Isotopes of neptunium

{{Anchor|Neptunium-221|Neptunium-245}}

{{Isotopes table

|symbol=Np

|refs=NUBASE2020, AME202020 II

|notes=m, unc(), mass#, exen#, spin(), spin#, daughter-nst, SF, EC, CD, IT

}}

|-id=Neptunium-219

| {{SimpleNuclide|Neptunium|219}}{{refn|group="n"|Heaviest known nucleus, {{as of|2025|lc=y}}, that is beyond the proton drip line.{{cite journal |last1=Yang |first1=H |last2=Ma |first2=L |last3=Zhang |first3=Z |last4=Yang |first4=C |last5=Gan |first5=Z |last6=Zhang |first6=M |display-authors=et al. |title=Alpha decay properties of the semi-magic nucleus ²¹⁹Np |journal=Physics Letters B |date=2018 |volume=777 |pages=212–216 |doi=10.1016/j.physletb.2017.12.017 |bibcode=2018PhLB..777..212Y |url=https://www.researchgate.net/publication/321843830|doi-access=free }}}}

| style="text-align:right" | 93

| style="text-align:right" | 126

| 219.031602(99)

| 570(450) μs

| α

| ²¹⁵Pa

| 9/2−#

|

|-id=Neptunium-220

| {{SimpleNuclide|Neptunium|220}}

| style="text-align:right" | 93

| style="text-align:right" | 127

| 220.032716(33)

| {{val|25|14|7|u=μs}}

| α

| ²¹⁶Pa

| 1−#

|

|-id=Neptunium-222

| {{SimpleNuclide|Neptunium|222}}

| style="text-align:right" | 93

| style="text-align:right" | 129

| 222.033575(41)

| 480(190) ns

| α

| ²¹⁸Pa

| 1−#

|

|-id=Neptunium-223

| {{SimpleNuclide|Neptunium|223}}

| style="text-align:right" | 93

| style="text-align:right" | 130

| 223.032913(89)

| 2.5(8) μs

| α

| ²¹⁹Pa

| (9/2−)

|

|-id=Neptunium-224

| rowspan=2|{{SimpleNuclide|Neptunium|224}}{{cite journal|last=Huang|first=T. H.|display-authors=etal|date=2018|title=Identification of the new isotope ²²⁴Np|url=https://www.researchgate.net/publication/328038265|format=pdf|journal=Physical Review C|volume=98|issue=4|pages=044302|doi=10.1103/PhysRevC.98.044302|bibcode=2018PhRvC..98d4302H|s2cid=125251822 }}

| rowspan=2 style="text-align:right" | 93

| rowspan=2 style="text-align:right" | 131

| rowspan=2|224.034388(31)

| rowspan=2|{{val|38|26|11|u=μs}}

| α (83%)

| ^220m1Pa

| rowspan=2|2−#

| rowspan=2|

|-

| α (17%)

| ^220m2Pa

|-id=Neptunium-225

| {{SimpleNuclide|Neptunium|225}}

| style="text-align:right" | 93

| style="text-align:right" | 132

| 225.033943(98)

| 6.5(35) ms

| α

| ²²¹Pa

| 9/2−#

|

|-id=Neptunium-226

| {{SimpleNuclide|Neptunium|226}}

| style="text-align:right" | 93

| style="text-align:right" | 133

| 226.03523(11)

| 35(10) ms

| α

| ²²²Pa

|

|

|-id=Neptunium-227

| {{SimpleNuclide|Neptunium|227}}

| style="text-align:right" | 93

| style="text-align:right" | 134

| 227.034975(83)

| 510(60) ms

| α

| ²²³Pa

| 5/2+#

|

|-id=Neptunium-228

| rowspan=3|{{SimpleNuclide|Neptunium|228}}

| rowspan=3 style="text-align:right" | 93

| rowspan=3 style="text-align:right" | 135

| rowspan=3|228.03631(11)#

| rowspan=3|61.4(14) s

| EC (59%)

