The decay of Bismuth-210 to Lead-206 involves two steps:

Step 1: Beta decay

* Bismuth-210 (²¹⁰Bi) decays into Polonium-210 (²¹⁰Po) by emitting a beta particle (electron) and an antineutrino:

²¹⁰Bi → ²¹⁰Po + e⁻ + ν̅ₑ

Step 2: Alpha decay

* Polonium-210 (²¹⁰Po) then decays into Lead-206 (²⁰⁶Pb) by emitting an alpha particle (helium nucleus):

²¹⁰Po → ²⁰⁶Pb + ⁴He

Overall reaction:

The overall reaction can be summarized as:

²¹⁰Bi → ²⁰⁶Pb + ⁴He + e⁻ + ν̅ₑ

Note:

* The half-life of Bismuth-210 is 5.013 days, while Polonium-210 has a half-life of 138.376 days.

* This decay series is an example of a radioactive decay chain, where one radioactive isotope decays into another, eventually leading to a stable isotope (Lead-206 in this case).