Video Transcript
In solar fusion reactions, how many
hydrogen nuclei must fuse to create one helium nucleus and two positrons? (A) One hydrogen nuclei, (B) two
hydrogen nuclei, (C) three hydrogen nuclei, (D) four hydrogen nuclei, or (E) five
hydrogen nuclei.
In a fusion reaction, small nuclei
combine and form larger ones, releasing large amounts of energy in the process. To understand how hydrogen fuses
into helium, we have to look at how many particles are in hydrogen and helium
nuclei. Each standard hydrogen nucleus
contains just one proton and no neutrons. Each standard helium nucleus
contains two protons and two neutrons. So the hydrogen nucleus contains
just one particle, whereas the helium nucleus contains four.
It follows that we would need four
hydrogen nuclei to produce one helium nucleus as it contains four particles. However, if we took four hydrogens
and put them together, we would have four protons, not two protons and two
neutrons. This is why positrons are
important. A positron is released when a
proton is converted to a neutron and neutrino. So when we have our four hydrogen
nuclei and fuse them together, we have four protons. Then, when we release two
positrons, two of those protons become neutrons, leaving us with two protons and two
neutrons, a helium nucleus.
So the number of hydrogen nuclei
that must fuse to create one helium nucleus and two positrons is (D), four hydrogen
nuclei.
