Question

Let us consider emission of $\alpha$-particle from uranium nucleus:
${}_{92}{U}^{235}{\to }_2{He}^4\to$ ${}_{90}{Th}^{231}$
$e=92$ $e=0$ $e=90$
$p=92$ $p=2$ $p=90$
$n=143$ $n=2$ $n=141$
Shortage of two electrons in thorium is due to:

• A. conversion of electron to positron
• B. combination with positron to evolve energy
• C. annihilation
• D. absorption in the nucleus

Answer 1

Answer: (B), (C)

combination with positron to evolve energy
annihilation

Storage of two $e^{-}s$ in thorium is due to combination with positron to evolve energy and annihilation. As this reaction is nuclear fission, giving lighter particle from heavier particle.