3.6 Nuclear Energy

Question 1

What is the unified atomic mass unit, u?

Answer 1

It is exactly one twelfth of the mass of one atom of carbon-12. Thus one atom of carbon-12 has a mass of exactly 12u.

It is also the mean mass for a nucleon (Neutron/ proton)

1.66 x 10^-27 kg

Question 2

What is the binding energy of a nucleus?

Answer 2

The energy that has to be supplied in order to dissociate a nucleus into its constituent nucleons. (it is NOT the energy that a nucleus possesses)

Question 3

What is the energy of one u?

Answer 3

u: 931MeV

Question 4

What is the mass defect and what is it equal to?

Answer 4

The difference in mass between the total mass of individual nucleons of an atom compared to the actual mass

The mass difference is the binding energy

Question 5

What is the binding energy per nucleon?

Answer 5

The binding energy of an atom divided by the mass number (nucleon number)

Question 6

What is fusion?

Answer 6

When smaller nucleon number nuclei combine to form larger nuclei with a larger nucleon number.

Question 7

What is fission?

Answer 7

Larger nucleon number nuclei split to form smaller nuclei with a smaller nucleon number.

Question 8

Explain the binding energy per nucleon curve and why energy is released from fission and fusion.
Explain fission and fusion in relation to the curve.

Answer 8

Fission
Energy is needed to break the atoms into their constituent nuclei but as they combine energy is released due to a mass defect. As the heavier atoms such as uranium have a lower binding energy per nucleon compared to its two products, when the atom is split their is a mass defect causing energy to be released.

Fusion
When two hydrogen atoms combine to create a helium atom, the helium has a greater binding energy per nucleon than the two hyrdrogen causing energy to release from the mass defect

Question 9

How is hydrogen atoms fused into helium?

Answer 9

Start with 6 hydrogen atoms and they need to be a very very very hot plasma to overcome the coulombic interactions (nuclei are positive so repel unless they have a high kinetic energy)

1) Two hydrogen combine to create deuterium, positron and electron neutrino. ¹H + ¹H -> ²H + (B+) + Ve
2) Another hydrogen combines with the deuterium to create an isotope of helium and gamma (energy). H + ²H -> ³He + γ
(repeat step 1 and 2)
3) Two helium isotopes combine to create a normal helium and two hydrogen
³He + ³He -> ⁴He +2¹H

The mass of the helium is less than mass of 6 hydrogen