Neptunium (Np) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 239Np in 1940, produced by bombarding 238U with neutrons to produce 239U, which then underwent beta decay to 239Np.
Trace quantities are found in nature from neutron capture by uranium atoms.
Twenty 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 4 meta states, with the most stable being 236m
Np (t½ 22.5 hours).
The isotopes of neptunium range in atomic weight from 225.0339 u (225
Np) to 244.068 u (244
Np). 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.
Contents |
Neptunium-235 has 142 neutrons and a half-life of 400 days. This isotope of Neptunium either decays by:
This particular isotope of neptunium has a weight of 235.0440633 grams/mole.
Neptunium-236 has 143 neutrons and a half-life of 154,000 years. It can decay by the following methods -
This particular isotope of neptunium has a mass of 236.04657 grams/mole. It is a fissile material with a critical mass of 6.79 kg.[1]
possible parent nuclides: alpha from Am-240
| Actinides | Half-life | Fission products | ||||||
|---|---|---|---|---|---|---|---|---|
| 244Cm | 241Pu f | 250Cf | 243Cmf | 10–30 y | 137Cs | 90Sr | 85Kr | |
| 232U f | 238Pu | f is for fissile |
69–90 y | 151Sm nc➔ | ||||
| 4n | 249Cf f | 242Amf | 141–351 | No fission product has half-life 102 to 2×105 years |
||||
| 241Am | 251Cf f | 431–898 | ||||||
| 240Pu | 229Th | 246Cm | 243Am | 5–7 ky | ||||
| 4n | 245Cmf | 250Cm | 239Pu f | 8–24 ky | ||||
| 233U f | 230Th | 231Pa | 32–160 | |||||
| 4n+1 | 234U | 4n+3 | 211–290 | 99Tc | 126Sn | 79Se | ||
| 248Cm | 242Pu | 340–373 | Long-lived fission products | |||||
| 237Np | 4n+2 | 1–2 My | 93Zr | 135Cs nc➔ | ||||
| 236U | 4n+1 | 247Cmf | 6–23 My | 107Pd | 129I | |||
| 244Pu | 80 My | >7% | >5% | >1% | >.1% | |||
| 232Th | 238U | 235U f | 0.7–12 Gy | fission product yield | ||||
237
Np decays via the neptunium series to thallium, unlike most other actinides which decay to isotopes of lead.
237
Np was recently shown to be capable of sustaining a chain reaction with fast neutrons, as in a nuclear weapon.[2] However, it has a low probability of fission on bombardment with thermal neutrons, which makes it unsuitable as a fuel for nuclear power plants.
237
Np is the only neptunium isotope produced in significant quantity in the nuclear fuel cycle, both by successive neutron capture on uranium-235 (which fissions most but not all of the time) and uranium-236, or (n,2n) reactions where a fast neutron occasionally knocks a neutron loose from uranium-238 or isotopes of plutonium. Over the long term, 237
Np also forms in spent nuclear fuel as the decay product of americium-241.
237
Np is projected to be one of the most mobile nuclides at the Yucca Mountain nuclear waste repository.
| nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s)[3][n 1] |
daughter isotope(s) |
nuclear spin |
|---|---|---|---|---|---|---|---|
| excitation energy | |||||||
| 225 Np |
93 | 132 | 225.03391(8) | 3# ms [>2 µs] | α | 221Pa | 9/2-# |
| 226 Np |
93 | 133 | 226.03515(10)# | 35(10) ms | α | 222Pa | |
| 227 Np |
93 | 134 | 227.03496(8) | 510(60) ms | α (99.95%) | 223Pa | 5/2-# |
| β+ (.05%) | 227U | ||||||
| 228 Np |
93 | 135 | 228.03618(21)# | 61.4(14) s | β+ (59%) | 228U | |
| α (41%) | 224Pa | ||||||
| β+, SF (.012%) | (various) | ||||||
| 229 Np |
93 | 136 | 229.03626(9) | 4.0(2) min | α (51%) | 225Pa | 5/2+# |
| β+ (49%) | 229U | ||||||
| 230 Np |
93 | 137 | 230.03783(6) | 4.6(3) min | β+ (97%) | 230U | |
| α (3%) | 226Pa | ||||||
| 231 Np |
93 | 138 | 231.03825(5) | 48.8(2) min | β+ (98%) | 231U | (5/2)(+#) |
| α (2%) | 227Pa | ||||||
| 232 Np |
93 | 139 | 232.04011(11)# | 14.7(3) min | β+ (99.99%) | 232U | (4+) |
| α (.003%) | 228Pa | ||||||
| 233 Np |
93 | 140 | 233.04074(5) | 36.2(1) min | β+ (99.99%) | 233U | (5/2+) |
| α (.001%) | 229Pa | ||||||
| 234 Np |
93 | 141 | 234.042895(9) | 4.4(1) d | β+ | 234U | (0+) |
| 235 Np |
93 | 142 | 235.0440633(21) | 396.1(12) d | EC | 235U | 5/2+ |
| α (.0026%) | 231Pa | ||||||
| 236 Np |
93 | 143 | 236.04657(5) | 1.54(6)×105 a | EC (87.3%) | 236U | (6-) |
| β- (12.5%) | 236Pu | ||||||
| α (.16%) | 232Pa | ||||||
| 236m Np |
60(50) keV | 22.5(4) h | EC (52%) | 236U | 1 | ||
| β- (48%) | 236Pu | ||||||
| 237 Np[n 2][n 3] |
93 | 144 | 237.0481734(20) | 2.144(7)×106 a | α | 233Pa | 5/2+ |
| SF (2×10−10%) | (various) | ||||||
| CD (4×10−12%) | 207Tl 30Mg |
||||||
| 238 Np |
93 | 145 | 238.0509464(20) | 2.117(2) d | β- | 238Pu | 2+ |
| 238m Np |
2300(200)# keV | 112(39) ns | |||||
| 239 Np |
93 | 146 | 239.0529390(22) | 2.356(3) d | β- | 239Pu | 5/2+ |
| 240 Np |
93 | 147 | 240.056162(16) | 61.9(2) min | β- | 240Pu | (5+) |
| 240m Np |
20(15) keV | 7.22(2) min | β- (99.89%) | 240Pu | 1(+) | ||
| IT (.11%) | 240Np | ||||||
| 241 Np |
93 | 148 | 241.05825(8) | 13.9(2) min | β- | 241Pu | (5/2+) |
| 242 Np |
93 | 149 | 242.06164(21) | 2.2(2) min | β- | 242Pu | (1+) |
| 242m Np |
0(50)# keV | 5.5(1) min | 6+# | ||||
| 243 Np |
93 | 150 | 243.06428(3)# | 1.85(15) min | β- | 243Pu | (5/2-) |
| 244 Np |
93 | 151 | 244.06785(32)# | 2.29(16) min | β- | 244Pu | (7-) |
| Isotopes of uranium | Isotopes of neptunium | Isotopes of plutonium |
| Index to isotope pages · Table of nuclides | ||