Lanthanum-126m

Properties and data of the isotope ¹²⁶La.

Content

General data

Name of the isotope:Lanthanum-126m; La-126mSymbol:¹²⁶La or 12657LaMass number A:126 (= number of nucleons)Atomic number Z:57 (= number of protons)Neutrons N:69Isotopic mass:125.91951(10) u (atomic weight of Lanthanum-126m)
Excitation energy: +z keVNuclide mass:125.8882431 u (calculated nuclear mass without electrons)Mass excess:-74.97595 MeVMass defect:1.124396028 u (per nucleus)Nuclear binding energy:1047.36815371 MeV (per nucleus)
8.31244566 MeV (average binding energy per nucleon)Half-life:50 sDecay constant λ:0.013862943611199 s^-1Specific activity α:6.678767932 × 10⁺¹⁹ Bq g^-1
1805072414.2703 Ci g^-1Spin and parity:
(nuclear angular momentum)

Radioactive Decay

Half-life T_½ = 50 s respectively 5 × 10¹ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EE/β⁺	¹²⁶Ba	?
Iso	¹²⁶La	?

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
¹²⁶La		54(2) s	(5+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 69) and isobaric (same nucleon number A = 126) with Lanthanum-126m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 69	Isobar A = 126
38	¹⁰⁷Sr
39	¹⁰⁸Y
40	¹⁰⁹Zr
41	¹¹⁰Nb
42	¹¹¹Mo
43	¹¹²Tc
44	¹¹³Ru
45	¹¹⁴Rh	¹²⁶Rh
46	¹¹⁵Pd	¹²⁶Pd
47	¹¹⁶Ag	¹²⁶Ag
48	¹¹⁷Cd	¹²⁶Cd
49	¹¹⁸In	¹²⁶In
50	¹¹⁹Sn	¹²⁶Sn
51	¹²⁰Sb	¹²⁶Sb
52	¹²¹Te	¹²⁶Te
53	¹²²I	¹²⁶I
54	¹²³Xe	¹²⁶Xe
55	¹²⁴Cs	¹²⁶Cs
56	¹²⁵Ba	¹²⁶Ba
57	¹²⁶La	¹²⁶La
58	¹²⁷Ce	¹²⁶Ce
59	¹²⁸Pr	¹²⁶Pr
60	¹²⁹Nd	¹²⁶Nd
61	¹³⁰Pm	¹²⁶Pm
62	¹³¹Sm
63	¹³²Eu