Neptunium (Np)
actinideSolid
Masse atomique relative standard
[237]Configuration électronique
[Rn] 7s2 5f4 6d1Point de fusion
643,85 °CPoint d’ébullition
3901,85 °CMasse volumique
2,025e+4 kg/m³États d’oxydation
+2, +3, +4, +5, +6, +7Électronégativité (Pauling)
1,36Énergie d’ionisation (1re)
6,265608 eVAnnée de découverte
1940Rayon atomique
175 pmDétails
Neptunium is a radioactive actinide and the first transuranium element. It is produced mainly by neutron reactions involving uranium in nuclear reactors and occurs naturally only in minute amounts from neutron capture and decay processes in uranium ores. Its chemistry bridges uranium and plutonium, with several accessible oxidation states in solution. The isotope ²³⁷Np is the most important for handling and study because of its long half-life and availability as a reactor by-product.
Neptunium metal buttons (photo courtesy Lawrence Berkeley National Laboratory)
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.
Metallic neptunium has been prepared in visible quantities. Fresh metal is silvery, dense, and chemically reactive, but it tarnishes in air as oxide layers form. It has several solid allotropes, and bulk physical measurements are limited by radioactivity, scarcity, and self-heating.
Neptunium has no broad commercial use as an element. ²³⁷Np is used in research on actinide chemistry, nuclear fuel cycles, and long-lived radioactive waste behavior. It is also the principal target material for producing ²³⁸Pu by neutron irradiation; ²³⁸Pu is then used in radioisotope heat sources and power systems. Small quantities of neptunium compounds have been used as analytical standards and in radiochemical method development.
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.
Isotopes in Industry
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] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [603] P. Weiss. Science News.162, 259 (2002)., [604] T. Kenna. J. Anal. At. Spectrom.17, 1471 (2002).. 237Np is used in neutron detection instruments [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf..
Isotopes Used as a Source of Radioactive Isotope(s)
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] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf..
Neptunium forms compounds in oxidation states from +3 to +7, with +4, +5, and +6 especially important in aqueous chemistry. The neptunyl ion NpO₂⁺ is a characteristic +5 species and is often relatively mobile in oxidizing waters, while NpO₂²⁺ represents +6 chemistry. Neptunium dioxide NpO₂ is a stable refractory oxide and an important solid phase. Halides such as neptunium tetrachloride NpCl₄ and neptunium hexafluoride NpF₆ illustrate the element’s actinide-like coordination and redox behavior.
See more information at the Neptunium compound page.
All neptunium isotopes are radioactive, and hazards depend strongly on isotope, chemical form, and exposure route. ²³⁷Np emits mainly alpha radiation with associated gamma emissions from decay products, so ingestion, inhalation, or contamination of wounds is the principal concern. Finely divided metal and soluble compounds require strict radiological containment. External dose rates can be significant for some samples because of accompanying gamma-emitting impurities or daughters.
Natural neptunium is extremely scarce, but anthropogenic neptunium occurs in spent nuclear fuel, reprocessing wastes, and fallout residues. Environmental behavior is controlled by oxidation state, complexation, mineral sorption, and reducing conditions. Np(V) as NpO₂⁺ can migrate more readily than many tetravalent actinides, whereas Np(IV) tends to form less soluble solids or strongly sorbed species. Its long half-life makes it important in repository performance assessments.
Neptunium is not traded as a commodity and has no ordinary industrial supply chain. Recoverable ²³⁷Np is generated as a by-product in irradiated uranium fuel and can be separated only in specialized nuclear facilities under heavy regulation. Demand is small and centered on research inventories and on target preparation for ²³⁸Pu production. Costs are dominated by radiochemical separation, safeguards, licensing, waste management, and secure storage rather than by ore mining or conventional refining.
Produced by bombarding uranium with slow neutrons.
Neptunium has no stable isotopes, so any primordial neptunium has decayed away. It can be formed in trace amounts by neutron capture in uranium-bearing materials and in nuclear explosions or reactors, and transient neptunium isotopes may occur in astrophysical rapid neutron-capture processes. Its extraterrestrial abundance is effectively negligible compared with long-lived actinides such as uranium and thorium.
- Neptunium was named after Neptune, following uranium’s naming after Uranus.
- ²³⁷Np has a half-life of about 2.14 million years.
- Neptunium was the first element beyond uranium to be identified.
- NpF₆ is volatile, a property relevant to actinide fluoride chemistry.
- The common aqueous Np(V) ion is linear neptunyl, NpO₂⁺.
- Separated neptunium metal darkens on exposure to air.
