Lanthanum-129

Properties and data of the isotope ¹²⁹La.

Content

General data

Name of the isotope:Lanthanum-129; La-129Symbol:¹²⁹La or 12957LaMass number A:129 (= number of nucleons)Atomic number Z:57 (= number of protons)Neutrons N:72Isotopic mass:128.912694(23) u (atomic weight of Lanthanum-129)Nuclide mass:128.8814271 u (calculated nuclear mass without electrons)Mass excess:-81.32502 MeVMass defect:1.157206776 u (per nucleus)Nuclear binding energy:1077.9311686 MeV (per nucleus)
8.35605557 MeV (average binding energy per nucleon)Separation energy:S_N = 10.77(6) MeV (first neutron)
S_P = 3.235(22) MeV (first proton)Half-life:11.6(2) minDecay constant λ:0.00099590112149417 s^-1Specific activity α:4.685513153286 × 10⁺¹⁸ Bq g^-1
126635490.62937 Ci g^-1Spin and parity:
(nuclear angular momentum)(3/2+)Year of discovery:1963

Radioactive Decay

Half-life T_½ = 11.6(2) min (minutes) respectively 6.96 × 10² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β⁺	¹²⁹Ba	100 %	3.739(24) MeV

Parent Nuclides

Direct parent isotope is: ¹²⁹Ce.

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
^129mLa	172.33(20) keV	0.56(5) s	(11/2-)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 72) and isobaric (same nucleon number A = 129) with Lanthanum-129. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 72	Isobar A = 129
40	¹¹²Zr
41	¹¹³Nb
42	¹¹⁴Mo
43	¹¹⁵Tc
44	¹¹⁶Ru
45	¹¹⁷Rh
46	¹¹⁸Pd	¹²⁹Pd
47	¹¹⁹Ag	¹²⁹Ag
48	¹²⁰Cd	¹²⁹Cd
49	¹²¹In	¹²⁹In
50	¹²²Sn	¹²⁹Sn
51	¹²³Sb	¹²⁹Sb
52	¹²⁴Te	¹²⁹Te
53	¹²⁵I	¹²⁹I
54	¹²⁶Xe	¹²⁹Xe
55	¹²⁷Cs	¹²⁹Cs
56	¹²⁸Ba	¹²⁹Ba
57	¹²⁹La	¹²⁹La
58	¹³⁰Ce	¹²⁹Ce
59	¹³¹Pr	¹²⁹Pr
60	¹³²Nd	¹²⁹Nd
61	¹³³Pm	¹²⁹Pm
62	¹³⁴Sm	¹²⁹Sm
63	¹³⁵Eu
64	¹³⁶Gd
65	¹³⁷Tb
66	¹³⁸Dy