Protactinium-229 (Pa-229)

Identity

Protons

91

Neutrons

138

Mass number

229

Mass

229.0 ± 3.5 u

Mass excess

29.897 MeV

Spin

5/2+

Stability

Half-life: 1.55 days

Natural occurrence

Not found in nature

Decays to

• electron capture 99.5 % → Th-229
• alpha 0.49 % → Ac-225