Isotopes of neptunium

Isotopes of neptunium (₉₃Np)
ε	235U
β−	236Pu
α	232Pa
	view; talk; edit;

Neptunium (₉₃Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be synthesized and identified was ²³⁹Np in 1940, produced by bombarding ²³⁸
U
with neutrons to produce ²³⁹
U
, which then underwent beta decay to ²³⁹
Np
.

Trace quantities are found in nature from neutron capture reactions by uranium atoms, a fact not discovered until 1951.^[2]

Twenty-five neptunium radioisotopes have been characterized, with the most stable being ²³⁷
Np
with a half-life of 2.14 million years, ²³⁶
Np
with a half-life of 154,000 years, and ²³⁵
Np
with a half-life of 396.1 days. All of the remaining radioactive isotopes have half-lives that are less than 4.5 days, and the majority of these have half-lives that are less than 50 minutes. This element also has five meta states, with the most stable being ^236m
Np
(t_1/2 22.5 hours).

The isotopes of neptunium range from ²¹⁹
Np
to ²⁴⁴
Np
, though the intermediate isotope ²²¹
Np
has not yet been observed. The primary decay mode before the most stable isotope, ²³⁷
Np
, is electron capture (with a good deal of alpha emission), and the primary mode after is beta emission. The primary decay products before ²³⁷
Np
are isotopes of uranium and protactinium, and the primary products after are isotopes of plutonium. Neptunium is the heaviest element for which the location of the proton drip line is known; the lightest bound isotope is ²²⁰Np.^[3]

^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^ Peppard, D. F.; Mason, G. W.; Gray, P. R.; Mech, J. F. (1952). "Occurrence of the (4n + 1) series in nature" (PDF). Journal of the American Chemical Society. 74 (23): 6081–6084. doi:10.1021/ja01143a074.
^ Zhang, Z. Y.; Gan, Z. G.; Yang, H. B.; et al. (2019). "New isotope ²²⁰Np: Probing the robustness of the N = 126 shell closure in neptunium". Physical Review Letters. 122 (19): 192503. Bibcode:2019PhRvL.122s2503Z. doi:10.1103/PhysRevLett.122.192503. PMID 31144958. S2CID 169038981.

[NUBASE2020-1] Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

[4n1-2] Peppard, D. F.; Mason, G. W.; Gray, P. R.; Mech, J. F. (1952). "Occurrence of the (4n + 1) series in nature" (PDF). Journal of the American Chemical Society. 74 (23): 6081–6084. doi:10.1021/ja01143a074.

[220Np-3] Zhang, Z. Y.; Gan, Z. G.; Yang, H. B.; et al. (2019). "New isotope ²²⁰Np: Probing the robustness of the N = 126 shell closure in neptunium". Physical Review Letters. 122 (19): 192503. Bibcode:2019PhRvL.122s2503Z. doi:10.1103/PhysRevLett.122.192503. PMID 31144958. S2CID 169038981.

[1]

[2]

[3]