| ²²⁸U

| rowspan=3|4+#

| rowspan=3|

|-

| α (41%)

| ²²⁴Pa

|-

| β⁺, SF (0.0126%)

| (various)

|-id=Neptunium-229

| rowspan=2|{{SimpleNuclide|Neptunium|229}}

| rowspan=2 style="text-align:right" | 93

| rowspan=2 style="text-align:right" | 136

| rowspan=2|229.03629(11)

| rowspan=2|4.00(18) min

| α (68%)

| ²²⁵Pa

| rowspan=2|5/2+#

| rowspan=2|

|-

| β⁺ (32%)

| ²²⁹U

|-id=Neptunium-230

| rowspan=2|{{SimpleNuclide|Neptunium|230}}

| rowspan=2 style="text-align:right" | 93

| rowspan=2 style="text-align:right" | 137

| rowspan=2|230.037828(59)

| rowspan=2|4.6(3) min

| β⁺ (>97%)

| ²³⁰U

| rowspan=2|4+#

| rowspan=2|

|-

| α (<3%)

| ²²⁶Pa

|-id=Neptunium-231

| rowspan=2|{{SimpleNuclide|Neptunium|231}}

| rowspan=2 style="text-align:right" | 93

| rowspan=2 style="text-align:right" | 138

| rowspan=2|231.038244(55)

| rowspan=2|48.8(2) min

| β⁺ (98%)

| ²³¹U

| rowspan=2|5/2+#

| rowspan=2|

|-

| α (2%)

| ²²⁷Pa

|-id=Neptunium-232

| {{SimpleNuclide|Neptunium|232}}

| style="text-align:right" | 93

| style="text-align:right" | 139

| 232.04011(11)#

| 14.7(3) min

| β⁺

| ²³²U

| (5−)

|

|-id=Neptunium-233

| rowspan=2|{{SimpleNuclide|Neptunium|233}}

| rowspan=2 style="text-align:right" | 93

| rowspan=2 style="text-align:right" | 140

| rowspan=2|233.040739(55)

| rowspan=2|36.2(1) min

| β⁺

| ²³³U

| rowspan=2|5/2+#

| rowspan=2|

|-

| α (0.0007%)

| ²²⁹Pa

|-id=Neptunium-234

| {{SimpleNuclide|Neptunium|234}}

| style="text-align:right" | 93

| style="text-align:right" | 141

| 234.0428932(90)

| 4.4(1) d

| β⁺

| ²³⁴U

| (0+)

|

|-id=Neptunium-234m

| rowspan=2 style="text-indent:1em" |{{SimpleNuclide|Neptunium|234m}}{{cite report |title=Discovery of 234 Np isomer and its decay properties |last1=Asai |first1=M. |last2=Suekawa |first2=Y. |last3=Higashi |first3=M. |display-authors=et al. |url=http://www.radiochem.org/jnrs-abst/pdf/64-501.pdf |language=Japanese |date=2020}}

| rowspan=2 colspan="3" style="text-indent:2em" |

| rowspan=2|~9 min

| IT

| ²³⁴Np

| rowspan=2|5+

| rowspan=2|

|-

| EC

| ²³⁴U

|-

| rowspan=2|{{SimpleNuclide|Neptunium|235}}

| rowspan=2 style="text-align:right" | 93

| rowspan=2 style="text-align:right" | 142

| rowspan=2|235.0440615(15)

| rowspan=2|396.1(12) d

| EC

| ²³⁵U

| rowspan=2|5/2+

| rowspan=2|

|-

| α (0.00260%)

| ²³¹Pa

|-

| rowspan=3|{{SimpleNuclide|Neptunium|236}}Fissile nuclide

| rowspan=3 style="text-align:right" | 93

| rowspan=3 style="text-align:right" | 143

| rowspan=3|236.046568(54)

| rowspan=3|1.53(5)×10⁵ y

| EC (86.3%)

| ²³⁶U

| rowspan=3|(6−)

| rowspan=3|

|-

| β⁻ (13.5%)

| ²³⁶Pu

|-

| α (0.16%)

| ²³²Pa

|-id=Neptunium-236m

| rowspan=2 style="text-indent:1em" | {{SimpleNuclide|Neptunium|236m}}Order of ground state and isomer is uncertain.

