What is the product element (isotope) produced when protactinium undergoes alpha decay?
Protactinium (Pr) is element number 91. It has 91 protons and 75 neutrons. Alpha decay reduces the atomic number by 2 and the atomic number (also, and better, called 'nucleon number') by 4 (2 protons and 2 neutrons). The product element is element number 89, actinium (Ac), with 162 nucleons, so Ac-162.