Scandium-45m

Properties and data of the isotope ^45mSc.

Contents

Scandium-45m is an excited nuclear state of the nuclide ⁴⁵Sc, characterized by a defined excitation energy (12.40 keV). Its spin and parity quantum numbers differ from those of the ground state (gs). Simultaneously, this metastable nuclear isomer possesses an independent, experimentally measurable lifetime: decay occurs via an isomeric transition to Sc-45 in the ground state with a half-life of approximately 0.318 seconds. The nuclear isomer was first detected in 1964 [1].

The nuclear transition in ⁴⁵Sc from the ground state to the isomer at 12.389 keV (lifetime: 0.46 s) (more recent values [2]) exhibits an exceptionally small natural linewidth Γ₀ = 1.4 feV. This results in a quality factor of Q₀ ≃ 10¹⁹.

This combination of low transition energy, short isomer lifetime, and extremely narrow natural linewidth makes ⁴⁵Sc particularly attractive for high-precision metrology: the transition can in principle be used as a frequency-stable reference and thus qualifies as a candidate for nuclear-based clock concepts. The achievable intrinsic Q factor lies in a range that at least meets, and may prospectively exceed, the stability requirements of modern atomic clocks [3].

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

General data

Name of the isotope:Scandium-45m; Sc-45mSymbol:^45mSc or 45m21ScMass number A:45 (= number of nucleons)Atomic number Z:21 (= number of protons)Neutrons N:24Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.1428571428571 (= neutron-proton ratio)Neutron excess (N-Z):3Excitation energy:12.40(5) keVIsotopic mass:44.955908(5) u (atomic weight of Scandium-45m)Nuclide mass:44.944388 u (calculated nuclear mass without electrons)Mass excess:-41.07143 MeVMass defect:0.41637565600001 u (per nucleus)Nuclear binding energy:387.85142531 MeV (per nucleus)
8.61892056 MeV (average binding energy per nucleon)Half-life:318(7) msDecay constant λ:2.1797081149684 s^-1Specific activity α:2.983297568610 × 10⁺²² Bq g^-1
806296640165.03 Ci g^-1Spin and parity:
(nuclear angular momentum)3/2+Magnetic dipole moment:μ(μ_N) = + 0.368(5)Quadrupole moment Q:0.318(22) barn (100 fm²)Nuclear g-factor:g_l = 0.24533333333333Mirror nucleus:chromium-45mYear of discovery:1964

Radioactive Decay

Half-life T_½ = 318(7) ms respectively 3.18 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	⁴⁵Sc	100 %		001240(5) MeV [0.236(5) %]]

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
⁴⁵Sc		stable	7/2-

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 24) and isobaric (same nucleon number A = 45) with Scandium-45m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 24	Isobar A = 45
10	³⁴Ne
11	³⁵Na
12	³⁶Mg
13	³⁷Al
14	³⁸Si
15	³⁹P	⁴⁵P
16	⁴⁰S	⁴⁵S
17	⁴¹Cl	⁴⁵Cl
18	⁴²Ar	⁴⁵Ar
19	⁴³K	⁴⁵K
20	⁴⁴Ca	⁴⁵Ca
21	⁴⁵Sc	⁴⁵Sc
22	⁴⁶Ti	⁴⁵Ti
23	⁴⁷V	⁴⁵V
24	⁴⁸Cr	⁴⁵Cr
25	⁴⁹Mn	⁴⁵Mn
26	⁵⁰Fe	⁴⁵Fe
27	⁵¹Co
28	⁵²Ni
29	⁵³Cu
30	⁵⁴Zn

Data changes (history)

2023: The transition energy was newly measured: 12.38959 ± 0.15 (stat) and +0.12 (syst) keV [2]. A lifetime of 0.46 s is specified at the same publication.

External data and identifiers

Adopted Levels, Gammas:NuDat 45Sc

Literature and References

[1] - R. E. Holland, F. J. Lynch, K.-E. Nystén:
Lifetimes of d_3/2 Hole States in Scandium Isotopes.
In: Physical Review Letters, 13, 241, (1964), DOI 10.1103/PhysRevLett.13.241.

[2] - Yuri Shvyd´ko, Ralf Röhlsberger, Olga Kocharovskaya et al.:
Resonant X-ray excitation of the nuclear clock isomer ⁴⁵Sc.
In: Nature, 622, (2023), DOI 10.1038/s41586-023-06491-w.

[3] - Peifan Liu, Miriam Gerharz, Berit Marx-Glowna et al.:
Probing the Linewidth of the 12.4-keV Solid-State ⁴⁵Sc Isomeric Resonance.
In: arXiv:2508.17538, (2025), DOI 10.48550/arXiv.2508.17538.