Deuterium (2D) is an isotope of hydrogen with a nucleus containing one proton and one neutron. In a 2D-2D fusion reaction, two deuterium nuclei combine to form a helium nucleus plus a neutron, releasing energy in the process.
The two 2D nuclei must overcome the electrical repulsion of the positively charged nuclei (q = + e) to get close enough for the reaction to occur. The radius of a deuterium nucleus is about 1 fm, so the centers of the nuclei must get within about 2 fm of one another. To estimate the temperature that a gas of deuterium atoms must have for this fusion reaction to occur, find the temperature at which the average kinetic energy of the deuterium atoms is 5% of the required activation energy for the reaction.