Xenon-129m

Properties and data of the isotope ¹²⁹Xe.

Content

General data

Name of the isotope:Xenon-129m; Xe-129mSymbol:¹²⁹Xe or 12954XeMass number A:129 (= number of nucleons)Atomic number Z:54 (= number of protons)Neutrons N:75Isotopic mass:128.90478086(4) u (atomic weight of Xenon-129m)
Excitation energy: 236.14(3) keVNuclide mass:128.8751595 u (calculated nuclear mass without electrons)Mass excess:-88.69606 MeVMass defect:1.167639568 u (per nucleus)Nuclear binding energy:1087.64925175 MeV (per nucleus)
8.43138955 MeV (average binding energy per nucleon)Half-life:8.88(2) dDecay constant λ:9.034388301842 × 10^-7 s^-1Specific activity α:4.25049679195 × 10⁺¹⁵ Bq g^-1
114878.29167454 Ci g^-1Spin and parity:
(nuclear angular momentum)11/2-Magnetic dipole moment:μ(μ_N) = -0.891170(10)Quadrupole moment Q:+0.63(2) barn (100 fm²)Nuclear g-factor:g_l = -0.16203090909091

Radioactive Decay

Half-life T_½ = 8.88(2) d respectively 7.67232 × 10⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	¹²⁹Xe	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
¹²⁹Xe		stable	1/2+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 75) and isobaric (same nucleon number A = 129) with Xenon-129m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 75	Isobar A = 129
42	¹¹⁷Mo
43	¹¹⁸Tc
44	¹¹⁹Ru
45	¹²⁰Rh
46	¹²¹Pd	¹²⁹Pd
47	¹²²Ag	¹²⁹Ag
48	¹²³Cd	¹²⁹Cd
49	¹²⁴In	¹²⁹In
50	¹²⁵Sn	¹²⁹Sn
51	¹²⁶Sb	¹²⁹Sb
52	¹²⁷Te	¹²⁹Te
53	¹²⁸I	¹²⁹I
54	¹²⁹Xe	¹²⁹Xe
55	¹³⁰Cs	¹²⁹Cs
56	¹³¹Ba	¹²⁹Ba
57	¹³²La	¹²⁹La
58	¹³³Ce	¹²⁹Ce
59	¹³⁴Pr	¹²⁹Pr
60	¹³⁵Nd	¹²⁹Nd
61	¹³⁶Pm	¹²⁹Pm
62	¹³⁷Sm	¹²⁹Sm
63	¹³⁸Eu
64	¹³⁹Gd
65	¹⁴⁰Tb
66	¹⁴¹Dy
67	¹⁴²Ho
68	¹⁴³Er
69	¹⁴⁴Tm