Neptunium (Np)
actinideSolid
標準原子量
[237]電子配置
[Rn] 7s2 5f4 6d1融点
643.85 °C沸点
3901.85 °C密度
2.025e+4 kg/m³酸化数
+2, +3, +4, +5, +6, +7電気陰性度（Pauling）
1.36第1イオン化エネルギー
6.265608 eV発見年
1940原子半径
175 pm詳細
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.
画像
性質
物理的性質
- 原子半径（経験値）
- 175 pm 全元素の原子半径（経験値）を比較 →
- 共有結合半径
- 190 pm 全元素の共有結合半径を比較 →
- ファンデルワールス半径
- 221 pm 全元素のファンデルワールス半径を比較 →
- 密度
- 2.025 × 104 kg/m³ 全元素の密度を比較 →
- モル体積
- 0.0211 L/mol
- 標準温度・圧力（STP）での相
- 固体 全元素の標準温度・圧力（STP）での相を比較 →
- 融点
- 643.85 °C 全元素の融点を比較 →
- 沸点
- 3901.85 °C 全元素の沸点を比較 →
- 結晶構造
- 斜方晶系 全元素の結晶構造を比較 →
化学的性質
- 電気陰性度（Pauling）
- 1.36 全元素の電気陰性度（Pauling）を比較 →
- 電子親和力
- 0.48 eV
- 第1イオン化エネルギー
- 6.265608 eV 全元素の第1イオン化エネルギーを比較 →
- 第2イオン化エネルギー
- 11.50004 eV 全元素の第2イオン化エネルギーを比較 →
- 第3イオン化エネルギー
- 19.700068 eV 全元素の第3イオン化エネルギーを比較 →
- 第4イオン化エネルギー
- 33.800116 eV 全元素の第4イオン化エネルギーを比較 →
- 第5イオン化エネルギー
- 48.000165 eV 全元素の第5イオン化エネルギーを比較 →
- 酸化数
- +2, +3, +4, +5, +6, +7 全元素の酸化数を比較 →
- 価電子
- 3 全元素の価電子を比較 →
- 電子配置
- [Rn] 7s2 5f4 6d1
熱力学的性質
- 融解熱
- 0.10364305 eV 全元素の融解熱を比較 →
- 蒸発熱
- 3.482407 eV 全元素の蒸発熱を比較 →
- 昇華熱
- 4.33228 eV
- 原子化熱
- 4.33228 eV
- 原子化エンタルピー
- 4.817329 eV
原子核
- 陽子数
- 93 全元素の陽子数を比較 →
- 中性子数
- 144 全元素の中性子数を比較 →
- 既知の同位体
- 27 全元素の既知の同位体を比較 →
- 安定同位体
- 0 全元素の安定同位体を比較 →
- 質量数（最も安定な同位体）
- 237
- 最も安定な同位体
- Np-237
- 発見年
- 1940
存在度
データなし
結晶構造
- 格子定数a
- 472 pm
電子構造
- 各電子殻の電子数
- 2, 8, 18, 32, 22, 9, 2 全元素の各電子殻の電子数を比較 →
識別子
- CAS登録番号
- 7439-99-8 全元素のCAS登録番号を比較 →
- 項記号
- 6L11/2
- InChI
- InChI=1S/Np
- InChI Key
- LFNLGNPSGWYGGD-UHFFFAOYSA-N
電子配置 測定値
Np: 5f⁴ 6d¹ 7s²[Rn] 5f⁴ 6d¹ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f⁴ 6d¹ 7s²原子モデル
同位体によって中性子数、質量、安定性は変わりますが、中性原子の電子配置は変わりません。
模式的な原子モデルです。実際の縮尺とは異なります。
原子の指紋
発光／吸収スペクトル
同位体分布
安定同位体はありません。
| 質量数 | 原子質量（u） | 天然存在比 | 半減期 |
|---|---|---|---|
| 219 放射性 | 219.03143 ± 0.00021 | データなし | 570 us |
| 227 放射性 | 227.034957 ± 0.000078 | データなし | 510 ms |
| 222 放射性 | 222.0333 ± 0.00021 | データなし | 480 ns |
| 235 放射性 | 235.0440635 ± 0.0000021 | データなし | 396.1 日 |
| 236 放射性 | 236.04657 ± 0.000054 | データなし | 153 ky |
相／状態
理由: 融点（643.85 °C）より618.9 °C低い
模式図、実際の縮尺とは異なります
相転移点
相転移エネルギー
融点で1 molを融解させるのに必要なエネルギー
沸点で1 molを蒸発させるのに必要なエネルギー
昇華点で1 molを昇華させるのに必要なエネルギー
密度
標準条件下
標準条件下
原子スペクトル
全93件中10件を表示しています。 イオンの電荷の昇順で並べています。
準位データの収録状況 ?
| イオン | 電荷 | 準位 |
|---|---|---|
| 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 |
イオン半径
| 電荷 | 配位 | スピン | 半径 |
|---|---|---|---|
| +2 | 6 | データなし | 110.00000000000001 pm |
| +3 | 6 | データなし | 101 pm |
| +3 | 9 | データなし | 117.8 pm |
| +4 | 6 | データなし | 87 pm |
| +4 | 8 | データなし | 98 pm |
| +5 | 6 | データなし | 75 pm |
| +6 | 6 | データなし | 72 pm |
| +7 | 6 | データなし | 71 pm |
化合物
同位体 (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.
| 質量数 | 原子質量（u） | 天然存在比 | 半減期 | 崩壊形式 | |
|---|---|---|---|---|---|
| 219 放射性 | 219.03143 ± 0.00021 | データなし | 570 us | α =100% | |
| 227 放射性 | 227.034957 ± 0.000078 | データなし | 510 ms | α ≈100%β+ ? | |
| 222 放射性 | 222.0333 ± 0.00021 | データなし | 480 ns | α =100% | |
| 235 放射性 | 235.0440635 ± 0.0000021 | データなし | 396.1 日 | ε =99.99740±1.3%α =0.00260±1.3% | |
| 236 放射性 | 236.04657 ± 0.000054 | データなし | 153 ky | ε =86.3±0.8%β- =13.5±0.8%α =0.16±0.4% |
詳細な性質
共有結合半径（詳細）
- 共有結合半径（Pyykkö）
- 171 pm
- 共有結合半径（Pyykkö、二重結合）
- 136 pm
- 共有結合半径（Pyykkö、三重結合）
- 116 pm
ファンデルワールス半径
- Alvarez
- 282 pm
- UFF
- 342.4 pm
- MM3
- 252 pm
原子半径と金属半径
- 原子半径（Rahm）
- 281 pm
番号付けの尺度
- Mendeleev
- 22
- Pettifor
- 44
- Glawe
- 37
電気陰性度の尺度
- Ghosh
- 0
分極率と分散
- 双極子分極率
- 151 a.u.
- 双極子分極率（不確かさ）
- 20 a.u.
相転移と同素体
| 融点 | 917.15 K |
酸化数の分類
専門参考データ
結晶半径の詳細 (8)
| 電荷 | CN | スピン | rcrystal (pm) | 由来 |
|---|---|---|---|---|
| 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 |
同位体の崩壊形式 (44)
| 同位体 | モード | 強度 |
|---|---|---|
| 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+ | — |
追加データ
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
参考文献 (1)
- [5] Neptunium https://education.jlab.org/itselemental/ele093.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
参考文献 (1)
- [5] Neptunium https://education.jlab.org/itselemental/ele093.html
参考文献
(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.