Images
Propriétés
Propriétés physiques
- Rayon atomique (empirique)
- 175 pm Comparer : Rayon atomique (empirique) de tous les éléments →
- Rayon covalent
- 190 pm Comparer : Rayon covalent de tous les éléments →
- Rayon de van der Waals
- 221 pm Comparer : Rayon de van der Waals de tous les éléments →
- Masse volumique
- 2,025 × 104 kg/m³ Comparer : Masse volumique de tous les éléments →
- Volume molaire
- 0,0211 L/mol
- Phase aux CNTP
- Solide Comparer : Phase aux CNTP de tous les éléments →
- Point de fusion
- 643,85 °C Comparer : Point de fusion de tous les éléments →
- Point d’ébullition
- 3901,85 °C Comparer : Point d’ébullition de tous les éléments →
- Structure cristalline
- Orthorhombique Comparer : Structure cristalline de tous les éléments →
Propriétés chimiques
- Électronégativité (Pauling)
- 1,36 Comparer : Électronégativité (Pauling) de tous les éléments →
- Affinité électronique
- 0,48 eV
- Énergie d’ionisation (1re)
- 6,265608 eV Comparer : Énergie d’ionisation (1re) de tous les éléments →
- Énergie d’ionisation (2e)
- 11,50004 eV Comparer : Énergie d’ionisation (2e) de tous les éléments →
- Énergie d’ionisation (3e)
- 19,700068 eV Comparer : Énergie d’ionisation (3e) de tous les éléments →
- Énergie d’ionisation (4e)
- 33,800116 eV Comparer : Énergie d’ionisation (4e) de tous les éléments →
- Énergie d’ionisation (5e)
- 48,000165 eV Comparer : Énergie d’ionisation (5e) de tous les éléments →
- États d’oxydation
- +2, +3, +4, +5, +6, +7 Comparer : États d’oxydation de tous les éléments →
- Électrons de valence
- 3 Comparer : Électrons de valence de tous les éléments →
- Configuration électronique
- [Rn] 7s2 5f4 6d1
Propriétés thermodynamiques
- Enthalpie de fusion
- 0,10364305 eV Comparer : Enthalpie de fusion de tous les éléments →
- Enthalpie de vaporisation
- 3,482407 eV Comparer : Enthalpie de vaporisation de tous les éléments →
- Enthalpie de sublimation
- 4,33228 eV
- Enthalpie d’atomisation
- 4,33228 eV
- Enthalpie d’atomisation
- 4,817329 eV
Propriétés nucléaires
- Protons
- 93 Comparer : Protons de tous les éléments →
- Neutrons
- 144 Comparer : Neutrons de tous les éléments →
- Isotopes connus
- 27 Comparer : Isotopes connus de tous les éléments →
- Isotopes stables
- 0 Comparer : Isotopes stables de tous les éléments →
- Nombre de masse (isotope le plus stable)
- 237
- Isotope le plus stable
- Np-237
- Année de découverte
- 1940
Abondance
N/D
Structure cristalline
- Paramètre de maille a
- 472 pm
Structure électronique
- Électrons par couche
- 2, 8, 18, 32, 22, 9, 2 Comparer : Électrons par couche de tous les éléments →
Identifiants
- Numéro CAS
- 7439-99-8 Comparer : Numéro CAS de tous les éléments →
- Symbole de terme
- 6L11/2
- InChI
- InChI=1S/Np
- Clé InChI
- LFNLGNPSGWYGGD-UHFFFAOYSA-N
Configuration électronique Mesuré
Np: 5f⁴ 6d¹ 7s²[Rn] 5f⁴ 6d¹ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f⁴ 6d¹ 7s²Modèle atomique
Les isotopes diffèrent par leur nombre de neutrons, leur masse et leur stabilité — pas par la configuration électronique de l’atome neutre.
Modèle atomique schématique, non à l’échelle.
Empreinte atomique
Spectre d’émission / d’absorption
Distribution isotopique
Aucun isotope stable.
| Nombre de masse | Masse atomique (u) | Abondance naturelle | Demi-vie |
|---|---|---|---|
| 219 Radioactif | 219,03143 ± 0,00021 | N/D | 570 us |
| 227 Radioactif | 227,034957 ± 0,000078 | N/D | 510 ms |
| 222 Radioactif | 222,0333 ± 0,00021 | N/D | 480 ns |
| 235 Radioactif | 235,0440635 ± 0,0000021 | N/D | 396.1 jours |
| 236 Radioactif | 236,04657 ± 0,000054 | N/D | 153 ky |
Phase / État
Explication: 618,9 °C en dessous du point de fusion (643,85 °C)
Schématique, non à l’échelle
Points de transition de phase
Énergies de transition
Énergie nécessaire pour faire fondre 1 mol au point de fusion
Énergie nécessaire pour vaporiser 1 mol au point d’ébullition
Énergie nécessaire pour sublimer 1 mol au point de sublimation
Masse volumique
Dans les conditions standard
Dans les conditions standard
Spectres atomiques
Affichage de 10 sur 93. Tri par charge ionique croissante.
