The concept cross section what does it really means. Is that the maximum area for a fusion reaction to take place with a certain probability. Like the chans is more than 0,5 for fusion between boron and proton at 1 biljon K in an area less then 1*E-22 cm2. Then of course it must also be one proton and one boron nuclei in that area.

Cross section is more probabilistic due to particle-wave duality, but basically yes, the bigger the cross-section the more likely a fusion reaction will occur considering there is enough energy to overcome the coulomb barrier.

Cross section is more probabilistic due to particle-wave duality, but basically yes, the bigger the cross-section the more likely a fusion reaction will occur considering there is enough energy to overcome the coulomb barrier.

What I want to know is what and how you calculate it. If cross section is 10 exp -20 what does it means. An very simple calculated example is enough for me to understand I think.