Here's the nuclear reaction:

²⁴⁹Bk → ⁴He + ²⁴⁵Am

* ²⁴⁹Bk is the berkelium-249 isotope.

* ⁴He is the alpha particle (helium nucleus).

* ²⁴⁵Am is the americium-245 isotope.

Alpha decay involves the emission of an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. This process reduces the atomic number by 2 and the mass number by 4.