# Collison of two alpha particlesre

I was reading on nuclear chemistry - in particular, the bombardment of nuclei with alpha-particles - and was wondering what the effect of

$$\ce{^4_2He + ^4_2He -> ^8_4Be}$$

would be. My instinct is to recognize this as a "fusion"-like reaction, but I am not comfortable enough with the subject to fully calculate it on my own.

• The Be-8 nucleus lies almost 1MeV above a ground state of 2 alpha particles. The nuclear reaction Li7 (p,$\alpha$) $\alpha$ was the first human-controlled reaction by Cocroft and Walton. So, no, you can’t fuse two alphas. – Jon Custer Nov 16 '18 at 1:25
• Just to be clear, it isn't that you can't collide two alpha particles, the problem is that the $\ce{^8_4Be}$ nucleus is highly unstable and decays to yield two alpha particles. To get a stable product 3 helium nuclei have to collide within a very short time to yield $\ce{^12_6C}$ . – MaxW Nov 16 '18 at 1:41
• My memory is clearly failing - the $\alpha$+$\alpha$ state is only 98keV below Be-8. Still, the Be-8 lifetime is 6E-17 sec, so it really likes falling apart. – Jon Custer Nov 16 '18 at 14:03

This is a very important nuclear reaction that happens in red giant stars that have burned all their hydrogen so they start burning He instead. As stated by Jon Custer, the $$^8$$Be nucleus is unstable so its lifetime is short. At the temperature in a star, a lot of collisions between two alpha particles have the same energy as the Be nucleus with respect to two free alpha particles resulting in an efficient production due to resonance (the kinetic energy lies very close to the Gamow peak).