| rowspan=2 colspan="3" style="text-indent:2em" | 60(50) keV

| rowspan=2|22.5(4) h

| EC (50%)

| ²³⁶U

| rowspan=2|(1−)

| rowspan=2|

|-

| β⁻ (50%)

| ²³⁶Pu

|-

| rowspan=3|{{SimpleNuclide|Neptunium|237}}

| rowspan=3 style="text-align:right" | 93

| rowspan=3 style="text-align:right" | 144

| rowspan=3|237.0481716(12)

| rowspan=3|2.144(7)×10⁶ y

| α

| ²³³Pa

| rowspan=3|5/2+

| rowspan=3|TraceProduced by neutron capture in uranium ore

|-

| SF (<2×10⁻¹⁰%)

| (various)

|-

| CD (<4×10⁻¹²%)

| ²⁰⁷Tl
³⁰Mg

|-id=Neptunium-237m

| style="text-indent:1em" | {{SimpleNuclide|Neptunium|237m}}

| colspan="3" style="text-indent:2em" | 945.20(10) keV

| 710(40) ns

| IT

| ²³⁷Np

| 13/2−

|

|-id=Neptunium-238

| {{SimpleNuclide|Neptunium|238}}

| style="text-align:right" | 93

| style="text-align:right" | 145

| 238.0509446(12)

| 2.099(2) d

| β⁻

| ²³⁸Pu

| 2+

|

|-id=Neptunium-238m

| style="text-indent:1em" | {{SimpleNuclide|Neptunium|238m}}

| colspan="3" style="text-indent:2em" | 2300(200)# keV

| 112(39) ns

| SF

| (various)

|

|

|-

| {{SimpleNuclide|Neptunium|239}}

| style="text-align:right" | 93

| style="text-align:right" | 146

| 239.0529375(14)

| 2.356(3) d

| β⁻

| ²³⁹Pu

| 5/2+

| Trace

|-id=Neptunium-240

| {{SimpleNuclide|Neptunium|240}}

| style="text-align:right" | 93

| style="text-align:right" | 147

| 240.056164(18)

| 61.9(2) min

| β⁻

| ²⁴⁰Pu

| (5+)

| TraceIntermediate decay product of ²⁴⁴Pu

|-id=Neptunium-240m

| rowspan=2 style="text-indent:1em" | {{SimpleNuclide|Neptunium|240m}}

| rowspan=2 colspan="3" style="text-indent:2em" | 18(14) keV

| rowspan=2|7.22(2) min

| β⁻ (99.88%)

| ²⁴⁰Pu

| rowspan=2|(1+)

| rowspan=2|

|-

| IT (0.12%)

| ²⁴⁰Np

|-id=Neptunium-241

| {{SimpleNuclide|Neptunium|241}}

| style="text-align:right" | 93

| style="text-align:right" | 148

| 241.058349(33){{cite journal |title = Discovery of New Isotope {{sup|241}}U and Systematic High-Precision Atomic Mass Measurements of Neutron-Rich Pa-Pu Nuclei Produced via Multinucleon Transfer Reactions |author1= Niwase, T. |author2=Watanabe, Y. X. |author3=Hirayama, Y. |author4=Mukai, M. |author5=Schury, P. |author6=Andreyev, A. N. |author7=Hashimoto, T. |author8=Iimura, S. |author9=Ishiyama, H. |author10=Ito, Y. |author11=Jeong, S. C. |author12=Kaji, D. |author13=Kimura, S. |author14=Miyatake, H. |author15=Morimoto, K. |author16=Moon, J.-Y. |author17=Oyaizu, M. |author18=Rosenbusch, M. |author19=Taniguchi, A. |author20=Wada, M. |display-authors=3 |journal = Physical Review Letters |volume = 130 |issue = 13 |pages = 132502-1–132502-6 |year = 2023 |doi = 10.1103/PhysRevLett.130.132502|pmid= 37067317 |s2cid= 257976576 |url= https://eprints.whiterose.ac.uk/197980/1/PhysRevLett.130.132502.pdf }}

