Polonium-209 (Po-209)

Identity

Protons

84

Neutrons

125

Mass number

209

Mass

209.0 ± 1.9 u

Mass excess

-16.366 MeV

Spin

1/2-*

Stability

Half-life: 124 years

Natural occurrence

Not found in nature

Decays to

• alpha 99.5 % → Pb-205
• positron emission 0.45 % → Bi-209