Isotopes of neptunium

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

Some notable isotopes

Neptunium-235

Neptunium-235 has 142 neutrons and a half-life of 400 days. This isotope of Neptunium either decays by:

  • Emitting an alpha particle - Here, the decay energy is 5.2 MeV and the decay product is Protactinium-231.
  • Electron capture - Here, the decay energy is 0.125 MeV and the decay product is Uranium-235

This particular isotope of neptunium has a weight of 235.0440633 grams/mole.

Neptunium-236

Neptunium-236 has 143 neutrons and a half-life of 154,000 years. It can decay by the following methods -

  • Electron capture - here, the decay energy is 0.95 MeV and the decay product is Uranium-236.
  • Beta emission - Here, the decay energy is 0.94 MeV and the decay product is Plutonium-236.
  • Alpha emission - Here, the decay energy is 5.024 MeV and the decay product is Protactinium-232

This particular isotope of neptunium has a mass of 236.04657 grams/mole. It is a fissile material with a critical mass of 7 kg.

possible parent nuclides: alpha from Am-240

Neptunium-237

Neptunium-237 decay scheme (simplified)
Actinides Half-life Fission products
244Cm 241Pu f 250Cf 243Cmf 10–30 y 137Cs 90Sr 85Kr
232 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 Ty 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.[1] 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.

Table

nuclide
symbol
Z(p) N(n)  
isotopic mass (u)
 
half-life decay
mode(s)[2][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-)
  1. ^ Abbreviations:
    CD: Cluster decay
    EC: Electron capture
    IT: Isomeric transition
    SF: Spontaneous fission
  2. ^ Fissile nuclide
  3. ^ Most common nuclide

Notes

  • Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
  • Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

Isotopes of uranium Isotopes of neptunium Isotopes of plutonium
Index to isotope pages · Table of nuclides

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Isotopes du neptunium — Le neptunium (Np) est un élément synthétique qui n a par conséquent pas de masse atomique standard. Comme tous les éléments synthétiques, il ne possède aucun isotope stable. Le premier isotope synthétisé en 1940 fut le neptunium 239 (239Np) en… …   Wikipédia en Français

  • Neptunium — Uranium ← Neptunium → Plutonium Pm …   Wikipédia en Français

  • Neptunium-236 — is a radioactive isotope of neptunium with 93 electrons and protons and 143 neutrons. It has a half life of 154,000 years. It can decay by the following methods *Electron capture here, the decay energy is 0.95 MeV and the decay product is Uranium …   Wikipedia

  • Neptunium — uranium ← neptunium → plutonium Pm ↑ Np ↓ (Uqt) …   Wikipedia

  • Neptunium — Eigenschaften …   Deutsch Wikipedia

  • Neptunium 237 — Le neptunium 237, noté 237Np, est l isotope du neptunium dont le nombre de masse est égal à 237 : son noyau atomique compte 93 protons et 144 neutrons avec un spin 5/2+ pour une masse atomique de 237,0481734 g/mol. Il est caractérisé par un… …   Wikipédia en Français

  • NEPTUNIUM — Élément chimique de numéro atomique 93, le neptunium (symbole Np) est le premier membre de la série d’éléments lourds artificiels: les transuraniens. Comme tous ces éléments, il a de nombreux isotopes qui sont tous radio actifs et produits… …   Encyclopédie Universelle

  • neptunium — Symbol: Np Atomic number: 93 Atomic weight: (237) Radioactive metallic transuranic element, belongs to the actinoids. Np 237, the most stable isotope, has a half life of 2.2*10^6 years and is a by product of nuclear reactors. The other known… …   Elements of periodic system

  • Isotopes of plutonium — Plutonium (Pu) has no stable isotopes. A standard atomic mass cannot be given.Decay modesTwenty plutonium radioisotopes have been characterized. The most stable are Pu 244, with a half life of 80.8 million years, Pu 242, with a half life of… …   Wikipedia

  • neptunium — /nep tooh nee euhm, tyooh /, n. Chem., Physics. a transuranic element produced in nuclear reactors by the neutron bombardment of U 238: decays rapidly to plutonium and then to U 235. Symbol: Np; at. no.: 93. [1940 45; NEPTUNE + IUM] * * * ▪… …   Universalium


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.