thirolf

| journal=Measurement Techniques |volume=60 |issue=12 |pages=1178–1192 |date=March 2018

| doi=10.1007/s11018-018-1337-1

| arxiv=1811.03889

| bibcode=2018MeasT..60.1178V | s2cid=119359298

}}{{cite conference

|title='Phase Transition' in the 'Thorium-Isomer Story'

|first=Peter G. |last=Thirolf |display-authors=etal

|journal=Acta Physica Polonica B

|volume=51 |issue=3 |pages=561–570

|date=March 2020

|url=https://www.actaphys.uj.edu.pl/R/51/3/561/pdf

|conference=XXXVI Mazurian Lakes Conference on Physics (1–7 November 2019)

|conference-url=https://mazurian.fuw.edu.pl/wp-content/uploads/2019/09/2019Program.pdf

|location=Piaski, Pisz County, Poland

|doi=10.5506/APhysPolB.51.561 |doi-access=free

|arxiv=2108.13388

}} Originally presented as Characterization of the elusive ^229mTh isomer – milestones towards a nuclear clock. or as a qubit for quantum computing.{{cite journal

| first1=S. |last1=Raeder

| first2=V. |last2=Sonnenschein

| first3=T. |last3=Gottwald

| first4=I.D. |last4=Moore

| first5=M. |last5=Reponen

| first6=S. |last6=Rothe

| first7=N. |last7=Trautmann

| first8=K. |last8=Wendt

| title = Resonance ionization spectroscopy of thorium isotopes - towards a laser spectroscopic identification of the low-lying 7.6 eV isomer of ²²⁹Th

| journal = J. Phys. B: At. Mol. Opt. Phys.

| volume = 44 | issue = 16 | article-number = 165005

| page=

| date = July 2011

| doi = 10.1088/0953-4075/44/16/165005

| arxiv=1105.4646

|bibcode=2011JPhB...44p5005R

|s2cid=118379032

}}

These applications were for a long time impeded by imprecise measurements of the isomeric energy, as laser excitation's exquisite precision makes it difficult to use to search a wide frequency range. There were many investigations, both theoretical and experimental, trying to determine the transition energy precisely and to specify other properties of the isomeric state of ²²⁹Th (such as the lifetime and the magnetic moment) before the frequency was accurately measured in 2024.{{r|Tiedau2024|Thirolf2024|Elwell2024}}

Early measurements were performed via gamma ray spectroscopy, producing the {{val|29.5855|u=keV}} excited state of ²²⁹Th, and measuring the difference in emitted gamma ray energies as it decays to either the ^229mTh (90%) or ²²⁹Th (10%) isomeric states. In 1976, Kroger and Reich sought to understand coriolis force effects in deformed nuclei, and attempted to match thorium's gamma-ray spectrum to theoretical nuclear shape models. To their surprise, the known nuclear states could not be reasonably classified into different total angular momentum quantization levels. They concluded that some states previously identified as ²²⁹Th actually arose from a spin-{{sfrac|3|2}} nuclear isomer, ^229mTh, with a remarkably low excitation energy.{{cite journal

| first1=L.A. |last1=Kroger

| first2=C.W. |last2=Reich

| title = Features of the low energy level scheme of ²²⁹Th as observed in the α-decay of ²³³U

| journal = Nuclear Physics A

| volume = 259

| issue=1

| pages = 29–60

| date = 1976

| doi = 10.1016/0375-9474(76)90494-2

|bibcode=1976NuPhA.259...29K

}}

At that time the energy was inferred to be below 100 eV, purely based on the non-observation of the isomer's direct decay. However, in 1990, further measurements led to the conclusion that the energy is almost certainly below 10 eV,{{cite journal

| title = Energy separation of the doublet of intrinsic states at the ground state of ²²⁹Th

| last1=Reich |first1=C. W. |author2=Helmer, R. G.

| journal = Physical Review Letters

| volume = 64

| issue = 3

| pages = 271–273

|date=Jan 1990

| doi = 10.1103/PhysRevLett.64.271

|pmid=10041937 | publisher = American Physical Society

|bibcode = 1990PhRvL..64..271R |url=https://zenodo.org/record/1233878 }}

making it one of the lowest known isomeric excitation energies. In the following years, the energy was further constrained to {{val|3.5|1.0|u=eV}}, which was for a long time the accepted energy value.{{cite journal

| journal=Physical Review C

| volume=49 | issue=4| pages=1845–1858

| date=April 1994

| last1=Helmer |first1=R. G. |last2=Reich |first2=C. W.

