Samarium-156

Properties and data of the isotope ¹⁵⁶Sm.

Content

General data

Name of the isotope:Samarium-156; Sm-156Symbol:¹⁵⁶Sm or 15662SmMass number A:156 (= number of nucleons)Atomic number Z:62 (= number of protons)Neutrons N:94Isotopic mass:155.925539(9) u (atomic weight of Samarium-156)Nuclide mass:155.8915297 u (calculated nuclear mass without electrons)Mass excess:-69.35997 MeVMass defect:1.374115088 u (per nucleus)Nuclear binding energy:1279.97995978 MeV (per nucleus)
8.20499974 MeV (average binding energy per nucleon)Separation energy:S_N = 7.241(8) MeV (first neutron)
S_P = 9.709(10) MeV (first proton)Half-life:9.4(2) hDecay constant λ:2.048307271158 × 10^-5 s^-1Specific activity α:7.958190265385 × 10⁺¹⁶ Bq g^-1
2150862.233888 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Year of discovery:1951

Radioactive Decay

Half-life T_½ = 9.4(2) h (hours) respectively 3.3840 × 10⁴ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	¹⁵⁶Eu	100 %	0.722(8) MeV

Parent Nuclides

Direct parent isotope is: ¹⁵⁶Pm.

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^156mSm	1397.55(9) keV	185(7) ns	5-

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 94) and isobaric (same nucleon number A = 156) with Samarium-156. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 94	Isobar A = 156
54	¹⁴⁸Xe
55	¹⁴⁹Cs
56	¹⁵⁰Ba
57	¹⁵¹La	¹⁵⁶La
58	¹⁵²Ce	¹⁵⁶Ce
59	¹⁵³Pr	¹⁵⁶Pr
60	¹⁵⁴Nd	¹⁵⁶Nd
61	¹⁵⁵Pm	¹⁵⁶Pm
62	¹⁵⁶Sm	¹⁵⁶Sm
63	¹⁵⁷Eu	¹⁵⁶Eu
64	¹⁵⁸Gd	¹⁵⁶Gd
65	¹⁵⁹Tb	¹⁵⁶Tb
66	¹⁶⁰Dy	¹⁵⁶Dy
67	¹⁶¹Ho	¹⁵⁶Ho
68	¹⁶²Er	¹⁵⁶Er
69	¹⁶³Tm	¹⁵⁶Tm
70	¹⁶⁴Yb	¹⁵⁶Yb
71	¹⁶⁵Lu	¹⁵⁶Lu
72	¹⁶⁶Hf	¹⁵⁶Hf
73	¹⁶⁷Ta	¹⁵⁶Ta
74	¹⁶⁸W	¹⁵⁶W
75	¹⁶⁹Re
76	¹⁷⁰Os
77	¹⁷¹Ir
78	¹⁷²Pt
79	¹⁷³Au
80	¹⁷⁴Hg