Light Nuclei Light nuclei have relatively high rest masses. H-1: 1.008665 uH-1: 1.008665 u H-2: 2.014102 uH-2: 2.014102 u He-3: 3.016029 uHe-3: 3.016029 u He-4: 4.002603 uHe-4: 4.002603 u C-12: 12.000000 uC-12: 12.000000 u Energy is available compared to heavy mass nuclei. Si-28: 27.976926Si-28: 27.976926 Fe-56: 55.934942Fe-56: 55.934942
The Sun The energy output of the sun is inconsistent with chemical processes. Chemical bonds too weak Gravitational contraction would have to be too fast. Sun would last 100 My Nuclear fusion of light nuclei explains the energy output.
Nuclear Fusion Electric charge causes positive nuclei to repel. At high temperatures nuclei get close enough for the nuclear force to pull them together. fusion starting nuclei heavier nucleus other particles
Proton-Proton Cycle Fusion takes place two particles at a time. Step 1: two protons form a deuterium nucleus with positron and a neutrino. hydrogen nuclei with one proton each neutron neutrino: related to electrons by the weak nuclear force photons electron positron: positive charged electron; annihilates to form photons
Proton Fusion 2 Step 2: A deuterium nucleus absorbs a proton and becomes helium-3. The helium-3 is in an excited state and emits a photon when it goes to a ground state. neutron photon proton
Proton Fusion 3 Step 3: Two helium-3 nuclei collide. They rearrange particles so that very stable helium-4 is formed with two extra protons spit out. helium-3 helium-4 proton next
Excess Energy The fusion reaction in a star is exothermic. H-1: 1.0078 uH-1: 1.0078 u He-4: 4.0030 uHe-4: 4.0030 u This is less than 4 hydrogen masses so there is energy released. Find the mass energy difference. Q = 4(1.0078)-(4.0030) Q = 0.0282 u Convert to MeV. Q = (0.0282 u)(931.5 MeV/u) Q = 26.27 MeV This is per single fusion reaction.
Thermonuclear Blast next Fusion of deuterium into helium is exothermic. The high temperature of an uncontrolled fission reaction can overcome the nuclear charge. A fission bomb to ignite fusion device