Samarium-138

Properties and data of the isotope ¹³⁸Sm.

Content

General data

Name of the isotope:Samarium-138; Sm-138Symbol:¹³⁸Sm or 13862SmMass number A:138 (= number of nucleons)Atomic number Z:62 (= number of protons)Neutrons N:76Isotopic mass:137.923244(13) u (atomic weight of Samarium-138)Nuclide mass:137.8892347 u (calculated nuclear mass without electrons)Mass excess:-71.49775 MeVMass defect:1.2204416 u (per nucleus)Nuclear binding energy:1136.83402775 MeV (per nucleus)
8.23792774 MeV (average binding energy per nucleon)Separation energy:S_N = 11.54(4) MeV (first neutron)
S_P = 4.714(18) MeV (first proton)Half-life:3.1(2) minDecay constant λ:0.0037265977449459 s^-1Specific activity α:1.638109237108 × 10⁺¹⁹ Bq g^-1
442732226.24554 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Charge radius:4.9599(34) femtometer fmYear of discovery:1982

Radioactive Decay

Half-life T_½ = 3.1(2) min (minutes) respectively 1.86 × 10² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EE/β⁺	¹³⁸Pm	100 %	3.44(3) MeV

Parent Nuclides

Direct parent isotope is: ¹³⁸Eu.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 76) and isobaric (same nucleon number A = 138) with Samarium-138. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 76	Isobar A = 138
42	¹¹⁸Mo
43	¹¹⁹Tc
44	¹²⁰Ru
45	¹²¹Rh
46	¹²²Pd
47	¹²³Ag
48	¹²⁴Cd
49	¹²⁵In
50	¹²⁶Sn	¹³⁸Sn
51	¹²⁷Sb	¹³⁸Sb
52	¹²⁸Te	¹³⁸Te
53	¹²⁹I	¹³⁸I
54	¹³⁰Xe	¹³⁸Xe
55	¹³¹Cs	¹³⁸Cs
56	¹³²Ba	¹³⁸Ba
57	¹³³La	¹³⁸La
58	¹³⁴Ce	¹³⁸Ce
59	¹³⁵Pr	¹³⁸Pr
60	¹³⁶Nd	¹³⁸Nd
61	¹³⁷Pm	¹³⁸Pm
62	¹³⁸Sm	¹³⁸Sm
63	¹³⁹Eu	¹³⁸Eu
64	¹⁴⁰Gd	¹³⁸Gd
65	¹⁴¹Tb	¹³⁸Tb
66	¹⁴²Dy	¹³⁸Dy
67	¹⁴³Ho
68	¹⁴⁴Er
69	¹⁴⁵Tm