| title = An Excited State of ²²⁹Th at 3.5 eV

| doi=10.1103/PhysRevC.49.1845

| pmid=9969412 | bibcode = 1994PhRvC..49.1845H

| url=https://zenodo.org/record/1233767}}

Improved gamma ray spectroscopy measurements using an advanced high-resolution X-ray microcalorimeter were carried out in 2007, yielding a new value for the transition energy of {{val|7.6|0.5|u=eV}},{{cite journal |author=B. R. Beck |title=Energy splitting in the ground state doublet in the nucleus ²²⁹Th |journal=Physical Review Letters |volume=98 |issue=14 |pages=142501|date=2007-04-06 |doi=10.1103/PhysRevLett.98.142501 |pmid=17501268 |bibcode=2007PhRvL..98n2501B |s2cid=12092700 |url=https://zenodo.org/record/1233955 |display-authors=etal}} corrected to {{val|7.8|0.5|u=eV}} in 2009.{{cite conference

| title = Improved value for the energy splitting of the ground-state doublet in the nucleus ²²⁹Th

| vauthors = Beck BR, Wu CY, Beiersdorfer P, Brown GV, Becker JA, Moody KJ, Wilhelmy JB, Porter FS, Kilbourne CA, Kelley RL

| date = 2009-07-30

| conference = 12th Int. Conf. on Nuclear Reaction Mechanisms

| location = Varenna, Italy

| id = LLNL-PROC-415170

| url = https://e-reports-ext.llnl.gov/pdf/375773.pdf

| access-date = 2014-05-14

| archive-url = https://web.archive.org/web/20170127104504/https://e-reports-ext.llnl.gov/pdf/375773.pdf

| archive-date = 2017-01-27

| url-status = dead

}} This higher energy has two consequences which had not been considered by earlier attempts to observe emitted photons:

• Because it is above thorium's {{val|6.08|u=eV}} first ionization energy, neutral ^229mTh will decay radiatively with an extremely low likelihood, and
• Because it is above the {{val|6.2|u=eV}} vacuum ultraviolet cutoff, the produced photons cannot travel through air.

But even knowing the higher energy, most of the searches in the 2010s for light emitted by the isomeric decay failed to observe any signal,{{Cite journal

|last1=Jeet |first1=Justin |first2=Christian |last2=Schneider |first3=Scott T. |last3=Sullivan

|first4=Wade G. |last4=Rellergert |first5=Saed |last5=Mirzadeh |first6=A. |last6=Cassanho

|first7=H. P. |last7=Jenssen |first8=Eugene V. |last8=Tkalya |first9=Eric R. |last9=Hudson

|display-authors=6

|title=Results of a Direct Search Using Synchrotron Radiation for the Low-Energy

|journal=Physical Review Letters

|volume=114 |issue=25 |pages=253001 |date=23 June 2015

|doi=10.1103/physrevlett.114.253001 |pmid=26197124 |arxiv=1502.02189 |bibcode=2015PhRvL.114y3001J

|s2cid=1322253 }}{{Cite journal

|last1=Yamaguchi |first1=A. |last2=Kolbe |first2=M. |last3=Kaser |first3=H.

|last4=Reichel |first4=T. |last5=Gottwald |first5=A. |last6=Peik |first6=E.

|title=Experimental search for the low-energy nuclear transition in ²²⁹Th with undulator radiation

|journal=New Journal of Physics |language=en

|volume=17 |issue=5 |pages=053053 |date=May 2015

|doi=10.1088/1367-2630/17/5/053053 |bibcode=2015NJPh...17e3053Y |doi-access=free

}}{{cite thesis

| first = Lars | last = von der Wense

| degree = PhD

| title = On the direct detection of ^229mTh

| publisher = Ludwig Maximilian University of Munich

| date = 2016

| isbn=978-3-319-70461-6

| url = https://edoc.ub.uni-muenchen.de/20492/7/Wense_Lars_von_der.pdf

}}{{cite journal

| title=On an attempt to optically excite the nuclear isomer in Th-229

| first1=S. |last1=Stellmer

| first2=G. |last2=Kazakov

| first3=M. |last3=Schreitl

| first4=H. |last4=Kaser

| first5=M. |last5=Kolbe

| first6=T. |last6=Schumm

| journal=Physical Review A |volume=97 |pages=062506 |date=2018

| issue=6 | doi= 10.1103/PhysRevA.97.062506

| arxiv=1803.09294 | bibcode=2018PhRvA..97f2506S| s2cid=4946329 }} pointing towards a potentially strong non-radiative decay channel. A direct detection of photons emitted in the isomeric decay was claimed in 2012{{cite journal

