Europium-146

Properties and data of the isotope ¹⁴⁶Eu.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Europium-146 is a radioisotope of the chemical element europium, which has 83 neutrons in its atomic nucleus in addition to the element-specific 63 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 146.

In 1957 a report appeared that provided the first indications of the isotope europium-146. In the experiment described, 660-MeV protons from a synchrocyclotron struck a tantalum target, producing a wide range of neutron-deficient nuclei through spallation. Chromatographic separation enabled precise analysis of the emitted gamma radiation. During evaluation, the gamma lines at 636 and 745 keV - initially attributed to Eu-145 - were found to agree more convincingly with a nuclide of mass number 146. A note added in proof confirmed this reassignment, thereby establishing the identification of europium-146 [G. M. Gorodinskii et al., Bull. Acad. Sci. USSR Phys. Ser. 21, 1611, (1957)].

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

General data

Name of the isotope:Europium-146; Eu-146Symbol:¹⁴⁶Eu or 14663EuMass number A:146 (= number of nucleons)Atomic number Z:63 (= number of protons)Neutrons N:83Nucleon pairing (Z - N):odd - oddNuclear ratio (N/Z ratio):1.3174603174603 (= neutron-proton ratio)Neutron excess (N-Z):20Isotopic mass:145.917211(6) u (atomic weight of Europium-146)Nuclide mass:145.8826532 u (calculated nuclear mass without electrons)Mass excess:-77.11746 MeVMass defect:1.294954044 u (per nucleus)Nuclear binding energy:1206.24192226 MeV (per nucleus)
8.26193097 MeV (average binding energy per nucleon)Separation energy:S_N = 7.197(7) MeV (first neutron)
S_P = 3.755(6) MeV (first proton)Half-life:4.61(3) dDecay constant λ:1.74024659697 × 10^-6 s^-1Specific activity α:7.227593198610 × 10⁺¹⁵ Bq g^-1
195340.3567192 Ci g^-1Spin and parity:
(nuclear angular momentum)4-Magnetic dipole moment:μ(μ_N) = + 1.422(6)Quadrupole moment Q:- 0.179(5) barn (100 fm²)Nuclear g-factor:g_l = 0.3555Charge radius:4.9789(92) femtometer fmYear of discovery:1957

Radioactive Decay

Half-life T_½ = 4.61(3) d respectively 3.98304 × 10⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EC/β⁺	¹⁴⁶Sm	100 %	3.879(7) MeV	0.747159(16) MeV [98(3) %]

Parent Nuclides

Direct parent isotopes are: ¹⁴⁶Gd, ¹⁵⁰Tb.

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
^146mEu	666.33(11) keV	235(3) μs	9+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 83) and isobaric (same nucleon number A = 146) with Europium-146. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 83	Isobar A = 146
46	¹²⁹Pd
47	¹³⁰Ag
48	¹³¹Cd
49	¹³²In
50	¹³³Sn
51	¹³⁴Sb
52	¹³⁵Te
53	¹³⁶I
54	¹³⁷Xe	¹⁴⁶Xe
55	¹³⁸Cs	¹⁴⁶Cs
56	¹³⁹Ba	¹⁴⁶Ba
57	¹⁴⁰La	¹⁴⁶La
58	¹⁴¹Ce	¹⁴⁶Ce
59	¹⁴²Pr	¹⁴⁶Pr
60	¹⁴³Nd	¹⁴⁶Nd
61	¹⁴⁴Pm	¹⁴⁶Pm
62	¹⁴⁵Sm	¹⁴⁶Sm
63	¹⁴⁶Eu	¹⁴⁶Eu
64	¹⁴⁷Gd	¹⁴⁶Gd
65	¹⁴⁸Tb	¹⁴⁶Tb
66	¹⁴⁹Dy	¹⁴⁶Dy
67	¹⁵⁰Ho	¹⁴⁶Ho
68	¹⁵¹Er	¹⁴⁶Er
69	¹⁵²Tm	¹⁴⁶Tm
70	¹⁵³Yb
71	¹⁵⁴Lu
72	¹⁵⁵Hf
73	¹⁵⁶Ta
74	¹⁵⁷W

Data changes (history)

Half-life: The value for the half-life of the nuclide europium-146 was experimentally re-determined in 2025; the published value is t_1/2 = 4.21 ± 0.05 days [1].

External data and identifiers

Adopted Levels, Gammas:NuDat 146Eu

Literature and References

[1] - Changxin Guo et al.:
Half-life measurement of short-lived nuclide ¹⁴⁶Eu.
In: Nuclear Physics A, 1060, 123113, (2025), DOI 10.1016/j.nuclphysa.2025.123113.