| Atomic Mass | 237 |
|---|---|
| Electron Configuration | [Rn]7s25f46d1 |
| Oxidation States | +6, +5, +4, +3 |
| Year Discovered | 1940 |
| Atomic Mass | 237 |
|---|---|
| Electron Configuration | [Rn]7s25f46d1 |
| Oxidation States | +6, +5, +4, +3 |
| Year Discovered | 1940 |
| Element Name | Neptunium |
|---|---|
| Element Symbol | Np |
| InChI | InChI=1S/Np |
| InChIKey | LFNLGNPSGWYGGD-UHFFFAOYSA-N |
| Atomic Weight |
237 237 [237] |
|---|---|
| Electron Configuration |
[Rn]7s25f46d1 |
| Atomic Radius |
Van der Waals Atomic Radius : 221 pm (Van der Waals) Empirical Atomic Radius : 175pm (Empirical) Covalent Atomic Radius : 190(1) pm (Covalent) |
| Oxidation States |
+6, +5, +4, +3 7, 6, 5, 4, 3, 2 |
| Ground Level |
6L11/2 |
| Ionization Energy |
6.266 eV 6.265608 ± 0.000019 eV |
| Electronegativity |
Pauling Scale Electronegativity : 1.36(Pauling Scale) |
| Atomic Spectra |
Lines Holdings Levels Holdings |
| Physical Description |
Solid |
| Element Classification |
Metal |
| Element Period Number |
7 |
| Element Group Number |
- Actinide |
| Density |
20.25 grams per cubic centimeter |
| Melting Point |
917 K (644°C or 1191°F) 644°C |
| Boiling Point |
4175 K (3902°C or 7056°F) 4174°C |
| Estimated Crustal Abundance |
Not Applicable |
| Estimated Oceanic Abundance |
Not Applicable |
Neptunium was first produced by Edwin M. McMillian and Philip H. Abelson, working at the University of California, Berkeley, in 1940. They produced neptunium-239, an isotope of neptunium with a half-life of about 2.4 days, by bombarding uranium with slow moving neutrons.
Named for the planet Neptune (named after the Roman god of the sea), the next planet out from the Sun after Uranus. There were many early false reports of the discovery of neptunium. The most significant was by Enrico Fermi who believed that bombarding uranium with neutrons followed by beta decay would lead to the formation of element 93. In 1934, he bombarded uranium atoms with neutrons and reported that he had produced elements 93 and 94. As it turned out, Fermi had actually fissioned or split uranium atoms into many fragment radioisotopes. The explanation and announcement of the discovery of fission was later published by Hahn and Strassman, although it was their co-worker Lisa Meitner who had correctly interpreted the results of the experiments. In 1940, with excitement about fission reaching the University of California at Berkeley, Professor Edwin McMillan and graduate student Philip Abelson bombarded uranium with cyclotron-produced moderated (slow) neutrons, resulting not in “fission” but "fusion" of the reactants forming the new element 93, which they named "neptunium":
23892U + 10n → 23992U → 23993Np + β-
Neptunium-239 was the first transuranium element produced synthetically and the first actinide series transuranium element discovered. This isotope has a beta-decay half-life of 2.3565 days, which forms daughter product plutonium-239 with a half-life of 24,000 years.
| Year | Atomic Weight (uncertainty) [u] | Reference |
|---|
| 1969, 237.0482(1), doi:10.1351/pac197021010091 |
Neptunium metal buttons (photo courtesy Lawrence Berkeley National Laboratory)
Neptunium's most stable isotope, neptunium-237, has a half-life of about 2,144,000 years. It decays into protactinium-233 through alpha decay. Neptunium-237, which is produced in gram quantities as a by-product of the production of plutonium in nuclear reactors, is used in neutron detectors.
Once considered to be completely artificial, extremely small amounts of neptunium are produced naturally in uranium ores through the interaction of atoms of uranium in the ore with neutrons produced by the decay of other atoms of uranium in the ore.
