In the nuclear fusion reaction,
$$ H_1^2 + H_1^3 \rightarrow He_2^4 + n_0^1$$
suppose I have been given the repulsive potential energy (say $P$) between the two nuclei. I need to find the temperature (say $T$) at which the gases must be heated to initiate the reaction.
My textbook says that we can find $T$ using the equation
However, I could not understand why we should equate the formula for translational kinetic energy of monoatomic molecule with $P$ to find $T$. Can anyone explain why this equation will give correct value for $T$ ?