Lanthanum-121

Properties and data of the isotope ¹²¹La.

Contents

General data

Name of the isotope:Lanthanum-121; La-121Symbol:¹²¹La or 12157LaMass number A:121 (= number of nucleons)Atomic number Z:57 (= number of protons)Neutrons N:64Isotopic mass:120.93324(32) u (atomic weight of Lanthanum-121)Nuclide mass:120.9019731 u (calculated nuclear mass without electrons)Mass excess:-62.18654 MeVMass defect:1.067341448 u (per nucleus)Nuclear binding energy:994.22215476 MeV (per nucleus)
8.21671202 MeV (average binding energy per nucleon)Separation energy:S_N = 12.69(42) MeV (first neutron)
S_P = 0.59(42) MeV (first proton)Half-life:5.3(2) sDecay constant λ:0.1307824868981 s^-1Specific activity α:6.563254650943 × 10⁺²⁰ Bq g^-1
17738526083.631 Ci g^-1Spin and parity:
(nuclear angular momentum)(11/2-)Year of discovery:1988

Radioactive Decay

Half-life T_½ = 5.3(2) s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β⁺	¹²¹Ba	100 %	8.55(33) MeV

Parent Nuclides

Direct parent isotope is: ¹²¹Ce.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 64) and isobaric (same nucleon number A = 121) with Lanthanum-121. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 64	Isobar A = 121
36	¹⁰⁰Kr
37	¹⁰¹Rb
38	¹⁰²Sr
39	¹⁰³Y
40	¹⁰⁴Zr
41	¹⁰⁵Nb
42	¹⁰⁶Mo
43	¹⁰⁷Tc	¹²¹Tc
44	¹⁰⁸Ru	¹²¹Ru
45	¹⁰⁹Rh	¹²¹Rh
46	¹¹⁰Pd	¹²¹Pd
47	¹¹¹Ag	¹²¹Ag
48	¹¹²Cd	¹²¹Cd
49	¹¹³In	¹²¹In
50	¹¹⁴Sn	¹²¹Sn
51	¹¹⁵Sb	¹²¹Sb
52	¹¹⁶Te	¹²¹Te
53	¹¹⁷I	¹²¹I
54	¹¹⁸Xe	¹²¹Xe
55	¹¹⁹Cs	¹²¹Cs
56	¹²⁰Ba	¹²¹Ba
57	¹²¹La	¹²¹La
58	¹²²Ce	¹²¹Ce
59	¹²³Pr	¹²¹Pr
60	¹²⁴Nd