See more information at the Neptunium compound page.
| CID | Name | Formula | SMILES | Molecular Weight |
|---|---|---|---|---|
| 23933 | neptunium | Np | [Np] | 237.048172 |
| 104783 | neptunium-237 | Np | [237Np] | 237.04817 |
| 104958 | neptunium-239 | Np | [239Np] | 239.05294 |
| 167336 | neptunium-235 | Np | [235Np] | 235.04406 |
| 167335 | neptunium-236 | Np | [236Np] | 236.0466 |
| 167422 | neptunium-238 | Np | [238Np] | 238.05094 |
| 167240 | neptunium-234 | Np | [234Np] | 234.04289 |
| 167334 | neptunium-240 | Np | [240Np] | 240.0562 |
| 167437 | neptunium-233 | Np | [233Np] | 233.0407 |
| 169073 | neptunium-232 | Np | [232Np] | 232.040 |
| Stable Isotope Count | 0 |
|---|---|
| Summary | There are 25 known radioactive isotopes of neptunium ranging in atomic weights from 225 to 244 with 5 of those as metastable isotopes. The most stable are Np-237 with a half-life of 2.14 million years; Np-236 with a half-life of 154,000 years; and Np-235 with a half-life of 396 days. All of the remaining isotopes have half-lives less than 4.5 days, with most less than 50 minutes. The primary decay mode for isotopes lighter than 237Np is by electron capture with a great deal of alpha emission. The products are mostly isotopes of uranium. The primary decay mode for Np-237 is by alpha-decay forming protactinium. The primary decay mode for the isotopes heavier than Np-237 is by beta-decay, forming plutonium. Neptunium-237, after decaying to protactinium then to uranium, eventually decays to form bismuth-209 and thallium-205. Unlike most other common heavy nuclei which decay to make isotopes of lead this decay chain is known as the neptunium series. |
237Np (with a half-life of 2.14×106 years) is fissionable, meaning that neptunium can be bombarded with neutrons and, as a result, create more neutrons that are free to interact with nearby material and can be used in fast neutron reactors or in nuclear weapons (Fig. IUPAC.93.1) [75], [603], [604]. 237Np is used in neutron detection instruments [75].
![Fig. IUPAC.93.1: ²³⁷Np is fissionable and is used in fast neutron reactors and in nuclear weapons. (U.S. Air Force photo by Senior Airman Alexandra Longfellow, U.S. Department of Energy) [605].](https://pubchem.ncbi.nlm.nih.gov/images/iupac/j_pac-2015-0703_fig_127.jpg)
237Np is used in the production of 238Pu (with a half-life of 87.7 years), which is an emitter of alpha particles used in thermoelectric generators and radioisotope-heater units. When 237Np captures a neutron, it becomes 238Np, with a half-life of 2.117 days, which decays to 238Pu [75].
