Lanthanum-138m

Properties and data of the isotope ¹³⁸La.

Content

General data

Name of the isotope:Lanthanum-138m; La-138mSymbol:¹³⁸La or 13857LaMass number A:138 (= number of nucleons)Atomic number Z:57 (= number of protons)Neutrons N:81Isotopic mass:137.907118(3) u (atomic weight of Lanthanum-138m)
Excitation energy: 72.57(3) keVNuclide mass:137.8758511 u (calculated nuclear mass without electrons)Mass excess:-86.51903 MeVMass defect:1.24076702 u (per nucleus)Nuclear binding energy:1155.76703453 MeV (per nucleus)
8.37512344 MeV (average binding energy per nucleon)Half-life:116(5) nsDecay constant λ:5975406.728965 s^-1Specific activity α:2.626623431915 × 10⁺²⁸ Bq g^-1
7.0989822484 × 10⁺¹⁷ Ci g^-1Spin and parity:
(nuclear angular momentum)(3)+Magnetic dipole moment:μ(μ_N) = +2.89(5)Nuclear g-factor:g_l = 0.96333333333333

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
¹³⁸La		1.02(1) × 10¹¹ a	5+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 81) and isobaric (same nucleon number A = 138) with Lanthanum-138m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 81	Isobar A = 138
45	¹²⁶Rh
46	¹²⁷Pd
47	¹²⁸Ag
48	¹²⁹Cd
49	¹³⁰In
50	¹³¹Sn	¹³⁸Sn
51	¹³²Sb	¹³⁸Sb
52	¹³³Te	¹³⁸Te
53	¹³⁴I	¹³⁸I
54	¹³⁵Xe	¹³⁸Xe
55	¹³⁶Cs	¹³⁸Cs
56	¹³⁷Ba	¹³⁸Ba
57	¹³⁸La	¹³⁸La
58	¹³⁹Ce	¹³⁸Ce
59	¹⁴⁰Pr	¹³⁸Pr
60	¹⁴¹Nd	¹³⁸Nd
61	¹⁴²Pm	¹³⁸Pm
62	¹⁴³Sm	¹³⁸Sm
63	¹⁴⁴Eu	¹³⁸Eu
64	¹⁴⁵Gd	¹³⁸Gd
65	¹⁴⁶Tb	¹³⁸Tb
66	¹⁴⁷Dy	¹³⁸Dy
67	¹⁴⁸Ho
68	¹⁴⁹Er
69	¹⁵⁰Tm
70	¹⁵¹Yb
71	¹⁵²Lu
72	¹⁵³Hf