Science 10 - 11.5 Nuclear Reactions: Fusion
Series of nuclear reaction to produce helium-4
1. Fusion of two hydrogen nuclei results in deuterium nucleus 2. Fusion of deuterium with another hydrogen produces helium-3 3. Two helium-3 produce helium-4 and 2 hydrogen atoms
Fusion Bomb
A fission bomb using plutonium or enriched uranium could be used to start a fusion bomb (also called thermonuclear or hydrogen bomb) The fusion bomb would be many times more powerful than a fission bomb
Difficulty of using fusion to produce energy
A major difficulty is the very high temperatures needed to give the particles the high speeds they need to overcome their electrostatic repulsion - the high temps make it impossible to hold the material in any containiner
Neutrino
A neutrino is a particle that has energy, but no mass or charge
Positron
A positron is identical to an electron except that it has a positive charge, whereas an electron has a negative charge Can be written as ⁰+₁e
Atomic numbers and masses for fusion reactions (before and after)
As with other nuclear reactions, the total of the atomic numbers and masses are the same before and after the fusion reaction
Decay of ²₂He
Because the ²₂He is unstable, it decays immediately to a deuterium nucleus (²₁H) by radioactive emission of a positron and a neutrino
Nuclei overcoming their natural electrostatic repulsion
For two nuclei to join, their natural electrostatic repulsion needs to be overcome. To do this, the nuclei must collide at very high speeds. These high speeds can only occur at very high temperatures, such as in the Sun and stars
Fusion bomb (tritium and deuterium)
In a fusion bomb, tritium is used with deuterium. This produces more than four times the energy of only using deuterium
Production of heavy isotopes
Many heavy isotopes are only produced in the nuclear reactions in supernova explosions at the end of the life of some heavy stars
Nuclear Fusion
Nuclear fusion is the fusing or joining of two small nuclei to make one larger nucleus
Where do nuclear fusion reactions occur?
Nuclear fusion reactions occur in the Sun and supply the energy needed to sustain life on Earth.
Advantage of using fusion to produce energy
One of the advantages of using fusion to produce energy is that the process does not produce harmful waste products in the form of long-lived radioisotopes
Triple-Alpha Process
Production of carbon two helium nuclei produce beryllium and a gamma ray then helium and beryllium produce carbon and a a gamma ray
Stars (making elements)
Stars are the factories of the universe that make up all of the elements in the periodic table
Where does the energy from fusion reactions come from?
The energy from fusion reactions comes from the conversion of mass, as with nuclear fission
Fusion of two deuterium atoms
The fusion of two deuterium atoms produces the following: ²₁H + ²₁H → ³₁H + ¹₁H
Nuclear process - helium-4
The nuclear process starts with one helium-4 nucleus and ends with two helium-4 nuclei
Nuclear processes that occur in stars
The nuclear processes that occur in stars follow the stages in the life of the star and allow for different combinations
Nuclear fusion between hydrogen nuclei
The simplest nuclear fusion is between two hydrogen nuclei (protons) This type of fusion reaction takes place in the sun
Tritium Half-life
Tritium is radioactive with a half-life of 12 years, which means it is not very plentiful on earth, whereas deuterium is plentiful
Helium-4 and other elements
When all of the hydrogen is converted into helium-4, the temperature of the star rises and then helium-4 begins to produce heavier elements
Nuclear Fusion Mass
When two nuclei join together, the mass of the product nucleus is less than the sum of the masses of the original nuclei. The loss of mass is converted into energy and released.
Nuclear reaction for the decay of ²₂He
²₂He → ²₁H + ⁰+₁e + a neutrino
Nuclear fusion between hydrogen nuclei - Nuclear equation
¹₁H + ¹₁H → ²₂He