| Isotope | Atomic Mass (uncertainty) [u] | Abundance (uncertainty) |
|---|---|---|
| 236Np | 236.046570(54) | |
| 237Np | 237.0481736(19) |
| Nuclide | Atomic Mass and Uncertainty [u] | Half Life and Uncertainty | Discovery Year | Decay Modes, Intensities and Uncertainties [%] |
|---|---|---|---|---|
| 219Np | 219.031601865 ± 0.000098732 | 570 us ± 450 | 2015 | α=100% |
| 220Np | 220.032716280 ± 0.000032977 | 29 ns ± 11 | 2019 | α=100% |
| 221Np | 221.032110 ± 0.000215 [Estimated] | 30 ns [Estimated] | α ? | |
| 222Np | 222.033574706 ± 0.000040849 | 480 ns ± 190 | 2020 | α=100% |
| 223Np | 223.032913340 ± 0.000088956 | 2.5 us ± 0.8 | 2017 | α=100% |
| 224Np | 224.034388030 ± 0.000031052 | 48 us ± 19 | 2018 | α=100% |
| 225Np | 225.033943422 ± 0.000098355 | 6.5 ms ± 3.5 | 1994 | α=100%; β+ ? |
| 226Np | 226.035230364 ± 0.000109568 | 35 ms ± 10 | 1990 | α=100%; β+ ? |
| 227Np | 227.034975012 ± 0.000082651 | 510 ms ± 60 | 1990 | α≈100%; β+ ? |
| 228Np | 228.036313 ± 0.000108 [Estimated] | 61.4 s ± 1.4 | 1994 | ε=59±0.7%; α=41±0.7%; β+SF=0.012±0.6% |
| 229Np | 229.036287269 ± 0.000108618 | 4.00 m ± 0.18 | 1968 | α=68±1.1%; β+ ? |
| 229Npp | 229.036287269 ± 0.000108618 | Not-specified | ||
| 230Np | 230.037828060 ± 0.000059051 | 4.6 m ± 0.3 | 1968 | β+<97%; α>3% |
| 231Np | 231.038243598 ± 0.000054916 | 48.8 m ± 0.2 | 1950 | β+=98±0.1%; α=2±0.1% |
| 232Np | 232.040107 ± 0.000107 [Estimated] | 14.7 m ± 0.3 | 1950 | β+≈100%; α ? |
| 233Np | 233.040739421 ± 0.000054729 | 36.2 m ± 0.1 | 1950 | β+≈100%; α≈0.0007% |
| 233Npp | 233.040739421 ± 0.000054729 | Not-specified | ||
| 234Np | 234.042893245 ± 0.000009014 | 4.4 d ± 0.1 | 1949 | β+=100% |
| 235Np | 235.044061518 ± 0.00000149 | 396.1 d ± 1.2 | 1949 | ε=99.99740±1.3%; ; α=0.00260±1.3% |
| 236Np | 236.046568296 ± 0.000054129 | 153 ky ± 5 | 1949 | ε=86.3±0.8%; β-=13.5±0.8%; α=0.16±0.4% |
| 236Npm | 236.046568296 ± 0.000054129 | 22.5 h ± 0.4 | 1949 | ε=50±0.3%; β-=50±0.3% |
| 236Npp | 236.046568296 ± 0.000054129 | Not-specified | ||
| 237Np | 237.048171640 ± 0.000001201 | 2.144 My ± 0.007 | 1948 | α=100%; SF<2e-10%; 30Mg<4e-12% |
| 237Npm | 237.048171640 ± 0.000001201 | 710 ns ± 40 | 1990 | IT=100% |
| 238Np | 238.050944603 ± 0.00000122 | 2.099 d ± 0.002 | 1949 | β-=100% |
| 238Npm | 238.050944603 ± 0.00000122 | 112 ns ± 39 | 1970 | SF≈100%; IT ? |
| 239Np | 239.052937538 ± 0.000001406 | 2.356 d ± 0.003 | 1940 | β-=100%; α ? |
| 240Np | 240.056163778 ± 0.000018284 | 61.9 m ± 0.2 | 1953 | β-=100% |
| 240Npm | 240.056163778 ± 0.000018284 | 7.22 m ± 0.02 | 1948 | β-=99.88±0.1%; IT=0.12±0.1% |
| 241Np | 241.058309671 ± 0.00010736 | 13.9 m ± 0.2 | 1959 | β-=100%; α ? |
| 242Np | 242.061639548 ± 0.000214712 | 2.2 m ± 0.2 | 1979 | β-=100% |
| 242Npm | 242.061639548 ± 0.000214712 | 5.5 m ± 0.1 | 1981 | β-=100% |
| 243Np | 243.064204 ± 0.000034 [Estimated] | 1.85 m ± 0.15 | 1979 | β-=100% |
| 243Npp | 243.064204 ± 0.000034 [Estimated] | Not-specified | ||
| 244Np | 244.067891 ± 0.000107 [Estimated] | 2.29 m ± 0.16 | 1987 | β-=100% |
| 245Np | 245.070693 ± 0.000215 [Estimated] | 6 m [Estimated] | β- ? |
