In the nuclear fusion reaction ${ }_1^2 \mathrm{H}+{ }_1^3 \mathrm{H} \rightarrow{ }_2^4 \mathrm{He}+\mathrm{n}$ given that the repulsive potential energy between the two nuclei is $\sim 7.7 \times 10^{-14} \mathrm{~J}$, the temperature at which the gases must be heated to initiate the reaction is nearly [Boltzmann's Constant $\mathrm{k}=1.38 \times 10^{-23} \mathrm{~J} / \mathrm{K}$ ]