U-238 reacts with what particle to make 3 neutrons and 239Pu?

Question

U-238 reacts with what particle to make 3 neutrons and ²³⁹Pu?

Can someone explain why it's an alpha particle??

Answer 1

239Pu has 94 protons and 239- 94 = 145 neutrons.

238U has 92 protons and 238 - 92 = 146 neutrons

238U + 2 protons + 2 neutrons (that is 238U + alpha particle) makes 94 protons + 148 neutrons

This is the same as 239PU + 3 neutrons