|last1=Zhao |first1=Xinxin

|date=18 October 2012

|title=Observation of the Deexcitation of the ^229mTh Nuclear Isomer

|journal=Physical Review Letters |volume=109 |issue=16 |article-number=160801

|doi=10.1103/PhysRevLett.109.160801

|first2=Yenny Natali |last2=Martinez de Escobar

|first3=Robert |last3=Rundberg

|first4=Evelyn M. |last4=Bond

|first5=Allen |last5=Moody

|first6=David J. |last6=Vieira

|page=

|bibcode=2012PhRvL.109p0801Z

|pmid=23215066

|doi-access=free

}} and again in 2018.{{Cite arXiv

|last1=Borisyuk|first1=P. V. |last2=Chubunova|first2=E. V. |last3=Kolachevsky|first3=N. N.

|last4=Lebedinskii|first4=Yu Yu |last5=Vasiliev|first5=O. S. |last6=Tkalya|first6=E. V.

|date=2018-04-01

|title=Excitation of ²²⁹Th nuclei in laser plasma: the energy and half-life of the low-lying isomeric state

|eprint=1804.00299 |class=nucl-th

}} However, both reports were subject to controversial discussions within the community.{{Cite journal

|last1=Peik|first1=Ekkehard

|last2=Zimmermann|first2=Kai

|date=2013-07-03

|title=Comment on "Observation of the Deexcitation of the ^229mTh Nuclear Isomer"

|journal=Physical Review Letters |volume=111 |issue=1

|article-number=018901

|doi=10.1103/PhysRevLett.111.018901

|pmid=23863029 |bibcode=2013PhRvL.111a8901P

|quote=While we do not exclude that the decay of the ^229mTh isomer has contributed to the photon emission observed in [1], we conclude that the sought-after signal would be heavily masked by background from other nuclear decays and radioluminescence induced in the MgF₂ plates.

}}{{Cite journal

|last1=Thirolf|first1=Peter G. |last2=Seiferle|first2=Benedict |last3=von der Wense |first3=Lars

|date=2019-10-28

|title=The 229-thorium isomer: doorway to the road from the atomic clock to the nuclear clock

|journal=Journal of Physics B: Atomic, Molecular and Optical Physics

|volume=52 |issue=20 |article-number=203001

|doi=10.1088/1361-6455/ab29b8 |bibcode=2019JPhB...52t3001T |doi-access=free

|url=https://s3.cern.ch/inspire-prod-files-6/6da1f99f16760317d4532b9394b15842

}}

A direct detection of electrons being emitted in the internal conversion decay channel of ^229mTh was achieved in 2016.{{cite journal

| journal=Nature

| volume=533 | issue=7601 | pages=47–51

| date=5 May 2016

| title = Direct detection of the ²²⁹Th nuclear clock transition

| first1=Lars | last1=von der Wense

| first2=Benedict | last2=Seiferle

| first3=Mustapha | last3=Laatiaoui

| first4=Jürgen B. | last4=Neumayr

| first5=Hans-Jörg | last5=Maier

| first6=Hans-Friedrich | last6=Wirth

| first7=Christoph | last7=Mokry

| first8=Jörg | last8=Runke

| first9=Klaus | last9=Eberhardt

| first10=Christoph E. | last10=Düllmann

| first11=Norbert G. | last11=Trautmann

| first12=Peter G. | last12=Thirolf

| display-authors=6

| doi=10.1038/nature17669

| pmid=27147026 | bibcode=2016Natur.533...47V| arxiv=1710.11398| s2cid=205248786 }} However, at the time the isomer's transition energy could only be weakly constrained to between 6.3 and 18.3 eV. Finally, in 2019, non-optical electron spectroscopy of the internal conversion electrons emitted in the isomeric decay allowed for a determination of the isomer's excitation energy to {{val|8.28|0.17|u=eV}}.{{cite journal

