Cerium-138m

Properties and data of the isotope ^138mCe.

Contents

Cer-138m is a nuclear isomeric state of the isotope cerium-138 with an excitation energy of 2129.28 keV, a spin/parity of 7⁻, and a half-life of 8.73 ms. It was first described around 1960 (presumably in connection with investigations of highly excited states in light rare earth elements). This state decays via an isomeric transition (IT) to the ground state of ¹³⁸Ce.

See also: List of individual Cerium isotopes (and general data sources).

General data

Name of the isotope:Cerium-138m; Ce-138mSymbol:^138mCe or 138m58CeMass number A:138 (= number of nucleons)Atomic number Z:58 (= number of protons)Neutrons N:80Isotopic mass:137.90599(7) u (atomic weight of Cerium-138m)
Excitation energy: 2129.28(12) keVNuclide mass:137.8741746 u (calculated nuclear mass without electrons)Mass excess:-87.56975 MeVMass defect:1.241055136 u (per nucleus)Nuclear binding energy:1156.03541285 MeV (per nucleus)
8.37706821 MeV (average binding energy per nucleon)Half-life:8.73(20) msDecay constant λ:79.398302469639 s^-1Specific activity α:3.490129646073 × 10⁺²³ Bq g^-1
9432782827224.9 Ci g^-1Spin and parity:
(nuclear angular momentum)7-Year of discovery:1960

Radioactive Decay

Half-life T_½ = 8.73(20) ms respectively 8.73 × 10^-3 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	¹³⁸Ce	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
¹³⁸Ce		stable	0+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 80) and isobaric (same nucleon number A = 138) with Cerium-138m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 80	Isobar A = 138
44	¹²⁴Ru
45	¹²⁵Rh
46	¹²⁶Pd
47	¹²⁷Ag
48	¹²⁸Cd
49	¹²⁹In
50	¹³⁰Sn	¹³⁸Sn
51	¹³¹Sb	¹³⁸Sb
52	¹³²Te	¹³⁸Te
53	¹³³I	¹³⁸I
54	¹³⁴Xe	¹³⁸Xe
55	¹³⁵Cs	¹³⁸Cs
56	¹³⁶Ba	¹³⁸Ba
57	¹³⁷La	¹³⁸La
58	¹³⁸Ce	¹³⁸Ce
59	¹³⁹Pr	¹³⁸Pr
60	¹⁴⁰Nd	¹³⁸Nd
61	¹⁴¹Pm	¹³⁸Pm
62	¹⁴²Sm	¹³⁸Sm
63	¹⁴³Eu	¹³⁸Eu
64	¹⁴⁴Gd	¹³⁸Gd
65	¹⁴⁵Tb	¹³⁸Tb
66	¹⁴⁶Dy	¹³⁸Dy
67	¹⁴⁷Ho
68	¹⁴⁸Er
69	¹⁴⁹Tm
70	¹⁵⁰Yb
71	¹⁵¹Lu