Lanthanum-128

Properties and data of the isotope ¹²⁸La.

Contents

General data

Name of the isotope:Lanthanum-128; La-128Symbol:¹²⁸La or 12857LaMass number A:128 (= number of nucleons)Atomic number Z:57 (= number of protons)Neutrons N:71Isotopic mass:127.91559(6) u (atomic weight of Lanthanum-128)Nuclide mass:127.8843231 u (calculated nuclear mass without electrons)Mass excess:-78.62741 MeVMass defect:1.14564586 u (per nucleus)Nuclear binding energy:1067.16224471 MeV (per nucleus)
8.33720504 MeV (average binding energy per nucleon)Separation energy:S_N = 8.80(6) MeV (first neutron)
S_P = 3.10(6) MeV (first proton)Half-life:5.18(14) minDecay constant λ:0.0022302032836549 s^-1Specific activity α:1.057527426808 × 10⁺¹⁹ Bq g^-1
285818223.46165 Ci g^-1Spin and parity:
(nuclear angular momentum)(5+)Year of discovery:1961

Radioactive Decay

Half-life T_½ = 5.18(14) min (minutes) respectively 3.108 × 10² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EC/β⁺	¹²⁸Ba	100 %	6.75(5) MeV

Parent Nuclides

Direct parent isotope is: ¹²⁸Ce.

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
^128mLa	~ 100 keV	1.4 min	(1+,2-)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 71) and isobaric (same nucleon number A = 128) with Lanthanum-128. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 71	Isobar A = 128
40	¹¹¹Zr
41	¹¹²Nb
42	¹¹³Mo
43	¹¹⁴Tc
44	¹¹⁵Ru
45	¹¹⁶Rh
46	¹¹⁷Pd	¹²⁸Pd
47	¹¹⁸Ag	¹²⁸Ag
48	¹¹⁹Cd	¹²⁸Cd
49	¹²⁰In	¹²⁸In
50	¹²¹Sn	¹²⁸Sn
51	¹²²Sb	¹²⁸Sb
52	¹²³Te	¹²⁸Te
53	¹²⁴I	¹²⁸I
54	¹²⁵Xe	¹²⁸Xe
55	¹²⁶Cs	¹²⁸Cs
56	¹²⁷Ba	¹²⁸Ba
57	¹²⁸La	¹²⁸La
58	¹²⁹Ce	¹²⁸Ce
59	¹³⁰Pr	¹²⁸Pr
60	¹³¹Nd	¹²⁸Nd
61	¹³²Pm	¹²⁸Pm
62	¹³³Sm	¹²⁸Sm
63	¹³⁴Eu
64	¹³⁵Gd
65	¹³⁶Tb