Neptunium atoms undergo radioactive decay, which means they spontaneously transform into other elements. The specific forms produced depend on the type of decay process:

* Alpha Decay: Neptunium-237, the most common isotope, decays by alpha emission. This means it emits an alpha particle (a helium nucleus) and transforms into protactinium-233.

* Beta Decay: Some isotopes of neptunium can undergo beta decay, where a neutron turns into a proton, emitting an electron and an antineutrino. This process increases the atomic number and results in plutonium isotopes.

Other decay products:

Neptunium can also undergo various other decay modes, resulting in isotopes of uranium, americium, and other elements.

Important Note: The decay process is a random event, and the specific daughter nuclide produced depends on the specific isotope of neptunium and the decay mode.

Summary:

* Alpha decay of Neptunium-237 produces Protactinium-233.

* Beta decay of Neptunium isotopes can produce Plutonium isotopes.

* Other decay modes can produce various isotopes of Uranium, Americium, and other elements.