Lanthanum-129m

Properties and data of the isotope ¹²⁹La.

Content

General data

Name of the isotope:Lanthanum-129m; La-129mSymbol: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-129m)
Excitation energy: 172.33(20) keVNuclide 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)Half-life:0.56(5) sDecay constant λ:1.2377628224285 s^-1Specific activity α:5.823423490513 × 10⁺²¹ Bq g^-1
157389824067.93 Ci g^-1Spin and parity:
(nuclear angular momentum)(11/2-)

Radioactive Decay

Half-life T_½ = 0.56(5) s respectively 5.6 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	¹²⁹La	100 %

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
¹²⁹La		11.6(2) min	(3/2+)

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-129m. 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