Cerium-125m

Properties and data of the isotope ^125mCe.

Contents

Cerium-125m is a metastable state of the isotope cerium-125 with an excitation energy of 93.6(4) keV. Decay occurs predominantly by internal transition to the ground state, with a half-life of 13(10) s measured for neutral atoms. A spin/parity of (1/2⁺) is given for the isomer state.

In 2007, the same isomer state was experimentally investigated in a storage ring in fully ionized form. Under these conditions, a significantly longer lifetime of 193(1) s was determined due to the suppressed internal conversion, and the excitation energy was measured to be 103(12) keV. This difference reflects the influence of the electronic shell on the decay probability [1].

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

General data

Name of the isotope:Cerium-125m; Ce-125mSymbol:^125mCe or 125m58CeMass number A:125 (= number of nucleons)Atomic number Z:58 (= number of protons)Neutrons N:67Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):1.1551724137931 (= neutron-proton ratio)Neutron excess (N-Z):9Excitation energy:93.6(4) keVIsotopic mass:124.92844(21) u (atomic weight of Cerium-125m)Nuclide mass:124.8966246 u (calculated nuclear mass without electrons)Mass excess:-66.65771 MeVMass defect:1.105961228 u (per nucleus)Nuclear binding energy:1030.19624811 MeV (per nucleus)
8.24156998 MeV (average binding energy per nucleon)Half-life:13(10) sDecay constant λ:0.053319013889227 s^-1Specific activity α:2.5894726786 × 10⁺²⁰ Bq g^-1
6998574807.1892 Ci g^-1Spin and parity:
(nuclear angular momentum)(1/2+)Year of discovery:2007

Radioactive Decay

Half-life T_½ = 13(10) s respectively 1.3 × 10¹ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	¹²⁵Ce	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
¹²⁵Ce		9.7(3) s	(7/2-)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 67) and isobaric (same nucleon number A = 125) with Cerium-125m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

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

Literature and References

[1] - B. Sun, Yu. A. Litvinov, P. M. Walker et al.:
Discovery of a new long-lived isomeric state in ¹²⁵Ce.
In: The European Physical Journal A, 31, (2007), DOI 10.1140/epja/i2006-10252-0.