Samarium-146

Properties and data of the isotope ¹⁴⁶Sm.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Samarium-146 is a weakly radioactive isotope of the chemical element samarium, which has 84 neutrons in its atomic nucleus in addition to the element-specific 62 protons, resulting in a mass number of 146.

The radioisotope that emits α particles has no practical significance in a technical sense.

The natural isotope ratio of samarium-146 to Neodymium-142 (¹⁴²Nd is the stable decay product of ¹⁴⁶Sm and accumulates over time in corresponding samples) is occasionally used to determine the age (isotope chronometer) of geochemical processes and extraterrestrial samples (meteorites, moon rocks, etc.).

General data

Name of the isotope:Samarium-146; Sm-146Symbol:¹⁴⁶Sm or 14662SmMass number A:146 (= number of nucleons)Atomic number Z:62 (= number of protons)Neutrons N:84Isotopic mass:145.913047(3) u (atomic weight of Samarium-146)Nuclide mass:145.8790377 u (calculated nuclear mass without electrons)Mass excess:-80.9962 MeVMass defect:1.299957928 u (per nucleus)Nuclear binding energy:1210.90301018 MeV (per nucleus)
8.29385623 MeV (average binding energy per nucleon)Separation energy:S_N = 8.4163(29) MeV (first neutron)
S_P = 7.018(4) MeV (first proton)Half-life:9.20 (26) × 10⁷ aDecay constant λ:2.389081838009 × 10^-16 s^-1Specific activity α:992233.61064901 Bq g^-1
2.681712461213 × 10^-5 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Charge radius:4.9808(35) femtometer fmYear of discovery:1953

Radioactive Decay

Samarium-146 is a pure alpha emitter: During radioactive decay, the nuclide emits exclusively Helium-4 particles (α particles, ⁴He).

Here you will find a value for the half-life of ¹⁴⁶Sm published in 2024 with an uncertainty factor k = 1, which has not yet been verified by other working groups [3]. So far, various other data with an uncertainty factor of k = 2 have been used: 6.8(7) × 10⁷ a (withdrawn in 2012 [1]) and 103(4) × 10⁷ a. The IUPAC/IUGS recommends the use of double calculation series for radiometric dating [2].

Half-life T_½ = 9.20 (26) × 10⁷ a respectively 2.901312 × 10¹⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	¹⁴²Nd	100 %	2.5288(28) MeV

The parent nuclides and the radioactive decay of Samarium-146.

Parent Nuclides

Direct parent isotopes are: ¹⁴⁶Eu, ¹⁴⁶Pm, ¹⁵⁰Gd.

Occurrence

Comparison of the natural Samarium isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Samarium Isotopic mixture	150.36 u	100 %
Isotope ¹⁴⁴Sm	143.91201(2) u	3.08(4) %	stable	0+
Isotope ¹⁴⁸Sm	147.91483(2) u	11.25(9) %	7(3)×10¹⁵ a	0+
Isotope ¹⁴⁹Sm	148.91719(2) u	13.82(10) %	stable	7/2-
Isotope ¹⁵⁰Sm	149.91728(2) u	7.37(9) %	stable	0+
Isotope ¹⁵²Sm	151.91974(2) u	26.74(9) %	stable	0+
Isotope ¹⁵⁴Sm	153.92222(2) u	22.74(14) %	stable	0+
Isotope ¹⁴⁷Sm	146.91490(2) u	15.00(14) %	1.0625(38) × 10¹¹ a	7/2-
Isotope ¹⁴⁶Sm	145.913047(3) u	[trace]	9.20 (26) × 10⁷ a	0+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 84) and isobaric (same nucleon number A = 146) with Samarium-146. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 84	Isobar A = 146
47	¹³¹Ag
48	¹³²Cd
49	¹³³In
50	¹³⁴Sn
51	¹³⁵Sb
52	¹³⁶Te
53	¹³⁷I
54	¹³⁸Xe	¹⁴⁶Xe
55	¹³⁹Cs	¹⁴⁶Cs
56	¹⁴⁰Ba	¹⁴⁶Ba
57	¹⁴¹La	¹⁴⁶La
58	¹⁴²Ce	¹⁴⁶Ce
59	¹⁴³Pr	¹⁴⁶Pr
60	¹⁴⁴Nd	¹⁴⁶Nd
61	¹⁴⁵Pm	¹⁴⁶Pm
62	¹⁴⁶Sm	¹⁴⁶Sm
63	¹⁴⁷Eu	¹⁴⁶Eu
64	¹⁴⁸Gd	¹⁴⁶Gd
65	¹⁴⁹Tb	¹⁴⁶Tb
66	¹⁵⁰Dy	¹⁴⁶Dy
67	¹⁵¹Ho	¹⁴⁶Ho
68	¹⁵²Er	¹⁴⁶Er
69	¹⁵³Tm	¹⁴⁶Tm
70	¹⁵⁴Yb
71	¹⁵⁵Lu
72	¹⁵⁶Hf
73	¹⁵⁷Ta
74	¹⁵⁸W
75	¹⁵⁹Re
76	¹⁶⁰Os

External data and identifiers

CAS:14280-31-0InChI Code:KZUNJOHGWZRPMI-AHCXROLUSA-NSMILES:[146Sm]PubChem:ID 44154635Adopted Levels, Gammas:NuDat 146Sm

Literature and References

[1] - N. Kinoshita et al:
RETRACTED: A Shorter ¹⁴⁶Sm Half-Life Measured and Implications for ¹⁴⁶Sm-¹⁴²Nd Chronology in the Solar System.
In: Science, (2012), DOI 10.1126/science.1215510.

[2] - I. M. Villa, N. E. Holden, A. Possolo, R. B. Ickert, D. B. Hibbert, P. R. Renne:
IUPAC-IUGS recommendation on the half-lives of ¹⁴⁷Sm and ¹⁴⁶Sm.
In: Geochimica et Cosmochimica Acta, 285, 70-77, (2020), DOI 10.1016/j.gca.2020.06.022.

[3] - Nadine M. Chiera, Peter Sprung, Yuri Amelin, Rugard Dressler, Dorothea Schumann, Zeynep Talip:
The ¹⁴⁶Sm half-life re-measured: consolidating the chronometer for events in the early Solar System.
In: Scientific Reports, 14, 17436, (2024), DOI 10.1038/s41598-024-64104-6.