| title = Energy of the ²²⁹Th nuclear clock transition

| journal=Nature

| volume=573 | issue=7773 | pages=243–246

| date=12 September 2019

| first1=B. |last1=Seiferle

| first2=L. |last2=von der Wense

| first3=P.V. |last3=Bilous

| first4=I. |last4=Amersdorffer

| first5=C. |last5=Lemell

| first6=F. |last6=Libisch

| first7=S. |last7=Stellmer

| first8=T. |last8=Schumm

| first9=C.E. |last9=Düllmann

| first10=A. |last10=Pálffy

| first11=P.G. |last11=Thirolf

| doi=10.1038/s41586-019-1533-4

| pmid=31511684

| arxiv=1905.06308

| bibcode=2019Natur.573..243S

| s2cid=155090121

}} However, this value appeared at odds with the 2018 preprint showing that a similar signal as an {{val|8.4|u=eV}} xenon VUV photon can be shown, but with about {{val|1.3|0.2|0.1|u=eV}} less energy and a (retrospectively correct) {{val|1880|170|u=s}} lifetime. In that paper, ²²⁹Th was embedded in SiO₂, possibly resulting in an energy shift and altered lifetime, although the states involved are primarily nuclear, shielding them from electronic interactions.

In another 2018 experiment, it was possible to perform a first laser-spectroscopic characterization of the nuclear properties of ^229mTh.{{cite journal

| last1=Thielking |first1=J. |last2=Okhapkin |first2=M.V. |last3=Przemyslaw |first3=G.

| last4=Meier |first4=D.M. |last5=von der Wense |first5=L. |last6=Seiferle |first6=B.

| last7=Düllmann |first7=C.E. |last8=Thirolf |first8=P.G. |last9=Peik |first9=E.

| title = Laser spectroscopic characterization of the nuclear-clock isomer ^229mTh

| journal = Nature

| volume = 556

| issue=7701 | year = 2018

| pages = 321–325

| doi = 10.1038/s41586-018-0011-8

|pmid=29670266 | arxiv=1709.05325

|bibcode=2018Natur.556..321T |s2cid=4990345 }} In this experiment, laser spectroscopy of the ²²⁹Th atomic shell was conducted using a ²²⁹Th²⁺ ion cloud with 2% of the ions in the nuclear excited state. This allowed probing for the hyperfine shift induced by the different nuclear spin states of the ground and the isomeric state. In this way, a first experimental value for the magnetic dipole and the electric quadrupole moment of ^229mTh could be inferred.

In 2019, the isomer's excitation energy was constrained to {{val|8.28|0.17|u=eV}} based on the direct detection of internal conversion electrons and a secure population of ^229mTh from the nuclear ground state was achieved by excitation of the {{val|29|u=keV}} nuclear excited state via synchrotron radiation.{{cite journal

| title = X-ray pumping of the ²²⁹Th nuclear clock isomer

| journal=Nature

| volume=573 | issue=7773 | pages=238–242

| date=12 September 2019

| first1=T. |last1=Masuda

| first2=A. |last2=Yoshimi

| first3=A. |last3=Fujieda

| first4=H. |last4=Fujimoto

| first5=H. |last5=Haba

| first6=H. |last6=Hara

| first7=T. |last7=Hiraki

| first8=H. |last8=Kaino

| first9=Y. |last9=Kasamatsu

| first10=S. |last10=Kitao

| first11=K. |last11=Konashi

| first12=Y. |last12= Miyamoto

| first13=K. |last13=Okai

| first14=S. |last14=Okubo

| first15=N. |last15=Sasao

| first16=M. |last16=Seto

| first17=T. |last17=Schumm

| first18=Y. |last18=Shigekawa

| first19=K. |last19=Suzuki

| first20=S. |last20=Stellmer

| first21=K. |last21=Tamasaku

| first22=S. |last22=Uetake

| first23=M. |last23=Watanabe

| first24=T. |last24=Watanabe

| first25=Y. |last25=Yasuda

| first26=A. |last26=Yamaguchi

| first27=Y. |last27=Yoda

| first28=T. |last28=Yokokita

| first29=M. |last29=Yoshimura

| first30=K. |last30=Yoshimura

| display-authors=6

| doi=10.1038/s41586-019-1542-3

| pmid=31511686

| arxiv=1902.04823

| bibcode=2019Natur.573..238M

| s2cid=119083861

}} Additional measurements by a different group in 2020 produced a figure of {{val|8.10|0.17|u=eV}} ({{val|153.1|3.2|u=nm}} wavelength).{{cite journal

