Neptunium-242m

Properties and data of the isotope ^242mNp.

Contents

Neptunium-242m is an excited nuclear state of the nuclide ²⁴²Np, characterized by a defined excitation energy (approximately 50 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 and undergoes β^- decay to plutonium-242 with a half-life of approximately 5.5 minutes.

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

General data

Name of the isotope:Neptunium-242m; Np-242mSymbol:^242mNp or 242m93NpMass number A:242 (= number of nucleons)Atomic number Z:93 (= number of protons)Neutrons N:149Nucleon pairing (Z - N):odd - oddNuclear ratio (N/Z ratio):1.6021505376344 (= neutron-proton ratio)Neutron excess (N-Z):56Excitation energy:50(50) keVIsotopic mass:242.061640(210) u (atomic weight of Neptunium-242m)Nuclide mass:242.0106289 u (calculated nuclear mass without electrons)Mass excess:57.41729 MeVMass defect:1.95716046 u (per nucleus)Nuclear binding energy:1823.08322553 MeV (per nucleus)
7.53340176 MeV (average binding energy per nucleon)Half-life:5.5(1) minDecay constant λ:0.0021004460016968 s^-1Specific activity α:5.226934583020 × 10⁺¹⁸ Bq g^-1
141268502.24379 Ci g^-1Spin and parity:
(nuclear angular momentum)(6+)Year of discovery:1981

Radioactive Decay

Half-life T_½ = 5.5(1) min (minutes) respectively 3.30 × 10² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	²⁴²Pu	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
²⁴²Np		2.2(2) min	(1+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 149) and isobaric (same nucleon number A = 242) with Neptunium-242m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 149	Isobar A = 242
91	²⁴⁰Pa
92	²⁴¹U	²⁴²U
93	²⁴²Np	²⁴²Np
94	²⁴³Pu	²⁴²Pu
95	²⁴⁴Am	²⁴²Am
96	²⁴⁵Cm	²⁴²Cm
97	²⁴⁶Bk	²⁴²Bk
98	²⁴⁷Cf	²⁴²Cf
99	²⁴⁸Es	²⁴²Es
100	²⁴⁹Fm	²⁴²Fm
101	²⁵⁰Md
102	²⁵¹No
103	²⁵²Lr
104	²⁵³Rf