Neptunium-239 (Np-239)

Identity

Protons

93

Neutrons

146

Mass number

239

Mass

239.1 ± 1.4 u

Mass excess

49.311 MeV

Spin

5/2+*

Stability

Half-life: 2.36 days

Natural occurrence

Not found in nature

Decays to

• beta minus → Pu-239

Produced by

• Am-243