Neptunium-237

Properties and data of the isotope ²³⁷Np.

Contents

General Data

Radioactive Decay

Parent Nuclides

Formation

NMR Data

Isotones und Isobares

Literature

Neptunium-237 is a radioisotope of the chemical element neptunium, which has 144 neutrons in its atomic nucleus in addition to the element-specific 93 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 237.

In 1948 a report was published in which the isotope neptunium-237 was described for the first time. In the experiments presented there, a uranyl nitrate-hexahydrate target was irradiated with fast neutrons that were produced by bombarding a beryllium target with deuterons (hydrogen-2 nuclei) from a cyclotron, forming uranium-237 via the reaction

²³⁸U(n,2n)²³⁷U.

The subsequent β-decay of this uranium isotope gave rise to ²³⁷Np [1].

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

General data

Name of the isotope:Neptunium-237; Np-237Symbol:²³⁷Np or 23793NpMass number A:237 (= number of nucleons)Atomic number Z:93 (= number of protons)Neutrons N:144Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.5483870967742 (= neutron-proton ratio)Neutron excess (N-Z):51Isotopic mass:237.0481716(12) u (atomic weight of Neptunium-237)Nuclide mass:236.9971605 u (calculated nuclear mass without electrons)Mass excess:44.87156 MeVMass defect:1.92730428 u (per nucleus)Nuclear binding energy:1795.27237299 MeV (per nucleus)
7.57498892 MeV (average binding energy per nucleon)Separation energy:S_N = 6.578(50) MeV (first neutron)
S_P = 4.86195(25) MeV (first proton)Half-life:2.144(7) × 10⁶ aDecay constant λ:1.024485907942 × 10^-14 s^-1Specific activity α:26032060.956328 Bq g^-1
0.00070356921503589 Ci g^-1Spin and parity:
(nuclear angular momentum)5/2+Magnetic dipole moment:μ(μ_N) = + 3.14(4)Year of discovery:1948

Radioactive Decay

Half-life T_½ = 2.144(7) × 10⁶ a respectively 6.7658049289525 × 10¹³ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²³³Pa	ca. 100 %	4.9573(7) MeV
SZ	^div	< 2 · 10^-10 %

Neptunium Series

The neptunium series is the natural decay series of the neptunium isotope ²³⁷Np. Their final nuclide is the thallium isotope ²⁰⁵Tl. The series can also be continued beyond the Neptunium to even heavier transuranic elements.

Parent Nuclides

Direct parent isotopes are: ²⁴¹Am, ²³⁷Pu, ²³⁷U.

Formation

Small amounts of neptunium-237 are formed by (n,2n) reactions in uranium-238. The fast neutrons required for this come from spontaneous fission or cosmic rays. However, this reaction is so rare that man-made Np-237 is now present on Earth in far greater abundance than that resulting from this process.

Occurrence

Comparison of the natural Neptunium isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Neptunium Isotopic mixture	237.048174914 u	100 %
Isotope ²³⁷Np	237.0481716(12) u	100 %	2.144(7) × 10⁶ a	5/2+

NMR data

Nuclear magnetic properties and parameters of the NMR active Nuclide ²³⁷Np

Isotope:²³⁷Np-NMRQuantity:100 %Spin:5/2+Nuclearmagnetic moment
μ/μ_N:+ 3.14(4)Gyromagnetic ratio γ:3.1 · 10⁷ rad T^-1 s^-1
4.93380 MHz T^-1Nuclear g-factor:g_l = 1.256Quadrupole moment Q:+ 3.886(6) barn (100 fm²)Resonance frequency:v₀ = 9.57 MHz at 1 TRelative Sensitivity:[related to ¹H = 1.000]:
0.13264 (H₀ = const.)
2.6234 (v₀ = const.)

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
^237mNp	945.2(1) keV	0.71(4) μs	(13/2-)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 144) and isobaric (same nucleon number A = 237) with Neptunium-237. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 144	Isobar A = 237
85	²²⁹At
86	²³⁰Rn
87	²³¹Fr
88	²³²Ra
89	²³³Ac
90	²³⁴Th	²³⁷Th
91	²³⁵Pa	²³⁷Pa
92	²³⁶U	²³⁷U
93	²³⁷Np	²³⁷Np
94	²³⁸Pu	²³⁷Pu
95	²³⁹Am	²³⁷Am
96	²⁴⁰Cm	²³⁷Cm
97	²⁴¹Bk	²³⁷Bk
98	²⁴²Cf	²³⁷Cf
99	²⁴³Es
100	²⁴⁴Fm
101	²⁴⁵Md