|first1=Tomas |last1=Sikorsky |first2=Jeschua |last2=Geist |first3=Daniel |last3=Hengstler

|first4=Sebastian |last4=Kempf |first5=Loredana |last5=Gastaldo |first6=Christian |last6=Enss

|first7=Christoph |last7=Mokry |first8=Jörg |last8=Runke |first9=Christoph E. |last9=Düllmann

|first10=Peter |last10=Wobrauschek |first11=Kjeld |last11=Beeks |first12=Veronika |last12=Rosecker

|first13=Johannes H. |last13=Sterba |first14=Georgy |last14=Kazakov |first15=Thorsten |last15=Schumm

|first16=Andreas |last16=Fleischmann

|display-authors=6

|title=Measurement of the ²²⁹Th Isomer Energy with a Magnetic Microcalorimeter

|journal=Physical Review Letters

|volume=125 |issue=14 |article-number=142503 |date=2 October 2020

|page=

|doi=10.1103/PhysRevLett.125.142503 |pmid=33064540 |arxiv=2005.13340

|bibcode=2020PhRvL.125n2503S |s2cid=218900580

}} Combining these measurements, the expected transition energy is {{val|8.12|0.11|u=eV}}.{{cite news

|first=Lars |last=von der Wense

|title=Ticking Toward a Nuclear Clock

|journal=Physics |volume=13 |article-number=152 |date=28 September 2020

|url=https://physics.aps.org/articles/v13/152

}}

In September 2022, spectroscopy on decaying samples determined the excitation energy to be {{val|8.338|0.024|u=eV}}.{{Cite journal |last1=Kraemer |first1=Sandro |last2=Moens |first2=Janni |last3=Athanasakis-Kaklamanakis |first3=Michail |last4=Bara |first4=Silvia |last5=Beeks |first5=Kjeld |last6=Chhetri |first6=Premaditya |last7=Chrysalidis |first7=Katerina |last8=Claessens |first8=Arno |last9=Cocolios |first9=Thomas E. |last10=Correia |first10=João G. M. |last11=Witte |first11=Hilde De |last12=Ferrer |first12=Rafael |last13=Geldhof |first13=Sarina |last14=Heinke |first14=Reinhard |last15=Hosseini |first15=Niyusha |date=May 2023 |title=Observation of the radiative decay of the 229Th nuclear clock isomer |url=https://www.nature.com/articles/s41586-023-05894-z |journal=Nature |language=en |volume=617 |issue=7962 |pages=706–710 |doi=10.1038/s41586-023-05894-z |pmid=37225880 |bibcode=2023Natur.617..706K |issn=1476-4687|arxiv=2209.10276 }}

In April 2024, two separate groups finally reported precision laser excitation Th⁴⁺ cations doped into ionic crystals (of CaF₂ and LiSrAlF₆ with additional interstitial F⁻ anions for charge compensation), giving a precise (~1 part per million) measurement of the transition energy.{{cite journal

|title=Shedding Light on the Thorium-229 Nuclear Clock Isomer

|first=Peter |last=Thirolf

|date=April 29, 2024

|journal=Physics |volume=17 |article-number=71

|page=

|doi=10.1103/Physics.17.71

|url=https://physics.aps.org/articles/v17/71

}}{{cite press release

|title=Atomic Nucleus Excited with Laser: A Breakthrough after Decades

|date=29 April 2024

|publisher=TU Wien

|url=https://www.tuwien.at/en/tu-wien/news/news-articles/news/lange-erhoffter-durchbruch-erstmals-atomkern-mit-laser-angeregt

|access-date=29 April 2024

}}{{cite journal

|title=Laser Excitation of the Th-229 Nucleus

|first1=J. |last1=Tiedau |first2=M. V. |last2=Okhapkin |first3=K. |last3=Zhang

|first4=J. |last4=Thielking |first5=G. |last5=Zitzer |first6=E. |last6=Peik

|first7=F. |last7=Schaden |first8=T. |last8=Pronebner |first9=I. |last9=Morawetz

|first10=L. |last10=Toscani De Col |first11=F. |last11=Schneider |first12=A. |last12=Leitner

