Neptunium Neptunium is a chemical element; it has chemical symbol, symbol Np and atomic number 93. A radioactivity, radioactive actinide metal, neptunium is the first transuranic element. It is named after Neptune, the planet beyond Uranus in the Solar Syste ...

(₉₃Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

to be synthesized and identified was ²³⁹Np in 1940, produced by bombarding with

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

s to produce , which then underwent

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

to . Trace quantities are found in nature from

neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

reactions by

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

atoms, a fact not discovered until 1951. Twenty-five neptunium

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

s have been characterized, with the most stable being with a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of 2.14 million years, with a half-life of 154,000 years, and with a half-life of 396.1 days. All of the remaining

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

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 five meta states, with the most stable being (t_1/2 22.5 hours). The isotopes of neptunium range from to , though the intermediate isotope has not yet been observed. The primary

decay mode Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

before the most stable isotope, , is

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

(with a good deal of alpha emission), and the primary mode after is beta emission. The primary

decay product In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps ( d ...

s before are

isotopes of uranium Uranium (U) is a naturally occurring radioactive element (radioelement) with no stable isotopes. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in Earth's crust. The d ...

and

protactinium Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, silvery-gray actinide metal which readily reacts with oxygen, water vapor, and inorganic acids. It forms various chemical compounds, in which p ...

, and the primary products after are isotopes of plutonium. Neptunium is the heaviest element for which the location of the

proton drip line The nuclear drip line is the boundary beyond which atomic nuclei are unbound with respect to the emission of a proton or neutron. An arbitrary combination of protons and neutrons does not necessarily yield a stable nucleus. One can think of m ...

is known; the lightest bound isotope is ²²⁰Np.

List of isotopes

, -id=Neptunium-219 , , style="text-align:right" , 93 , style="text-align:right" , 126 , 219.031602(99) , 570(450) μs , α , ²¹⁵Pa , 9/2−# , , -id=Neptunium-220 , , style="text-align:right" , 93 , style="text-align:right" , 127 , 220.032716(33) , , α , ²¹⁶Pa , 1−# , , -id=Neptunium-222 , , style="text-align:right" , 93 , style="text-align:right" , 129 , 222.033575(41) , 480(190) ns , α , ²¹⁸Pa , 1−# , , -id=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, , rowspan=2 style="text-align:right" , 93 , rowspan=2 style="text-align:right" , 131 , rowspan=2, 224.034388(31) , rowspan=2, , α (83%) , ^220m1Pa , rowspan=2, 2−# , rowspan=2, , - , α (17%) , ^220m2Pa , -id=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 , , style="text-align:right" , 93 , style="text-align:right" , 133 , 226.03523(11) , 35(10) ms , α , ²²²Pa , , , -id=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, , 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, , 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, , 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, , 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 , , 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, , 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 , , 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" , , rowspan=2 colspan="3" style="text-indent:2em" , , rowspan=2, ~9 min , IT , ²³⁴Np , rowspan=2, 5+ , rowspan=2, , - , EC , ²³⁴U , - , rowspan=2, , 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,

Fissile In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal Nuclear chain reaction#Fission chain reaction, chain reaction can only be achieved with fissil ...

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" , 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, , 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

in uranium ore , - , SF (<2×10⁻¹⁰%) , (various) , - , CD (<4×10⁻¹²%) , ²⁰⁷Tl
³⁰Mg , -id=Neptunium-237m , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , 945.20(10) keV , 710(40) ns , IT , ²³⁷Np , 13/2− , , -id=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" , , colspan="3" style="text-indent:2em" , 2300(200)# keV , 112(39) ns , SF , (various) , , , - , , 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 , , 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" , , 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 , , style="text-align:right" , 93 , style="text-align:right" , 148 , 241.058349(33) , 13.9(2) min , β⁻ , ²⁴¹Pu , (5/2+) , , -id=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" , , colspan="3" style="text-indent:2em" , 50(50)# keV , 5.5(1) min , β⁻ , ²⁴²Pu , (6+) , , -id=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 , , style="text-align:right" , 93 , style="text-align:right" , 151 , 244.06789(11)# , 2.29(16) min , β⁻ , ²⁴⁴Pu , 7−# ,

Actinides vs fission products

Notable isotopes

Neptunium-235

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

decay energy The decay energy is the energy change of a nucleus having undergone a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energ ...

is 5.2 MeV and the decay product is

protactinium-231 Protactinium (91Pa) has no stable isotopes. The four naturally occurring isotopes allow a standard atomic weight to be given. Thirty radioisotopes of protactinium have been characterized, ranging from 210Pa to 239Pa. The most stable isotope is 2 ...

. *Electron capture: the decay energy is 0.125 MeV and the decay product is

uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...

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

Neptunium-236

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 Uranium-236 ( or U-236) is an isotope of uranium that is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in ...

. This usually decays (with a half-life of 23 million years) to

thorium-232 Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14.05 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its de ...

. *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 Lead (82Pb) has four observationally stable isotopes: 204Pb, 206Pb, 207Pb, 208Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay ...

. *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 In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal Nuclear chain reaction#Fission chain reaction, chain reaction can only be achieved with fissil ...

material; it has an estimated critical mass of , though precise experimental data is not available. is produced in small quantities via the (n,2n) and (γ,n) capture reactions of ,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 .** 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, has been considered for use in

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...

and as a

radioactive tracer A radioactive tracer, radiotracer, or radioactive label is a synthetic derivative of a natural compound in which one or more atoms have been replaced by a radionuclide (a radioactive atom). By virtue of its radioactive decay, it can be used to ...