| 13.9(2) min

| β⁻

| ²⁴¹Pu

| (5/2+)

|

|-id=Neptunium-242

| {{SimpleNuclide|Neptunium|242}}

| style="text-align:right" | 93

| style="text-align:right" | 149

| 242.061738(87)

| 2.2(2) min

| β⁻

| ²⁴²Pu

| (1+)

|

|-id=Neptunium-242m

| style="text-indent:1em" | {{SimpleNuclide|Neptunium|242m}}

| colspan="3" style="text-indent:2em" | 50(50)# keV

| 5.5(1) min

| β⁻

| ²⁴²Pu

| (6+)

|

|-id=Neptunium-243

| {{SimpleNuclide|Neptunium|243}}

| style="text-align:right" | 93

| style="text-align:right" | 150

| 243.064204(34)#

| 1.85(15) min

| β⁻

| ²⁴³Pu

| 5/2+#

|

|-id=Neptunium-244

| {{SimpleNuclide|Neptunium|244}}

| style="text-align:right" | 93

| style="text-align:right" | 151

| 244.06789(11)#

| 2.29(16) min

| β⁻

| ²⁴⁴Pu

| 7−#

|

{{Isotopes table/footer}}

{{Actinidesvsfissionproducts}}

{{clear}}

Neptunium-235 has 142 neutrons and a half-life of 396.1 days. This isotope decays by:

• Alpha emission: the decay energy is 5.2 MeV and the decay product is protactinium-231.
• Electron capture: the decay energy is 0.125 MeV and the decay product is uranium-235

This isotope of neptunium has a weight of 235.044 063 3 u.

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

• Electron capture: the decay energy is 0.93 MeV and the decay product is uranium-236. This usually decays (with a half-life of 23 million years) to thorium-232.
• Beta emission: the decay energy is 0.48 MeV and the decay product is plutonium-236. This usually decays (half-life 2.8 years) to uranium-232, which usually decays (half-life 69 years) to thorium-228, which decays in a few years to lead-208.
• Alpha emission: the decay energy is 5.007 MeV and the decay product is protactinium-232. This decays with a half-life of 1.3 days to uranium-232.

This particular isotope of neptunium has a mass of 236.04657 u. It is a fissile material; it has an estimated critical mass of {{cvt|6.79|kg}},{{cite report |url=http://ec.europa.eu/energy/nuclear/transport/doc/irsn_sect03_146.pdf |title=Final Report, Evaluation of nuclear criticality safety data and limits for actinides in transport |archive-url=https://web.archive.org/web/20110519171204/http://ec.europa.eu/energy/nuclear/transport/doc/irsn_sect03_146.pdf |archive-date=2011-05-19 |url-status=dead |publisher=Republic of France, Institut de Radioprotection et de Sûreté Nucléaire, Département de Prévention et d'étude des Accidents.}} though precise experimental data is not available.{{cite journal |last=Reed |first=B. C. |date=2017 |title=An examination of the potential fission-bomb weaponizability of nuclides other than ²³⁵U and ²³⁹Pu |journal=American Journal of Physics |volume=85 |pages=38–44 |doi=10.1119/1.4966630}}