|first13=M. |last13=Pressler |first14=G.A. |last14=Kazakov |first15=K. |last15=Beeks

|first16=T. |last16=Sikorsky |first17=T. |last17=Schumm

|display-authors=6

|journal=Physical Review Letters |volume=132 |issue=18 |article-number=182501

|date=29 April 2024

|page=

|doi=10.1103/PhysRevLett.132.182501

|bibcode=2024PhRvL.132r2501T |url=https://www.tuwien.at/fileadmin/Assets/tu-wien/News/2024/Thorium_Preprint.pdf

|quote=The nuclear resonance for the Th⁴⁺ ions in Th:CaF₂ is measured at the wavelength {{val|148.3821|(5)|u=nm}}, frequency {{val|2020.409|(7)|u=THz}}, and the fluorescence lifetime in the crystal is {{val|630|(15)|u=s}}, corresponding to an isomer half-life of {{val|1740|(50)|u=s}} for a nucleus isolated in vacuum.

}}{{cite arXiv

|title=Laser excitation of the ²²⁹Th nuclear isomeric transition in a solid-state host

|first1=R. |last1=Elwell |first2=Christian |last2=Schneider |first3=Justin |last3=Jeet

|first4=J. E. S. |last4=Terhune |first5=H. W. T. |last5=Morgan |first6=A. N. |last6=Alexandrova

|first7=Hoang Bao |last7=Tran Tan |first8=Andrei |last8=Derevianko |first9=Eric R. |last9=Hudson

|eprint=2404.12311 |class=physics.atom-ph

|date=18 April 2024

|quote=a narrow, laser-linewidth-limited spectral feature at {{val|148.38219|(4)|errend=_stat(20)_sys|u=nm}} ({{val|2020407.3|(5)|errend=_stat(30)_sys|u=GHz}}) that decays with a lifetime of {{val|568|(13)|errend=_stat(20)_sys|u=s}}. This feature is assigned to the excitation of the ²²⁹Th nuclear isomeric state, whose energy is found to be {{val|8.355733|(2)|errend=_stat(10)_sys|u=eV}} in ²²⁹Th:LiSrAlF₆.

}} A one-part-per-trillion ({{val|e=-12}}) measurement soon followed in June 2024,{{cite news

| first=Joseph |last=Howlett

| title=The First Nuclear Clock Will Test if Fundamental Constants Change

| date=4 September 2024

| journal=Quanta Magazine

| url=https://www.quantamagazine.org/the-first-nuclear-clock-will-test-if-fundamental-constants-change-20240904/

}} and future high-precision lasers will measure the frequency up to the {{val|e=-18}} accuracy of the best atomic clocks.{{r|Zhang2024|Campbell2012|Thirolf2020}}

²³⁰Th is a radioactive isotope of thorium that can be used to date corals and determine ocean current flux. Ionium was a name given early in the study of radioactive elements to the ²³⁰Th isotope produced in the decay chain of ²³⁸U before it was realized that ionium and thorium are chemically identical. The symbol Io was used for this supposed element. (The name is still used in ionium–thorium dating.)

²³¹Th has 141 neutrons. It is the decay product of uranium-235. It is found in very small amounts on the earth and has a half-life of 25.5 hours.{{cite journal|first1=G. B.|last1=Knight|first2=R. L.|last2=Macklin|title=Radiations of Uranium Y|journal=Physical Review|date=1 January 1949|pages=34–38|volume=75|issue=1|doi=10.1103/PhysRev.75.34|bibcode=1949PhRv...75...34K}} When it decays, it emits a beta ray and forms protactinium-231. It has a decay energy of 0.39 MeV. It has a mass of 231.0363043 u.

{{main|Thorium-232}}

²³²Th is the only primordial nuclide of thorium and makes up effectively all of natural thorium, with other isotopes of thorium appearing only in trace amounts as relatively short-lived decay products of uranium and thorium.{{cite web |url=http://ie.lbl.gov/education/parent/Th_iso.htm |title=Isotopes of Thorium (Z=90) |work=Isotopes Project |publisher=Lawrence Berkeley National Laboratory |access-date=2010-01-18 |url-status=dead |archive-url=https://web.archive.org/web/20100203162843/http://ie.lbl.gov/education/parent/Th_iso.htm |archive-date=2010-02-03 }}

The isotope decays by alpha decay with a half-life of 1.405{{E|10}} years, over three times the age of the Earth and approximately the age of the universe.

