Nuclear Fusion: How It Works Trivia Quiz

Answer: mass(reactants) > mass(products)

Note: one product is more massive than individual reactants. The total mass of the reaction decreases.
Nuclear fusion reactions form nuclei (or a nucleus) that possess less mass and binding energies than the original reactants, in energy-releasing (exergic)reations. Exergic reactions are more common in the sun and fusion reactor than endergic (energy-consuming reactions) reactions. Often, endergic consume thermal energy and yield increased mass (eg. the formation of deuterium from two protons (hydrogen)).
The binding energy is the amount of energy holding nuclear particles (protons and neutrons) together in the nucleus. At very small nuclear distances, these particles all attract one another, so larger isotopes (versions of nuclei) and certain densely-packed configurations have lower binding energies and mass. When a fusion reaction produces a lower mass/binding energy, energy is released.

Answer: proton - proton chain --> helium-4

The proton - proton fusion reaction has a very slow rate of fusion. It occurs in the core of the sun, where the temperature (14 million degrees C) is much colder than fusion can occur in a laboratory setting (200 million degrees C). Gravitational confinement of the fuel and low surface heat loss inside the core (less than one quarter of the heat lost on the surface of the human body) ensure than the reaction meets the Lawson criteria (i.e. a density x energy confinement factor than exceeds a certain number) for fusion.

There are other products of fusion reactions such as neutrinos and gamma rays.

Answer: carbon-12, oxygen-16

Beryllium-8 is produced from the fusion of two helium-4 ions. Beryllium-8 has a very short half-life and decays rapidly. In very hot stars (>100 million degrees C and more than 10X the mass of Earth's sun), helium-4 combines with beryllium-8 to form carbon-12.

Helium-4 combines with carbon-12 to form oxygen-16. Protons combine with some of these isotopes to produce new isotopes (nitrogen-14, etc.) in the CNO cycle.

Answer: deuterium-tritium

Deuterium-tritium fusion requires a temperature of about 14 keV or 200 million degrees C/K to ignite. Deuterium-deuterium is the second best in terms of activation temperature. The reaction rate is a very crucial factor because, in the fusion reactor, heat is lost very rapidly.

Heat must be sustained in order to achieve a self-sustaining reaction and overcome the breakeven point (where the power input equals the power output).

Answer: electrostatic

The electrostatic force causes positively charged protons to repel each other, preventing two nuclei from getting close enough to react. The weak nuclear force holds protons and neutrons together in the nucleus; the strong nuclear force holds protons together in the nucleus.

At the distances between adjacent nuclei, the electrostatic (repeling) force supercedes the strong nuclear force. The gravitational force pulls objects with mass together.

Answer: very hot matter with unbonded ions and electrons

The plasma phase occurs at higher temperatures than the gas phase. In plasma, all atoms are dissociated from molecules and electrons are dissociated from atoms. Protons do not dissociate from the nuclei - the strong and weak nuclear forces hold nuclei together. Nuclear particles dissociate from the nuclei in fusion reaction but quickly re-associate to form new nuclei.

Answer: positron

The charge of the reaction is conserved so that the (neutrally-charged) neutron derived from the (positively-charged) proton releases a particle equal to the lost charge - the positron. Thus, the positron annihilates with an extra electron, no net charge is produced, and a high energy photon (gamma radiation) results from the conversion of mass to energy. Despite the gamma raditation energy gain, this reaction results in a net increase in mass and binding energy, consuming thermal energy from the surroundings.
proton + proton + 2 electrons* --> proton-neutron (deuterium)* + 2 electrons + 1 positron --> deuterium + 1 electron (free) + gamma radiation
* not a reactant

Answer: 50-60

Given that 1 gram of (1:1 ratio) D-T fusion reactants yields 328 GJ of thermal energy (about 90,000 kWh) and 1 barrel of oil yields 6.12 GJ, 1 gram of D-T fusion gives out 53 barrels of oil worth of energy. The energy released in nuclear fusion is conversion of mass (actually, nuclear binding energies) to useful energy (thermal), in a relativistic manner.

In D-T fusion, 0.3% of the original mass is converted to energy. In 2004, the world consumed 131,400 TWh (trillion watt hours) of energy (87% from fossil fuels). If this was derived from D-T fusion, 1.5 thousand metric tons would be needed (at 100% efficiency), per year.

Answer: cross-section

An energy diagram expressed with distance between nuclei on the x-axis shows an energy peak (activation barrier) at a certain distance. The distance between the peak energy (approaching) and the peak energy (escaping) of the particle correlates with the cross-section (expressed particles/area). This cone-shaped area represents the area in which fusion between particles will occur.
The cross-section X particle velocity/volume X density of reactants = the rate of reaction.

Answer: quantum tunneling

Quantum tunneling is a property that allows a particle to overcome the energy barrier even though it does not have enough energy to do so. Nuclear fusion can also occur at temperatures below the activation temperature because the temperature represents the average kinetic energy of particles; many faster-than-average particles possess enough kinetic energy to overcome the energy barrier and fuse with other nuclei.