{{SimpleNuclide|Neptunium|236}} is produced in small quantities via the (n,2n) and (γ,n) capture reactions of {{SimpleNuclide|Neptunium|237}},[http://info.ornl.gov/sites/publications/files/Pub14204.pdf Analysis of the Reuse of Uranium Recovered from the Reprocessing of Commercial LWR Spent Fuel], United States Department of Energy, Oak Ridge National Laboratory. however, it is nearly impossible to separate in any significant quantities from its parent {{SimpleNuclide|Neptunium|237}}.**{{cite book |author=Jukka Lehto |author2=Xiaolin Hou |year=2011|chapter=15.15: Neptunium |title=Chemistry and Analysis of Radionuclides |page=231 |no-pp=yes |edition=1st |publisher=John Wiley & Sons |isbn=978-3527633029}} It is for this reason that despite its low critical mass and high neutron cross section, it has not been researched extensively as a nuclear fuel in weapons or reactors. Nevertheless, {{SimpleNuclide|Neptunium|236}} has been considered for use in mass spectrometry and as a radioactive tracer, because it decays predominantly by beta emission with a long half-life.{{cite journal|last1=Jerome|first1=S.M.|last2=Ivanov|first2=P.|last3=Larijani|first3=C. |last4=Parker|first4=D.J.|last5=Regan|first5=P.H.|title=The production of Neptunium-236g|date=2014|journal=Journal of Environmental Radioactivity|volume=138|pages=315–322|doi=10.1016/j.jenvrad.2014.02.029|pmid=24731718 }} Several alternative production routes for this isotope have been investigated, namely those that reduce isotopic separation from {{SimpleNuclide|Neptunium|237}} or the isomer {{SimpleNuclide|Neptunium|236m}}. The most favorable reactions to accumulate {{SimpleNuclide|Neptunium|236}} were shown to be proton and deuteron irradiation of uranium-238.

File:Neptunium-237-decay-scheme-simplified.svg

{{SimpleNuclide|Neptunium|237}} decays via the neptunium series, which terminates with thallium-205, which is stable, unlike most other actinides, which decay to stable isotopes of lead.

In 2002, {{SimpleNuclide|Neptunium|237}} was shown to be capable of sustaining a chain reaction with fast neutrons, as in a nuclear weapon, with a critical mass of around 60 kg.

{{cite journal

|author=P. Weiss

|date=26 October 2002

|title=Neptunium Nukes? Little-studied metal goes critical

|url=http://www.sciencenews.org/view/generic/id/3246/title/Neptunium_Nukes%3F_Little-studied_metal_goes_critical

|archive-url=https://archive.today/20240526102438/https://www.webcitation.org/6Cw9Vnt0Q?url=http://www.sciencenews.org/view/generic/id/3246/title/Neptunium_Nukes%3F_Little-studied_metal_goes_critical

|archive-date=26 May 2024

|journal=Science News

|volume=162

|issue=17

|page=259

|access-date=7 November 2013

|url-status=dead

|doi=10.2307/4014034

|jstor=4014034

}} However, it has a low probability of fission on bombardment with thermal neutrons, which makes it unsuitable as a fuel for light water nuclear power plants (as opposed to fast reactor or accelerator-driven systems, for example).

{{SimpleNuclide|Neptunium|237}} is the only neptunium isotope produced in significant quantity in the nuclear fuel cycle, both by successive neutron capture by 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, {{SimpleNuclide|Neptunium|237}} also forms in spent nuclear fuel as the decay product of americium-241.

{{SimpleNuclide|Neptunium|237}} is considered to be one of the most mobile radionuclides at the site of the Yucca Mountain nuclear waste repository (Nevada) where oxidizing conditions prevail in the unsaturated zone of the volcanic tuff above the water table.