Its decay chain is the thorium series, eventually ending in lead-208. The remainder of the chain is quick; the longest half-lives in it are 5.75 years for radium-228 and 1.91 years for thorium-228, with all other half-lives totaling less than 15 days.{{cite web |url=http://hepwww.rl.ac.uk/ukdmc/Radioactivity/Th_chain/Th_chain.html |title=Th-232 Decay Chain |author=Rutherford Appleton Laboratory |access-date=2010-01-25 |author-link=Rutherford Appleton Laboratory |archive-url=https://web.archive.org/web/20120319190834/http://hepwww.rl.ac.uk/ukdmc/Radioactivity/Th_chain/Th_chain.html |archive-date=2012-03-19 |url-status=dead }}

²³²Th is a fertile material able to absorb a neutron and undergo transmutation into the fissile nuclide uranium-233, which is the basis of the thorium fuel cycle.{{cite web |url=http://www.world-nuclear.org/info/inf62.html |title=Thorium |author=World Nuclear Association |access-date=2010-01-25 |author-link=World Nuclear Association |archive-date=2013-02-16 |archive-url=https://web.archive.org/web/20130216102005/http://www.world-nuclear.org/info/inf62.html |url-status=dead }}

In the form of Thorotrast, a thorium dioxide suspension, it was used as a contrast medium in early X-ray diagnostics. Thorium-232 is now classified as carcinogenic.{{cite journal |last1= Krasinskas |first1= Alyssa M |last2= Minda |first2= Justina |last3= Saul |first3= Scott H |last4= Shaked |first4= Abraham |last5= Furth |first5= Emma E |title=Redistribution of thorotrast into a liver allograft several years following transplantation: a case report |journal= Mod. Pathol. |volume= 17 |pages= 117–120 |year= 2004 |doi= 10.1038/modpathol.3800008 |pmid=14631374 |issue=1|doi-access= free }}

²³³Th is an isotope of thorium that decays into protactinium-233 through beta decay. It has a half-life of 21.83 minutes.{{NUBASE2020|ref}} Traces occur in nature as the result of natural neutron activation of ²³²Th.{{cite journal |last1=Peppard |first1=D. F. |last2=Mason |first2=G. W. |last3=Gray |first3=P. R. |last4=Mech |first4=J. F. |title=Occurrence of the (4n + 1) series in nature |journal=Journal of the American Chemical Society |date=1952 |volume=74 |issue=23 |pages=6081–6084 |doi=10.1021/ja01143a074 |url=https://digital.library.unt.edu/ark:/67531/metadc172698/m2/1/high_res_d/metadc172698.pdf |archive-url=https://web.archive.org/web/20190429182951/https://digital.library.unt.edu/ark:/67531/metadc172698/m2/1/high_res_d/metadc172698.pdf |archive-date=2019-04-29 |url-status=live }}

²³⁴Th is an isotope of thorium whose nuclei contain 144 neutrons. ²³⁴Th has a half-life of 24.1 days, and when it decays, it emits a beta particle, and in doing so, it transmutes into protactinium-234. ²³⁴Th has a mass of 234.0436 atomic mass units, and it has a decay energy of about 270 keV. Uranium-238 usually decays into this isotope of thorium (although in rare cases it can undergo spontaneous fission instead).

{{Reflist}}

• Isotope masses from:
• {{NUBASE 2003}}
• Isotopic compositions and standard atomic masses from:
• {{CIAAW2003}}
• {{CIAAW 2005}}
• Half-life, spin, and isomer data selected from the following sources.
• {{cite journal |author=G. Audi |author2=A. H. Wapstra |author3=C. Thibault |author4=J. Blachot |author5=O. Bersillon |year=2003 |title=The NUBASE evaluation of nuclear and decay properties |url=http://amdc.in2p3.fr/nubase/Nubase2003.pdf |journal=Nuclear Physics A |volume=729 |issue=1 |pages=3–128 |doi=10.1016/j.nuclphysa.2003.11.001 |bibcode=2003NuPhA.729....3A |url-status=dead |archive-url=https://web.archive.org/web/20110720233206/http://amdc.in2p3.fr/nubase/Nubase2003.pdf |archive-date=2011-07-20 }}
• {{NNDC}}
• {{CRC85|chapter=11}}

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Category:Thorium

Thorium