Raies répertoriées ?
| Ion | Charge | Nombre total de raies | Probabilités de transition | Désignations des niveaux |
|---|---|---|---|---|
| Np I | 0 | 96 | 0 | 0 |
Niveaux répertoriés ?
| Ion | Charge | Niveaux |
|---|---|---|
| Np I | 0 | 2 |
| Np II | +1 | 2 |
| Np III | +2 | 2 |
| Np IV | +3 | 2 |
| Np V | +4 | 2 |
| Np VI | +5 | 2 |
| Np VII | +6 | 2 |
| Np VIII | +7 | 2 |
| Np IX | +8 | 2 |
| Np X | +9 | 2 |
Rayons ioniques
| Charge | Coordinence | Spin | Rayon |
|---|---|---|---|
| +2 | 6 | N/D | 110.00000000000001 pm |
| +3 | 6 | N/D | 101 pm |
| +3 | 9 | N/D | 117.8 pm |
| +4 | 6 | N/D | 87 pm |
| +4 | 8 | N/D | 98 pm |
| +5 | 6 | N/D | 75 pm |
| +6 | 6 | N/D | 72 pm |
| +7 | 6 | N/D | 71 pm |
Composés
Isotopes (5)
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.
| Nombre de masse | Masse atomique (u) | Abondance naturelle | Demi-vie | Mode de désintégration | |
|---|---|---|---|---|---|
| 219 Radioactif | 219,03143 ± 0,00021 | N/D | 570 us | α =100% | |
| 227 Radioactif | 227,034957 ± 0,000078 | N/D | 510 ms | α ≈100%β+ ? | |
| 222 Radioactif | 222,0333 ± 0,00021 | N/D | 480 ns | α =100% | |
| 235 Radioactif | 235,0440635 ± 0,0000021 | N/D | 396.1 jours | ε =99.99740±1.3%α =0.00260±1.3% | |
| 236 Radioactif | 236,04657 ± 0,000054 | N/D | 153 ky | ε =86.3±0.8%β- =13.5±0.8%α =0.16±0.4% |
Propriétés étendues
Rayons covalents (données étendues)
- Rayon covalent (Pyykkö)
- 171 pm
- Rayon covalent (Pyykkö, liaison double)
- 136 pm
- Rayon covalent (Pyykkö, liaison triple)
- 116 pm
Rayons de van der Waals
- Alvarez
- 282 pm
- UFF
- 342,4 pm
- MM3
- 252 pm
Rayons atomiques et métalliques
- Rayon atomique (Rahm)
- 281 pm
Échelles de numérotation
- Mendeleev
- 22
- Pettifor
- 44
- Glawe
- 37
Échelles d’électronégativité
- Ghosh
- 0
Polarisabilité et dispersion
- Polarisabilité dipolaire
- 151 a.u.
- Polarisabilité dipolaire (incertitude)
- 20 a.u.
Transitions de phase et allotropes
| Point de fusion | 917,15 K |
Catégories d’états d’oxydation
Données de référence avancées
Détail des rayons cristallins (8)
| Charge | CN | Spin | rcrystal (pm) | Origine |
|---|---|---|---|---|
| 2 | VI | 124 | ||
| 3 | VI | 115 | from r^3 vs V plots, | |
| 4 | VI | 101 | from r^3 vs V plots, | |
| 4 | VIII | 112 | from r^3 vs V plots, | |
| 5 | VI | 89 | ||
| 6 | VI | 86 | from r^3 vs V plots, | |
| 7 | VI | 85 | Ahrens (1952) ionic radius, | |
| 3 | IX | — | 131,8 |
Modes de désintégration des isotopes (44)
| Isotope | Mode | Intensité |
|---|---|---|
| 219 | A | 100% |
| 220 | A | 100% |
| 221 | A | — |
| 222 | A | 100% |
| 223 | A | 100% |
| 224 | A | 100% |
| 225 | A | 100% |
| 225 | B+ | — |
| 226 | A | 100% |
| 226 | B+ | — |
Données complémentaires
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
Références (1)
- [5] Neptunium https://education.jlab.org/itselemental/ele093.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
Références (1)
- [5] Neptunium https://education.jlab.org/itselemental/ele093.html
Références
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/
The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Neptunium.
The element property data was retrieved from publications.