{{Main article|Plutonium-238|Radioisotope thermoelectric generator}}

When exposed to neutron bombardment {{SimpleNuclide|Neptunium|237}} can capture a neutron, undergo beta decay, and become {{SimpleNuclide|Plutonium|238|link=yes}}, this product being useful as a thermal energy source in a radioisotope thermoelectric generator (RTG or RITEG) for the production of electricity and heat. The first type of thermoelectric generator SNAP (Systems for Nuclear Auxiliary Power) was developed and used by NASA in the 1960's and during the Apollo missions to power the instruments left on the Moon surface by the astronauts. Thermoelectric generators were also embarked on board of deep space probes such as for the Pioneer 10 and 11 missions, the Voyager program, the Cassini–Huygens mission, and New Horizons. They also deliver electrical and thermal power to the Mars Science Laboratory (Curiosity rover) and Mars 2020 mission (Perseverance rover) both exploring the cold surface of Mars. Curiosity and Perseverance rovers are both equipped with the last version of multi-mission RTG, a more efficient and standardized system dubbed MMRTG.

These applications are economically practical where photovoltaic power sources are weak or inconsistent due to probes being too far from the sun or rovers facing climate events that may obstruct sunlight for long periods (like Martian dust storms). Space probes and rovers also make use of the heat output of the generator to keep their instruments and internals warm.{{Cite journal|last=Witze|first=Alexandra|date=2014-11-27|title=Nuclear power: Desperately seeking plutonium|journal=Nature|language=en|volume=515|issue=7528|pages=484–486|doi=10.1038/515484a|pmid=25428482 |bibcode=2014Natur.515..484W|doi-access=free}}

The long half-life (T{{sub|1/2}} ~ 88 years) of {{SimpleNuclide|Plutonium|238}} and the absence of γ-radiation that could interfere with the operation of on-board electronic components, or irradiate people, makes it the radionuclide of choice for electric thermogenerators.

{{SimpleNuclide|Neptunium|237}} is therefore a key radionuclide for the production of {{SimpleNuclide|Plutonium|238}}, which is essential for deep space probes requiring a reliable and long-lasting source of energy without maintenance.

Stockpiles of {{SimpleNuclide|Plutonium|238|link=yes}} built up in the United States since the Manhattan Project, thanks to the Hanford nuclear complex (operating in Washington State from 1943 to 1977) and the development of atomic weapons, are now almost exhausted. The extraction and purification of sufficient new quantities of {{SimpleNuclide|Neptunium|237}} from irradiated nuclear fuels is therefore necessary for the resumption of {{SimpleNuclide|Plutonium|238}} production in order to replenish the stocks needed for space exploration by robotic probes.

Neptunium-239 has 146 neutrons and a half-life of 2.356 days. It is produced via β⁻ decay of the short-lived uranium-239, and undergoes another β⁻ decay to plutonium-239. This is the primary route for making plutonium, as ²³⁹U can be made by neutron capture in uranium-238.{{cite web| url=http://periodic.lanl.gov/93.shtml| title=Periodic Table Of Elements: LANL - Neptunium| publisher=Los Alamos National Laboratory| access-date=2013-10-13}}

Uranium-237 and neptunium-239 are regarded as the leading hazardous radioisotopes in the first hour-to-week period following nuclear fallout from a nuclear detonation, with ²³⁹Np dominating "the spectrum for several days".[Film Badge Dosimetry in Atmospheric Nuclear Tests, By Committee on Film Badge Dosimetry in Atmospheric Nuclear Tests, Commission on Engineering and Technical Systems, Division on Engineering and Physical Sciences, National Research Council. pg24-35][http://www.dtra.mil/Portals/61/Documents/NTPR/4-Rad_Exp_Rpts/30_DTRA-TR-07-5_Fractionation_Report.pdf Bounding Analysis of Effects of Fractionation of Radionuclides in Fallout on Estimation of Doses to Atomic Veterans DTRA-TR-07-5. 2007]

{{reflist}}

• Isotope masses from:
• {{NUBASE 2003}}
• Half-life, spin, and isomer data selected from the following sources.
• {{NUBASE 2003}}
• {{NNDC}}
• {{CRC85|chapter=11}}

{{Navbox element isotopes}}

Category:Neptunium

Neptunium