Lanthanum-123

Properties and data of the isotope ¹²³La.

Content

General data

Name of the isotope:Lanthanum-123; La-123Symbol:¹²³La or 12357LaMass number A:123 (= number of nucleons)Atomic number Z:57 (= number of protons)Neutrons N:66Isotopic mass:122.92630(21) u (atomic weight of Lanthanum-123)Nuclide mass:122.8950331 u (calculated nuclear mass without electrons)Mass excess:-68.65111 MeVMass defect:1.09161128 u (per nucleus)Nuclear binding energy:1016.82935765 MeV (per nucleus)
8.26690535 MeV (average binding energy per nucleon)Separation energy:S_N = 12.18(36) MeV (first neutron)
S_P = 1.33(20) MeV (first proton)Half-life:17(3) sDecay constant λ:0.04077336356235 s^-1Specific activity α:2.012647038572 × 10⁺²⁰ Bq g^-1
5439586590.7373 Ci g^-1Spin and parity:
(nuclear angular momentum)(11/2-)Year of discovery:1978

Radioactive Decay

Half-life T_½ = 17(3) s respectively 1.7 × 10¹ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EE/β⁺	¹²³Ba	100 %	7.00(20) MeV

Parent Nuclides

Direct parent isotope is: ¹²³Ce.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 66) and isobaric (same nucleon number A = 123) with Lanthanum-123. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 66	Isobar A = 123
37	¹⁰³Rb
38	¹⁰⁴Sr
39	¹⁰⁵Y
40	¹⁰⁶Zr
41	¹⁰⁷Nb
42	¹⁰⁸Mo
43	¹⁰⁹Tc
44	¹¹⁰Ru	¹²³Ru
45	¹¹¹Rh	¹²³Rh
46	¹¹²Pd	¹²³Pd
47	¹¹³Ag	¹²³Ag
48	¹¹⁴Cd	¹²³Cd
49	¹¹⁵In	¹²³In
50	¹¹⁶Sn	¹²³Sn
51	¹¹⁷Sb	¹²³Sb
52	¹¹⁸Te	¹²³Te
53	¹¹⁹I	¹²³I
54	¹²⁰Xe	¹²³Xe
55	¹²¹Cs	¹²³Cs
56	¹²²Ba	¹²³Ba
57	¹²³La	¹²³La
58	¹²⁴Ce	¹²³Ce
59	¹²⁵Pr	¹²³Pr
60	¹²⁶Nd
61	¹²⁷Pm
62	¹²⁸Sm