, because it decays predominantly by beta emission with a long half-life. Several alternative production routes for this isotope have been investigated, namely those that reduce isotopic separation from or the

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

. The most favorable reactions to accumulate were shown to be

proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

and

deuteron Deuterium (hydrogen-2, symbol H or D, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen; the other is protium, or hydrogen-1, H. The deuterium atomic nucleus, nucleus (deuteron) contains one proton and ...

irradiation of

uranium-238 Uranium-238 ( or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it i ...

Neptunium-237

decays via the

neptunium series In nuclear science a decay chain refers to the predictable series of radioactive decay, radioactive disintegrations undergone by the nuclei of certain unstable chemical elements. Radionuclide, Radioactive isotopes do not usually decay directly ...

, which terminates with thallium-205, which is stable, unlike most other

actinide The actinide () or actinoid () series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. Number 103, lawrencium, is also generally included despite being part ...

s, which decay to stable isotopes of lead. In 2002, was shown to be capable of sustaining a chain reaction with fast neutrons, as in a

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

, with a critical mass of around 60 kg. However, it has a low probability of fission on bombardment with

thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium wit ...

s, which makes it unsuitable as a fuel for light water nuclear power plants (as opposed to fast reactor or accelerator-driven systems, for example).

Inventory in spent nuclear fuel

is the only neptunium isotope produced in significant quantity in the

nuclear fuel cycle The nuclear fuel cycle, also known as the nuclear fuel chain, describes the series of stages that nuclear fuel undergoes during its production, use, and recycling or disposal. It consists of steps in the ''front end'', which are the preparation o ...

, both by successive

(which fissions most but not all of the time) and

, or (n,2n) reactions where a fast neutron occasionally knocks a neutron loose from

or isotopes of plutonium. Over the long term, also forms in

spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and ...

as the decay product of

americium-241 Americium-241 (Am, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of . Am is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It ...

. is considered to be one of the most mobile

radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

s at the site of the

Yucca Mountain nuclear waste repository The Yucca Mountain Nuclear Waste Repository, as designated by the Nuclear Waste Policy Act amendments of 1987, is a proposed deep geological repository storage facility within Yucca Mountain for spent nuclear fuel and other high-level radioact ...

(

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

) where

oxidizing Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

conditions prevail in the

unsaturated zone The vadose zone (from the Latin word for "shallow"), also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at ...

of the volcanic tuff above the

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

Raw material for production

When exposed to neutron bombardment can capture a neutron, undergo beta decay, and become , this product being useful as a thermal energy source in a

radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), or radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the Decay heat, heat released by the decay of a suitable radioactive material i ...

(RTG or RITEG) for the production of electricity and heat. The first type of thermoelectric generator SNAP (

Systems for Nuclear Auxiliary Power The Systems Nuclear Auxiliary POWER (SNAP) program was a program of experimental radioisotope thermoelectric generators (RTGs) and Nuclear power in space, space nuclear reactors flown during the 1960s by NASA. The SNAP program developed as a resul ...

) was developed and used by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

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 probe Uncrewed spacecraft or robotic spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input, such as remote control, or remote guidance. They may also be autonomous, in which th ...

s such as for the Pioneer 10 and 11 missions, the

Voyager program The Voyager program is an American scientific program that employs two interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable planetary alignment to explore the two gas giants Jupiter ...

, the

Cassini–Huygens ''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space research, space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, i ...

mission, and

New Horizons ''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institut ...

. They also deliver electrical and thermal power to the

Mars Science Laboratory Mars Science Laboratory (MSL) is a robotic spacecraft, robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity (rover), Curiosity'', a Mars rover, in Gale (crater), Gale Crater on Augus ...

(Curiosity rover) and

Mars 2020 Mars 2020 is a NASA mission that includes the rover ''Perseverance (rover), Perseverance'', the now-retired small robotic helicopter ''Ingenuity (helicopter), Ingenuity'', and associated delivery systems, as part of the Mars Exploration Progra ...

mission ( Perseverance rover) both exploring the cold surface of

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

. 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.

Shortage of stockpiles

The long

(T ~ 88 years) of 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. is therefore a key radionuclide for the production of , which is essential for deep space probes requiring a reliable and long-lasting source of energy without maintenance. Stockpiles of built up in the United States since the

Manhattan Project The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the ...

, thanks to the Hanford nuclear complex (operating in

Washington State Washington, officially the State of Washington, is a state in the Pacific Northwest region of the United States. It is often referred to as Washington State to distinguish it from the national capital, both named after George Washington ...

from 1943 to 1977) and the development of atomic weapons, are now almost exhausted. The extraction and purification of sufficient new quantities of from irradiated nuclear fuels is therefore necessary for the resumption of production in order to replenish the stocks needed for space exploration by robotic probes.

Neptunium-239

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 Uranium (U) is a naturally occurring radioactive element (radioelement) with no stable isotopes. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in Earth's crust. Th ...

, and undergoes another β⁻ decay to

plutonium-239 Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main iso ...

. This is the primary route for making plutonium, as ²³⁹U can be made by

. Uranium-237 and neptunium-239 are regarded as the leading hazardous radioisotopes in the first hour-to-week period following

nuclear fallout Nuclear fallout is residual radioactive material that is created by the reactions producing a nuclear explosion. It is initially present in the mushroom cloud, radioactive cloud created by the explosion, and "falls out" of the cloud as it is ...

from a nuclear detonation, with ²³⁹Np dominating "the spectrum for several days".Bounding Analysis of Effects of Fractionation of Radionuclides in Fallout on Estimation of Doses to Atomic Veterans DTRA-TR-07-5. 2007
/ref>

References

* Isotope masses from: ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Navbox element isotopes Neptunium