Isotopes of neptunium

[19] 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.

[21] 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).

237Np 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.

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).

[22] The long half-life (T½ ~ 88 years) of 238Pu 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.

237Np is therefore a key radionuclide for the production of 238Pu, which is essential for deep space probes requiring a reliable and long-lasting source of energy without maintenance.

The extraction and purification of sufficient new quantities of 237Np from irradiated nuclear fuels is therefore necessary for the resumption of 238Pu production in order to replenish the stocks needed for space exploration by robotic probes.