Samarium-129

Properties and data of the isotope ¹²⁹Sm.

Content

General data

Name of the isotope:Samarium-129; Sm-129Symbol:¹²⁹Sm or 12962SmMass number A:129 (= number of nucleons)Atomic number Z:62 (= number of protons)Neutrons N:67Isotopic mass:128.95491(54) u (atomic weight of Samarium-129)Nuclide mass:128.9209007 u (calculated nuclear mass without electrons)Mass excess:-42.00106 MeVMass defect:1.110791356 u (per nucleus)Nuclear binding energy:1034.69548337 MeV (per nucleus)
8.02089522 MeV (average binding energy per nucleon)Separation energy:S_N = 11.40(71) MeV (first neutron)
S_P = 1.50(58) MeV (first proton)Half-life:0.55(10) sDecay constant λ:1.2602676010181 s^-1Specific activity α:5.929303917613 × 10⁺²¹ Bq g^-1
160251457232.8 Ci g^-1Spin and parity:
(nuclear angular momentum)(1/2+.3/2+)Year of discovery:1999

Radioactive Decay

Half-life T_½ = 0.55(10) s respectively 5.5 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EE/β⁺	¹²⁹Pm	< 100 %	10.88(58) MeV
EE, p	¹²⁸Nd	> 0 %

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 67) and isobaric (same nucleon number A = 129) with Samarium-129. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 67	Isobar A = 129
38	¹⁰⁵Sr
39	¹⁰⁶Y
40	¹⁰⁷Zr
41	¹⁰⁸Nb
42	¹⁰⁹Mo
43	¹¹⁰Tc
44	¹¹¹Ru
45	¹¹²Rh
46	¹¹³Pd	¹²⁹Pd
47	¹¹⁴Ag	¹²⁹Ag
48	¹¹⁵Cd	¹²⁹Cd
49	¹¹⁶In	¹²⁹In
50	¹¹⁷Sn	¹²⁹Sn
51	¹¹⁸Sb	¹²⁹Sb
52	¹¹⁹Te	¹²⁹Te
53	¹²⁰I	¹²⁹I
54	¹²¹Xe	¹²⁹Xe
55	¹²²Cs	¹²⁹Cs
56	¹²³Ba	¹²⁹Ba
57	¹²⁴La	¹²⁹La
58	¹²⁵Ce	¹²⁹Ce
59	¹²⁶Pr	¹²⁹Pr
60	¹²⁷Nd	¹²⁹Nd
61	¹²⁸Pm	¹²⁹Pm
62	¹²⁹Sm	¹²⁹Sm
63	¹³⁰Eu